Toshbar

Since getting my Edge CTS, I've noticed something weird:

After descending 5+ miles of 6-7% grade, in 3rd/2nd gear for engine braking, zero throttle input, my engine coolant temps will drop ~20 degrees. Normal operating temp for my truck is 188*F. After descending the temp will be around 165*F.


Anyone know why?

Mod (Ret.)

Normal.

With my Edge, I monitor the engine coolant and transmission temps. When towing my camper, I notice increases in temps when going up hills; the temps drop 10 degrees or more (back to normal) as soon as I reach level ground.

Toshbar

Yours is climbing and going back to baseline.

Mine is dropping below baseline.

Toshbar

Dropped down to 156 today while descending Idaho Springs -> Denver

a56nomad

I noticed that my 2004 Ford does the same thing, mostly when it is close to 0 degrees, going down hill it will loose about half the temp and the heater/defroster doesn't work that well when it reads only about half of what normal is on the temp gauge. I purchased a new thermostat but haven't replaced it yet.

jkenprice1

Here's my theory. Going down hill, thete's less load on the engine. It produces less heat. If the amount of removed by the air passing over the engine exceeds the amount being produced by the engine, the coolant temp goes down. Also a possible factor is the location of the temp sensors. Look at Semi's, they partially close off their grills in winter to maintain engine temps.

MetalCutter

Check your coolant level maybe? I had a Chevy truck that did this, sometimes even when coming to a quick stop. Turns out the coolant was low and it would rush out of the heater core into the block and when I accelerated back to normal driving it would return to the heater core and all would be normal again.

chayes627

I believe the 5.4 reads cylinder head temp then and bases coolant temp from that. Your coolant temps should not be dropping like that. Ther thermostat should close soe to maintain temp. I would check coolant level. If it's good I would possibly look into the thermostat.

Dirttracker18

This ^^^^^

No load to produce heat and excessive cooling as you are still moving at speed equals dropping temps. When under load your clutch fan helps to moderate temps but going downhill the speed keeps the cooling air moving through the rad without the engine producing higher heat.

Normal in the situation you have described.

chayes627

If it was below freezing then I might agree but I have been monitoring my coolant temps with Torque for well over a year and now with my SCT X4 and haven't ever seen temps drop 20+ degrees below normal operating temps no matter what the temp is outside.

On an engine without a thermostat like my dirt bike, then yes this would be totally normal.