View Full Version : Persistant coolant leak

06-13-2007, 11:10 PM
I find that there is a persistent coolant leak at the T-Stat housing. I have tried a new gasket....even permatexed both mating surfaces......scrubbed both surfaces to ensure they are free from debris....and it STILL starts to drip coolant after the motor goes into "heat-soak" when it is shut down from a drive.

I am at a loss as to how to correct this problem. I was told by one individual tonight, that what's on there is an aluminum T-Stat housing and the reason it leaks is because it 'warps' when it is tightened down. What they say I need is a cast-iron housing.

Does this make any sense to any of you people?

Also, what is considered to be a "normal" operating range for the coolant temps during a 90 day with a mixture of 50 mph boulevard driving and some stop and go driving? Mine was right at 190-200.

And I see there is a 13# pressure cap on the radiator. Is that the correct setting?

This is the last "gremlin" I need to get fixed in order to have a hopefully smooth drive out to SB in a few days. Any helpful suggestions are appreciated.


1962 GT Hawk 4sp

06-13-2007, 11:43 PM
The leak: If you think the base of the housing is warped, take it off and sand it flat using a piece of 100 grit sandpaper and a flat surface. I would be more suspicious of the hose connection. This is what leaked on my car and because the coolant runs down where it is hard to see, it looks like the gasket is leaking.
Operating temp: My Hawk runs up to 210 at times. Check your gage for reference by sticking a thermometer into the radiator. Compare this to the reading on the dash gage.
Pressure cap: 13 is correct. It should raise the boiling temp to around 220 I think. This would be a temperature when you might start to worry.
I find that my Hawk gets the hottest while cruising the interstate at speed or when stuck in traffic on a hot day. I've had the radiator recored, checked the water pump, changed thermostats, thoroughly cleaned the engine and it still seems to run a bit hot. When it burns up, at least I'll have a clear conscience.

Tim K.
'64 R2 GT Hawk

06-14-2007, 08:42 AM
One other thing to consider is porosity of the aluminum neck.
You might want to clean and inspect the inside of the housing and check for a pinhole. You can take a dab of Permatex #1 hardening sealer and smooth it over the inside of the housing to seal it up.
Just keep the amount very small and thin on the inside of the housing. Let it set up overnight and clean the thermostat groove and sand the surface flat.
It's amazing what 6-15 psi will push through a weeping pinhole.
You can do this fix for free.
Hope the info helps.


DEEPNHOCK at Gmail.com
Brooklet, Georgia
'37 Coupe Express (never ending project)
'37 Coupe Express Trailer (project)
'61 Hawk (project)

06-14-2007, 09:29 AM
Be positive that it is not the hose leaking.
Been there !

1961 Hawk 4BC,4-SPEED,TT
(formerly chevpartsman)

06-14-2007, 02:27 PM
Ok, so far problem seems to be solved, although I am not sure what one thing solved it.

I sanded down the mating surfaces (even though I had already thoroughly cleaned the off previously)....checked for porosity in the neck of the aluminum housing and there were indications of pitting, so I went and applied as suggested a touch of #1 permatex and let it set up.....and went and bought a Chebbie T-stat gasket which had a little rubber liner built into it, that fit perfectly.

Buttoned the whole thing back up, drove all around in 87 heat, some at 70 mph, lots of stop and go stuff, back to 70 mph again for 10 miles or so, shut it down and waited.

All the while driving the temp gauge never went over 190. As the motor went into heat-soak, nary a drop of coolant snuck out. Alright!

I don't know who to thank, so I will thank ya all for the help.

Now, I gotta keep my fingers, my toes, and my eyes crossed, that nothing else happens.


06-14-2007, 06:27 PM
Cool, Karl, see you in SB

Tim K.
'64 R2 GT Hawk

06-14-2007, 07:38 PM
I think the gasket makes a big difference, you have to use a good thick gasket for some reason. I second the other comments, you need to sand mating surfaces flat with sandpaper on glass or other similar method to get them perfectly straight. Might want to actually use a torque wrench to insure that you don't succumb to the temptation to get the bolts TOO tight and warp the housing after you sanded it flat! Also make sure that the threads aren't pulling out of the water manifold from previous overtightening; a little chamfer with a large drill bit will fix it if they are. The correct housing for your car is aluminum; only the earlier four bolt housings were cast iron.

If you have a 180 degree thermostat 190 degrees at the back of the head is perfectly acceptable. 13 lbs. is factory.

I realize you've already pronounced success, just posting for the benefit of others that may have this problem (I know that in the past, I have.)


55 Commander Starlight

06-14-2007, 08:01 PM
Most automotive temp senders should be considered "indicative only". They are not very exact when new, and certainly don't improve with age.
If the only concern is a "hot" running engine, do check what the temperature actually is, the car temp gauge might not give a very true "indication".
Use one of the new-age laser gauges. Borrow or buy one, they are excellent value. Just point it at various surfaces and read off the temp. Simple and clever, and rather precise readings.
With good info, you can make the right decision.