79 351M Overheating
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Trailering
Joined: Oct 2023
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79 351M Overheating
Recently rebuilt my 79 F150 4x4 engine. Complete rebuild .30 over, new cam,intake, 4 barrel carb.I am the original owner of this truck..Seems to run hot on hot days..Added mechanical water temp gauge. Gets up to 210 on stopping and idling . Dash gauge shows above normal..Runs around 190 to 200 at high speeds on midday heat in Florida When turn off truck coolant blows out cap .3 row radiator,water pump,belts ,hoses,are new. Dont remember it running this hot before . Have Robert Shaw thermostat 180 degree . Original fan and shroud installed .Was thinking of going to 4 row radiator What are your thoughts ?
Last edited by Ray79F150; Jul 2, 2024 at 08:26 AM. Reason: more info
Hotshot
Joined: Feb 2004
Posts: 10,788
Likes: 2,595
From: The Shenandoah Valley
It's not unheard of for a newly rebuilt engine to run a little warmer until run in good, friction in cylinder walls will build heat. Late ignition timing can increase heat transferred to water jackets too.
Questions ...
I have a correct 180" T-stat which means it's just opening at about 180*. I also have a flow cooler water pump with the added anti-cavitation disc in place.
My stock fan was a 5 blade / no clutch type. I put a 7 blade inch smaller diameter fan in place like was used on a lot of AC cars, and a new fan shroud.
I also moved my transmission extra cooler from behind the radiator in the shroud to under / behind the front bumper, like laying down on a DIY bracket.
Questions ...
- Are you running a coolant recovery setup or just letting it puke coolant out on the ground?
- Radiator cap is fresh?
- Are you running a correct for 351M/400 thermostat?
- Do you have a well fitted fan shroud?
- The term "high speeds" means?
- Bottom radiator hose isn't collapsing when the T-stat opens and coolant moves?
I have a correct 180" T-stat which means it's just opening at about 180*. I also have a flow cooler water pump with the added anti-cavitation disc in place.
My stock fan was a 5 blade / no clutch type. I put a 7 blade inch smaller diameter fan in place like was used on a lot of AC cars, and a new fan shroud.
I also moved my transmission extra cooler from behind the radiator in the shroud to under / behind the front bumper, like laying down on a DIY bracket.
Laughing Gas
Joined: Feb 2011
Posts: 995
Likes: 317
Up to 210 in FL stopping and idling. Thats no problem. Make sure the radiator level is not too high. Very common to overfill on these old vehicles. Make sure you have a new and correct pressure radiator cap. I think 13lb is stock. Could go to a 15. I've run 15s in many older vehicles with A/C that run a bit hotter.
What condition is your radiator? OEM, recored original, aftermarket?
What condition is your radiator? OEM, recored original, aftermarket?
Thread Starter
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Trailering
Joined: Oct 2023
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I have the original 7 blade fan with new fan clutch..original shroud in good condition. I have a 13 lb radiator cap ordered .... saved original to try... maybe weak spring.
Only drive short trips to town high speed 55 mph. 300 miles total on fresh engine. Just concerned with damaging new rebuild with this problem . mechanic suggested putting old radiator back in to test.He says some of the new radiators they dont put correct baffles in them to allow proper cooling. Radiator is a new brass OEM 3 core. Not sure of brand made in mexico Thanks for your suggestions
Only drive short trips to town high speed 55 mph. 300 miles total on fresh engine. Just concerned with damaging new rebuild with this problem . mechanic suggested putting old radiator back in to test.He says some of the new radiators they dont put correct baffles in them to allow proper cooling. Radiator is a new brass OEM 3 core. Not sure of brand made in mexico Thanks for your suggestions
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Lead Driver
Joined: Nov 2000
Posts: 6,625
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From: Albuquerque
Your radiator should be as full as you can get it! A coolant recovery tank is good if you don't already have one. I wouldn't think the radiator would be a problem at your HP level. Make sure the bottom hose isn't collapsing. Pure water is a better coolant than antifreeze! If you don't worry about freezing you could try that with a lube/water wetter.
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Lead Driver
Joined: Jul 2017
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From: San Jose, CA
Just to assuage some fears here, 210° will never damage your engine.
As someone mentioned earlier, it could cause a little fuel delivery issue when you stop, as the fuel could percolate in the carb, or heat soak in the line ahead of the pump. But that temperature is in no way damaging.
I know this is apples to oranges, but modern engines often run at 215 as a normal temperature.
Check your ignition timing, of course, but just keep running it. The more you run it the more you will know about it. 300 miles is hardly past the cam break-in!
Yes, that’s an exaggeration on my part. But I’m trying to make the point that you should just keep out and drive it.
You’re doing the right thing by monitoring the temperature, and making sure it doesn’t go too high, but 5 to15° above the thermostat rating is not in any kind of a danger zone.
As someone mentioned earlier, it could cause a little fuel delivery issue when you stop, as the fuel could percolate in the carb, or heat soak in the line ahead of the pump. But that temperature is in no way damaging.
I know this is apples to oranges, but modern engines often run at 215 as a normal temperature.
Check your ignition timing, of course, but just keep running it. The more you run it the more you will know about it. 300 miles is hardly past the cam break-in!
Yes, that’s an exaggeration on my part. But I’m trying to make the point that you should just keep out and drive it.
You’re doing the right thing by monitoring the temperature, and making sure it doesn’t go too high, but 5 to15° above the thermostat rating is not in any kind of a danger zone.
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Trailering
Joined: Oct 2023
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Thanks for the replies. Just wanted to be sure of no problems . Very hot and humid now in Florida so this is the worst case for heat .Truck has been stored in a garage for 30 years . Original paint and interior.. Bought it new in 79..Its fun to drive now turns lots of heads. Ill try to post a pic..Thanks for all the help and assuring me of this issue
Hotshot
Joined: Feb 2004
Posts: 10,788
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From: The Shenandoah Valley
Not pretty maybe, but I tied a gallon jug beside the radiator sitting on the frame on a pad on driver side, cut a 3/8 or maybe is 5/16 hole in the top of handle on side opposite the cap, run a copper tube with limiter to keep it up off the bottom, and run a hose from that to overflow tube on radiator neck. Any coolant pumped out by heat expansion is saved in the jug to be returned as the radiator cools down and coolant contracts. The tube does not get sealed to the jug, so it can let air out / in as the coolant moves back and forth. Been fine for 30+ years. Add coolant at jug if ever needed (I check it occasionally, like it half or more full), radiator stays full.
I do use a 13 lb. cap.
I do use a 13 lb. cap.
Lead Driver
Joined: Oct 2018
Posts: 7,864
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The cap is the same.
once it finds the level it likes it will stop. the tank is totally unnecessary, but you can add one if it makes you feel better.
sometimes I wonder how we survived without all the things we now know you can't live without.
once it finds the level it likes it will stop. the tank is totally unnecessary, but you can add one if it makes you feel better.
sometimes I wonder how we survived without all the things we now know you can't live without.