Not letting engine "cool down" before shutoff
 

They say after driving a diesel engine, your supposed to let it idle for about a minute or so before shutting it off.
2 questions:

-Should you do this in a gasoline engine?

-What happens if you DON'T let it "cool down", (shut the engine off as soon as you are parked)? I know about letting it warm up before pulling off right after starting, but what can happen if you never let it cool down?

It can be hard on the turbo, not letting the oil cool down inside it. But an intercooled turbo cools down quicker. The turbo gets much hotter than the motor, yet shares the same oil. If you dont let it cool and recirculate out, it can bake, and leave hard crust inside and cause wear on the bearing surfaces.

If you don't let the truck "cool down" properly, say goodbye to your turbo. Only thing worse would running down the road with the hammer down and shutting the truck off, nearly guaranteed to lose the turbo that way. I see a lot of construction equipment that lose turbo's due to inept operator's not letting the thing cool down. They just shut it off with the throttle still wide open.

As long as your pyrometer is reading 300 or below it is safe to shut the engine down. The bearing technology has changed, and the newer engine oil doesn't bake on the bearings like in the old days. Most time by the time you exit the highway and drive at low speed into wherever you are going to park the turbo will have cooled sufficiently.

this is true.

In turbo cars they sell whats called a turbo timer. After the key is turned off and you walk away the engine will remain running for 2 minutes or so then turn off once its cooled down to prevent oil coking inside the turbo. Also another trick would be not running the car hard for 2-3 miles before you turn it off.

I had a car (can't remember what it was) with a turbo. It had an electric oil pump that kicked on after shutting off the engine that circulated the oil solely through the turbo for about 10 minutes.

Worked real good - I had to replace the turbo about 6 months after buying the car (it was used when I got it). It's a great idea though.

gasoline engines with a turbocharger usually have the turbo water cooled, so it's a moot point on those engines.

Besides, EGT's on gasoline engines don't vary as much as diesel engines, even at idle they're way over 1000 F due to more constant A/F ratio.

my MACK will not shut off. When you take the key out of it it will run for 4 mins and shut off on its own. Mack did it with the comptuer i hate it. It shuts off after 5 mins of idleing also. If it ever goes back to the dealer am gettin them to take that crap off. But you can get past the shut off thing. If you turn the key off and turn it on and off real quick again it will over ride it and shut the truck down. Back to the turbo timer thing they sell it for my diesel pickup but i think if you really needed one they would put them on right at the factory and it wouldnt be after market.

I usually let my engine idle with the fan on until it reaches the 150* range (ambient) when i shut it down. Shutting off a hot engine is never a bad thing.

I consider shutting an engine off hot is like not letting your engine warm up before a run.

The drive off of the highway and into the parking area or fuel pumps is plenty of time to get the things cool enough to shut the truck off. it is actually much longer to get off the highway and into the truck stop than the idle cool down that some say is necessary. Cooling down a turbo after the time it takes to get to the parking is just a waste of fuel for the most part.

Partially true fozzy, but sometimes I'm still at 200 after a climb into a rest area or out west in the summertime. I usually kick my engine fan on at an exit ramp though, and it usually is plenty cool by the time I pull in.

Are any of you guys opening the hood to help the cool down? I've seen people do it with VW's

The best way to do it is find someone with an empty reefer. Pull up behind the trailer with the doors open and fire up the TK, put the engine fan on and kick the idle up to 1200 rpm.. Cools that baby down in no time I tell you. :lol:

On My GMC Typhoon I used to open the hood :) The KW engine fn does a great job though

A time for new thermostats maybe? :lol: I usually keep my engine at 150degrees and around 170 on a steep climb with the engine fan on.
200 is just 50 short of overheating on a freightliner.

I run around 150-170, but on a long western hill, I hit 200, but never more. My KW is tip top, except for the front fender, but Teal can share that story :)

150-170? That's a bit cold. I'd check the thermostats.

Mine won't go below 190 no matter what you do with it. Even when it's -20 out. That is normal operating range.

Anything below 180-190 you're accelerating wear on the engine.

The point of idling isn't to get the water temp down, the engine doesn't care what the water temp is. It's 100% about the turbo. If our engines didn't have a turbo, it wouldn't matter.

The engine does care. When metal heat up or cools down too rapidly, that is when damage can happen like cracking or warping.

That won't happen. You'd need to pour ice cold water in a hot engine for that to happen.

Simply cutting off the supply of heat(engine running) won't screw it up. There's enough tolerances in the engine that it won't hurt it.

Like I said it's all about the turbo, more specifically, the oil inside the turbo.

Look at it this way, idling a gas engine never cools it down. The combustion temps stay exactly the same, have you ever heard of anyone "cooling down" a gas engine?

A gas engine also runs hotter then a diesel engine(inside combustion chamber).

I learned that you always warm an engine up so that all the metal expands evenly in cars that have steel blocks and aluminum heads. I'm not refuting the turbo issue, in fact I support it as I owned a GMC Typhoon with a turbo bigger than the Rev's Ego and blows more hot air than him as well :lol:

The device described above about the car with the oil pump on the turbo car is called a "turbo timer" and has a few other neat features as well. i dont have one, but my buddy's supra.

This man knows what he's talking about...

Here's a tidbit from cummins website:

Engine Operating Temperature (Coolant and Lube Oil)
Low coolant temperatures indicate an engine that is too cold for efficient combustion. Fuel liquefies on the cold cylinder walls and fails to burn. Of course, excess heat causes engine failure.
Lube oil below the ideal temperature is more viscous and harder to pump. Oil above the ideal temperature is too thin to lubricate properly. Either way, the engine suffers.
Coolant and lube oil operating temperatures can contribute greatly to fuel efficiency. Typical cooling system operating temperatures are above 180° F. A 0.4% fuel economy loss is associated with every 30° decrease in temperature.

Aluminum expands twice as much as iron does, no matter what you do.

That's why pistons have a decent clearance in the bore. Room to grow.

That's also why overheated engines scuff the pistons in the cylinder, they've expanded too much.

I always let the engine idle while doing paperwork then shut down. On my personal truck, I usually idle through the neighborhood on the way to the house and it's good to go. Either way, it should idle a few minutes as stated above.

I agree that the reason to idle the engine for a few minutes before shutting down is specifically for the turbo to cool down and is important to do. Also I'm all about letting a engine warm up. I usually start it up and let it idle for about 5 minutes and then kick the idle up to about 800-900 rpm for another 5 minutes and then hit the road taking it easy for the first mile or two. In cold weather I let it idle a couple extra minutes on the initial start up. I see drivers start their truck cold and not even 20 seconds goes by and they're bangin' through the gears goin' down the road. Nothing may go wrong for thousands and thousands of miles but eventually it will take a toll on the engine. I installed a remote start on duramax pick up so I could let it warm up a little bit and idle for a minute or two when shutting it down. :) :)