Car manuals say: "Don't let your engine run idle for long"

[AstroGuardian]

I was reading my Chevy Spark's user manual when i came across this:
"Don't allow the engine to idle for long"
But it does not say for HOW long... And frankly, why not? It doesn't say the reason also.
I have read this about Skoda, Ford and Folkswagen but none of them writes as to why should't i leave the engine to idle.

Anyone has an idea? I mean from technical point of view aside for CO2 emission, fuel consumption or so...

 

[JCH13]

Idling gets more fuel in your engine oil than running the engine under load. Fuel in your oil screws up the oil's viscosity and ability to lubricate your engine. Bad news.

 

[skyking]

^ all that, plus the exhaust system is too cool, etc. The powertrain is not designed to idle for long periods of time. It is designed for a median amount of work.

 

[Bignate603]

There's no point where it's suddenly damaging, like 5, 10, or 20 minutes. It's more of cumulative problem over the life of the car. The only immediate thing that you might run into is overheating, especially if you're running accessories like the AC.

 

[darkswordsman17]

Also, idling is one of the worst things in regards to efficiency as no work is being accomplished so its usually fairly wasteful. Plus, I've actually seen people complain about how few miles they get out of a tank of gas and come to find out, they let their car idle a lot.

 

[DivideBYZero]

The manuals focus is emmisions and fuel consumption.

 

[WhoBeDaPlaya]

I usually let my car idle for 3-5 mins in the mornings and after work, then drive it easy for the first couple of miles.

 

[HarryLui]

Idling your car is a waste of gas when the engine is in its operation temperature.

 

[amdhunter]

Pollution and emissions more than anything else I bet.

 

[mb]

I usually let my car idle for 3-5 mins in the mornings and after work, then drive it easy for the first couple of miles.

Unless you do that with a remote starter to cool/heat your car, that is 100% pointless.

 

[AstroManLuca]

On the other hand, you shouldn't stop and start your car too much either. I made that mistake while waiting in line for a car wash. Rather than idling for ~3 minutes while each car ahead of me got washed, I just shut the engine off. Third or fourth time, the car wouldn't start. Luckily it did eventually start after it sat around for a few minutes. Scared me though.

 

[JulesMaximus]

I usually let my car idle for 3-5 mins in the mornings and after work, then drive it easy for the first couple of miles.

There is really zero need to do that. Unless it is brutally cold outside you can safely drive off within 10-15 seconds after starting the engine. Just don't romp on it until it is up to normal operating temperature.

 

[exar333]

The only time I let my car idle is to warm it up in the winter; sub-zero temps don't agree with vehicles to well (assuming it is left outside). Usually 3-5 minutes is plenty.

 

[JCH13]

There is really zero need to do that. Unless it is brutally cold outside you can safely drive off within 10-15 seconds after starting the engine. Just don't romp on it until it is up to normal operating temperature.

Exactly. Your engine warms up faster under a light load anyway.

The only time I let my car idle is to warm it up in the winter; sub-zero temps don't agree with vehicles to well (assuming it is left outside). Usually 3-5 minutes is plenty.

This too, otherwise the transmission fluid feels like sludge and makes shifting a bitch.

 

[thescreensavers]

hmm, dont trunks idle for hours on end?

I never heard about idleing causing issues :O, what about people who sit in a drive through?

 

[Vette73]

hmm, dont trunks idle for hours on end?

I never heard about idleing causing issues :O, what about people who sit in a drive through?

Leting your car idel use to be bad when cars came with Carbs and they dumped to much fuel in. With FuelInjection it is not really an issue anymore. Waste gas; but should not damage the engine.

 

[JCH13]

Leting your car idel use to be bad when cars came with Carbs and they dumped to much fuel in. With FuelInjection it is not really an issue anymore. Waste gas; but should not damage the engine.

Blackstone oil testers frequently link excessive idling (even lots of stop-and-go) to abnormally high levels of fuel in the oil, at least from what I've read. Granted it would take a bit of gas to cause immediate damage, cumulative effects will be bad.

 

[AstroGuardian]

Idling gets more fuel in your engine oil than running the engine under load. Fuel in your oil screws up the oil's viscosity and ability to lubricate your engine. Bad news.

What you say here mate IMO is contrary to logic. If the engine idles there is minimal stress to the piston rings and therefore minimal chance that a fuel would pass through and mix with the oil. I don't understand how would fuel mix with oil?

 

[AstroGuardian]

^ all that, plus the exhaust system is too cool, etc. The powertrain is not designed to idle for long periods of time. It is designed for a median amount of work.

Sorry i forgot to mention that it is a manual transmission vehicle which means that when in neutral there is zero stress to the transmission...

Why do you say that the powertrain is not designed to idle? I mean a machine is machine, it should work better with less stress than with more stress...

What does exhaust system temperature have to do with anything?

 

[AstroGuardian]

There's no point where it's suddenly damaging, like 5, 10, or 20 minutes. It's more of cumulative problem over the life of the car. The only immediate thing that you might run into is overheating, especially if you're running accessories like the AC.

This is the most logical explanation by far. let's say that the AC is not on (i rarely use it).
Overheating should not happen even with AC turned on. In one occasion after climbing a mountain road for a whole hour i left the engine to idle a bit in order to cool off. I forgot it for at least 45 minutes. The temperature was only 85c and the cooling fan was off.

I didn't mention that it is a 0,8L three cylinder engine with 55 horsepower and 75nm torque...
I know you Americans will laugh... but at least i get 65mpg in Europe (autobahn)

 

[AstroGuardian]

I usually let my car idle for 3-5 mins in the mornings and after work, then drive it easy for the first couple of miles.

Whatever anyone says that's a smart thing to do especially during cold winter mornings. The oil does not lubricate the engine and transmission before it's heated up to at least 5c.
That's why the Germans tanks lost the war in Russia during second world war cause their oil froze and mutilated their engines

 

[AstroGuardian]

I am only guessing that there might be less oil pressure during low RPM and therefore less lubrication. But i have seen the engine valves (i don't know the english terminology for this. Actually i peeked through the oil cap on the top of the engine and all visible parts are juicy lubricated even during cold start) and they were all lubricated.

What is you opinion on this?

 

[JCH13]

What you say here mate IMO is contrary to logic. If the engine idles there is minimal stress to the piston rings and therefore minimal chance that a fuel would pass through and mix with the oil. I don't understand how would fuel mix with oil?

This happens for a couple of reasons that I am aware of:

1) Piston speed is low, so there is a longer time for air/fuel mixture to slip past the piston ring.

2) Timing is retarded, so again there is a longer amount of time that there is unburnt fuel in the cylinder, and therefore more time for it to slip past.

3) Idle is generally at a very low MAP (manifold absolute pressure) and your PCV (positive crankcase vent) brings the crank case pressure down very low. This creates a larger pressure difference across the piston rings, which results in more air/fuel being pushed across the piston rings.

Does that make sense?

The stress that piston rings see (I believe) are not large enough to create significantly more leakage.

 

[mb]

Whatever anyone says that's a smart thing to do especially during cold winter mornings. The oil does not lubricate the engine and transmission before it's heated up to at least 5c.
That's why the Germans tanks lost the war in Russia during second world war cause their oil froze and mutilated their engines

Incorrect.

Maybe a full minute or two on those super cold mornings (or however long it takes for the interior to warm up anyway), but for the other 360 days of the year, it is not needed. By the time you buckle your seat belt and release your parking brake (if applied), you're good to go.

Next you'll be telling us we need to inflate our tires to sidewall.

 

[AstroManLuca]

Incorrect.

Maybe a full minute or two on those super cold mornings (or however long it takes for the interior to warm up anyway), but for the other 360 days of the year, it is not needed. By the time you buckle your seat belt and release your parking brake (if applied), you're good to go.

Next you'll be telling us we need to inflate our tires to sidewall.

How cold is "super cold"? Should you let your car warm up for a few minutes when it's below 15? Below zero? If you live in California you may never have to let your car warm up but if you're in Minnesota or Michigan there are a few months of very cold weather every year.