1979 351M overheating
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From: pennsylvania
1979 351M overheating
I have a 1979 F250 with a 351M...it tends to overheat at idle, ive never had the truck on the road to see how it runs, i was wondering what the problem could be, there is no fan shrowd on the radiator but that shouldnt affect it....i was thinking about 2 electric fans and eliminate the flexfan?
Last edited by Torque1st; Sep 3, 2006 at 11:42 PM.
Posting Legend
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Welcome to FTE!
Sounds like you have everything wrong with that setup, no wonder it overheats. Put a fan shroud on. The fan shroud is what makes the fan pull air thru the radiator at low speeds or idle otherwise the fan just stirs the air. Put a good thermostatic clutch fan on and get rid of the flex fan.
Sounds like you have everything wrong with that setup, no wonder it overheats. Put a fan shroud on. The fan shroud is what makes the fan pull air thru the radiator at low speeds or idle otherwise the fan just stirs the air. Put a good thermostatic clutch fan on and get rid of the flex fan.
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From: western montana
theres a good informational thread on that- and definitely some benifit to running electric fans- also some very real drawbacks as far as finding the right set up- with their own shroud- and the drain on the alternator, reliability and your wallet. Also you gotta do it right as many of the generic set ups will damage your radiator over time. The only benefit was a slight gain in economy but it would take a while to make up the cost.
Anyway, as i remember,the basic summary was for cost and reliablity the thermostatic clutch was the best bet but you have to have the shroud- as you do for any fan set up your going to run. The draw back on the flex- as i remember was it's performance at higher rpm or highway speed- flexed too much.
Welcome to my fav site- good folks here and the search function will net some information on anything you may ever want/need to know. And please keep us informed as to your choice and results.
also thee engines take a very specific thermostat and many parts stores will sell you one that will cause problems- I've run into that half a dozen times myself.
Anyway, as i remember,the basic summary was for cost and reliablity the thermostatic clutch was the best bet but you have to have the shroud- as you do for any fan set up your going to run. The draw back on the flex- as i remember was it's performance at higher rpm or highway speed- flexed too much.
Welcome to my fav site- good folks here and the search function will net some information on anything you may ever want/need to know. And please keep us informed as to your choice and results.
also thee engines take a very specific thermostat and many parts stores will sell you one that will cause problems- I've run into that half a dozen times myself.
Last edited by roger dowty; Sep 4, 2006 at 01:55 AM. Reason: thermostat
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Like Roger said: Use the proper configuration for a 335 series engine.
A stock 195° thermostat is good, a Cooper-Robertshaw unit if you can find one is best. The 195 gives the best engine life and efficiency in a 335 engine.
An electric fan requires a larger alternator and power wires to transmit the power required by the fan. Electrics are great for a backup to the stock unit but the complexity decreases reliability. Electrics are good for deep water use tho.
The fan provides the airflow for the radiator at low speeds under 30-40 MPH. Above that the motion of the vehicle thru the air forces air thru the radiator. Make sure the flaps are intact that direct air thru the radiator. If they are missing airflow can bypass the radiator on the highway and overheating will result.
A stock 195° thermostat is good, a Cooper-Robertshaw unit if you can find one is best. The 195 gives the best engine life and efficiency in a 335 engine.
An electric fan requires a larger alternator and power wires to transmit the power required by the fan. Electrics are great for a backup to the stock unit but the complexity decreases reliability. Electrics are good for deep water use tho.
The fan provides the airflow for the radiator at low speeds under 30-40 MPH. Above that the motion of the vehicle thru the air forces air thru the radiator. Make sure the flaps are intact that direct air thru the radiator. If they are missing airflow can bypass the radiator on the highway and overheating will result.
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From: near pittsburgh pa
When you say flex fen, are you saying the aftermarket flex fan or are you meaning the Ford factory flex fan?
Pure electric fans are a pain unless its a racecar.
A extra electric fan mounted properly is nice in heavy slow moving hot traffic.
The factory set up should handle your temp. If there is a problem ( for sure get a shroud) it will need fixed even with electric fans. Good luck
Pure electric fans are a pain unless its a racecar.
A extra electric fan mounted properly is nice in heavy slow moving hot traffic.
The factory set up should handle your temp. If there is a problem ( for sure get a shroud) it will need fixed even with electric fans. Good luck
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Posting Guru
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From: western montana
aftermarket- didn't know ford had a factory flex on the 335 series- ???
yep, shroud is mandatory regardless...learned the hard way on that 15 or so ago.
yep, shroud is mandatory regardless...learned the hard way on that 15 or so ago.
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From: near pittsburgh pa
Yes, they have a flex fan. If you rev the engine up and watch the fan blades you will see that they flex to a straighter position. Its a good fan, much better, imho, than the aftermarketed flexfan. Plus they fill the shrouds better.
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From: pennsylvania
I think that the thermostat was sticking...i let the truck run for a bit over the past cupple of days and it hasnt heated up since.....im still gonna get a fan shroud for it as well as a new thermostat...thanks for all your help guys
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From: Kalispell,Montana
Fordman,just to illustrate how important the shroud is!! I busted my shroud tinkering with stuff on the engine,I pulled the shroud off to keep it from hitting the fan which is stock no factory flex stuff on my truck,but I instantly noticed an easy 20 - 30 degree rise in operating temp,my temp gauge went from always being between the R and the M of normal to running close to the
A on the gauge.No problem on the highway,but in town and doing the usual stopping and going I noticed a definite affect on power and starting,replaced the shroud and everything was normal. As long as you aren't doing extreme hauling or rampant crawling your stock cooling system should be fine,replace the thermo and the shroud and you should be fine.Just my .02. John
A on the gauge.No problem on the highway,but in town and doing the usual stopping and going I noticed a definite affect on power and starting,replaced the shroud and everything was normal. As long as you aren't doing extreme hauling or rampant crawling your stock cooling system should be fine,replace the thermo and the shroud and you should be fine.Just my .02. John
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From: western montana
Originally Posted by Torque1st
I have a factory flex fan pulled off a 400 in a Lincoln hanging on the wall in the shop. It IS a much better fan than aftermarket units. 
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You notice the location tho... It will never go on a vehicle.
I think they used it for overhung weight reduction because it was stuck WAY out front with a long shroud. That cars hood was so long it felt like driving from the back seat, very strange...
I think they used it for overhung weight reduction because it was stuck WAY out front with a long shroud. That cars hood was so long it felt like driving from the back seat, very strange...
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i had the same thing happen to me before i went to a 460 i was told over and over again that the rear main seal spins out a little and the oil holes dont match up and it causes it to over heat but also my waterpump wasnt that great and my head had a blown gasket
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