Overheating !

[ryno8]

Just purchased a 75 f100 302. I am looking to overhaul It. One problem, Overheating. It was ok until 1 week ago. Temps in Nebraska got into the 90s for the first time. I replaced the water pump. Some people tell me to take out the thermostat. And replace it when the weather gets cold and need heater. any help? Need more info? let me know please.

[fellro86]

You don't want to run without the thermostat, it needs a restriction to help cool, as with no restriction the coolant is free to flow around the system without slowing down long enough to effectively cool. You can take an old thermostat and take the center out and use the plate, making a resrictor plate for the coolant. Check the radiator cap, and also check the radiator. When the engine is hot, feel the radiator. If you find that parts are cool, you have blockage in the radiator.

[SR71]

If everything was working ok before sounds like your radiator might not be up to the task. You can do a visual inspection by just taking off the rad cap and looking inside it wont tell you everything but its a place to start. Also is the fan shroud in tact and is it the rigth one IE doe sit conform to the fan with only a small gap between the outside of the fan blade and the shroud. I have seen many of these older trucks that have engine swaps done and they did not put in the correct shroud. You can take out the thermostat and see if it helps but I think that is just a bandage on a bigger problem.

[81-F-150-Explorer]

I'd replace the Thermostat. They tend to get sticky after a while.

You could have a clogged cooling system too. When you change the thermostat, I'd backflush the cooling system too.

Prestone makes a backflush kit that hooks up to one of the heater hoses...

I just hook a garden hose up to the outlet on the heater core. Just remember to turn the heater controls to warm, and Take the Radiator cap off and just watch the dirt come out!! It will scare ya if it hasn't been done for a long time! Also clean out all the little bugs in the radiator that have stuck there, cause after a while it can build up.

BTW does your truck have a fan shroud? That can reduce your temps too!

Good Luck.

[ryno8]

This gives me a good place to start. Thanks to all. Will keep you in touch. Keep on posting if any other ideas. thanks again.

[200000+F150]

Nine times out of ten, in my experience, if a cooling system works Okay in the cooler outside temps, but gets hot when the weather does, it's the radiator. A partial internal blockage will make it "marginal" like that. I had a Chevelle with one like that once (clogged up inside). You could actually watch the temp gauge rise and fall when driving depending on whether you were in the shadows or brightly lit areas. Sounds crazy, but it's true. I could be driving through hilly country in the morning and it would start climbing to around 210 degrees. Drop down into a valley where the air was cooler and it would fall to the 180 mark(had a 180 thermostat in it). Up into the bright sunny area again, and up it would go. It was the only time I've ever seen one that "borderline", but it did that for weeks until I got the radiator re-cored, and then it would sit dead on whatever temp thermostat I installed regardless of outside temps.