Temperature/Heater issue
Thread Starter
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Senior User
Joined: Jan 2011
Posts: 226
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From: Goldthwaite,Tx
Temperature/Heater issue
I recently bought an 81 F150 Supercab with the 351W. The temperature gauge only moves to the C mark. And when I run the heater or defroster
it'll blow warm for only a few minutes then blow cool. I've checked the
sending unit for a good connection,it seems to have a good connection.
After the engine has run a few minutes the upper radiator hose is warm.
I'm thinking the thermostat may be stuck open or there may not be one.
I don't want to start throwing parts at it needlessly so any thoughts or
ideas,suggestions.
Thanks.
it'll blow warm for only a few minutes then blow cool. I've checked the
sending unit for a good connection,it seems to have a good connection.
After the engine has run a few minutes the upper radiator hose is warm.
I'm thinking the thermostat may be stuck open or there may not be one.
I don't want to start throwing parts at it needlessly so any thoughts or
ideas,suggestions.
Thanks.
Laughing Gas
Joined: Apr 2013
Posts: 1,047
Likes: 63
A point and shoot infrared thermometer is a mighty handy tool. Buy one for the kitchen (look what I got for you honey), then use it in the garage! LOL.
Take some readings at the t-stat housing, then you'll know a lot more about the temps you're running. Then at least you'll know if you're actually running cold or if it's an instrumentation issue.
Beyond that you might have a valve in one of the heater hose lines that controls the flow of water through the heater core stuck closed (I have one that's vacuum controlled) or the heater core itself could be clogged, or maybe something's messed up in the heater controls and doors (many vacuum controlled). Is it blowing air and switching from defrost to floor okay?
Since you get some heat out of it for a short while that suggests a low flow through the core.
Take some readings at the t-stat housing, then you'll know a lot more about the temps you're running. Then at least you'll know if you're actually running cold or if it's an instrumentation issue.
Beyond that you might have a valve in one of the heater hose lines that controls the flow of water through the heater core stuck closed (I have one that's vacuum controlled) or the heater core itself could be clogged, or maybe something's messed up in the heater controls and doors (many vacuum controlled). Is it blowing air and switching from defrost to floor okay?
Since you get some heat out of it for a short while that suggests a low flow through the core.
Thread Starter
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Senior User
Joined: Jan 2011
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From: Goldthwaite,Tx
There isn't any valves in the heater lines between the engine and heater.
There is what appears to be a vacuum controller(?) on top of the heater
case in the engine compartment. Probably controls the heater door. It
moves when I switch from defrost to heater and back.
There is what appears to be a vacuum controller(?) on top of the heater
case in the engine compartment. Probably controls the heater door. It
moves when I switch from defrost to heater and back.
Elder User
Joined: Jul 2012
Posts: 553
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From: Raleigh, NC
Where are the heater hoses connected? The input to the heater should come from the intake manifold and go into the bottom of the heater core. I once tried connecting the heater hose to the thermostat housing -- doesn't work well.
Its important for the input to be to the bottom of the heater core so air can be driven out the top. I'm not sure which heater core nipple connects to the bottom of the core and which to the top. My core is leaking and has to be changed. I'll know soon when the old one is pulled out.
Its important for the input to be to the bottom of the heater core so air can be driven out the top. I'm not sure which heater core nipple connects to the bottom of the core and which to the top. My core is leaking and has to be changed. I'll know soon when the old one is pulled out.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
It really sounds like you have a failed (or no) thermostat.
For under $10 and a half hours time I would definitely change it out.
Do you really have a 351W in an '81?
I noted yesterday that Gary said 351 trucks were all M until 1983.
Be aware that Windsor's and Cleavland's use different thermostat styles although they will psychically interchange.
For under $10 and a half hours time I would definitely change it out.
Do you really have a 351W in an '81?
I noted yesterday that Gary said 351 trucks were all M until 1983.
Be aware that Windsor's and Cleavland's use different thermostat styles although they will psychically interchange.
Thread Starter
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Senior User
Joined: Jan 2011
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From: Goldthwaite,Tx
I have compared the placement of the 2 hoses with a Chilton's manual
and a 1984 Ford shop manual that I have and the hoses look to be hooked
up right. On mine the connections at the heater core are side by side
horizontally.
and a 1984 Ford shop manual that I have and the hoses look to be hooked
up right. On mine the connections at the heater core are side by side
horizontally.
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pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
Last year I cut a heater core in half and posted the pic's to prove there was no 'in' or 'out'.
It really does not matter which hose is connected where.
Let me see if I can dig up the thread.
It really does not matter which hose is connected where.
Let me see if I can dig up the thread.
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Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
These symptoms appear to me as if the t-stat is either stuck open, or missing completely. Been there, done that, too many times. I used to have a stuck open t-stat nearly every year. A non-A/C 6cyl rad, with no shroud, and dealer added A/C make for rather warm running engine in the summer when running the A/C, particularly in traffic....... Thankfully, the t-stat can be changed on a 300 in less than 10 minutes. I quit using the "failsafe" type stat, and no longer have to access it every fall.
The upper rad hose should remain cool until the temp gets up to "normal", and then it will get quite warm, quite quickly.
If the engine is not getting warm enough, the heater will never put out any real warm air.
The upper rad hose should remain cool until the temp gets up to "normal", and then it will get quite warm, quite quickly.
If the engine is not getting warm enough, the heater will never put out any real warm air.
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
It really sounds like you have a failed (or no) thermostat.
For under $10 and a half hours time I would definitely change it out.
Do you really have a 351W in an '81?
I noted yesterday that Gary said 351 trucks were all M until 1983.
Be aware that Windsor's and Cleavland's use different thermostat styles although they will psychically interchange.
For under $10 and a half hours time I would definitely change it out.
Do you really have a 351W in an '81?
I noted yesterday that Gary said 351 trucks were all M until 1983.
Be aware that Windsor's and Cleavland's use different thermostat styles although they will psychically interchange.
However, the 351W first appeared in trucks in 82.
Being the OP says it's an 81 with 351W, I suspect it was swapped in place of a 302, or it is actually a 302. They do look almost identical.......
351M/400 does need a different style t-stat, even though most parts books *claim* it uses the same as the 302/351W.
Moderator
Joined: Jan 2001
Posts: 56,949
Likes: 2,718
From: Virginia
With the engine cold, take the radiator cap off. Then start the engine. Go around and look down the radiator. If you can see water flowing in the radiator right after a cold start, your thermostat is stuck open.
Thread Starter
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Senior User
Joined: Jan 2011
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From: Goldthwaite,Tx
I double checked the vin. If the 8th digit is the engine then the letter
is G. On a couple of charts I have that shows a 351W-2BBL. On the sticker
on the radiator support it says engine family 5.8M/6.6NA.
On the pass. side valve cover on the sticker it shows C2 where the
engine code is. A chart in the Chilton's manual shows a 1980 engine ID
label with C2 being Cleveland engine PLT 2.
is G. On a couple of charts I have that shows a 351W-2BBL. On the sticker
on the radiator support it says engine family 5.8M/6.6NA.
On the pass. side valve cover on the sticker it shows C2 where the
engine code is. A chart in the Chilton's manual shows a 1980 engine ID
label with C2 being Cleveland engine PLT 2.
Post Fiend
Joined: Dec 2007
Posts: 8,521
Likes: 16
From: Lost
NP. I do not know if both the M and W were used in 82 though. Some sources say yes, others say no...... Dunno who to believe.