Engine running too cool (Jeep 4.0L)

[Porkchop]

Poof.

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Your fan is not coming on at higheay speeds because the engine is not getting hot enough to need it. Most engines will run cooler on the highway because of a constant rpm and better air flow. Running cold as you say shouldn't be a problem. If the fan stops coming on and the engine is running hot then I would be worried. I havn't driven my Dodge Ram in a while because of gas prices but if I remember correctly it too runs cooler on the highway because of reasons mentioned above.

[bman]

Originally Posted by Porkchop

What is strange though is it used to be consistent at 210 regardless of idle or highway speed. The thermostat should close some to compensate for it running colder but either it isn't, or the fan clutch is keeping the mechanical fan engaged at highway speeds. I'd just hate to spend the money on a fan clutch and that not fix the problem - was just wondering if anyone had ever had the same problem.

I'm not a Jeep owner so I cannot say with experience, but my first inclination would be to check that thermostat.

Don't assume it works because at idle the engine is up to temp. All that means is that there isn't as much cooling happening because you're not moving.

It could be that your thermostat is stuck open (or partially) and so idle would seem okay but driving would cause things to cool below normal as the thermostat wouldn't fully close when needed.

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bman has a good point. I never would have thought that running cool could be a problem, but after reading this it makes me wonder about my Dodge. I'll have to check to see if I may have the same problem. Thanks for posting this.