So, I have a 1977 F150 4x4 with a 400. I just replaced the thermostat with a Motorcraft RT139 with the spring going in the block. I am still overheating. I thought it was the temperature sending unit but it checks out. At this point should I be thinking about a rebuild?

 

Are you losing coolant? Does the level of the radiator fluctuate? warm it up with the cap off and watch it lower and raise, also try bypassing the heater core, it could have a partial blockage...

If there is something wrong with the pump it should be obvious, but you never know.

 

The heater core is new. Not losing any coolant. When I let the truck warm up I can sit inside the cab and with the heater blowing and I can feel the heat increase as the truck starts to overheat. The fluid is flowing and doing it's job. I'm not losing oil either. It's at the same level from when I did the oil change. I'm getting stumped here ... frustrating.

 

is there a clutch on the fan?

 

It doesn't have a clutch and it also doesn't have a shroud. I thought about the shroud but I'm having issues with it being 35 degrees outside (current) as apposed to 85 degrees during last summer.

 

I have come to the conclusion that my over heating issues may be related to the engine timing. Isn't this thing supposed to ping if it's too advanced?

 

it should, but I don't think that is related, the opposite is true though if it runs too hot it could detonate before it is supposed to...

Know what you mean about frustrating... I would have guessed that you still had air in the system but the fact that the heat works tells me otherwise.

 

what tells you it is over heating? the stock electric dash temp gauge?

 

6fifty;
That makes sense. I posted a thread a while ago about how I couldn't advance my distributor far enough without the vacuum advance hitting the thermostat inlet. I figure it has a cam and the PO didn't install the distributor at TDC.

80broncoman
After market. I bought a new sending unit also.

 

once you veryfy the timing is ok. how old is the radiator?
it it is original, you might need to just get it rodded out.
where they take the ends off and stick a brush of some type
through the inside of the radiator and get the build up out.
once it is done it will be like new!

 

Run yout hand across the radiator core when the motor is warm. It should be evenly warm. Any cold spots will indicate some blocked tubes.

Also if you can't turn the dist to set the timing, it could be due to a sloppy timing chain, and the cam and dist are retarded.

You can just move the plug wires one position, then rotate the distributor back so the vacuum advance points to the front. Set the crank to TDC with the rotor pointing to #1, then move the plug wires, then rotate the housing until the rotor again points to #1.

 

Do you have trick to find TDC? I have seen the clear tube and oil trick but leaves a mess and your engine burns smoke afterwards.

 

At TDC the motor is on it's compression stroke on #1 cylinder. If you remove #1 spark plug and put your finger in the plug hole. you will feel the compression and a puff of air when the piston nears TDC. Then if you look at the marks on the damper, you should see the timing mark near the timing pointer. It works better if you rotate the crankshaft manually with a socket on the crank pulley bolt.

Another way is to remove the valve cover and observe the rockers on #1 cylinder. Since both valves are closed on the compression cycle, you can manually rotate the motor until both rockers stop moving and have a little play between them and the valve. again the timinh mark should be near the timing pointer.

TDC is where the Timing Pointer lines up with the 0 degree timing mark on the compression stroke.

 

I have a sneaky suspicion that the timing mark on the damper wont line up. I will take a look at it some time this week. I'm changing C bushings and radius bushings now.

 

The damper is keyed (or should be) to make it >improbable< that it isn't in the correct position.