Rich Fuel cylinder wall wash

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Hey just saw a post on another forum where a guy said that letting a car idle and not taking off right away in the cold can cause damage because the rich fuel mixture the fuel can wash the oil from the cylinder walls causing cylinder wall wear?

I tried searching BTOG forums for this but my search string doesn't yield much useful so if its been beat to death I'm sorry just point me in the right direction. Oh and I did a google search too and it did bring back a book written on automotive maintenance that says it too. I just think the mix has to be really really rich for anything like that to occur.

 

[NHGUY]

Back with carburetors and chokes I could see it.Not so much so with EFI.Also,running a rich mixture and driving right off (hammer down) should put a heck of a load on those cold pistons and cylinder walls,whereas idling shouldnt load it at all.

 

[Bamaro]

Rich is rich whether from a carburetor or fuel injection.

 

[92saturnsl2]

Originally Posted By: Bamaro
Rich is rich whether from a carburetor or fuel injection.


+1. Carb is obviously not as precise a mixture and has the potential to go richer than necessary, so fuel injection has the advantage in the engine wear department. If the carb is in good tune, there shouldn't be a big difference.

Anything you can do to speed up warm-up time (short of romping on the engine while cold) will lessen wear and fuel dilution of the oil. I wouldn't go so far as to say a rich mixture is going to "wash" the cylinder wall, but there IS incomplete combustion going on, so invariably some fuel is going to make it past the rings into the crankcase.

Those engines that sit for 20 minutes idling, will have more wear (a negligible amount perhaps, but more nonetheless) than an engine that is brought up to operating temp quickly with casual driving. Those twenty minutes each morning add up over the years, so one could be causing premature wear, not to mention all the fuel wasted.

Keep in mind, that depending on the engine, it can take over twice as long to warm an engine up at idle, as opposed to just getting in and driving it. The mixture will be rich until the coolant temperature (on a fuel inj. engine) is brought up, or until the choke fully opens on a carb engine. Give it about 10-15 seconds to get the fluids moving, and go if your goal is a quick warm-up / minimal wear.

 

[92saturnsl2]

Also, this is the primary reason why frequent short trips are so detrimental to oils and engine longevity. This is exacerbated by long warm-ups, so if you don't have a long drive where the engine is good and warmed up, this can be a very real problem. A car that spends 20 minutes idling in the driveway each morning, then driven a couple miles to work, only to do the same thing on the return trip, will have substantial extra wear. The only way to help is to change the oil more frequently, but most are unaware of this.

The mixture can drop down as low as 5:1 (about 2:1 to start the engine) for reliable running in the cold. Cold fuel does not vaporize easily, so some tends to puddle in the intake or even in the cylinder (moreso far carbs) where it cannot burn. That fuel either goes out the exhaust, or "washes" down the walls past the rings, into the crankcase where it dilutes the oil. I still think fuel "washing" the walls is an exaggeration of sorts, but the problem is real.

Sorry for the long winded respons(es), but the fellow on the forum is definitely right.

 

[Rolla07]

I think long idling in cold isnt good but I think its absolute nonsense to think letting a cold car idle for a few minutes will cause any kind of detrimental wear. I start my car let it run for 1-3 mins, and put it in drive and drive gently until it warms up. couple mins to get the oil to flow and than driving gently to warm it up.

 

[Kuato]

Having a dead cylinder and being forced to drive it for 100 miles is about as much cylinder wash I can think of. Our Jeep Wrangler 2.4 had a spark failure on #4. Once repaired, it has been fine for nearly 50k.

This seems like a YMMV thing, might be oil dependent. The oil was changed just before and just after this incident.

 

[rslifkin]

Originally Posted By: 92saturnsl2
The mixture can drop down as low as 5:1 (about 2:1 to start the engine) for reliable running in the cold.


It'll never go that rich. If it were, the engine would be absolutely pouring black smoke out the exhaust and would foul the plugs before it ever warmed up. Plus, most engines won't even run that rich.

FWIW, my EFI engine hits closed loop within 30 seconds of startup regardless of coolant temp (and doesn't run particularly rich at startup either). I've got a wideband on it and have the narrowband signal to the ECU set to switch at about 15.5:1. It's got no problem running that lean with coolant temps under 30* F.

 

[brandini]

With DI engines it's entirely possible for the fuel to hit the cylinder walls... many pictures of spray patterns in engines show that it's probable, and with cold cylinders and rings I don't see why it wouldn't happen. The more extreme the cold, the more likely to happen.

You can let it idle in the cold, it's not the 'taking off' it's the short tripping and not getting all the fluid fully warm so fuel can vaporize out of the oil that will cause issues.

 

[Garak]

Originally Posted By: NHGUY
Back with carburetors and chokes I could see it.Not so much so with EFI.

I would agree. We can talk about carbs in good tune, but we all know how that works out. After fiddling with carbs in the old F-150, I immediately was reminded of why I liked propane so much.

 

[Shannow]

Originally Posted By: Bamaro
Rich is rich whether from a carburetor or fuel injection.


Not even close...

Carbs and throttle bodies will have up to 10+% of the fuel running as a stream along the manifold floor, which really WILL wash cylinders. As a result of the pooled fuel they have to be richer even still...

 

[SteveSRT8]

Originally Posted By: Shannow
Originally Posted By: Bamaro
Rich is rich whether from a carburetor or fuel injection.


Not even close...

Carbs and throttle bodies will have up to 10+% of the fuel running as a stream along the manifold floor, which really WILL wash cylinders. As a result of the pooled fuel they have to be richer even still...


Still a lot of variance in design. Some of my old car intakes were heated by coolant and others by exhaust to stop puddling/pooling.

But IME an injected engine simply cannot experience the huge gobs of fuel a big 4 barrel can dump in!

 

[Shannow]

Especially when cold, and before the exhaust and coolant are up to temp...

 

[Olas]

Fuel pooling on the manifold runners can be a problem in some designs, depends on the length and diameter of the runners (velocity), wether or not they're heated ( i have coolant circulating through my carb AND my manifold), inlet air temp/density/humidity and the type/grade of fuel used.

My scirocco has a weber carb, and my last emissions check showed 0.4% CO (limit is 4.5%) and 240ppm HC (limit is 1800) and I get roughly 40-45mpg so its not like I'm dumping big globs of fuel in there..and the last time I had the head off (HG, cambelt&tensioner) I dropped my internal verniers down the cylinder bores and they were all within spec...I know that is only correlation, not proven causation, but it makes sense to me that if I can still see the honing marks in my bores and the measurements check out then there must be at least some lube on the cylinder walls and my carb can't be washing it all away..

IMO its more about the individual set up and running conditions, rather than a blanket statement of 'this system is more prone to this phenomena than the other system'

 

[Clevy]

Originally Posted By: Bamaro
Rich is rich whether from a carburetor or fuel injection.
Originally Posted By: 92saturnsl2
Originally Posted By: Bamaro
Rich is rich whether from a carburetor or fuel injection.


A fuel injected vehicle even while running rich atomizes the fuel more effectively thereby negating any potential cylinder wash.
A carb pouring raw fuel in could puddle in the intake. Today that a non issue.

+1. Carb is obviously not as precise a mixture and has the potential to go richer than necessary, so fuel injection has the advantage in the engine wear department. If the carb is in good tune, there shouldn't be a big difference.

Perhaps however we still have the potential puddling issue especially when ambient temps dip to -25c and colder. The fuel has a more difficult time evaporating,especially in a cold or frozen intake manifold.

Anything you can do to speed up warm-up time (short of romping on the engine while cold) will lessen wear and fuel dilution of the oil. I wouldn't go so far as to say a rich mixture is going to "wash" the cylinder wall, but there IS incomplete combustion going on, so invariably some fuel is going to make it past the rings into the crankcase.

Lessen wear? If anything a warm up period at idle would create less blow-by into the crankcase because the pistons would thermally expand creating a more positive seal before increasing combustion chamber pressures and adding significantly more fuel which inevitably gets past the rings.
I live in the bald Canadian prairie where temps this year have already dipped beyond -40c. I let my car warm up for a half hour,even an hour.
Why?
Because I've driven it with no warm up and there is no doubt in my mind with the sounds it was making and how sluggish it moved along that wear was certainly in an accelerated state.

Those engines that sit for 20 minutes idling, will have more wear (a negligible amount perhaps, but more nonetheless) than an engine that is brought up to operating temp quickly with casual driving. Those twenty minutes each morning add up over the years, so one could be causing premature wear, not to mention all the fuel wasted.


Premature wear? I seriously doubt there would be any increase in wear. In fact in the winter conditions we experience I feel there would be less.
I check my oil often. Even with my 45 minute warm ups the oil never smells like fuel. Never.
This past week I wanted to see what kind of fuel dilution I was getting with these extended warm ups so I've been checking the oil for a fuel smell of which there isn't any.
Not scientific however but definitely a good method of indicating raw fuel.

Keep in mind, that depending on the engine, it can take over twice as long to warm an engine up at idle, as opposed to just getting in and driving it. The mixture will be rich until the coolant temperature (on a fuel inj. engine) is brought up, or until the choke fully opens on a carb engine. Give it about 10-15 seconds to get the fluids moving, and go if your goal is a quick warm-up / minimal wear.


Yes it might take twice as long to warm up however there is no load whatsoever cylinder pressures are low, there is less fuel not atomizing thereby lessening blow by into the crankcase which lessons fuel dilution.
Or you can put a load on the engine which increases fuel administered,which may not burn completely, which increases cylinder pressures which increases blow by and so on.
And let's not forget that cold oil flows poorly so we can expect a by-pass event and even a potential pressure release which flows the oil right back into the pan and doesn't circulate whatsoever.



Originally Posted By: NHGUY
Back with carburetors and chokes I could see it.Not so much so with EFI.Also,running a rich mixture and driving right off (hammer down) should put a heck of a load on those cold pistons and cylinder walls,whereas idling shouldnt load it at all.


Agreed.

Originally Posted By: 92saturnsl2
Also, this is the primary reason why frequent short trips are so detrimental to oils and engine longevity. This is exacerbated by long warm-ups, so if you don't have a long drive where the engine is good and warmed up, this can be a very real problem. A car that spends 20 minutes idling in the driveway each morning, then driven a couple miles to work, only to do the same thing on the return trip, will have substantial extra wear. The only way to help is to change the oil more frequently, but most are unaware of this.

The mixture can drop down as low as 5:1 (about 2:1 to start the engine) for reliable running in the cold. Cold fuel does not vaporize easily, so some tends to puddle in the intake or even in the cylinder (moreso far carbs) where it cannot burn. That fuel either goes out the exhaust, or "washes" down the walls past the rings, into the crankcase where it dilutes the oil. I still think fuel "washing" the walls is an exaggeration of sorts, but the problem is real.

Sorry for the long winded respons(es), but the fellow on the forum is definitely right.


Substantial extra wear? 5-1 air/fuel with a possible 2-1?
Do you really believe this?
I seriously doubt any fuel injected vehicle would richen the a/f to this extreme.
And honestly your 20 minute idle comment with a few mile drive would actually lessen wear,not increase it,and the oil will be hot enough to evaporate more fuel from the crankcase rather than a cold start and few mile trip.
The cold start/few mile trip would certainly increase fuel dilution however add 20 minutes idling to each start before applying a load and the oil is now up to operating temp and hot enough to effectively evaporate raw fuel.

In the frigid temps we've had the past weeks I've let my car idle for at least a half hour and I've been actively checking the oil because of all I've read on this forum about fuel dilution and long idle times etc and I've come to realize with my daily checks is long idle times aren't contributing to any raw fuel smell in my cars sump,in fact I drip the oil off the dipstick onto an old business card and the oil isn't even flammable without some effort on my part.
I've seen vehicles with fuel diluted oil that you could take a lighter to the freshly removed dipstick and the oil would burn a flame for a split second,yet those vehicles drove an easy 350000 miles before rust,not engine failure sent it for its last ride to the wrecker.
So I'm leaning toward the belief that your entire second post is total absurdity. Internet amplified fear with no actual data to support your comments. An eclectic mess of regurgitated wives tales.
Substantial wear unless the oil is changed more frequently. Truly absurd. Try 20 minutes on the highway a week and the fuel dilution is cured.

 

[Garak]

Originally Posted By: Shannow
Especially when cold, and before the exhaust and coolant are up to temp...

And when running Ford's ridiculous feedback carb they used as a stopgap measure before real fuel injection. I swear 10% of my fuel consumption went straight to fuel dilution.

Thankfully all my trips were long ones.

 

[92saturnsl2]

Originally Posted By: Clevy
A carb pouring raw fuel in could puddle in the intake. Today that a non issue.


If a carb dumps raw fuel in, what exactly does a fuel injector dump in? Milk?

Also, have you ever used a scan tool and watched commanded AFR or injector pulse width? Or looked at the fuel tables in your PCM? I have. 2:1 is certainly not outside the realm of possibility. Go start a car at -10, and see what AFR value the PCM commands. Does it run 2:1 for any extended period of time? Heck no. Once the engine is started, you'll see a quick rise to stoichiometric, especially if you have a heated oxygen sensor (all new gasoline engines do) which brings the PCM into closed loop very quickly.

Quote:
Premature wear? I seriously doubt there would be any increase in wear. In fact in the winter conditions we experience I feel there would be less.


Believe what you want to believe. Idle will hardly heat the oil anywhere near what sustained driving will. And cold temps with a rich mixture WILL cause incomplete combustion (can't argue science), fuel injected or not. Incomplete combustion is incomplete combustion whether it happens inside the cylinder, or from fuel being sucked in that's puddled at the bottom of the intake.

Quote:
I check my oil often. Even with my 45 minute warm ups the oil never smells like fuel. Never.
This past week I wanted to see what kind of fuel dilution I was getting with these extended warm ups so I've been checking the oil for a fuel smell of which there isn't any.
Not scientific however but definitely a good method of indicating raw fuel.


Very UNscientific, and definitely NOT a good method of indicating raw fuel. Who told you this?

Quote:
And honestly your 20 minute idle comment with a few mile drive would actually lessen wear,not increase it,and the oil will be hot enough to evaporate more fuel from the crankcase rather than a cold start and few mile trip.


Again, to each their own. Short trips fall under "severe service" for a reason. Bad for the oil, bad oil = bad for the engine. If you change your oil often, you will lessen the effect.

Quote:
in fact I drip the oil off the dipstick onto an old business card and the oil isn't even flammable without some effort on my part.


Complete waste of time and nothing more.

 

[Shannow]

Originally Posted By: 92saturnsl2
Originally Posted By: Clevy
A carb pouring raw fuel in could puddle in the intake. Today that a non issue.


If a carb dumps raw fuel in, what exactly does a fuel injector dump in? Milk?


Think where the carb (or TBI) is in relation to multiple cylinders, then think where the port fuel injector is...

Surely, even up on the high horse, you can see that there's a difference...

The carb/TBI will literally have a stream of fuel running along the floor of the manifold, that will be running into the engine as a stream, hugging any boundary layer into the cylinder...it WILL wash.

Port fuel injector will attempt to atomise the fuel, not hose a river into the cylinder.

 

[OVERKILL]

Originally Posted By: Shannow
Originally Posted By: 92saturnsl2
Originally Posted By: Clevy
A carb pouring raw fuel in could puddle in the intake. Today that a non issue.


If a carb dumps raw fuel in, what exactly does a fuel injector dump in? Milk?


Think where the carb (or TBI) is in relation to multiple cylinders, then think where the port fuel injector is...

Surely, even up on the high horse, you can see that there's a difference...

The carb/TBI will literally have a stream of fuel running along the floor of the manifold, that will be running into the engine as a stream, hugging any boundary layer into the cylinder...it WILL wash.

Port fuel injector will attempt to atomise the fuel, not hose a river into the cylinder.


Bingo

Port injection sprays the fuel under pressure in a mist onto the back of the intake valve. This is a far cry from the long path from the venturi on a carb to the back of the valve, where in cold conditions the fuel WILL condense/not atomize in the first place/pool/all of the above en-route to the valve.

And with respect to datalogging a cold start, yes, I have, with a Innovate wideband O2 setup. The richest I've ever observed on start was around 8:1, a far cry from 2:1 that's for sure.