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Overheating issue

I have a '95 E250 with the 300 6 cylinder that I can't figure out the overheating problem. There's no problem during the colder winter months but this last week with the temperature in the 50's and 60's, it's been overheating. I'll be driving along and the idiot gauge will be at the first quarter mark, sometimes it stays there but lately after a few miles driving, highway or city, it'll climb to the half way mark. Sometimes it'll stay there but usually it will climb up to the hazard area.
There are times when it will bounce back and forth a little before shooting up. I can pull over and hear the coolant boiling in the overflow tank. I've pressure tested the cap and radiator and replaced the thermostat. The fan clutch is working and no leaks can be found.
A mechanic thought the problem is a plugged head gasket but if that was the case wouldn't it also overheat in the northwest winters?
Anyhow, this is my work truck, that I need to fix. Any help is much appreciated.
 

Fellro

Moderator
Staff member
First thing to be certain of is that the radiator itself is not clogged. A clogged head gasket is a stretch in my opinion. A radiator will clog up before ahead gasket will. It used to be a common practice to boil them out when you would have issues, but these days you just replace them. The old radiators were all brass, so you could generally clean them that way, but the aluminums are not able to be done intact, so the cost is much higher than just buying another radiator. When it is hot, feel the radiator cores. If it is cooler at the bottom than at the top, you can figure the cores are plugged. (obviously this should be done when the engine is shut off)
 
Thanks, I'll inspect the radiator tomorrow. Also will take another look at the fan clutch. Doesn't seem to be speeding up when I increase the rpm but that was with a cold engine. Any idea what type of clutch it is, thermal or non thermal?
 

Fellro

Moderator
Staff member
Factory would be thermal, but it depends on whether it has been replaced since then.
 
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