Idling and Oil Life

[JD Green]

Most, if not all of us here at BITOG would agree that exsessive idling is detremental to an engine oil's life.

I think it's also safe to say that we've seen and know that highway driving or conditions where the engine RPM is more "constant" is more favourable to and leads to longer oil life.

What is it exactly about exsessive idling that kills oil life? I mean idling is a constant operating condition (500 to 1000 rpm) for most applications versus 1500 to 3000 rpm for most applications under highway driving.

Any thoughts?

 

[tackleberry625]

As far as the engine is concerned, when the engine is at a higher RPM, there is more oil pressure and faster oil flow. When an engine is idling for long periods of time, the engine does not receive a good amount of lubrication.

Oil runs hotter and the excess heat breaks down the oil faster than when the vehicle is running down the road at a slightly higher RPM and getting cooler air through it. Also the engine oil can get overwhelmed with excess fuel, ie fuel dilution.

 

[ChiTDI]

Fuel dilution was my thought.

 

[Doug Hillary]

Hi,
JD Green - A comprehensive study on a Bus fleet (diesel engines) by the US Dept of Energy during 2005/6 showed that constant idling had no detrimental effect on engine life as long as normal service routines were followed. In fact the lubricant's condition was better after 1000hrs idling than after 5k miles of normal running!

That said, in my heavy diesels (DD Series 60 - 500hp) I had a maximum allowed operating idle time of 3 mins (policed via the ECU). This time was rarely reached as they were typically shut down earlier by the Driver using the pyrometer's reading

I have never ever allowed my petrol engines to idle beyond actual need

 

[Mr Nice]

Our Accord idled for five hours over night cause a transformer in our neighborhood blow up and we were without electrictiy. This happened during the peak of summer with close to 90% humidity.

At 2:30 AM , my wife told me she was going outside to sleep in the car (I'm thinking with the windows down). So at 7:30 AM, I wake up , I go outside and I find her asleep curled up in the back seat with the windows rolled up, A/C running.

I asked her how long has the car been running..... she tells me since 2:30 AM when she started the engine.

I did not get an oil sample cause I immediately drained the oil, but now that you guys are talking about 'Idling and Oil Life' ....I wished that I sent that oil out for a UOA.

 

[rg200amp]

Originally Posted By: LT4 Vette
Our Accord idled for five hours over night cause a transformer in our neighborhood blow up and we were without electrictiy. This happened during the peak of summer with close to 90% humidity.

At 2:30 AM , my wife told me she was going outside to sleep in the car (I'm thinking with the windows down). So at 7:30 AM, I wake up , I go outside and I find her asleep curled up in the back seat with the windows rolled up, A/C running.

I asked her how long has the car been running..... she tells me since 2:30 AM when she started the engine.

I did not get an oil sample cause I immediately drained the oil, but now that you guys are talking about 'Idling and Oil Life' ....I wished that I sent that oil out for a UOA.

Who refilled the gas tank, you or her???

 

[trail_rated]

I idle my Jeep on a regular basis. Think about it this way, start = no oil, run = plenty of oil. I have 150,000 miles on her, but that could also be because she has a 4.0L in it (indestructable engine).

 

[Jim Allen]

I think you'd need to qualify this a bit more. If you do a cold (I mean COLD) start and let an engine idle, it takes forever to get a gas engine out of open loop. Diesels don't generate much heat idling, so they would slobber on a cold start... at least the old mechanically injected. What I would wonder is whether the oil would get hot enough to cook out the fuel or condensation? Now that gas is cheaper, maybe I'll idle my truck and see how long it takes to get the oil up to temp. If the engine was idled after running for a period, I imagine the negative effects would be negligible.

 

[Johnny]

If you let a car set and idle all day long, the oil will never get up to optimum operating temp. If you drive around town all day long, 25-45 mph, stop light to stop light, the oil will never get up to optimum operating temps. Steady constant highway speeds for at least 30 minutes is the only way to reach the optimum operating temps of motor oil. Until the optimum temps are reached you will have fuel and condensation contamination.

 

[Ken2]

Quote:
Until the optimum temps are reached you will have fuel and condensation contamination.
YES.

Diesels are much worse than gasoline engines. At light load a diesel engine doesn't burn hot enough to burn cleanly. The oil that gets past the rings (and some oil must get past them to lube the cylinder walls and rings) doesn't burn cleanly at light load and low temperatures, and there is a chance of the fuel not burning completely. I've been trained at two diesel factories, and both said to shut the engine down, if possible, or load it up, rather than run at light load.

 

[Steve S]

Like the rest of the articles we read yet can't really comprehend .Don't worry about it .If for some reason you must idle the engine idle it .When you don't have to idle it don't .You will save some Gas.

 

[Steve S]

Usually the reason freeway driving is considered better for the engine is because the engine is at operating temps which is the lowest wearing mode of operating conditions.

 

[Steve S]

Originally Posted By: Jim Allen
I think you'd need to qualify this a bit more. If you do a cold (I mean COLD) start and let an engine idle, it takes forever to get a gas engine out of open loop. Diesels don't generate much heat idling, so they would slobber on a cold start... at least the old mechanically injected. What I would wonder is whether the oil would get hot enough to cook out the fuel or condensation? Now that gas is cheaper, maybe I'll idle my truck and see how long it takes to get the oil up to temp. If the engine was idled after running for a period, I imagine the negative effects would be negligible.
Years ago "1977" i was driving trucks and got snowed in for almost 2 weeks I shut my truck off and another trucker let his truck Idle for the whole time .When the roads were clear he was on the road .I couldn't get the truck started even after charging the batteries over night .I had to have the truck towed to a place to warm it up. I would have saved me a large sum of $$$ if I kept it running.

 

[Jimbo]

My 1994 Ford truck owners manual recommended installing an engine hour meter and changing every 200 hours if the truck was used in such a way that it was idling more than driving. This was for gasoline engines. The diesel manual could have said the same thing, but I didnt have it.

 

[Gary Allan]

Quote:
What is it exactly about exsessive idling that kills oil life?


Next to nothing, assuming that everything else is working right and we're talking hot idling. What fatigues the oil is the mismatch between mileage and fuel consumption. You're getting ZERO mpg ..so how can a mileage criteria be accurate in determining oil life?? Taxi cabs use 3-4k miles as a basis for OCI's ..yet almost all of it is at operating temp. They're consuming (probably) 50% more fuel per mile on average.

The engine should swap in and out of open and closed loop just like it does with variations that everyone encounters on suburban and even highway driving (to a lessor degree).

Fuel and moisture components take longer to purge the lower the temp. They still purge, just not as fast. That's why short trip usage plays havoc in moisture retention. If you only reach 180F oil temp, you require a longer duration @ 180F than you would if you peaked @ 215F+. It's a time weighted thing. A glass of water will evaporate at room temp if you leave it there long enough.

 

[jldcol]

I think the engine's cooling is sized for worst case scenario, maybe hauling in high summer heat with a/c on. Most of the time it's way oversized. Idling is the lowest load state and therefore not much heat being generated. Your oil will stay cooler than coolant,(about 50deg). Even if radiator fan cycles on/off you oil's probably only 150deg. Is this hot enough to fully activate all oil additives? I also think even electronic engines run a little rich at idle, to ease thru the off idle rpm range, then back to ~14/15 to 1 range at cruise rpms.

 

[pzev]

Several times in my cars life it has idled for hours at a time. No ill effects. In fact, my engine spends a good amount of time at idle, as I will eat lunch or just listen to music waiting for my next appointment.
That said, no UOA's....so my evidence is purely anecdodal.

I run group 3 synthetics changed at 5k on average...with the occasional 7-9k oci depending on how busy I am. My engine is relataively easy on oil. Most of the time spent at idle is with the engine nice and hot.

 

[Nyquist]

Originally Posted By: Johnny
If you let a car set and idle all day long, the oil will never get up to optimum operating temp. If you drive around town all day long, 25-45 mph, stop light to stop light, the oil will never get up to optimum operating temps. Steady constant highway speeds for at least 30 minutes is the only way to reach the optimum operating temps of motor oil. Until the optimum temps are reached you will have fuel and condensation contamination.


Do you suppose that this may be more tied in with engine RPM too? There are times where I turn more RPMs in the city than on the open road.

 

[zulu]

FWIW, the GM Oil Life Monitor HEAVILY penalizes cold idling. Not so much at operating temp, like sitting in traffic. I've noticed if I start either of my GM vehicles and let them warm up for 5 minutes or so, the OLM has a tendency increase oil life decay significantly.

 

[wileyE]

Think idling was worse back in the carb days than it is with FI. Less fuel dilution also the newer vehicle use hotter stats and roller cam followers.