cool idle.....

[Highbeam]

I think I would disagree since at load, the amount of gasoline being burned is large and the efficiency roughly the same (actually a bit better) as at idle so the power being produced is much higher and therefor the waste heat load to the engine higher. I see the gas engine in my pickup heat up on a hill and not at idle. If the engine is 40% efficient then 60% of whatever fuel you are burning is going right into the coolant systems and out the exhaust.

True, at idle a gas engine is sucking against the throttle plate. But the amount of fuel required to do that isn't much at such a low rpm. Some of the older ford diesels had a flapper in the exhaust that would close to allow warm up at idle. That flapper could be modified to make it also serve as an exhaust brake!

 

[HGM]

Good points.I still tend to believe the gas burner might be warmer at idle than its diesel counterpart. My reasoning is simply because the diesel requires less energy to keep it running due to the lack of throttle plate, its a big air pump requiring little fuel, using mostly centrifical force of the flywheel and crank. Who truly knows? I've never actually measured it..../forums/images/graemlins/grin.gif

As for the PowerStroke Exhaust Backpressure Valve, yes I've seen it too. Seen it cause alot of pedistal failures because of high RPM oil pressures being diverted into the valve that is designed to be operated at idle only. /forums/images/graemlins/blush.gif

 

[cp1969]

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Didnt this make sense???? )</font>

No.

Highbeam's response illustrates what is wrong with your reasoning. Pulling against a throttle plate doesn't take all that much power--I figure it would take about 5.2 horsepower to spin a 350 ci engine at 800 rpm against a perfectly sealed intake.

 

[SkyPup]

Typically spark ignition gasoline engine combustion chamber temperatures are higher than diesels by about 400-500*F, including the piston crown and exhaust valves.

Don't worry about it unless you are operating under a heavy load for an extended period of time or you accidentally forgot to fill your radiator. /forums/images/graemlins/blush.gif

 

[SkyPup]

Diesels also have a difficult time reaching the minimum exhaust temperature to even reach the minimum temperature required to operate the catalytic converter, whereas gasoline engines do not experience that problem sine their exhaust gases at idle are so much hotter.