Toshbar

Does the fuel injection shutoff fuel completely above a certain RPM with no throttle input? I know some cars do this and that would eliminate any heat production other than friction inside the engine. With pure cold air coming inside the engine and no combustion, it would cool the heads from the inside.

What dirt bike do you have? My 2009 YZ450F and 2004 200EXC had external thermostats between the cylinder head and radiators.

chayes627

2007 crf250r

Especial86

iTrader: (1)

Cold air sinks. The lower the elevation you travel, the cooler the atmosphere becomes.. Plus while coasting down grades your riding the brakes more than the engine. The momentum from a downhill coast takes a significant load off your trans and motor while in OD or neutral.. Plus, since your coming down grades it also implies that you went up a grade in order to descend one. Expect your temps to be all over the map.. High going up, and drastically cooling going down..

Toshbar

Have you ever been to the mountains?


I'm not sure if you're just joking now.
If you ride your brakes down the mountains in neutral, you will die or at least have to use the runaway truck ramp.

PerryB

Good question regarding the injection. The diesels shut down during zero throttle decel, but I don't know about the gassers. I am surprised that your temps drop as much as they do, but sender location may be causing this. Im guessing its being influenced by exhaust temp. I remember several years ago Lycoming was having oil temp. issues on certain aircraft (Cessna 172's, I think ) and it was discovered that the sender was being influenced by being in a hot, poor airflow area and the muffler was making the temps. appear higher than actual. The high tech. fix was a small (about 3/4") tube that blew cool air on it, tapped in from the cold side of the cowl. My only other thought is maybe the thermostat isn't closing completely and the engine over cools during extended coasting.

Mod (Ret.)

He was not suggesting this, but simply offering an answer as to why the temps may be lower going downhill.

Dirttracker18

What?

The outdoor temp will ALWAYS be lower than the operating temperature of any internal combustion engine thus a drop of temp while moving but not under load. It does not need to be below freezing outside to see a drop in engine temps when going downhill. Temps can still drop below the thermostat engagement temp under the right conditions.

It is very simple. High load during accent leads to a rise in engine temperature while descending while off the throttle will result in a drop.

It's not rocket science.

jamie930

I have noticed this in my truck also when going down hill, foot off the gas, for a long period of time when temps were around freezing. The temp gauge had dropped below where it normally is.

I do not know how the fuel injection system works when you have 0 throttle. I do know the car I have, 4 cylinder 5 speed, at 0 throttle it shuts the fuel off as long as the rpms stay above idle.

So an engine the is just free wheeling, not burning fuel the engine heat source, sucking in cold air and cold air moving across the engine should drop the engine temp.

Ford already uses this when the motor overheats it will shut off fuel to cylinders to keep the heat down

Toshbar

Coolant temp got down to 152, from a normal operating temperature of 188 while coasting downhill in 3rd gear for about 3 miles. Outside air temp was -31*F.

Toshbar

Another observation is that my Edge CTS does not display negative Intake Air Tempuratures.