Not my week. if it wasn't painful it would be funny. I am not joking I think everyday this week has seen a new issue pop up. Now the truck is overheating at idle only. Its a 351m motor. Going down the freeway is no problem but if I stop at a red light or get stuck in traffic things happen fast! within maybe 3 minutes the temperature gauge is nearly out of the normal zone. I don't think this truck has a clutch fan right? I mean it has a fan but it seems fixed. No clutch. I choked the thermostat in hot water and it opened up about 1/4 inch at 190. I bought another thermostat anyway and will stall it tomorrow. What would be some other things to check??

 

how is your fan shroud?

my '79 f250 overheated fast if the temp was up outside. i had forgotten to reinstall it after doing some work.

Some guys say that they run without a shroud, mine wouldnt.

 

Are you sure you are using the correct thermostat? And it is installed correctily? The 351C/M/400 takes a special thermostat with a kind of collar around it. A 192-5°F thermostat is the one to use. Use only the Cooper-Robert Shaw thermostat. This has been discussed many times in the 335 series engine forum.

Where to buy a 335 Series thermostat
3 options:
-Find a dealer with a RT-139 still in stock.
-Robert Shaw 333-180
-Napa*THM 297 After calling a local Ford dealer, I was able to track down a dealer that has the RT-139. It’s a dealer in Kansas but they will ship it to you. Bob Allen Ford 1(800)676-0675

Also have you ever flushed the block and radiator/entire cooling system? Do you have a/c and not use it at all and there for have a a/c condenser (small radiator looking thing) in front of the main radiator and maybe need to remove it? Correct fan and fan shroud? Did you swap in a 460 and still have a small 3 core radiator?

 

"Nearly" out of the normal zone? I'd make sure the thermostat is good and continue on until it actually leaves the normal zone. Mine goes past halfway all the time out towards "nearly out of the normal zone". Its an old truck, not quite gonna sit at dead center like newer cars.

Correct, no fan clutch. Definitely make sure that you are running a fan shroud.

Assuming you already checked the fluid level in the radiator itself since you're as far as pulling the thermostat...

I'd flush the whole system since you're already at it, and I don't mean drain and refill. They make coolant flush kits, BG makes the best but you gotta find a mechanic that has them, BG doesnt sell their products in stores. Its a coolant additive that you put in, run for about 100 miles, then drain. It cleans everything out pretty nicely, I've used it in two of my cars.

Make sure that your radiator is free of debris, lots of things get clogged into the fins after 37 years. Some compressed air will really knock some stuff loose.

 

Check rad hoses also. Bottom hose is notorious for collapsing when it goes bad. Also if you buy a bottle of "iron out" and add it to radiator and run for a few days you wont believe the crap that will come out when you drain it. Refill rad with straight water and run for a few more days then drain again. Also you didnt mention whether you use anti-freeze or not. If not then use it. It also raises the boiling point of water depending on the mix. And lastly if everything else is checked out and ok throw in a bottle of royal purple additive. I use it here in Florida and my ol Bronco runs around 190 even idleing on a 98 degree day.

 

how old is the radiator cap? if it's been on there a while I would change it.. cheap insurance.. I never trust an old cap, even if it looks good..

 

DOAZ-8575-A .. 351C/351M/400 Thermostat-192 degree (Motorcraft RT-139) / Obsolete

Last MSRP: $8.62 / Dealer net cost: $4.31.

HIGH BUCK! BOB ALLEN FORD in Overland Park KS has 1 = 913-381-2999/3000. This snake wants MEGA-BUCKS for obsolete parts!

ALBIA MOTOR CO. in Albia IA has 2 = 641-932-5416.

FREESE MOTOR CO. in Monticello IA has 2 = 319-465-3541.

ZUBEC FORD in Oscoda MI has 4 = 989-739-3606.

AL WHITE MOTORS in Manchester TN has 5 = 931-728-9700.

MILLER OBSOLETE PARTS in Binghamton NY has 5 = 607-722-5371.

CARPENTER NOS OBSOLETE PARTS in Concord NC has 12 = 800-476-9653.
-------------------------------------------------------------------------------------
D7PZ-8575-A .. 351C/351M/400 Thermostat-180 degree (Motorcraft RT-310) / Obsolete

Last MSRP: $7.52 / Dealer net cost: $3.76.

WOLFE FORD in Lidgerwood ND has 1 = 701-538-7337.

GRIESEL MOTOR CO. in Okarche OK has 1 = 405-263-7242.

KORF CONTINENTAL in Julesburg CO has 1 = 970-474-3391.

CARPENTER NOS OBSOLETE PARTS has 3.

 

I got the new thermostat which seems to have solved the problem...I dont know why the thermostat makes a difference but it does!. I mean why doesnt a standard thermostat work?...oh well does not matter ...the truck is running cool!..