Engine temp gets cold on the highway

[Hartman]

Hey guys, I have somewhat of an interesting problem. I just replaced my thermostat because the old one was stuck open, now the engine warms up pretty fast and the heat works fine, except when I get on the highway. It seems when I'm going a constant speed, the engine temp drops all the way to 'C', and of course the heat goes cold. When I'm on the highway, I usually use the cruise control, I don't know if that might have anything to do with it because I have been told that I have a vac leak somewhere but I can't find it for the life of me. I'm also thinking it might be my fan clutch.

Any thoughts?

 

[JDraper]

Could be a fan clutch. Symptom is right for that. Either that or your new t-stat is defective....

 

[ipozestu]

Hartman it sounds like you got another bad thermostst, or the wrong one. That is the only thing it could be IMO..

 

[ipozestu]

Originally posted by JDraper
Could be a fan clutch. Symptom is right for that. Either that or your new t-stat is defective....

If the fan clutch was sticking it wouldn't matter if the thermostat is functioning properly.

 

[Hartman]

I really don't think it's the thermostat because it works fine during city driving? I know it's the right one, I got a 195 degree Stant. Is there anything I can do to check the condition of the fan clutch?

 

[JDraper]

With the motor cold (and turned off!!!) spin the fan by hand and note how much resistance is there. Then get the motor good and warm, shut it off (duh ) and spin the fan by hand again. The resistance should be higher. If it's the same as when it was cold, the clutch is probably toast.

 

[RAZOR]

It's the thermostat!

 

[ipozestu]

There is no way that the fan clutch sticking at highway speeds would cause the motor to get cold. The fan could never pull as much air as what is rammed into the coil at highway speed. If the t-stat was functioning normally it would not open when it gets so cold. It should be closed. It obviously is not.

 

[Crankcase]

Maybe you put the T-STAT in backwards????

 

[Hartman]

I'm pretty sure I installed it right! I'll check tomorrow, is the pointier end supposed to face the front or the rear of the truck?

 

[ipozestu]

Front.

 

[smiley1]

Crankcase is right

I know this because I have been there. I put mine in backwards and had the same symptoms you are describing. DOH!

Just flip it around

 

[Hartman]

Damn I'm stupid!

 

[ipozestu]

:smoke:

 

[Hartman]

I swear, I end up doing everything twice.

 

[ipozestu]

good practice

 

['96explorereddiebauer]

Different scenario...it takes a little longer than expected for my engine to warm up. My dad and I installed a new t-stat a few months ago. Is there a problem??

 

[ipozestu]

I'd say as long as it get warm, stays warm and doesn't over heat, your fine.

 

[Crankcase]

Originally posted by Hartman
Damn I'm stupid!

It WAS in backwards, or you haven't checked yet?

 

[Hartman]

Haven't checked yet but if the pointier end of the thermostat points towards the front of the truck, I think I might have put it in backwards.