What I did find interesting in this video is that fuel dilution seems to increase to a certain threshold quite rapidly until it reaches a certain point of equilibrium, not gradually over an extended oil change interval as seems to be common knowledge? I don't think that a shorter oil change interval will reduce fuel dilution appreciably if the fuel will dilute again after just 10-15 minutes of idling. With that said maybe newer/fresher oil performs better in the presence of the same amount of fuel dilution. I really don't know. I'm going to do a 500 mile oil oil analysis sample on my engine after normal winter cold starts and idling and compare it to a 5000 mile one. In about 6 months maybe I will have an answer for my particular engine, at least.
Cold weather idling does increase fuel in oil!
- Thread starter Drew99GT
- Start date
- Joined
- Oct 25, 2021
- Messages
- 2,024
We often idled our Suburbans in Iraq for hours on end waiting for VIPs to come to a helipad or get out of meetings. They had the 8.1l so not a DI engine obviously but we never had any issues with the engines or oil.
I have read of ex cop cars for example with Hemis and LS engines suffering from cam wear due to hours on end of idling, makes sense, on a pushrod V engine the cam lobes are only lubed by splash lubrication from the crank, even modern ones, correct me if i am wrong.
But at least that's why with flat tappets you have to break in the cam at 2-3k rpm or else the cam won't get enough oil film on it.
But at least that's why with flat tappets you have to break in the cam at 2-3k rpm or else the cam won't get enough oil film on it.
Living in a very cold climate means both of our vehicles get their fair share of idling. Fuel dilution is never bad enough to the point that I can smell it on the dipstick, but I do run a grade higher in viscosity for more protection as inevitably some dilution is occuring. As I write this waiting in a grocery store parking lot for my wife, over half of the cars are idling (vacant). It's the way of life around here when it's below zero.
- Joined
- Mar 13, 2024
- Messages
- 224
My car (1st year Miata) is 35 years old and has about 225K miles on it. It drives and idles perfectly and is on it's original drivetrain. I take good care of it but don't baby it, depending on your definition of 'babying', lol. I do however take care of it a bit differently than a lot of people. For starters, I idle it for 3-5 minutes no matter what the temps are at start up in the morning. I believe this is better for the motor and everything connected to it than just starting it and driving away. Yes a car warms up faster being driven immediately, but it's also harder on the components imo. Also I let the car idle while I go into stores or wherever. I lock it and have 2 sets of keys so I can leave it running. I firmly believe leaving it idling is much better than the constant stop/start up I would be doing when running multiple errands.
I know many will probably not agree with my car care routine (haha) but as I said, it runs much better than many newer cars. I daily it to work and my wife and I usually drive it for a multi hundreds of miles day trips over the weekend to see new things. Never an issue with the car, always starts fast and strong and drives perfectly, so I feel like I'm doing something right. I'm hoping to reach 500K miles on the factory drivetrain.
I know many will probably not agree with my car care routine (haha) but as I said, it runs much better than many newer cars. I daily it to work and my wife and I usually drive it for a multi hundreds of miles day trips over the weekend to see new things. Never an issue with the car, always starts fast and strong and drives perfectly, so I feel like I'm doing something right. I'm hoping to reach 500K miles on the factory drivetrain.
Diesels are quite a different animal from four stroke gasoline engines. Their behavior mimics more two stroke gas engines IMO. That is, they don’t “like” to be idled or operated at low loads. Both will experience much heavier combustion deposits when operated lightly.
In essence, diesel engines are work horses. They need to see load and boost to operate properly.
In essence, diesel engines are work horses. They need to see load and boost to operate properly.
Lots of mystique and urban myths around diesel pickup culture and overuse of the word "properly." Proper this, proper that.
Mine reaches operating temperatures just fine on an unloaded sunday trip to the hardware store. Yeah, it's never going to trip a passive regen under those conditions but otherwise short/cold tripping is no more harmful on it than on a corolla. If you idle more or short trip, you should probably consider that in your oil change intervals. Goes for any engine.
The ford 6.7 has low tension rings, which increases blowby at idle (cold or hot) and incomplete combustion (due to cold intake temperatures, cold combustion chambers) can lead to fuel blowby in any engine, especially diesels where the combustion process is slow and fuel burns from liquid droplets, not from vapor. Light duty pickup diesels also lack a PCV system. The only crankcase ventilation comes from the release of blowby (push combustion gas out with more combustion gas)...quite a bit different than using a vacuum source to draw fresh air into the crankcase and draw diluted combustion gasses out.
The fearmongering of pop culture diesel experts (dave included) is a bit extreme but it gets youtoob followers and advertising clicks which ultimately sells aftermarket diesel hardware, additives, etc. Yeah, you probably shouldn't do heavy loads on ANY car until fluids are circulating well. Gently getting out of the neighborhood isn't going to do any damage and is the faster path to warmup.
Then you have this guy...another self-proclaimed youtube master mechanic expert...who promotes idling to warm things up. He says that idling in cold temps (EGT 350 F) gets your engine warm and happy.
Last edited:
No more harmful than on a Corolla you say?
Just wait until your EGR or DPF plugs up and then you’ll understand. It’s not just about changing oil and fuel dilution. It’s about soot production.
Here is some more fear mongering for you.
This is the sort of mess I helped my FIL clean up in his 2001 Jetta TDI. And that’s a much simpler diesel engine than the new ones.
Excessive cold operation would be harmful for either from a stance of fuel/water accumulation in the crankcase. We've seen milkshake oil changes on this forum from gassers that never get hot.No more harmful than on a Corolla you say?
Just wait until your EGR or DPF plugs up and then you’ll understand. It’s not just about changing oil and fuel dilution. It’s about soot production.
Here is some more fear mongering for you.
This is the sort of mess I helped my FIL clean up in his 2001 Jetta TDI. And that’s a much simpler diesel engine than the new ones.
View attachment 264099
If we're talking about exhaust soot accumulation, my 1997 honda accord clogged it's egr passages. So did my 1988 buick skylark with the invincible iron duke. So your anecdotal photograph is not specific to diesel. When we take hot exhaust gasses and cool them, we can get liquids and potentially even solids out of them. Gas or diesel doesn't matter, still happens under the wrong conditions. Woodstove and chimney, yep. This is not a unique phenomenon. The most modern diesels have the ability to bypass the EGR cooler to help reduce this effect.
That said, my diesel truck isn't a daily driver. It would be a little excessive and expensive to punish with a 4 mile commute. Camper season is around the corner and it will be duly worked.
Last edited:
The point is that diesel engines are much more prone to this because they produce much more soot.
It’s funny to see you saying in one post that short tripping a diesel is no more harmful than short tripping a Corolla, and then in another post you say it would be excessive to punish your diesel with a 4 mile commute. So which one is it?
It would be harmful for any car in my fleet to never reach operating temperature. So I have a cheap beater car which happens to also be a mechanically simpler machine. It is maintained accordingly for a short tripped vehicle. Those maintenance items are much cheaper on the beater than the truck, so it's overall a money save, fuel save, insurance save, etc. I save the larger consumable investment for the purpose that requires it. Where's the irony? To do it "properly", I'd start riding a bicycle again.
IIRC, my 1997 honda sooted the egr passages shut sufficiently enough to cause a MIL...twice...prior to the first timing belt (100,000 miles.) I just got into the habit of cleaning the manifold every valve adjustment. My 2006 duramax had 220k when it was deleted and had no degraded function at that point. My 2014 cummins is only at 82k and has a 42 mph lifetime average. I'll be sure come back to this thread when it requires an EGR cooler, valve, etc. (Then again, those are known maintenance items.) Anecdotally it appears my honda was more prone to egr system obstruction than either of my diesels.
Any ICE will suffer greater soot accumulation and crankcase vapor accumulation when greater operating hours are spent in warmup mode. Lake Speed points to the piston ring gaps. All my ICEs have piston rings. This is not a diesel phenomenon.
- Joined
- Nov 29, 2009
- Messages
- 9,279
This has been a known fact for years
I never claimed short tripping a gas engine has no effect. That’s not my contention. My contention is with your claim that short tripping a diesel engine is the same as gas engine. That’s simply not true.
Your Honda problems with EGR were likely related to oil burning, as they were quite famous for it in the 90s.
Diesel engines produce orders of magnitude more soot than gasoline engines and short tripping them has more negative effects than gasoline engine because of that.
Ring seal is more a function of cylinder pressure than temperature. The end gap is not a major contributor to leak down. Most leakage is around the back of the ring via the ring groove in the piston.
This part is true. Which is why diesel rated-oils are heavy on soot dispersants
...but this part is not true. Higher soot generation isn't much of a factor at all in short-tripping diesels.
Short tripping a diesel causes several issues, but it's not because of soot generation. Cummins allows 5% soot for every engine except the newer B and C engines which can only go to 3%. (ref TSB 5411406 "Fluids for Cummins Engines.")
The primary thing you will see in short tripping diesels is fuel dilution, not soot. Cummins has a 5% limit for fuel dilution as well. Especially in cold weather, a cold diesel generates white smoke, not black. It smells different for sure. Better and less acrid to my nose.
What is soot? It's essentially microscopic charcoal. It's fuel that got hot enough to burn, but was in an oxygen deprived locality while exposed to that heat. So just as you convert wood to charcoal be heating it in an oxygen-depleted environment, you can make soot the same way from liquid diesel fuel. Usually this is the result of poor cylinder mixing. (remember, diesel combustion is a diffusion flame and is not premixed. Gasoline flames are premixed even in a GDI/TGDI application because fuel and oxygen are intermixed before ignition. In a diesel combustion, the mixing occurs *during* combustion).
Soot particles are tiny-- sub micron typically < 0.1 micron. A red blood cell is 4-6 microns, or 40x-60x the size of a large soot particle. This is why soot in the oil cannot be filtered out and the only way to reduce soot loading of oil is prevention. Even the much-loved bypass filters won't remove soot (although I've seen evidence the centrifuges can because they work differently.
Tribologically, soot increases the viscosity of oil at higher soot loads. Because soot particles are much smaller than MOFT, they have very little effect (i.e. none) on lubricity and abrasive wear. At least, when they are small individual soot particles.
But soot particles like to stick to other soot particles and form carbonaceous deposit. These deposits seem attracted to piston crowns and top ring lands. If they get hot enough and hard enough, they can create some nasty abrasive wear on bores/liners and ring lands. Carbon crusting the guts of a modern diesel is a big problem because all that crud that used to go out the tailpipe is now contained. Yes, we're emitting a LOT less. But we're only making slightly less. Hence why DPFs are needed and why soot management is a big part of CK-4.
How healthy would be your colon if the government banned sewage generation? Yeah, that's what's happening here. Even if you eat a lot less and drastically upsize your pants, you're still going to have a problem keeping fresh underwear in place.
Anyway, the point of this aside is that, while diesel are slower to warm up, they can manage that pretty doggone well. This is partly because the fuel dilution is from a light oil (diesel fuel) that has pretty good lubricity compared to the light solvent that is gasoline.
Also, the fuel dilution of diesel fuel can be burned off almost entirely with prolonged operation at higher load. Hard to do in a pickup or small car, easy to do in a generator or other industrial equipment.
Ah, the good old days of grabbing some tired old 6.5s out of WRM from the local Dyncorp reps.
I'd love to have one of those.
my 2 cents. Start, wait 30 seconds then light throttle when cold. Idling in general is not the greatest for any engine. ... or the enviroment. I do sometimes especially if its real cold and snowy. In general a good OCI with a good product, its a moot point. As said, a diesel is 100% air in all the time. Its best not to idle long.
Similar threads
