Warm-up....good or bad?

[bobboyer5]

Question:

I have read in past threads, that warming up car by letting it idle for a bit is not good; that it's better to just drive off.

Is this true? Why so?

Thanks.

[mzsmbs]

I think idling first is a good thing especially in the winter. I believe it is better to get the oils warm and in all the places they need to be before you load the motor and stress the tranny and the diff...
In the owners manual of my Pathy it actually says to let it warm up before driving.
I usually wait till the temp needle moves even just a bit in all my vehicles.

I also believe that a warm up is good but there are different definitions of what form a warm up should take.

One is that the car should sit and idle until its at or near normal working temperature.

Another is that one should start driving before the car warms up but to drive gently, not using the full throttle until the engine has warmed up fully.

In very very cold climates one MUST warm up the car to thaw out frozen components or use an engine block heater to keep the oil within its operating temperature.

I live in a climate zone where temperature rarely drops below zero. I drive the car to warm up. One car in the family which has been owned for 12 years from new has now done 120000 miles (1.3 litre engine). The engine is perfect in every way, not having had any rebuilds or replacements of major engine components. It doesn't need any work in the near future either.

This may not constitute proof but I think that it's a decent indicator w.r.t. newer cars.

In the past 15 years at least, manufacturers recommend that cars do not sit to warm up for environmental reasons. The sooner the engine is at operating temperature, the sooner it will warm up the cats and lead to cleaner emissions.

Adam

[Tomguy]

I have a vehicle in my family, also 12 years old, with 145K+ miles on it... the engine runs like new on it as well. It's never warmed up before a run and used ALL THE TIME in cold weather.

Of course, it is the legendary indestructible 4.0 in the Jeep Cherokee... but still, it's never warmed up and it runs fine! We ALWAYS use it in temps below freezing because it has 4WD... perfect for, say, 2 years ago at Christmas, when we had 2' of snow and I was the only one driving on I-81!

[jas2wa]

It is certainly needless and wasteful to let a new(er) car warm up- they're designed to reach operating temp quickly in order that the catalytic converter will do its job- just idling takes a lot longer for a new car to warm, and all it is doing during that time is polluting more than if the car was driven immediately and warmed faster.

With an old car, like my 280SEL 4.5, the general rule of thumb I use is to at least let it warm to the point that it goes off the initial, fast idle.

Of course, I realize my environmental concerns with new cars warming vs. my 73 non-cat-equipped pollution-mobile are rather contradicitory....

[300SDog]

Incomplete combustion of fuel when the engine warms up without being under load is the only reason I can think of for *not* warming up the engine at idle speed. Theoretically, this could have the effect of bore lubrication being thinned.

When cold starting the CIS fuel injected 280SE twincam 6 cyl, I used to wait until the high idle auto choke mechanism could be kicked down to normal idle speed with the accelerator pedal before driving the car.

[j9fd3s]

i start the car, spend the 10-15 seconds to put on my seat belt and make sure theres oil pressure and then drive slowly until its warm.

i have never had engine problems, and these are 90% rotary too

mike

[bobboyer5]

Well....after 3 days of this thread, I'm convinced (and I love all you guys) that there is NO possibility of a consensus of opinion in this forum.

Remember my simple topic 2 weeks ago as to which side went in first on the oil filter? Took 23 responses before we even had a grudgingly consistent view.

And here'ss another simple topic: Good or not to warm up engine (idling) before driving off?

Let's see. We got everything from: driving off immediately never harmed my car (well, that's a good approach - all's OK until thehammer falls) - to: idling the car too long thins out the oil and could thin out the bore lubrication. Hmmm...novel, but no cigar.

After listening to all, I'm going to apply common sense. which is: Let the car idle a bit until the needle starts to move and the fast idle can be kciked down, then drive off. Just makes sense.

This wasn't meant to be sarcastic or making fun of anybody, for I appreciate it all...and we need each other's help.

Just an observation. Great weekend to all!!

Bob

[mzsmbs]

Bob,

I think that's the best approach to any threads. Find something in the "middle" that seems comfortable to you and there you go.



BTW, if you want to see how many opinions there are just look at any oil thread.

[300SDog]

LOL, but I didnt make that up about idling resulting in incomplete combustion compared with driving under load. And especially with cold engine choked rich, you gotta expect less complete combustion with unburnt fuel fouling plugs and possibly eroding the bores....... yeah i know it sounds theoretical and far fetched but "Fuel Sloshing" the chambers is how it was explained to me at truck driving school when somebody asked about idling engines all night long.

[psfred]

Several thoughts here.

First, in the bad old days of lousy gas and crappy 1925 carbs (used by GM until 1972), the stinking car COULDN'T be driven until it was warmed up, it would stall. Had to get the manifold heat up to the point opening the throttle wouldn't lean it out so much it quit. Idle was way rich, too, most of the time (for the same reason), and you could fill the crankcase with fuel with extended idle. Much less true with FI systems.

Second, even though the engine on a D-jet will run fine stone cold, you are blowing HUGE amounts of fuel through it (it was designed for the same lousy fuel referenced above). Idling for a minute or so will GREATLY reduce this problem, and markedly improve the milage, too -- probably getting 8 mpg or less stone cold. Takes a couple miles on my 280 to get up to operating temp, so a couple minutes in the drive makes a BIG difference. The engine warms up fast idling.

Third, stone cold oil won't flow well, so even though the pressure is high, it's only going out the pressure relief valve and back into the pan. Some Italian cars require that rpm be limited until the oil pressure drops, or the cam bearings will sieze from lack of lubrication.

Forth, water condenses out of the blowby and collects in the crankcase on a cold engine, where it combines with other exhaust gases to make fairly corrosive acids. It will harmlessly boil off on a warm engine. The key here is to get the engine warm as fast as possible, and driving under load heats it up faster.

So here is what I do: If the weather is warm, I start up and drive off, slowly. Light throttle and 25 mph for the first half mile or so. If the weather is cool, I wait until the engine runs smoothly in the diesels and let the 280 come to fast idle, then drive off. In bitter cold weather I wait about a minute, no more, then drive gently for that first half mile. The diesels are sluggish anyway, and the Volvo knocks like crazy from advanced timing.

My rational: I don't want to put the engine under heavy load until the oil is flowing freely and the engine parts have warmed up to prevent oil starvation and thermal stress problems. RPM isn't the problem, just load, so once the engine is running smoothly, I heat it up faster by putting it under light load until the temp gauge moves, then drive normally.

If you live somewhere where you MUST accelerate hard before the engine has a chance to warm up (e.i. you are stuck taking a freeway entrance ramp less than a mile from the drive) I would definitely give a longer warm up -- you certainly don't want to stuff your foot down on a cold engine, this will greatly reduce engine life. The Volvo TD is known for worn cylinder bores from doing this -- the injection timing is greatly advanced (about 5 degrees) for better starting and running, so cylinder peak pressures are way too high until the timing backs off.

Peter