Oil ring/general internal de carbonization and maintenance strategy Toyota 2a-fze. Advice needed, and plan to keep a log

[KJH]

I have a 2008 Scion Tc with 139xxx miles that I picked up for cheap in the summer about 5k miles ago. I love the car overall but it does burn about 1qt every 1000-1500 miles. This is most certainly due to the low tension piston ring design, and general high-efficiency-at-all-costs design that we see in so many modern 4 cylinders that wreaks havoc on the oil system. I keep it topped up and have observed no other issues, but want to avoid clogging the cat eventually.

I know the only way to truly solve this problem is replacing the rings/pistons. I will delete that cat converters and do 02 plug extension, oil change/top up with cheapest synth I can find, then drive the car till its dead(which, based on others, is quite a while) before that happens.

As such, I am concocting a strategy to eliminate as much oil consumption as possible, and so the main goal is to clear as much carbon/gunk is possible on the combustion chamber and especially the piston rings, without removing the head, and then maintaining this state for as long as possible. I am (very optimistically)hoping for at least 50% reduction in consumption, but I would consider any reduction at all as a success. I am seeking any advice but I desperately seeking some that is backed with rational, technical knowledge and years of experience by professional level people, as I've read hundreds of anecdotes from randoms while researching. I am going to loosely post my research/tentative strategy below, if anyone sees flaws or has advice please do so!

---- De carbonization/engine cleaning
First things first, PCV valve, which I have already replaced.
Engine flush and piston soak seems to be the go to method to reduce oil consumption in these engines. I think I have read nearly every major thread on the internet and watched almost every youtube video on this engine and other engines with similar problem such as 2000s era Saturns. It theoretically makes sense, but consensus and trends are still somewhat ambiguous as to what product works the best. For engine flush BPG, Liqui Moly, Amsoil and ATF seem to have the most backers across all engine platforms with this problem.
BPG EPR, amsoil engine flush, ATF, diesel fuel, seafoam, berrymans, liqui moly, schaeffers, etc etc are all things ive seen recommended for engine flush/piston soak fluids. Overall, results seem to be slight majority see no effect on consumption at all, with the others seeing reduction from slight to almost completely fixed. Additives that evaporate quickly like seafoam generally seem to have the least results, so it holds to reason that the thicker, esther based additives mentioned as the slight consensus products work best for engine flush. For piston soak, berrymans and schaeffers seem to have the most backing. The number of succesfull attempts across many message boards and makes and models with this general process gives me hope, but I remain somewhat skeptical that simply running additive through will be enough to break down severe carbon deposits. Im sure any of these products would work great in conjuction with taking the piston out and a brush, but idk about in the engine.
Anyways
My tentative strategy is engine flush w/ liqui moly by adding before next oil change, add when engine is red hot, idle 10-15 mins, drive moderately hard for 25-50 miles, and shut off. Directly after, do a piston soak with berrymans overnight, and cranking motor w/o spark plugs. Do oil change with Valvoline advanced full synth w/ maxlife 5w-20 and wix xp oil filter.

The products I chose are from a combination of availability/price in my area, their frequent mention in anecdotally successful ring de carboning attempts, and their function fits my understanding of how the process works.


Oil---
What oil and viscosity.
As mentioned above, I am planning on using valv advanced full synth w/ maxlife in 5w-20. TBH, I have no concrete reasons I chose this oil over other full synth oils. I want an oil that prioritizes cleaning for reduction in carbon buildup, very high resistance to heat breakdown, and although Im not sure what mechanism would allow this: reduction in oil that gets past the carboned rings.
Conditions:
I drive this car hard. My commute is about 15 miles of high speed highway driving(80-90mph with occasional brief high speed runs, 3.5-4.2k rpm in 5th), about 5-15 miles of city driving for a total of 40-60 miles every weekday, I drive aggressively on the road and also regularly autocross the car, although the next time not till next spring as the season is done. Winters are somewhat harsh here, 0-40 degrees, but normally a bit above freezing during the day. I have done one oil change with 5w-20 Valvoline advanced full syn w/ maxlife, and topped it off with 5w-30 of the same stuff when it got low.

Any and all recommendations or insights appreciated. I am doing this during the weekend and will update with results after 2-300 miles

 

[Bailes1992]

Why not try the new High Performance Lubricants engine flush? I seen some pictures on facebook the other night after someone had used it for a 2000mile interval and there was tons of crap in the filter. I think an Ester based product is the only thing that might help you here.

 

[GR_CoB]

As mentioned - try the High Performance Lubricants engine flush. Then switch to Mobil1 0w-40, if cleanliness is your goal and if you need oil that will take the daily abuse (which sounds like you do based on your driving pattern). I've used M1 0w40 in my 2009 Scion xB (same 2AZ) with no ill effects. Cleaned my engine a little, but then two deer decided to test how strong the front end of a Scion xB is at 5am...
Berryman is strong, don't let it drip on paint as it will take the paint off. I learned that the hard way when I did piston soak with Berryman B12 (1/2 bottle in each cylinder) followed by Marvel Mystery Oil. I did see an improvement in oil consumption, but overall my engine is just too worn out. (2000 Honda CR-V, 225k miles)

 

[Blagoje]

Use this product as recommended before your next oil change for 30 minutes:

BG EPR® Engine Performance Restoration® – BG Products, Inc.

www.bgprod.com

Also consider adding this product to your motor oil afterwards:

BG Advanced Formula MOA® – BG Products, Inc.

www.bgprod.com

 

[BMWTurboDzl]

You regularly autocross/aggressively drive the car and complain about oil consumption? Okay well, for starters due to your usage get used to the oil consumption and at this point a "flush" product isn't going to do anything. I suppose you could do a dry/wet leak down test to determine the amount of wear and if your valve guides are leaking but no oil strategy is going to fix that.

One last thing is don't act the Jerrys kid by circumventing the emissions system.

 

[Chris142]

Removing catalytic converters is a federal crime and should not be posted on a public site.

 

[Trav]

I have a 2008 Scion Tc with 139xxx miles that I picked up for cheap in the summer about 5k miles ago. I love the car overall but it does burn about 1qt every 1000-1500 miles. This is most certainly due to the low tension piston ring design, and general high-efficiency-at-all-costs design that we see in so many modern 4 cylinders that wreaks havoc on the oil system. I keep it topped up and have observed no other issues, but want to avoid clogging the cat eventually.

I know the only way to truly solve this problem is replacing the rings/pistons. I will delete that cat converters and do 02 plug extension, oil change/top up with cheapest synth I can find, then drive the car till its dead(which, based on others, is quite a while) before that happens.

As such, I am concocting a strategy to eliminate as much oil consumption as possible, and so the main goal is to clear as much carbon/gunk is possible on the combustion chamber and especially the piston rings, without removing the head, and then maintaining this state for as long as possible. I am (very optimistically)hoping for at least 50% reduction in consumption, but I would consider any reduction at all as a success. I am seeking any advice but I desperately seeking some that is backed with rational, technical knowledge and years of experience by professional level people, as I've read hundreds of anecdotes from randoms while researching. I am going to loosely post my research/tentative strategy below, if anyone sees flaws or has advice please do so!

---- De carbonization/engine cleaning
First things first, PCV valve, which I have already replaced.
Engine flush and piston soak seems to be the go to method to reduce oil consumption in these engines. I think I have read nearly every major thread on the internet and watched almost every youtube video on this engine and other engines with similar problem such as 2000s era Saturns. It theoretically makes sense, but consensus and trends are still somewhat ambiguous as to what product works the best. For engine flush BPG, Liqui Moly, Amsoil and ATF seem to have the most backers across all engine platforms with this problem.
BPG EPR, amsoil engine flush, ATF, diesel fuel, seafoam, berrymans, liqui moly, schaeffers, etc etc are all things ive seen recommended for engine flush/piston soak fluids. Overall, results seem to be slight majority see no effect on consumption at all, with the others seeing reduction from slight to almost completely fixed. Additives that evaporate quickly like seafoam generally seem to have the least results, so it holds to reason that the thicker, esther based additives mentioned as the slight consensus products work best for engine flush. For piston soak, berrymans and schaeffers seem to have the most backing. The number of succesfull attempts across many message boards and makes and models with this general process gives me hope, but I remain somewhat skeptical that simply running additive through will be enough to break down severe carbon deposits. Im sure any of these products would work great in conjuction with taking the piston out and a brush, but idk about in the engine.
Anyways
My tentative strategy is engine flush w/ liqui moly by adding before next oil change, add when engine is red hot, idle 10-15 mins, drive moderately hard for 25-50 miles, and shut off. Directly after, do a piston soak with berrymans overnight, and cranking motor w/o spark plugs. Do oil change with Valvoline advanced full synth w/ maxlife 5w-20 and wix xp oil filter.

The products I chose are from a combination of availability/price in my area, their frequent mention in anecdotally successful ring de carboning attempts, and their function fits my understanding of how the process works.


Oil---
What oil and viscosity.
As mentioned above, I am planning on using valv advanced full synth w/ maxlife in 5w-20. TBH, I have no concrete reasons I chose this oil over other full synth oils. I want an oil that prioritizes cleaning for reduction in carbon buildup, very high resistance to heat breakdown, and although Im not sure what mechanism would allow this: reduction in oil that gets past the carboned rings.
Conditions:
I drive this car hard. My commute is about 15 miles of high speed highway driving(80-90mph with occasional brief high speed runs, 3.5-4.2k rpm in 5th), about 5-15 miles of city driving for a total of 40-60 miles every weekday, I drive aggressively on the road and also regularly autocross the car, although the next time not till next spring as the season is done. Winters are somewhat harsh here, 0-40 degrees, but normally a bit above freezing during the day. I have done one oil change with 5w-20 Valvoline advanced full syn w/ maxlife, and topped it off with 5w-30 of the same stuff when it got low.

Any and all recommendations or insights appreciated. I am doing this during the weekend and will update with results after 2-300 miles

The 4 cyl engine is a perfect candidate for a piston soak. Pull the plugs and pour 3-4 oz of Berrymans chemtool down each hole then loosely install the plugs (you can rotate the engine with a ratchet and socket to get the amount in the cylinders but do not crank it with the starter.
Do this 3-4 times over a weekend or few days without cranking the engine in between as all sorts of junk is going down into the oil. The longer the working time the better the result. After the last soaking period (8hrs or more) put 1 oz of oil in each cyl and dump the oil before starting the engine.

Fill the oil and change the filter then crank the engine a few revolutions with a ratchet with the plugs out then install the plugs and fire it up. Substituting a qt of oil for a qt of High Performance Lubricants engine flush would probably be a good idea.
Run it 100 miles and change the filter only then again at 500 miles, change the oil and filter at 1K using Mobil 1 0w40. Give it time to work, no rush.

 

[Highboy]

I have a 06 and an 08 Tc’s. The 08 oil consumption is terrible. Got it 8 years ago with 31k and now at 123k miles. I’ve done oil flushes and tried many brands and weights of oil. It’s our around town car and I just check the oil every 2 weeks. A piston soak is my next thing to do.

 

[KJH]

As mentioned - try the High Performance Lubricants engine flush. Then switch to Mobil1 0w-40, if cleanliness is your goal and if you need oil that will take the daily abuse (which sounds like you do based on your driving pattern). I've used M1 0w40 in my 2009 Scion xB (same 2AZ) with no ill effects. Cleaned my engine a little, but then two deer decided to test how strong the front end of a Scion xB is at 5am...
Berryman is strong, don't let it drip on paint as it will take the paint off. I learned that the hard way when I did piston soak with Berryman B12 (1/2 bottle in each cylinder) followed by Marvel Mystery Oil. I did see an improvement in oil consumption, but overall my engine is just too worn out. (2000 Honda CR-V, 225k miles)

Why not try the new High Performance Lubricants engine flush? I seen some pictures on facebook the other night after someone had used it for a 2000mile interval and there was tons of crap in the filter. I think an Ester based product is the only thing that might help you here.

Thank you for the suggestion. I have never heard of this product and will do some research. Also thanks for the heads up on the berrymans, I’ll be careful lol.

 

[KJH]

You regularly autocross/aggressively drive the car and complain about oil consumption? Okay well, for starters due to your usage get used to the oil consumption and at this point a "flush" product isn't going to do anything. I suppose you could do a dry/wet leak down test to determine the amount of wear and if your valve guides are leaking but no oil strategy is going to fix that.

One last thing is don't act the Jerrys kid by circumventing the emissions system.

Oil consumption in the Toyota 2a-fez is due to a well known and often discussed design flaw from use of low tension piston oil rings that cannot drain oil fast enough. This causes them to gunk up with carbon etc and further reduces oil drainage through piston holes, which increases consumption. It is also a common problem in many modern design engines across all makes, especially 4 cylinders. It is not due to wear of the cylinder walls or valve guides. Aggressive driving will probably marginally increase consumption in engines that already have clogged rings, but these things burn a ton of oil no matter how you drive them.



Second, conversely, driving aggressively in these situations in conjunction with high quality oil and short oci can potentially reduce or prevent oil consumption, as long as it’s done before very large amounts accumulation of carbon happens on the rings. This is because aggressive driving reduces carbon accumulation and can in some cases clean out carbon, were as slow driving will accumulate carbon like no tomorrow. Aggressive driving can of course increase cylinder wear IF in conjunction with poor oci and bad quality oil and general poor maintenance, but you will likely be worrying about rod and crank bearing wear before oil consumption if that’s the case. I have driven the same way and participated in motorsports with many different kinds of cars for over a decade, I have never had oil consumption problems till now.



In any case, I am not complaining about oil consumption, I am making a gameplan to best maintain and rectify this motor/vehicle based on my conditions and needs. I get an immense amount of enjoyment from Motorsport and spirited driving of fun cars, and will not modify my driving style or activities to optimize vehicle longevity, I instead will optimize my maintenance to prolong my motor/vehicle life with my driving applications in mind.

Removing catalytic converters is a federal crime and should not be posted on a public site.

Thank you for the concern, I will instead replace the cat

 

[KJH]

The 4 cyl engine is a perfect candidate for a piston soak. Pull the plugs and pour 3-4 oz of Berrymans chemtool down each hole then loosely install the plugs (you can rotate the engine with a ratchet and socket to get the amount in the cylinders but do not crank it with the starter.
Do this 3-4 times over a weekend or few days without cranking the engine in between as all sorts of junk is going down into the oil. The longer the working time the better the result. After the last soaking period (8hrs or more) put 1 oz of oil in each cyl and dump the oil before starting the engine.

Fill the oil and change the filter then crank the engine a few revolutions with a ratchet with the plugs out then install the plugs and fire it up. Substituting a qt of oil for a qt of High Performance Lubricants engine flush would probably be a good idea.
Run it 100 miles and change the filter only then again at 500 miles, change the oil and filter at 1K using Mobil 1 0w40. Give it time to work, no rush.

This piston soak method sounds much better than the plan I had outlined, thank you.

Also, I have seen two recommendations for Mobil 1 0-40w in this thread. What are the reasons for this brand and viscosity instead of oe 0 or 5w-20?

 

[KJH]

I have a 06 and an 08 Tc’s. The 08 oil consumption is terrible. Got it 8 years ago with 31k and now at 123k miles. I’ve done oil flushes and tried many brands and weights of oil. It’s our around town car and I just check the oil every 2 weeks. A piston soak is my next thing to do.View attachment 76564

Nice cars! Based on my reading the 08 and up before the slight redesign engines have it the worst. They added oil squirters in the engines in 08, which may be a factor. Good luck on the piston soak, post results if you have the time and inclination!

 

[BMWTurboDzl]

Oil consumption in the Toyota 2a-fez is due to a well known and often discussed design flaw from use of low tension piston oil rings that cannot drain oil fast enough. This causes them to gunk up with carbon etc and further reduces oil drainage through piston holes, which increases consumption. It is also a common problem in many modern design engines across all makes, especially 4 cylinders. It is not due to wear of the cylinder walls or valve guides. Aggressive driving will probably marginally increase consumption in engines that already have clogged rings, but these things burn a ton of oil no matter how you drive them.

Which shouldn't be surprising if the engine is just tee-toddling around town. Your usage (ie. autocross) should prevent the rings from getting stuck and in fact free them up because you're running around at max power (ie max pressure). This is the concept behind the "Italian Tuneup".

If there still is oil consumption then as you're already well aware it's an engineering issue which cannot be fixed with oil or oil additives no matter how much you wish it were otherwise.

BTW some high performance NA engines use low tension rings (ex, BMW S65 V8).

 

[KJH]

Which shouldn't be surprising if the engine is just tee-toddling around town. Your usage (ie. autocross) should prevent the rings from getting stuck and in fact free them up because you're running around at max power (ie max pressure). This is the concept behind the "Italian Tuneup".

If there still is oil consumption then as you're already well aware it's an engineering issue which cannot be fixed with oil or oil additives no matter how much you wish it were otherwise.

BTW some high performance NA engines use low tension rings (ex, BMW S65 V8).

I bought the car a couple months and 5k miles ago, so me simply autocrossing and driving aggressively in that time is unlikely to free up the rings as the car was in fact probably tee-toddling around town for 135xxx miles of its life which developed the problem in the first place. Certainly oil and oil additives(ie engine flush and piston soak) may not fix my problem and I am prepared for that outcome, but it has been known to work in some cases including with much worse case consumption than mine, and it makes sense in theory particularly the piston soak method. I am willing to try, it doesnt cost that much and its a fun experiment nonetheless.

Yep, many cars come with low tension rings these days and many perform just fine if the engineers know what they are doing to offset its weaknesses. The 2az-fe was Toyotas first "new age" high efficiency priority engine and the first time they used low tension rings, hence the problem. Especially with 4cylinders, as in the chase of fuel economy and efficiency, they have to build them lighter with thin aluminum blocks that cook oil, unlike most companies V8 offerings were they know the consumer isnt too concerned with economy and prefer power and smoothness so they overbuild. In fact I think Toyota has gone back to low tension with their new gen 4cyl engine as well and it has no reported problems. Nowadays, its when engineers dont know what they are doing or company rushes/cost cuts is where you run into problems, a prime example being Hyundais new Smartstream engine, were the low tension rings are so poorly designed and implemented that they not only clog very quickly, there are engine teardown reports coming out of Korea of piston slap at less than 10k miles, meaning they potentially were like that from the factory! A technician conducting one of the teardowns noted its like looking at an engine that was built with the ring gap wrong or rings incorrectly installed.

 

[KJH]

Update

Due to scheduling and supply constraints I just put a tiny bit of berrymans oil change engine flush( not B12), drove slow for 10 mins back to the house from napa, changed the oil and filter. The instructions on the berrymans said you can put the whole 500ml can in 3-6 quarts of oil, but the stuff was so thin i couldnt bring myself to do it and put maybe 100ml before stopping. I used Mobil euro car formula 0w-40 due to recommendations in this thread and a fram ultimate synthetic filter.

While I kind of knew this already from dipstick checks, the used oil(mix of 5w-20 and 5w-30 valvoline full synth HM) was completely jet black after 2.5k miles of use. I have done 2 autocross events in that time, one that was a on-racetrack course so quite a bit more aggresive than normal autocrossing.

The used filter was a mobil one extended performance (or whatever they call it), and I cut it open with a grinder. I was looking for a fram synthetic or wix xp but after going to the superstore and 3 parts stores without luck I settled on it. There was carbon accumulation every 4th or 5th fold, and i observed 3-4 tiny silver colored bits.

I was concerned with the metal but after a bunch of research and asking around, it seems split between people saying that any metal in a broken in engine means immanent death, or its not a big deal unless theres quite a bit in there and coming out of the used oil particularly right after you pull the plug, which i did not observe and checked the used oil for metal. I know 2 reputable mechanics and one said it may be cause for concern but probably fine, the other said he sees it all the time and not to worry. I also think it may have just been from my haphazard can opening method trying to wrangle the oily thing with my foot while cutting with the grinder since I didnt have a vise. We will see what happens...lol

This was my first time opening a oil filter so I dont really know what i was looking for besides the above, but the filter media of the mobil one tore pretty easily once I got it separated from the glue stuff holding it to the metal part of the filter. I know its a non synthetic media but it was still more fragile than I thought it would be, I am not sure if that is normal. Besides that, the drainback valve was in good condition and pliable despite not being 100% silicone, and the metal casings and clip thing looked to be of good quality. It had only been 2.5k miles after all so doesn't tell me much I suppose.

I overfilled it a bit on accident, maybe 1-2mm over on the dipstick, but left it in there. I drove it conservatively for about 20 minutes then lit her up for another 20, and everything seemed normal, seemed smoother and not quieter but smoother sounding, but I always chalk that up to my imagination. Ill report back next fillup with consumption which should be sometime this week.

 

[GR_CoB]

Correct me if I'm wrong, but don't instructions on the bottle say to only use this product in idle for 10-15 mins immediately before the oil change? As in - not drive the vehicle and put extra load on bearings while the oil is thinned and weakened by the oil flush? It makes me wonder if you start hearing some knocking pretty soon from wiped out bearings... Yes, the smaller amount shouldn't hurt that bad, but my brother is rebuilding his 2003 Lexus IS300 engine currently due to not following the instructions for Motor Medic oil flush. Completely wiped out bearings and ate the crackshaft at cylinder #6. Connecting rod was sticking out through the block 150 miles after the oil flush... And that's on "unkillable" 2JZ-GE engine.

P.S. Not blaming oil flush products, as I use them occasionally for the last 10 years with good results, but I always follow the instructions on bottle or manufacturer's website.

 

[KJH]

Correct me if I'm wrong, but don't instructions on the bottle say to only use this product in idle for 10-15 mins immediately before the oil change? As in - not drive the vehicle and put extra load on bearings while the oil is thinned and weakened by the oil flush? It makes me wonder if you start hearing some knocking pretty soon from wiped out bearings... Yes, the smaller amount shouldn't hurt that bad, but my brother is rebuilding his 2003 Lexus IS300 engine currently due to not following the instructions for Motor Medic oil flush. Completely wiped out bearings and ate the crackshaft at cylinder #6. Connecting rod was sticking out through the block 150 miles after the oil flush... And that's on "unkillable" 2JZ-GE engine.

P.S. Not blaming oil flush products, as I use them occasionally for the last 10 years with good results, but I always follow the instructions on bottle or manufacturer's website.

I drive about 2 miles home on a busy road, then drained it for oil change, never got over 2.5k hopefully nothing happened lol. I don’t hear anything out of the ordinary and have put over 200 miles on it since then but I’ll keep an eye on it. I don’t think I’ll use enfgine flush again unless it’s thick stuff regardless. I looked at it after opening, started pouring then stopping after the first glug, just seemed way too thin and I drove home very slow because of that too.

 

[GR_CoB]

I drive about 2 miles home on a busy road, then drained it for oil change, never got over 2.5k hopefully nothing happened lol. I don’t hear anything out of the ordinary and have put over 200 miles on it since then but I’ll keep an eye on it. I don’t think I’ll use enfgine flush again unless it’s thick stuff regardless. I looked at it after opening, started pouring then stopping after the first glug, just seemed way too thin and I drove home very slow because of that too.

Got it. Hoping for the best then. Don't be afraid to use that flush. I have used many, and that one from Berryman seemed to be the most effective, judging by what I found in the drain pan afterwards. Just use it as directed on the bottle: full bottle per 3-6qts of oil, and run for 10-15 mins at IDLE. On Berryman website they stated that for better cleaning 20-25 minutes is ok as well.

 

[53' Stude]

My 09’ Camry had consumption from a hardened, leaky valve cover gasket. I put KREEN in each cylinder, let sit for 3~ Hours

Then I put some EDGE 0w40 in with a tough guard filter. I don’t have any more oil leak/consumption. KREEN is a good recommendation, as it DOES work.

 

[KJH]

Got it. Hoping for the best then. Don't be afraid to use that flush. I have used many, and that one from Berryman seemed to be the most effective, judging by what I found in the drain pan afterwards. Just use it as directed on the bottle: full bottle per 3-6qts of oil, and run for 10-15 mins at IDLE. On Berryman website they stated that for better cleaning 20-25 minutes is ok as well.

Yep, thanks for the heads up. I was stupid to not follow the instructions, my mindset at the time was ive seen people put half a can of seafoam which is just as thin in a crankcase and run it for 100 miles so should be fine to put some in for the drive home, but couldn't bring myself to pour much once I saw the stuff actually going into the fill hole. If i do use it in the future ill be sure to just let it idle to temp.

I drove the car home from work today with radio and fans off and listened carefully, its at 235miles from the oil change now. Sounded and drove like it did before the flush, i could swear its actually quieter and smoother but again I always chalk that up to placebo when i do oil changes. I can faintly hear what Ive always assumed to be a bit of valvetrain or piston slap when pulling from stoplights in 2nd after the engine is fully warmed up, but that was there before and again it seems quieter, and im used to every old 4 banger ive owned being at least a bit noisy so never thought much of it. I think im in the clear but ill keep an eye on things. Ive had rod knock before when the oil pan on an old BMW 318is had a impromptu meeting with a large embedded rock and instantly lost all oil pressure, so I know BAD rod knock noise, but im not sure what slow onset bearing failure sounds like.