Car drops below operating temp with heat on

[MilTownSHO]

If the car is warmed up and I turn the heat on the temp guage drops to below normal range, or if I turn the heat on right away the car never fully warms up... Any ideas?

The car used to not want to idle right or it would die while doing this but it hasn't lately, I didn't change anything that I can think of besides clean my K&N but I really don't see how that would be related.

It's not a big problem right now being summer and all but when winter comes I don't feel like freezing just to make sure my car doesn't suck up pieces of the catalatic converter.

With the A/C on it stays in temp just fine...

 

[pete c]

coupla things. sounds like your A/C triggered secondary cooling fan is either always on or never on. It also sounds like your thermostat is stuck open. This results in just the right amount of coolant flow with the added load of the A/C and too much with the A/C off.

Does it run cool while sitting in traffic or is it only when moving.

I would go ahead and replace the thermostat first. Make sure you use the motorcrap one, not a cheap no name.

If it still runs cool this winter, do what the truckers do, stuff some cardboard in front of the radiator.

 

[AutoSHO]

pete c:

If it still runs cool this winter, do what the truckers do, stuff some cardboard in front of the radiator.

I would recommend against that. It ran perfectly normal temps from the factory, you shouldn't have to dehabilitate your cooling system to work properly in the winter months. A properly functioning thermostat will regulate the engine temperature perfectly.

 

[MilTownSHO]

pete c:

Does it run cool while sitting in traffic or is it only when moving.

It runs about normal operating temperature, it used to run hot and then drop like a stuck thermostat but its been fine lately. I was planning on a thermostat anyhow so I guess I will do it.

I think the fan works fine because I can hear it trigger on and off, but I'll have to watch it. Thanks!

 

[sdpatt]

Coolant temperature regulation is the sole responsibility of the thermostat. You need a new one.

 

[Shoaz]

Coolant temperature regulation is the sole responsibility of the thermostat. You need a new one.

Yup, I'll second that. Some thermostats seem to fail intermittently before they quit completely, apparently sticking occasionally before final failure. Mine seemed to do that when it died, too. At least the Motorcraft T-stats fail open...