Back pressure through cooling system???
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Back pressure through cooling system???
1979 ford 351m 4x4 just purchased and installed the rt139 thermostat with all new hoses and coolant and I'm greeting back pressure through the top radiator line (I've bled the system of all the air ) would a head gasket be the culprit ? Should I go out and purchase a new radiator as the old one seems to have lime scale or some kind of chalky substance ... thanks guys for all the help I hope one day to drive this beast it's just to hot down here to not have a working cooling system (AZ) 
Fleet Owner
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1979 ford 351m 4x4 just purchased and installed the rt139 thermostat with all new hoses and coolant and I'm greeting back pressure through the top radiator line (I've bled the system of all the air ) would a head gasket be the culprit ? Should I go out and purchase a new radiator as the old one seems to have lime scale or some kind of chalky substance ... thanks guys for all the help I hope one day to drive this beast it's just to hot down here to not have a working cooling system (AZ)
It could be a head gasket. It could also mean that the radiator cap isn't venting at 13 or 16 PSI.. I forget which applies to a 351M.
The coolant level at full cold should just barely cover the fins since it will expand when hot. ....What happens if the engine is running without a cap on?
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Yes I mean that the house is really hard and seems like it's over pressured ....What do you mean by fins the metal piece in the radiator ? I have a radiator cap I'll take a picture tomorrow afternoon to see if it's the right one
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The cap rating should be stamped or etched on the cap.... do you have one of those Stant radiator caps?
Regardless, look up the PN and determine its specification.
Cargo Master
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From: Great American SouthWest
I have the big radiator on my 78 f150 351m 4x4 with c6, and when you look into the top of the radiator, you can see the tops of the tubes. They should be covered, but if the coolant is much higher than that, it will over flow (presuming the system can vent)
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Ill try that tomorrow after work and see if it's still building high pressure... it seems to not be filling the over flow but I'll clean out the over fill line and go from there ....I blew on the house today and it seemed to bubble the over fill but I'll check once again tomorrow to be 100% sure ....
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Here's a picture of what I'm looking at I'll try to get a few pictures of the upper radiator hose tomorrow too so you guys can see what I'm looking at
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13lb cap top radiator cap as it's a new motorcraft one I purchased today .... top house at 135 bottom hose at 95 with infa red thermometer thermostat seemed to open up with a huge swoosh of water .... lots of lime scale build up on top of radiator do you guys recommend a certain flush ? No blue or black smoke coming from tail pipes (indicators of a head gasket ) mabe all the build up is straining the cooling system ....
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From: Saskatchewan
I've read your thread twice and I'm still not sure of the problem. If your head gasket is gone you will be puking coolant from the overflow hose on the top of the rad. Or you could see some white smoke out the exhaust. Also your heater might quit blowing warm air for awhile. Temp spikes are also related to head gasket failures.
After the truck has been running for awhile and its up to temp the rad hoses will be firm. 13 psi will do that. That's normal. If your not loosing coolant or any other symptom its prolly ok. Although a good flush may be in order to help remove some of that build up. Good luck.
After the truck has been running for awhile and its up to temp the rad hoses will be firm. 13 psi will do that. That's normal. If your not loosing coolant or any other symptom its prolly ok. Although a good flush may be in order to help remove some of that build up. Good luck.
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I'm going to buy the sending unit this weekend and see how it is after the install ... I think after changing to the correct thermostat and rad cap I finally had the correct pressure and it just looked like the line was under a lot of stress ..... any recommendations on the sending unit install ?
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