Gernby

I think this is a complete waste on an NA engine. If you hook up an OBD-II scan tool to monitor engine temp (coolant temp), you will see that the engine runs MUCH cooler at speed than it does at idle, since the water pump doesn't pump much coolant. By letting your engine idle in the parking lot for 1 minute, you could be raising the engine temp by another 30 degrees F.

koala

The only time I do this is after a track session. I pull it into the pits, let it idle for a minute then I turn it off.

For street driving I don't see the point.

Gernby

The only way you are going to cool the engine in a parking lot is if you turn your heater on full blast, and rev the engine to 3K RPMs for a bit.

ChrisD

Whoa, I'm way outnumbered here huh. My whole point is that what you said here isn't false, but that when you shut down the engine, the coolant temperature within the block will raise because it is no longer flowing and taking heat away from the engine and exchanging it with the radiator. I'd also be surprised if an OBD2 sensor showed a noticable rise in temperature because the probe is most likely not in the block.

Like I said, it's only a theoretical guess, and a few seconds of cool down can't hurt, can it? It's like that saying about religion: May as well believe in God and be proven right than NOT believe in God and be proven wrong.

wicky

I agree with gernby on this one. You must keep in mind when your are stopped and idling you are most likely to be increasing the engine temp, not decreasing it, since there is no air flow over the radiator, it's as good as the car sitting turned off, but you are still adding heat in it from combustion. Logic would suggest that turning the car off when the temp is the lowest would give the widest margin for the coolent to soak heat out of the block and prevent warping. By idling the motor, you are keeping the block AND the coolant temps up, thereby giving the heat less places to go. If your car runs hot then cools off when idling, it's my opinion the cooling system needs some upgrades to help dissipate heat generated from running hard.

Gernby

Again, the problem is that at idle, there is VERY LITTLE coolant flow, so it doesn't cool. There are apparently 2 temperature sensors. One for the coolant temp guage, and one for the ECU (OBD-II). Last fall, I could cruise with a temp of around 170F, but when I sat in a drive-thru, my OBD-II temp climbed to 230F. This was definitely NOT the temp of the radiator, or my temp guage would have gone to 4 bars.

Ubetit

[QUOTE]Originally posted by gernby
[B]I think this is a complete waste on an NA engine.

wickerbill

Anybody who has watched many F1 races knows that those cars can overheat in a matter of a minute or two sitting still at idle. While our cars are VERY far from that extreme, I don't see how the engine running at 900 RPM's is going to do any cooling of the engine while sitting still. It's just a waste of time and gas.

Prolene

[QUOTE]Originally posted by ChrisD
[B]By not running the engine, you can cause coolant to stagnate and even boil as it's no longer moving and whisking heat away from the engine, instead acting as a mild insulator. While the heat may not necessarily be damaging, it will certainly be higher than operating temperatures.

HARDtoTOP

The way I look at it is that this is a production car, and is designed to be driven and shut down, then driven some more, and shut down, etc..... Unless you have some crazy work done to the car or drive the streets like a madman, all thats being done by letting it sit is to kill a few more trees over the life of the car. How many people let their daily drivers of all makes and types idle at all after driveing? What would make this car any different?