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1986 5.0 overheating

bdl86

New Member
My car starting overheating this year. After 35 minutes of highway driving, at 65 degrees ,then while going 40mph through town I noticed the temp gauge run up just shy of red line. Took it out of gear gliding downhill the temp decreased to the 3/4 mark on the gauge. After a stop for 30 min. I ran on the highway again and the temp gauge was running over the halfway point then the temp ran up again after slowing down to 30-40 mph. New thermostat last year plus new radiator 5 years ago. Antifreeze looks good. What else should I be looking for ?

Thanks
 

broncojunkie

Well-Known Member
Might need some more info on this one. Is it standard or auto? If auto, do you have a separate cooler or is it running through the radiator? Is the radiator a stock replacement or did you upgrade to a 2 or 3 core?

I would begin by starting it up and letting it warm up. Note the temp. See if it runs hot just at idle. Once warmed up, feel the upper and lower radiator hoses and see if they're both hot. If one is warmer than the other, you have a circulation problem. You will need to figure out if you have a clog somewhere, a bad t-stat, or a bad water pump.

Since it's overheating on the highway, I'm going to presume the fan isn't the issue here.

A blown head gasket could cause your symptoms, but usually results in oil in your coolant or vice versa. Check both just to be sure. Also check transmission fluid, if you're auto and the lines run through your radiator. Check for high or low fluid as well as burnt fluid. If you've got a manual transmission, disregard this part.

That should get you started. Let us know what you find out.
 

broncojunkie

Well-Known Member
One more thing. I always suggest installing a flush & fill kit. I believe they're under $10 and allow you to easily back flush your cooling system. I do this to all my vehicles about every 2 years. Just look up "Prestone flush & fill kit".
 

bdl86

New Member
Turns out the fan clutch was bad. Luckily the fan blades were discovered badly cracked so that was replaced along with a new thermostat for good measure. Runs at the correct temp now.
Thanks for the inputs
 

broncojunkie

Well-Known Member
Glad you got it sorted out! Typically, a fan problem only shows up at idle or putting around town in stop and go traffic. I've never been a big fan (no pun intended lol) of the mechanical fan. I started upgrading all my old fords a few years ago with a 130a 3g alternator, aluminum 3-row radiator, and electric fan. It works so much better than the oem stuff. I can typically get everything I need for around $3-400. I wish the electric water pumps weren't so expensive or I'd use them too lol!
 

Canyon Red

New Member
Sorry for the "late-to-the-table" response here, but I had similar issues about 8 years back, and noticed that the core tubes were getting clogged. I tried several flushes, and they seemed to help, but after that exercise, it was better but not fully cured. I ended up ordering a brass and copper three core unit and just replaced it. She runs fine now even in 90 degree plus weather. I also changed out the heater core several years before that as it began to leak. I had read that the OEM of both of these units built below quality units. Also, I used distilled water on the new radiator refill, with the hopes that limiting minerals in water would keep the tubes open longer.
 

Erkenbrand

Active Member
And to add one more recommendation to the already solved problem - don't forget to replace your coolant hoses. When the years add up the old hoses start to collapse restricting flow. Give the hoses a squeeze to see if they're still solid, or if they are just soft rubber now.
 
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