Engine overheating

[paulj]

Took my '76 FJ 40 to go fishing on Friday, and when I stopped to get gas the coolant in the overflow reservoir was boiling. When I let it cool down I added about a half gallon of water then drove it a mile to the lake. I let it cool way down and then drove it home about 3 hours later with the radiator topped off and the heater turned on. When I stopped to check it, it was overheating again. No leaks in any of the hoses and the guage read normal. I know it wasn't stuck in that position because on the way home it started out reading cold and then climbed up to the mid point of the dial. When I stopped to check it, it was boiling again inside the overflow reservoir. Steam was coming out of the tube leading in to it, and when I was able to check the radiator it was full of coolant. The temp gauge never read hot. So how do I diagnose what's wrong with it? It's got a 3 year old CCOT replacement radiator, and the water pump was replaced about a year and a half ago. Everything is bone stock. 2F engine, Aisin carb, etc. I tried to replace the thermostat to see if that's all it was, and I can't get the #*!!# thing off! The cover is bolted on with some kind of weird bolts one of which I can't budge. Instead of a hex head they've got grooved cylindrical heads with hexagonal holes for an allen wrench. I can't get nearly enough torgue on it with an allen wrench. Tried to tap it loose, used liquid wrench, and put a torch on it to no avail. Does anyone have any suggestions as to a) why it's overheating and b) how to get the cover off the thermostat housing?

 

[fsusteve]

Sounds like a bad thermostat and guage/sender. Those allen head bolts suck, I just stripped some on my weed eater replacing the recoil. If the hole is stripped, I would try to get some channel locks or visegrips on the outside and then replace them with the proper hardware.

 

[burnt03]

Another possibility (though likely not the right one...)

I had a similar problem... the overflow tank would keep on boiling over and would eventually overheat after I lost enough coolant. Turned out my rad cap wasn't working (looked like the original one) and I guess it wasn't sealing the system when it should've been.

 

[Cruiserdrew]

Get that "boiling" overflow sniffed for exhaust gasses. Your symptoms could be those of a blown headgasket-ie pressurized exhaust in the cooling system. Try observing your radiator or overflow immediately after starting, if your have bubbles, then you have big problems. Boiling in the overflow without truely over heating doesn't sound right. I agree it seems reasonable to check the cap, but be prepared for a more significant problem. How about a bit more info. Is your truck using coolant? Any coolant in the exhaust(smells funny)? What's the maintence history on your truck?

 

[paulj]

Thanks to all for your input. Someone else (without seeing the truck) mentioned the possibility of a blown head gasket. I pray that's not the problem. Meanwhile I'll try again to get the bolt off the cover and replace the thermostat and will check the radiator cap. As for my truck's history: It was more or less "restored" by the PO. All the accessories such as radiator, belts, hoses, etc. are new, but the engine itself hasn't been rebuilt. The odometer reads 54 k and it does appear correct as there's good compression all around. I've driven it for 2 1/2 years with only one serious problem, a blown intake gasket. Other than that, it's driven just fine. Take it on short road trips about once a month and drive it around town on most weekends with no problems. I drive it down the highway at about 60 and almost never push it to it's top speed closer to 70. Yeah, it's got coolant; a 50/50 mix.