Quote:
Originally Posted by ATOWN4R
'06 4.0
Hopped in the truck today and started driving...got up to operating temperature and still had no heat. I noticed the temp gauge was jumping up higher and higher. I turned the heat off completely, and the temp dropped back down. As I drive the temp stays around normal, but then climbs back up until its high again, then drops back down. Anytime i turn the air on, it climbs back up to red. I am thinking it is a thermostat, but its weird that it goes high and then back to normal. Fan is spinning normal, don't think it's the fan clutch. Resevoir is filled to normal levels. Radiator has a small leak, but nothing catastrophic, although I will be replacing that soon.
Any thoughts/ideas/other things to check would be greatly appreciated.
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Check the level in the radiator when its cold. You may find it's low. The reservoir relies on a vacuum to draw coolant back into the radiator. If there's a leak it can jjst suck air back in through the leaky spot instead of coolant from the reservoir.
If it is indeed full, I would suspect thermostat as you suggested.