Hi all, working on 77 F150 4X4 AT 351M. I am at wits end with this mess. Temp gage goes to high end of range and sticks there, it will fluctuate a little, but not much. Not stupid hot, but can't be good in the long run. Checked with infrared thermometer, gage isn't telling lies. 4 thermostats, 195,180,160 degree(heard horror stories about bad ones new out of the box, maybe I am living it), no change. Changed sending unit, just in case it was confused. Flushed system thoroughly (block, core, radiator). Changed hoses, so no collapsed hoses. No air in system. Solid fan, so can't be bad clutch fan. Shroud is good. Tonight planning on changing fan belt (to eliminate slippage, maybe not turning water pump fast enough). I also got thermostat #5. Last thing on the list is water pump. Not leaking antifreeze, not burning it, oil is clean, exhaust is clean. Antifreeze level stays good. Anyone have any suggestions? Much appreciated. Thanks.

 

my 460 had a similar problem, several thermostats, different brands, cheap, expensive, same thing. it would overheat severely even in the winter at, no lie, -40c (-40F). finnally i found a thermostat designeed for towing, it wasn't listed for my application, but it has the same outside diameter, which is all that really matters for fitting in the housing. the opening that the fluid flows through is about a 1/4" larger diameter than all the other "stock" ones. i installed it and have not have a problem since even when towing about 15,000lbs (5th wheel camper and boat behind that).

O and if the parts and speedshop guys tell you that a high flow thermostat does not exist for your application, keep looking, they told me the same.

If you didn't build it, its not really yours.

 

I can't speek too much about the 351M, but I noticed on the FE engines that the factory AC setups had much different size pullies. When I pulled the AC from a junk yard, I took ALL the pullies and later noticed that they caused the water pump to spin a lot faster. This could be a dirt cheap fix, if the AC ones are different.
Also, on another car of mine, I switched the water pump from the cast iron impeller to the stamped steel one and it started running hotter right off the bat, the cast iron impellers flow better. Jegs offers a water pump backing plate that they say increases flow 30% and I noticed the Edelbrock Vic water pumps have this backing plate on the impeller as well so I think it would help.

The proper mix of antifreeze should be about 20~25%, water cools better that antifreeze.

 

[font color=red size=2]This sounds like my '73 390. It appears to be hot on the guage, but never acts over heated. On my factory guage it reads C TEMP H and mine is always on the P (once the engine is warm), no matter how hot or cold it is outside.

I too have tried and tried to get it to read correctly. I've changed thermostats 3 times, changed intake, changed temp senders twice, changed belts/hoses, flushed system and checked wiring to guage. It never acts hot, no boiling or hard starting. Nothing has changed it. The only thing left is a new guage - haven't tried that yet, maybe this summer.

Let us know what you find, when you get it fixed, I would like to fix mine too.

Marty

"Cleverly Disguised as a Responsible Adult"[/font]