1977 351M Temperature Issues
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1977 351M Temperature Issues
Recently purchased a '77 f150 with a 351M. Noticed that on the freeway it was running hot, pushing 220+ at about 68MPH. City driving it runs about 195-205ish.
Truck has 35" tires and has a manual granny tranny. I'm concerned with temperature changes and would like more consistency.
Planning to flush the system and install new thermostat (M.Craft RT-139)
Anyone have suggestions? Stock radiator, stock fan with shroud.
Truck has 35" tires and has a manual granny tranny. I'm concerned with temperature changes and would like more consistency.
Planning to flush the system and install new thermostat (M.Craft RT-139)
Anyone have suggestions? Stock radiator, stock fan with shroud.
Postmaster
Joined: Mar 2011
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From: Taxachusetts
That's a bit hot. You should be around 200 (give or take) city/freeway....about normal for M blocks.
If your water pump isn't leaking, hoses aren't bad/squishy and the heater core is good, a good flush would definitely be next in line.
No coolant leaks or needing to add any? I'm presupposing the T-stat number you posted is for the M blocks, yes?
If your water pump isn't leaking, hoses aren't bad/squishy and the heater core is good, a good flush would definitely be next in line.
No coolant leaks or needing to add any? I'm presupposing the T-stat number you posted is for the M blocks, yes?
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Heat Issue
Just noticed that I have some leaking from the heater core onto the interior of the passenger floor. Small amount but I think I neeed to replace that and then flush the system to see where I'm at.
I also assume the gauge is accurate (it's after market with numbers)
I also assume the gauge is accurate (it's after market with numbers)
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Make sure the truck has the right thermostat for a 351m/400. Sometimes a thermostat from a 351 windsor gets put in. They are different thermostats. The thermostat for a 351m/400 has a bypass in the block that needs to be covered up whenever the thermostat opens, if it has a windsor thermostat then it doesn't get covered up and the coolant does not cycle through the block like it should.
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Rad Hose
Since I have a 3 inch body lift how do I ensure I get the right length radiator hoses. Do I just have to take the old one and match up with another hose?
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More Turbo
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If you have a stock fan shroud, the radiator had to have been lowered. The stock hoses should fit fine.
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Make sure the truck has the right thermostat for a 351m/400. Sometimes a thermostat from a 351 windsor gets put in. They are different thermostats. The thermostat for a 351m/400 has a bypass in the block that needs to be covered up whenever the thermostat opens, if it has a windsor thermostat then it doesn't get covered up and the coolant does not cycle through the block like it should.
This^^^^^^^ I put the wrong t'stat in my truck thanks to the jerks at autozone.
Last edited by buttwheat; Jun 12, 2013 at 09:29 AM. Reason: didn't know A55hats was an unexecptable word sorry
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Lower Hose
No spring inside the lower radiator hose. NAPA parts do not have a spring in the facotry hose. Does everyone just add a spring or is there a unique part # I should consider to ge a hose with a spring.
NAPA said design has changed and no spring is needed now-a-days?
NAPA said design has changed and no spring is needed now-a-days?
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A spring is not necessary due to the stiffness of the modern hoses with the exception of running a high volume pump. If your lower hose is old and weak then yes it could collapse under the suction pressure.
Postmaster
Joined: Mar 2011
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From: Taxachusetts
Agreed.
I run a Gates hose, #21053, has an internal spring. Their website says what buttwheat indicated about the newer hose materials.
I guess it's an old hose...had it in there for a few years now.
I run a Gates hose, #21053, has an internal spring. Their website says what buttwheat indicated about the newer hose materials.
I guess it's an old hose...had it in there for a few years now.
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update
Replaced t-stat and of course it had the incorrect one it so that was good to get corrected. Also replaced leaking heater core. Flushed system and two new hoses and its been running cooler. Ranges from 195 to 205 now which is much better depending on my speeds.
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