let me start by saying i have read every post on every forum site regarding this and still have not found a solution... with that, heres the problem:

1977 F250 w 400M
after swapping carbs last friday immediately ran into cooling issues, after nothing cured this i went back to all oem parts (carb, egr valve, spacers, etc...) truck still sky rockets temp within five minutes at idle and doesnt improve while moving. heres what ive done so far:

new water pump, new thermostat, backflush x3, checked and rechecked the timing, made sure carb isnt too lean/rich, checked resistance on temp sending unit while running, checked radiator for clogs (flow test, no cool spots while running), burped the system enough times to have it down to a science .

anybody got any ideas? been working on these engines for years now and have never had any of my trucks pull this crap... anything would be greatly appreciated, thank ya

 

hows the fan clutch working? what intake are you running? hopefully the valley pan is not a defective aftermarket one with a missing port. Hopefully the impeller on the water pump is good.

 

fan is direct bolt, no clutch. it has the factory 2brl intake. engine is completely stock at this point. radiator has good flow across from pump.

 

what thermostat are you using? too much flow won't let the water cool enough in time before goin back into the engine.

 

Have you confirmed this with an aftermarket temp gauge? or are you reading the factory temp gauge?

 

FOMOCO only put there cheap guages in to fill up the space. Get a good aftermarket mechanical one and then you will know what the temp. is. Mine was showing to be running very hot ,but was really only about 190 to 198. It is a 460 with a 302 radiator and clutch fan, no shroud.

 

Check temp of top and lower radiator hoses with either infared or meat thermometer.

Then .... what Thermostat did you use anyway?

Ford's 351M and 400 engines take a different thermostat than any other Ford motor (well, maybe the 351C .... I forget about it, it also has the inblock bypass but has a pressed in disc restrictor?) and the correct one must be used as the bypass is cast into the block itself just below the thermostat and as the thermostat opens, it restricts the bypass, forcing more water to go through the thermostat. If the wrong thermostat is used, if it doesn't reach down and restrict the bypass, that will allow a certain amount of water to bypass the thermostat and radiator and just get pumped back through the block and heads hot.

I did once replace mine as a standard practice with antifreeze change one fall, used a correctly sized (diameter) one meant for a 302 / 351W as couldn't locate one for a 351m on the spur of the moment. She would slowly just keep warming up as you drove along, even on a cool day.

I changed it to a Robert Shaw Hi-Per Thermostat found at Auto Zone or Advance a few days later, one intended for 351m/400s. Cured the warming feature, it stays rock solid now once warmed up, winter or summer. That's the only kind I'll use in the truck now.

The water pump efficiency can also be greatly increased with a simple addition of a disc riveted to the back side of the water pump impellor with just three small rivets, keeps coolant from spilling off the back side of the vanes in use. That's what a "Flow Cooler" water pump does, I bought the disc when they sold it seperately as a mod.

Here is an old advert from the '70s that maybe shows it.




Robert Shaw 333-195 (180 will work) is correct and a proven best as far as I'm concerned.

 

Check your lower radiator hose and make sure it's not collapsing. Most aftermarket hoses (even Gates) don't have the spring inside them and the waterpump will pull so hard it will suck the hose shut, preventing any coolant flow.

Most of the time they only collapse off-idle but it's possible yours is collapsing at idle.

CarQuest carries hoses with the reinforcement springs in them and most other auto-parts suppliers sell a high-performance flex-hose without a spring but they're made from heavier material and won't suck closed.

Also with NW 150 - a 195* t-stat might work better for you because it will give the coolant in the radiator more time to cool off. In some situations a 160* t-stat will just keep pumping coolant through your radiator without giving it a chance to cool.

 

Is your fan shroud in good shape?

Mine was cracked/broken off and I was having some minor overheating issues. I drilled a piece of aluminum over the old shroud area and sure enough the heat problem was solved.

 

sry i havent posted back sooner (computer **** the bed).
lower hose has spring, the thermostat is new and is the correct replacement w the flared bottom, the shroud is in place. w gauge still hits 210 and i shut her down at that point. at this point im thinkin its something with the timing or egr because everything else is operating as per design with out flaw.

 

im having the same problems, only different events lead up to it. first bought 78 f150 with a bad radiator, had a crack in the top and bottom and side, as well as a half shroud that and been "bolted" through the fins of the radiator and caused another leak. i replaced that radiator with a new one. and have also replaced the thermostat. the next thing that i looked into was the hoses but the bottom has a good spring in it and the top one is new. no aftermarket gauge but, the factory one is working, when it says it hot its hot, cause it overflows fluid out the overflow line. and now im not sure what to do.