Engine Temp Drops when going down hill..............

[rowdyprouty]

Hey guys, just wanted to see if anyone else has ever experienced this.
Up front I want to just say, I have not even really started looking at the systems myself, I've got a few ideas of what it may be, but just wanted to see if anyone else has had this same thing happen, because this is the first time I've ever seen this myself.

The car is a 2003 with right @ 200K. Its had all the usual like the timing belt and water pump done right after about 120k.
It runs and drives perfect, but when I drive down hill(in Washington we have a lot) if it is prolonged for a few minutes of driving at the angle, my temp drops dramatically, sometimes to below the cold line, like when it is first started in the morning. Yet driving it around, the temp is fine and it never gets hot or cold, stays pretty consistent. I have checked fluid levels and they are fine. I am inclined to think it is something with the waterpump because, I've noticed when I pop it into neutral and coast with the engine speeds at idle it is much slower to drop than when it is in gear at, say, 2k rpms.

This make any sense to anyone?

I will be out working on a few things in the garage today, so I may not answer any questions right away, but do appreciate any input or suggestions you all may have.

Thanks

[OMEGA PHX]

I've seen this on other cars when they don't have a thermostat installed, or maybe it is stuck open, thats what I'd check.

[rowdyprouty]

Thanks omega, I thought about that but wasn't sure due to the RPM relation. I'll pick one up tomorrow and start there I guess.


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[OMEGA PHX]

The RPM relation you are talking about is because while slowing down in gear @ 2k rpms the water pump is spining faster and moving the coolant faster than when it is in neutral @ 700rpms.

[rowdyprouty]

I guess the correlation of going downhill didn't make sense. I can see the RPms but I let it idle in the driveway, warms up. I leave in neutral and rev and it stays the same, no load. I go downhill and do essentially the same thing and the temp drops. That's what's throwing me.

My old Bronco with a 6.0L 400 V8 did have an issue with the thermostat that it was stuck open but it just would never warm up, even in AZ heat.

I'm positive that's what it is, it's just a strange correlation I guess.


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[oakrdrs187]

The RPM relation you are talking about is because while slowing down in gear @ 2k rpms the water pump is spining faster and moving the coolant faster than when it is in neutral @ 700rpms.

And you factor windspeed (washington is cold right?) going through the radiator plus no real load = effective cooling.

[6G72gearhead]

The injectors shut off when the engine is being driven by the trans until the rpm gets low enough to idle. Think about it, when you lift throttle to slow down if fuel is injected does it do any good? If the weight of the car is pushing the engine just use that.

Its completely normal, I've got a Volvo I can cool nearly 40* if I plan out my highway exit, which is like 1/4 of the gauge.

On long hills there isn't enough heat generated to keep it at full temp and the thermostat can only help so much. If it warms up and doesn't overheat I'd run it.