I keep having a problem with leaking thermostat housings. I started out with a stock housing, sealed it probably 6 different times, different brand gaskets, different sealers, no help. Bought a MP chrome housing, still leaks. Not a bad leak, but weeps water out.


Anybody else have a similar problem? Any tips to keep this thing from leaking?

I have a chinese made aluminum WP housing. Kinda seems like the holes for the thermostat housing are a hair too close together. Maybe that is the problem?

Any help?

I have the same problem on my 67 R/T.I tried 3 different stock housings,and one replacement steel one from a local auto parts store.My car has the stock cast iron water pump housing.I have tried sand blasting the gasket surfaces prior to assembling them,also checked the thermostat housings for uneven gasket surfaces.Also made sure that the bolts were not bottoming out prematurely.All this and it still leaks.The only other thing I can think of, might be the gasket mating surface on the water pump housing itself.

Overpriced Mancini Billet housing cured mine. Chrome one leaked for me too.

Probably not the housing(s). If the mating surfaces are really flat, smooth, clean, and dry and you put a new gasket between them and torque the screws to the correct value, it will not leak. You can even omit the gasket and use a thin smear of RTV and will not leak. You don't even need any "sealer" if the parts fit right; just a dry gasket.

Check for warps, waves, knicks, scratches, hairline cracks, pinholes, old gasket/sealer material, etc. Magnifying glass and big wide sharp wood chisel and razor blade scraper works for me.

I have a chinese "Four Seasons" cast iron one on my 318. Heavy and ugly, but it don't leak and it would crack before I could overtighten and distort it.

My $0.02

the chrome housings rarely SEAL. mine and many others have not, stock replacement works fine here.

I fixed the problem by taking a large flat file and working the waterpump housing mating surface. The warped area will show up as the file will take the high area down first. Then take the tstat housing surface and work it on a sheet of sandpaper laid on a flat surface. As ithers have said, do not use the chrome as it does not seal.

had the same problem with my small block , then my friend told me about permatex product called "right stuff" so i figured id try it since ive tried 4 thermostat housings anyways it worked no leaks!!!! and for only 8 bucks woohooo

Got a thin sheet of cork gasket material and made my own. Works much better than the paper gasket. Fixed the leaking.

Take that POS chrome housing & throw it as far away as you can...

I take a wide flat file to it on the WP housing and the thermo housing

file till nice and smooth then it seals

the chrome one will seal after removing the chrome from the sealing surface

done this on old used headers that would not seal also

I have done the cyl head at the exhast ports by hand file when I had the engine out,like said you can see the high spots when the file is a workin

have hit all the flats on a few carb bases on alum intakes to make sure they are flat while I am doing the thermo surface

just dont take to much off the thermo housing,it needs some of the recesed lip/groove to let the thermostat be pinched inbetween the two surfaces

2 gackets and indian head gasket shelac has work before also

One last thing you might check. If your bolts that hold the housing down are threaded all the way thru to the water passage, you need to put sealer on those bolt threads. Not all holes are threaded all the way thru. Some are just blind holes. I've had about 50/50 on most S/B intakes going all the way thru. YMMV.

This has been a sore subject with me in the past; have tried the chrome and stock housings and they leaked. Finally after ensuring the water pump housing was true I purchased a billet thermo housing from Mancini; no leaks so far. I know for a fact that the chrome thermo housings warp as I have trued them up many times. Just my 2 cents.

Von, w/ what most everybody here has already told you. I had a chrome one that leaked like crazy no matter what I did to it. I tried a few different stock ones I had here and they all eventually started leaking no matter how I sealed it. I tried it w/ and w/o gaskets, w/ and w/o silicone, etc. I finally bought the billet piece from Mancini and finally NO MORE LEAKS!!
CHIP

The chrome water necks warp and leak. I tried truing mine up on a belt sander and it sealed for a while and leaked again.

Use a iron or billet piece and check flatness of the water neck and WP first. The easy check is to put the two cleaned parts together and check for rocking and/or gaps. File or belt sand to correct as needed.

With a good billet or iron neck, flat surfaces and correct torque it should seal with a gasket. Some sealer is insurance - I used the old hardening Permatex #1 type. Too much torque will warp the water neck and cause a leak.

Another vote for the Mancini Billet unit...I had mine powdercoated engine color and its perfect so far..

and,.......you just might be overtightening them and warping 'em.