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Discussion Starter · #1 ·
Im having an ongoing little problem with my 468 peanut port motor that I installed.
When I shut the car off,after awhile,coolant puddles on the manifold.
It used to occur at the thermostat housing seal.
After resealing a few times,and still weeping after shutdown(not immediately after shutdown,but the small amount is found BEFORE the next cold start up),I had changed to a 160*thermostat.
Housing is now leak free,but it weeps at the hose/neck location.Clamp cannot be any tighter,hose is new and square.
Radiator is the same new aluminum one Ive had in there,and I changed out the rad cap that came with the rad with another 16lb,still weeps after shutoff.
It does not leak or weep at all while running,or just after shut off.
Motor friend of mine says there is too much pressure in the upper hose,thats why I switched the rad cap,but its still doing it.
Driving me nuts.
What are some possible causes of too much pressure?
 

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if the cap is working you just have a leak that needs repaired. its normal to build some coolant pressure after the engine is shut off
 

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Sounds like the leak is at the hose to thermostat housing, right? Does it happen to be a shiny chrome plated one? If so, emery cloth the heck out of the chrome under the hose position.
 

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Discussion Starter · #9 ·
No chrome,the neck is an original,but its painted.And I have a habit of putting some dielectric grease on the neck where the hose goes,lol.
All that didnt start leaking until the gasket area was taken care of.
It just seemed as though as soon as a weak spot was taken care of,it sought another.
I was just looking for ideas of why there would be excessive pressure.
My engine friend recommended getting a 7lb cap for it,but everything I see calls for a 16lb,and maybe originally it mightve been a 15lb.
Theres no problems driving,its just a dime sized puddle after a few hours of sitting after shutoff.
 

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They also make 11lb caps, maybe that might be a good compromise.
If you tighten the hose clamps too tight you can damage the hose, I've done that before. The rubber will get tiny cracks where it gets crushed by the clamp, you might want to check that.
 

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Any chance of a pinhole in the hose at the neck?
Clean the housing neck with some Scotchbrite or steel wool and also inside the hose where it contacts the neck.
Might try a pressure tester to see if you can duplicate the seeping.
 

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Try a Gates heat shrink style hose clamp. Very even pressure all around the hose and looks better than a regular clamp.
 

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if the car does not over heat then you will not hurt a thing with a lower pressure cap.
for each PSI increase in cap pressure you increase the boiling point of the coolant 2-3 degrees.

I run the lowest pressure cap I can get by with, Of course my coolant temps stay in check.

Had an old Vega with the aluminum lined engine that was sleeved to Iron liners after 35,000 miles.
Anyway my older sister got the car as a first cat .. then my younger sister got it. Then it was sold.

It was never transferred into the buyers name and 2 years later the Police call the house and ask if we own a Vega as it is left abandoned behind TG&Y.
We got it back and drove it another 4 years But :::: the radiator had a pin hole in the upper part of the radiator when we got it back.

Dad removed the cap and drove it without a cap as the pressure in the system with a cap would squirt all the coolant out of the pin hole.
So 4 years with NO radiator cap!.. no overheating issues at all.. just add coolant about once a month.
 

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Funny how that works isn't it.
My son older got his 2nd car a 260Z datsun needed electrical work and had the stock carbs etc.
We worked it over and found out the engine was not treated well. was the only block I ever seen in those inline 6's that had wear on cylinder walls.
OH well stuck in a 280 block and ran the 260 head Ported it and added the internal oiling cam.
Had the head surfaced and stupid thing would leak coolant between cylinder 3 and 4 down the side of the block.. just a trickle.
He tried stop leak .. retorqued the heads.. I said remove that 16psi cap and stick on a low psi the lowest you can find.
He got a 7 psi I think.
Leak stopped.
He had it towed on a trailer to Ohio.. as he thought it would get bad MPG got a job there.

Well he hated Ohio and came back ..drove the 260 all the way and got 27 MPG and never used any coolant.

No the stock carbs were not used I made an intake from some mild steel and mounted a 4 barrel carter AFB onto it a little 465 cfm from an early Buick.
I think he still has the intake.. I welded beads in the plenum floor to keep fuel in suspension. I thought it should work well. It did.

Like mentioned try a low pressure cap.
 

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When I shut the car off,after awhile,coolant puddles on the manifold.
It used to occur at the thermostat housing seal.
After resealing a few times,and still weeping after shutdown(not immediately after shutdown,but the small amount is found BEFORE the next cold start up),
Coolant temperature increases after the engine is shut off. This can be verified on any engine with a temp gauge that still reads accurately after the key is turned "off".

If the temperature increases, pressure will increase unless relieved by the rad cap. Takes a long time for a fully-warm engine to return to "0" pressure again. For that entire time, the coolant is trying to escape. Any flaw in the cooling system sealing will result in a leak.

I had changed to a 160*thermostat.
Typically un-needed.

Housing is now leak free,but it weeps at the hose/neck location.Clamp cannot be any tighter,hose is new and square.
Something in the hose/housing neck/clamp system is faulty. First Guess: Crappy clamp. Second Guess: Hose fault due to over-tight clamp. Third Guess: Defect including gouges, scrapes, or cracks of the thermostat housing neck.

First thing I'd do is remove the clamp, inspect the hose for deformation.

I changed out the rad cap that came with the rad with another 16lb,still weeps after shutoff.
Tells me that the problem is VERY unlikely to be related to the rad cap. 16 psi is just not that tough to seal. 25+ psi gets interesting, and plenty of European cars have high-pressure caps and still remain leak-free.

Motor friend of mine says there is too much pressure in the upper hose
He's probably wrong.

What are some possible causes of too much pressure?
Wrong question. You almost certainly do not have too much pressure.

to much heat or a leak from the combustion chamber build pressure but your cap should pop off. what pressure is the cap rated
Yup. If this had anything to do with combustion pressure, the complaint would be that the overflow hose was gushing coolant, or that the overflow bottle was getting over-filled.

I have a habit of putting some dielectric grease on the neck where the hose goes,
Stop doing that. When I worked for the bus company, I was instructed to use Dow 111 silicone grease on silicone hoses. The engineering department had reviewed 'n' approved that lubricant.

Applying grease to what is likely neoprene or EDPM rubber may not be such a great idea.

There's also the idea that part of the hose sealing on the thermostat housing is the natural adhesion of the rubber to metal, which you're now interfering with. It's why they make tools to slide between hose and the metal neck, to break that adhesion.

It just seemed as though as soon as a weak spot was taken care of,it sought another.
Yup, that's the way it works. Life is full of trying to reinforce weak-spots.

I was just looking for ideas of why there would be excessive pressure.
And now you know that that isn't the problem.

My engine friend recommended getting a 7lb cap for it,but everything I see calls for a 16lb,and maybe originally it mightve been a 15lb.
You don't need a lower-pressure cap. You need to find out why the seal between hose and thermostat housing neck is defective.
 

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Take an old cap and drill a small hole in the center to relieve pressure, run the car with it and see what happens. It should run just fine with no pressure but be a little low on water..

I keep this cap in my car in case my radiator springs a leak..
 

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Take an old cap and drill a small hole in the center to relieve pressure, run the car with it and see what happens. It should run just fine with no pressure but be a little low on water..

I keep this cap in my car in case my radiator springs a leak..
No need for that.
If for some reason you want to run the car with no pressure on the system, simply loosen the cap.
 
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