I recently purchased a rebuilt 360 from MABBCO and installed in in my 1970 Ford F250. When we started it after 10 to 15 minutes of idling it would reach temperatures of 215 to 220 ( it has a 180 thermostat) and then we would shut it down as to not overheat the engine. We tested everything external (water pumps, thermostats, the original radiator and a new radiator and no matter what we had the same results. We then assumed it was a bad head gasket or head so we took it apart and had the gaskets looked fine so I had the heads tested and they were good. The block itself looks great so there appear to be no signs of internal issues.
We put it back together, checked the exhaust system to see if there were any issues there and it was fine so we put everything back together and started it up and we got the same results and the temp got as high as 230 and this is all at an idle. My mechanic and I are completely stumped on this one and are wondering if any of you might have ideas or suggestions.
What could be causing the engine to overheat? The cooling system appears to be working fine with the original system and the new system. I hope this is just something simple so please let me know if you might have an idea.

Thanks!

 

Tight bearing clearances.
A thermostat that doesn't open.

 

The temp rating on the thermostat doesn't mean the T-stat will be fully open at that temp. It's the 'cracking' temperature of when the T-stat will begin to open. It will take 20 degrees more above the rating stamped on it for the T-stat to be fully open.

A 180 degree T-stat won't be fully open until it reaches 200 degrees. A 195 degree T-stat won't be fully open until it reaches 215 degrees.

If the radiator isn't boiling over, then the engine probably isn't too hot. At idle, you aren't going to have as much air flow through the fins of the radiator to cool it. Above 25 MPH, a fan is useless since the ram effect of air flowing through the radiator takes over at that point.

If you don't have a fan shroud (assuming you have a mechanical fan), installing one would help funnel more air through the radiator when sitting still or at speeds of under 25 MPH.

 

Few things...

- Make sure you're getting the correct temp. Use a heat gun or temp probe to confirm you have the correct temp.
- New rebuilds sometimes get warm during the first few hundreds miles. They shouldn't but sometimes do.
- Make sure you're coolant is circulating. Also, did you change pulley sizes? I think the water pump pulley should be the same size or smaller than the crank pulley and definitely not bigger.
- Verify timing. Roughly 20-25 initial timing should be good (for example: 8-10 degrees mechanical advance plus 10-15 degrees vacuum advance should be fine)
- Like Ultraranger said, I kinda like a fan shroud when sitting still which I think they started using after 1967. And verify your fan is about half inside the shroud and half outside the shroud.

 

MAYBE the temp sending unit is bad ? replace it and buy a temp gun or use a Multimeter that has a k type thermo couple to read actual temp .

 

Take that T-stat throw it in a pot of water with a candy thermometer and watch the temperature when it opens. May just run a cooler T-stat

 

Trapped air behind T-stat?

 

I would question the accuracy of the temp gauge.

 

Tight bearing clearances? Seriously?
If the bearings were that tight it wouldn't turn over and it would quickly seize up if it did run.

 

Yes, seriously.

 

I went through this with my truck, I did everything to it, but nothing.
I put in a NOS thermostat, NOS temp gauge, Had the radiator rodded out, Put a shroud on it and my temp would still go up to 230° at this point I would shut it down for fear of ruining my engine.
After a couple of years of trial and error, I finally went to the "Fan Man" to have electric fans installed. When we installed the fans and ran the truck, temp gauge was hitting 230° again I shut it off. The guys at the shop replaced the sender with a known good one.
Fans will come on at 195° however my gauge would read 230° I'm not worried anymore. The problem has to be old wiring. Everything works so I haven't messed with the wiring to the dash.
Do like others have suggested and you'll be good.

 

Again, yes seriously.

Part of why clearances are checked when assembling and engine, and loosened up if need be.

 

Make sure that the engine, body & frame are all grounded .
Can you see the water moving in the radiator ? You could have a slipping water pump impeller.

 

Is the fan mounted the right way? These old vehicles do not do well sitting an idling in a driveway or heavy traffic...as said previously, they need to be moving to let air pass through the radiator.

 

Depends a little on the condition of the engine and/or quality of the rebuild. I had a rebuilt 390 that ran on the hot side for the first few hundred miles and tended to always run a little on the warm side. Now I have a stroked FE that never got hot and will idle forever at 185F and even cool 5 or so degrees while sitting still if it's less than 80F outside. Stock radiator and shroud with 6 blade aftermarket fan.