How to Determine the Correct Oil Grade for your Car

AEHaas

Thread starter
Messages
1,444
Location
Sarasota, Florida
Yes, the flow would be the same until the relief pressure was hit. The pressure would be less (with thinner oils) but the flow would be the same. I think it is time to revisit my original articles of 16 or 17 years ago. When the oil is at my Florida start up temperature the pop off valve is already hit. The pressure at idle is 80 PSI. That means that at any RPM from then on, before the oil temperature gets up, the flow is the same. There is no increase in flow with increasing RPM. 'Not good in my book.
 

AEHaas

Thread starter
Messages
1,444
Location
Sarasota, Florida
Let me add that in theory the flow to the engine in winter, northern temperatures, could be near zero. All the flow could be in bypass.

AEHaas
 
Messages
28,354
Location
PNW
Maybe I missed it from the "synopsis" in that thread, but where is the test data showing the different cold startup wear rates solely based on the oil viscosity used with the engine being ran through the same exact start-up procedure?
 

AEHaas

Thread starter
Messages
1,444
Location
Sarasota, Florida
I cannot remember if it was that paper or another but there was another variation. They measured wear as the engine warmed up and it was least at full operating temperature. Then they actually lowered the oil temperature gradually (pumping it through a cooling circuit) back down to 80F and the wear went right back up to the exact same level it was at start up.

AEHaas
 
Messages
1,941
Location
South Carolina
Some guys would freak out if they saw the oil pressure in my Camaro. At 200*F, the oil pressure is ~8 psi @ 900 rpm idle and just 30-35 psi at 6000+ rpm down the track. No issues with it at all.
 
Messages
1,972
Location
FL
Some guys would freak out if you saw the oil pressure in my Camaro. At 200*F, the oil pressure is ~8 psi @ 900 rpm idle and just 30-35 psi at 6000+ rpm down the track. No issues with it at all.
As long as there is no interruption in lubrication - "flow" - your Camaro will be happy.
 
Messages
938
Location
A Barrier Island
Italian cars are finicky about oil choices. My baby Ferrari 128 SemiFast would run fine on 10W-30 at any rpm. I wouldn't trust larger displacement models with that viscosity.

1616795336896.png
 

OVERKILL

$100 Site Donor 2021
Messages
46,513
Location
Ontario, Canada
Let me add that in theory the flow to the engine in winter, northern temperatures, could be near zero. All the flow could be in bypass.

AEHaas

The bypass is sized so that can't happen.

Funny story:

A buddy of mine's dad had a 2-bolt roller SBC built for his S10, they went with stock clearances but of course he had to have them toss in that HV oil pump. Relief pressure on that pump was 55psi IIRC and it would produce well north of 60 on a cold start with 15w-40 in it, clearly overwhelming both flow through the engine and the relief. If you drove it you could get upwards of 90psi IIRC. Once warmed up and thinned down idle pressure was around 40 and you were on the relief again by 2,000RPM. Just a complete waste, that engine would have been fine on an SV pump.

It would toss massive amounts of oil out the pushrods when cold (I remember crisp fall starts getting ready to take it to the track and having a valve cover off checking rocker lash) while of course sitting there with the relief wide open.

Ford had an issue with the 4.6L IIRC where the relief on the pump would stick and the oil filters would balloon, though I expect you could achieve the same by seriously overwhelming the bypass and increasing system pressure to something obscene.
 
Messages
2,862
Location
Caldwell Idaho
I cannot remember if it was that paper or another but there was another variation. They measured wear as the engine warmed up and it was least at full operating temperature. Then they actually lowered the oil temperature gradually (pumping it through a cooling circuit) back down to 80F and the wear went right back up to the exact same level it was at start up.

AEHaas
Metal expands when hot. If you mic a piston cold you will find it is not "round" it is "oval". When I used to build my drag boat motors, they were lake water cooled with out a thermostat and and ran cold. The piston to cylinder wall and ring end gap clearances were different due to the cold block operation. Startup wear and a higher rate of wear occurs until the engine and fluids reach a stabilized operation , the wear rates drop significantly.
 
Messages
2,044
Location
.
We know that the rate of engine wear follows the curve of oil viscosity. At start up (75F for test engines) the wear is highest and it gradually decreases as the oil temperature gradually increases over the 20-30 minutes it takes the oil and engine to warm up to the normal operating temperature. Then wear is at a steady state and at its minimum. If the thicker oil at the lower engine temperature has no ill effects then why is wear higher? If thicker oil lubricates better than thinner oil why is there more wear.
The answer cannot be that the engine parts are not fitting together well at start up. The oil lubricates or it doesn't.

One of the main reasons I like thinner oils is that they are not too thick during the start up interval. In Florida at mid summer the temperature may be 90F. This is COLD for your engine. The definition of a cold engine is not sub zero temperatures. Actually it (cold) is more like 75F for engine test purposes. A 0-20 oil may start out at 100cS mid summer when I leave the house. And yes, most trips are less than 30 minutes so the oil never reaches the appropriate operating viscosity of around 10 cS. The least engine wear does not occur when the oil is at 100cS as the "thick" people would lead you to believe. The least wear occurs when the oil is up to the normal operating temperature.

AEHaas

Many of us with DI/TGDI engines obsess over UOAs showing considerable decreases in 100C viscosity because of fuel dilution, with 20-grades sometimes getting to 6.xx cSt. In response to this, the default cure is to go up a grade. I gather you believe this is a false solution, even if, for example, a substituted 30-weight’s diluted viscosity isn’t much different from the spec’d 20-weight’s when new?
 
Messages
28,354
Location
PNW
Yes, the flow would be the same until the relief pressure was hit. The pressure would be less (with thinner oils) but the flow would be the same. I think it is time to revisit my original articles of 16 or 17 years ago. When the oil is at my Florida start up temperature the pop off valve is already hit. The pressure at idle is 80 PSI. That means that at any RPM from then on, before the oil temperature gets up, the flow is the same. There is no increase in flow with increasing RPM. 'Not good in my book.
So did Ferrari say anything in the owner's manual about letting the oil warm-up to X temperature before hammering the engine? Was there any ECU control of max engine RPM dependent on oil temperature like some more modern car use?

I highly doubt Ferrari would over-look guys getting in their Ferrari and going high RPM before the oil was at full operating temperature and allowing that to potentially harming the motor. Have you seen all the YouTube videos of guys in exotic V-12s bouncing the engine off the rev-limiter? :oops: :D
 
Messages
1,941
Location
South Carolina
The bypass is sized so that can't happen.

Funny story:

A buddy of mine's dad had a 2-bolt roller SBC built for his S10, they went with stock clearances but of course he had to have them toss in that HV oil pump. Relief pressure on that pump was 55psi IIRC and it would produce well north of 60 on a cold start with 15w-40 in it, clearly overwhelming both flow through the engine and the relief. If you drove it you could get upwards of 90psi IIRC. Once warmed up and thinned down idle pressure was around 40 and you were on the relief again by 2,000RPM. Just a complete waste, that engine would have been fine on an SV pump.

It would toss massive amounts of oil out the pushrods when cold (I remember crisp fall starts getting ready to take it to the track and having a valve cover off checking rocker lash) while of course sitting there with the relief wide open.

Ford had an issue with the 4.6L IIRC where the relief on the pump would stick and the oil filters would balloon, though I expect you could achieve the same by seriously overwhelming the bypass and increasing system pressure to something obscene.

Exactly. I see people do that all the time. I'd say >95% of people running a HV pump are just robbing power and increasing aeration with no benefit.
 
Messages
2,347
Location
WA
I have my own paper published below:

The theory that using thinner oil reduces wear during cold starts ... Even if somewhat true, it may increase the engine life by 1 day. That is one day of increase after the car has been in junkyard for 5 years ... Therefore its not significant or relevant.
on the other hand, I am biased towards oils with moly. Use it. lol

Proprietary scientific data from my paper:
I used to live in Idaho (i.e. very cold winters) and used 10W40 dino all year. Sold the car with over 400K miles and after a year or so a high school kid who eventually bought it (2nd owner after me) totaled it. He was ok so was the engine. I think he sold the engine.

btw, my typical oci used to be every 1800-2000 miles. Maybe 2500 max. :alien:
 
Last edited:
Messages
28,354
Location
PNW
I highly doubt Ferrari would over-look guys getting in their Ferrari and going high RPM before the oil was at full operating temperature and allowing that to potentially harming the motor. Have you seen all the YouTube videos of guys in exotic V-12s bouncing the engine off the rev-limiter? :oops: :D
Wonder what's going on in the oiling system in this V8 Coyote when he's revving near redline 40 seconds after a cold start. 😆

 

AEHaas

Thread starter
Messages
1,444
Location
Sarasota, Florida
"Wonder what's going on in the oiling system in this V8 Coyote when he's revving near redline 40 seconds after a cold start."

Ferrari dealers are constantly rebuilding engines that underwent just this type of treatment. The manual of the 812 SF does state that the engine must be fully warmed up before exceeding 4k RPM.

AEHaas
 
Messages
28,354
Location
PNW
"Wonder what's going on in the oiling system in this V8 Coyote when he's revving near redline 40 seconds after a cold start."

Ferrari dealers are constantly rebuilding engines that underwent just this type of treatment. The manual of the 812 SF does state that the engine must be fully warmed up before exceeding 4k RPM.

AEHaas
Guess Ford Coyote can take it and Ferraris can't ... :D Of course the best practice for any vehicle is to not hammer the RPM until the after the oil is warmed up to near full operating temperature.
 
Top