91 F150 overheat problems
 

Hey Guys... Ok 91 F150 302 - 200k ish miles

I seem to overheat when I'm not in motion. So if I stop at a stop sign the guage will rise. But anything above 45mph and I'm good. it will stay in the "R" or "NORMAL".


I've replaced the Radiator cap, and have Compared the temps of the upper and lower hoses. That seems to check out.

But 2 weird things.. One of which just started and is bad.

1. The overflow tank never fills (Checked for blocked passages, all ok)
2. Coolant escapes and boils on top of the engine. where the Fuel injectors are located on the driver side.

I'd say #2 is a sign of a bad Intake Manifold Gasket. Unless someone else can steer me in a better direction. I'm looking to replace it.

I'm wondering too.. if the overflow never fills... is the pressure forcing the gasket to blow?

Thanks,
Alloy

Two things to look at.
 

1) Fan clutch, You can test it by getting the motor up to operating temp,(let it idle in the driveway with the hood closed) shut off the motor open the hood, and spin the fan by hand. If it spins freely, replace the fan clutch. If the fan feels hard to turn, then I would look at replacing a therostat that is not opening like it should.
2)As for the leak, (with the motor still worm ), Take a shop vac or a yard blower and blow all the coolant off the motor till dry. Try to get it completly dry. Start motor and watch for the leak. 95 % of the time when a intake leaks coolant at the intake gasket you will find coolant (water) in the oil. I would look around the thermostat housing and hose going to it for the leak.
Hope this helps you.

Hey Thanks for your Input. I'll give those ideas a whirl and see what I come up with.

i had the 1992 302 f150. i kept having the same problem. got tired of screwing with it. went and bought an oversized racing radiator, new water pump, and new fan clutch and fan blade. electric fans weren't really out then, but thats definitely what i would have went with. oh yeah, put a lower thermostat on it too.

Two simple things to check: Look at your radiator fins to see if their plugged up with debris. If you have A/C will have to look from the engine side to see it cause the A/C condenser will block you view. Bet your fan clutch is shot also. If you don't hear it roaring on startup, it's a goner. Mine went tango uniform at 100k. About $60 at autozone. 'Mo

Based on your description, your radiator is fine, but your fan clutch needs to be replaced. Do not install a lower t-stat. Shoot for a cooling mixture with 30% coolant / 70% water.

As far as your leak at the intake, that needs to be fixed first. The best way to identify exactly where it is is to pressure test your cooling system. If you don't have access to a cooling system pressure tester, most auto parts stores will loan you one.

Your overflow is most likely fine, the reason it's not filling is because the leak you have doesn't allow enough pressure to build up to force any fluid past the cap.

Fix the leak, replace the fan clutch, and make your fluid mix 30%/70%, and you'll be good to go.

So I checked the fan. I agree the Clutch is out. So that's one issue out of the way.


Now the coolant on top of the motor. I'm thinking it has to be that lower Manifold gasket. I don't seem to have any coolant in my oil. But I can't see where or how any of the Coolant lines would leak right in that spot.

It's no where near the thermostat housing, I don't have coolant dripping from the hood or anywhere else. So I don't believe it's being sprayed.

Now If I squeeze the upper coolant hose.. I can almost hear gurgling from the top of the engine.


Are there any coolant lines near the back of the engine that could be causing this? I just cant see the leak.

There are coolant journals in the heads at the front & back of the intake manifold - the rear ones are blocked off by the manifold &/or the gaskets. A leak from any of them could run across the top of the gasket & spill onto the manifold where you see it. Coolant can also leak past the gasket to the manifold bolts, and then spring up around a bolt head.

https://www.supermotors.net/getfile/...0lexploded.jpg . https://www.supermotors.net/getfile/...ockcooling.jpg