Sorry about the long thread, this is my first post. I've done a search for similar problems but haven't come up with a concrete solution yet.

I have a 68 F100 with a 390, I bought it at the beginning of this year. The previous owner had the engine rebuilt about a year ago and it might have 6,000 miles on it. I noticed that the temp guage always read a little on the hot side but it didn't seem bad. The old carb leaked so I replaced the setup with a 4 barrel intake and new 4 barrel carb. The fuel evaporated on the way in to the carb and had issues with that so I changed to aluminum fuel lines and it fixed the problem. The engine always felt hot but the guage never seemed to be reading too hot. I just rewired the whole truck and hooked up a new aftermarket instrument panel because the old panel wires started falling apart when I was updating the wiring system. With the new instrument panel, I found the temp on the engine climbed upwards to 250 degrees when accelerating. It will cool down to about 230 degrees at idle but when driving, shoots back up to 250 degrees. Now I'm in the process of trying to find the problem. I don't think I shot a head gasket yet, but I'm afraid I've been driving at extreme temps for a while now until I changed out the guages and I'm suprised I didn't blow the engine yet.

The thermostat works fine (tested it) but I don't think I'm getting any flow in the engine. I think the water pump might be bad. Either that or the radiator is clogged. I get fluid to the thermostat housing but I'm unsure if the water pump is working like it should. The radiator and coolant doesn't get nearly as hot as the engine.

I just bought a Be Cool radiator, 4600 cfm electric fan, and new high flow water pump and I'm installing it this week, is there anything else I should consider? I couldn't figure out the exact problem so I'm replacing it all.

 

i am not sure where you are or where you bought the truck but there might be to much antifrezze in the mix, dont know if you ever chagned it. antifrezze is good for keeping the water from frezzing but does little to cool the engin down, that is what the water is for. (someone correct me if i am wrong). but it does sound like a bad pump because when you speed the engine up the temp drops so there is more flow....

if you end up with the same problem after all that stuff there might be a clog in the blocks water passages.

oh and welcome to the site, glad to have ya here!

duh reread your post, about the temp going up at higher RPM, yeah that would sound more like a radiator not a pump....

 

I had the same issue with mine, the temp would go up the faster I went. I replaced the radiator and it hasn't gotten over 200 since. It usually stays right around 190-195 now/ Before it would get up to over 210 in the dead of winter going down the highway! It has gotten over 230 before. I couldn't hardly drive it over 30 miles at a time without it heating up and having to stop and let it cool down. I think your new radiator is going to fix the problem.

Oh yeah, and before you put the thermostat back in drill a little hole in it and mount that up so as to make sure no air gets trapped behind it.

Welcome to FTE!!

 

rc1099, One thing for sure, your temps aint reaching 250º and you continue driving the truck. Will not happen.

How is the fluid holding out in the radiator? Is the level staying constant? As long as it aint boiling out it aint too hot. All them hi dollar fans and pumps are un-necessary.

These ol trucks don't have to be monitored real close, if the water and oil level, is staying constant the ol boy is minding his bidness and doing his job.

Hope you get your skunky wiring straightened out.



John

 

just a quick thought here on your problem. i had a vehicle do that a while back and the problem turned out to be the bottom radiator hose.it was old and mushy and would be sucked almost shut when accelerating.

 

The bottom hose seems fine, it has a spring in it and it isn't collapsing. I thought the same thing about the 250 degree heat being too much and still running but the temp sender and guage seem to be working correctly. I hooked another up just to test it. I already spent all the money to upgrade everything. I'd feel better knowing what's on there than relying on the previous owner. The radiator fluid doesn't change, no overflow, but it was 30 degrees outside today and the temp guage showed 230 within 10 minutes at idle. I guess I won't know for sure until I start pulling parts tomorrow.

 

if your antifreeze to water ratio is too rich your temps can get 230-250 degrees without it boiling. the ethylene glycol in it increases the boiling point as well as the freezing point, and like dude said it sucks at absorbing and displacing heat. water is where that comes into play. so with a normal mixture you might see bubbling in the pissjug. i had a 71 a couple of years ago with those similar overheating problems, and it was infact the radiator. bought a brand new radiator for 170 bucks and my problems were solved.

 

I guess that where the danger comes from Dave, but these ol motors will not achieve 230-250º and continue to run. It will not happen. I don't want to say that it hasn't happened in a $100,000.00 race engine but not in 40 year old truck.

rc1099, I can understand how you feel, but you will have to learn to trust your gut. My preference is a 50/50 coolant mix for antifreeze and grocery store distilled water. The distilled water does not introduce any contaminates into your system. Local well and spring waters while safe to drink can sometimes add minerals that can turn into rust and get thick like mud.

Again, if it is maintaining fluid level, leave it alone, it is not overheating.


John

 

Jowilker, I just got all my new parts in. I'm going to mess with the coolant mixture a little bit and try it out before I go overboard. I've been using the 50/50 mix ever since I changed out my intake 6 months ago. I'll just drain it all out and refill with a new mix and try it out to see if there's any change. I'm not beyond making a mistake. Maybe I missed something the first time through. The truck runs good, I'm just paranoid and can't stop staring at the guage buried in the hot. I'll post my results after all is done. I appreciate the responses.

 

on my 71 i had a anolog water temp gauge and it was reading above 230 at times.

 

The engine was rebuilt? What does that mean?

Was the engine bored out?

If so, I wonder how far it was bored?

While I don't recall what the safe limit is, if bored too far, the engine will overheat and there's little or nothing you can do about it without replacing the block.

 

Amazingly enough I'm with Jowilker on this one. 250 and the engine is pretty much done. Trace your new wires to your gauge make sure it's not grounded somewhere. You said you hooked up an external temp gauge? Same reading?
You may have the wrong sender.
I believe at 250 you would be spitting coolant everywhere.