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Strange Overheating Issue
#1
I've been having a problem with overheating lately in the rebuilt 351C in my '71 Mach. I expected to see somewhat higher temps with a tight motor, and I have about 1100 miles on the rebuild. This is a non-AC car.

Yesterday while driving in warm temps (maybe 85 degrees), the gauge went pretty far to the right and stayed there for a while, then dropped down to the halfway point, then below, fairly rapidly, and stayed there for the remainder of my trip (maybe another 15 minutes).

I was doing maybe 60mph at the time. Before jumping on the highway, I had been doing a fair amount of sitting and idling in traffic, so I had expected the temp to go up some, and it did, to maybe just above halfway on the gauge. But it started to really go up once I hit the highway, the reverse of what I expected.

To me, this strikes me as maybe a faulty thermostat (I did replace the thermostat when I built the engine). I'm running the factory-recommended 195 degree thermostat. Any other thoughts? I checked the coolant, and none had overflowed that I could tell.
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#2
are you running the brass restrictor?


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#3
Sometimes a thermostat can stick a bit and then suddenly open all the way; my Ranger was doing that for a while & a replacement thermostat solved it.
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#4
Well... it could be a retard tunned distribuitor if i recall correctly... I happen to have overheating problems in my I6... I have the warning light sensor so it was critical because once the light turns on, almost always is too late...

Well... i ordered new everything... from water pump to sensor... Everything in on its way to here, Uruguay... but in the midtime, a friend of mine came to my garagge with some tune up tools and told me my distribuitor was really far from his optimal point... It was retarded actually and he keeps telling me that is why the car overheated... I could go for a ride yet but that could be at least some % of the problem...

Maybe you have more than one issue and all contribuites to overheat your engine... I remember i had the most stupid overheating problem ever with a 351W in a 70 coupé... Engine was totally redone and everything but sometimes, somehow the temp went up quickly.... After 100 tests, we found out the guy who did the engine put too much sylicone to help the gasket so seal... Well... that excess of sylicone went into the water cameras on the block and just sometimes, that sylicone ball blocked the circuit and the engine temp went up as fast as the wind!!...

Well.. hope it is nothing serious men!!



Damián Cool

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#5
Check your ground to the body. Did you notice if any of the other guages moved? Is this a stock guage?

Do you have a temp gun? You should verify the information the guage is providing.

Normally I wouldn't be suspect but your symptoms sound a lot like what happens when the body ground is bad. I think originally it went from the engine to the body. Might have forgot to put it back on and/or broken it taking the motor out (it's easy to forget).

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
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#6
Tnfastbk;25478 Wrote:are you running the brass restrictor?

Yup. This just started the last week or so (I've seen it a couple times), I've been running the motor for about 2 months now.

will e;25483 Wrote:Check your ground to the body. Did you notice if any of the other guages moved? Is this a stock guage?

Do you have a temp gun? You should verify the information the guage is providing.

Normally I wouldn't be suspect but your symptoms sound a lot like what happens when the body ground is bad. I think originally it went from the engine to the body. Might have forgot to put it back on and/or broken it taking the motor out (it's easy to forget).

The ground is good. It's only the temp gauge.

dohebert;25481 Wrote:Sometimes a thermostat can stick a bit and then suddenly open all the way; my Ranger was doing that for a while & a replacement thermostat solved it.

That's what I'm thinking, too. For it to go up very high then gradually go back to normal temp, it was sure acting like the thermostat didn't want to open, then suddenly did.
URUGUAYAN_FASTBACK;25482 Wrote:Well... it could be a retard tunned distribuitor if i recall correctly... I happen to have overheating problems in my I6... I have the warning light sensor so it was critical because once the light turns on, almost always is too late...

The timing is set perfectly. But I appreciate the tip.
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#7
Tnfastbk;25478 Wrote:are you running the brass restrictor?

What is this & where does it go? Do we need to in the southern states?

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My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
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#8
the restrictor is located underneath the thermostat its pounded in place, originally the 351c was having issues with too much cooling and not running at the correct temperature so they placed a restrictor to the upper radiator hose to reduce the amount of coolant going to the radiator.

it made the 351C thermostat different from the 351W, the 351C sits on top of the restrictor and the valve opens up, the 351W thermostat opens down, so if you put a 351W in your car the thermostat would never be allowed to open, and the car would overheat.

if you do not have a restrictor in the 351C I was told that would actually make the engine run very cold not hot.

----

i would replace the thermostat with a new one, but first i would test the new thermostat in boiling water to make sure its working.
make sure its a 351C thermostat as well.

additionally did you install the anti-collapse spring inside the lower radiator hose? this prevents the lower hose from pinching off during cruise or high rpms, that can also cause erratic temp readings. they make 2 springs the smaller one is for the 302 the larger for the 351c, the spring goes inside the lower hose and fits up against the water pump inlet housing if you accidentally use the 302 spring it could get sucked into the water pump impellers and cause damage. the 351 spring is a pain in the butt to insert into the lower house its tight to the hose walls and you have to deal with that U shape area before the inlet. the reproduction and aftermarket hoses do not come with the spring installed


for southern state cars they had a 182 degree thermo. northern cars usually got the 192 degree, i've seen a 160 degree thermo also.
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#9
72HCODE;25506 Wrote:i would replace the thermostat with a new one, but first i would test the new thermostat in boiling water to make sure its working.
make sure its a 351C thermostat as well.

additionally did you install the anti-collapse spring inside the lower radiator hose? this prevents the lower hose from pinching off during cruise or high rpms, that can also cause erratic temp readings. they make 2 springs the smaller one is for the 302 the larger for the 351c, the spring goes inside the lower hose and fits up against the water pump inlet housing if you accidentally use the 302 spring it could get sucked into the water pump impellers and cause damage. the 351 spring is a pain in the butt to insert into the lower house its tight to the hose walls and you have to deal with that U shape area before the inlet. the reproduction and aftermarket hoses do not come with the spring installed


for southern state cars they had a 182 degree thermo. northern cars usually got the 192 degree, i've seen a 160 degree thermo also.

Here's an interesting article regarding hose springs, and what their original use is really for:

http://automotivemileposts.com/autobrevi...ecoil.html

I'm thinking of going to the 182 thermostat. I seldom if ever drive in winter, and we do get very hot days around here.

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#10
that article is mistaken, i have seen lower hoses pinch off on dynos without the spring installed. the spring prevents that from occurring, if that is simply an unintended side effect that is another story. the fact is the lower U shape radiator hose under higher rpms without something inside the hose to keep its shape will restrict. if you have a low rear ratio and drive today at 75-85mph on the highway with the tach over 4000 that hose starts to pinch off because its very soft.
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