SBF - Leaky Thermostat Housing

[BrewCityCobra]

Fellow small block ford-ers, I've been cursed with a leaky thermostat housing and wanted to address it before the body goes on for good. Any suggestions on gasket/sealant? I've read in some places that people will use Permatex form-a-gasket; otherwise I'm considering just giving the paper gasket another go and see if I get lucky.

Any suggestions or tricks of the trade?

[phileas_fogg]

Use a self-made paper template to make sure ALL the holes on the t-stat body match your engine; some t-stat bodies match better than others (my hazy memory is telling me that at some point Ford actually changed the dimensions on the block slightly). Check the t-stat body and engine mounting surface for flatness using a steel ruler set on edge. I like Permatex; follow the directions on the tube EXACTLY.


John

[egchewy79]

I smear a thin layer of RTV on both sides of my gasket. If you have a chrome housing, scuff the mating surface first

[Fman]

What water neck are you using? I had a cheaper off brand and could never get it to seal. Went with the Ford OEM and that did the trick. One other tip is to dab the t-stat with some gasket sealer and allow it to set up for about 45 mins to hold it in place, if it does not sit flush when you connect the neck to the manifold it will cause it to leak.

This is the neck I ended up buying and had zero leaks once I installed it. Unfortunately the price has gone up over $50 in the past couple years.

https://www.cjponyparts.com/ford-racing-thermostat-housing-90-degree-302-351w-1979-1995/p/M8592M90/?gclid=Cj0KCQjwn9CgBhDjARIsAD15h0C_dY-rUQdFuFh3cyQQRNpl1Qhu0IpNKjTdfDFqNX3vAIocjDSDv-gaAvL2EALw_wcB

Edit: Summit has one for a little cheaper price

https://www.summitracing.com/parts/fms-m-8592-m90

[cobrajj]

I finally cured my leaking thermo housing by using no gasket, and used Permatex " Right Stuff" sealer instead. Also on the water pump-no gaskets either. No leaks in 10 years!

[Bob Cowan]

The chrome housing with the threaded bypass hose nipple is pretty famous for leaking. Especially the threaded portion.

[steno]

Many aftermarket housing have a recess for the stat that’s not deep enough (like the Ford part). Put TWO gaskets on there and you’re set! That’s how it worked for me!

[i.e.427]

We've had really good luck with just about all of the "Stock Replacement" ones. The pretty/shiney ones always seem to leak.

Try here.
https://www.rockauto.com/en/catalog/ford,1993,mustang,5.0l+v8,1134076,cooling+system,t hermostat+housing+/+water+outlet,10337

[Tom Welch]

I had the Dorman 90 degree installed for a while. It leaked twice on my and getting the small bypass hose in place was a whole job in itself.
I recently installed this one from CVR and while the o-ring was a little difficult to keep in place during the install it has not leaked a bit and installing the bypass hose was a snap. You do need to relocate the fan switch if you were using the port in the stock style 90 degree housings but that was a simple task and well worth it for me.

181709


https://www.summitracing.com/parts/CVS-TSH7BL

[Papa]

I had a horrible time getting mine sealed when I did the new 8-stack install. I finally got it to seal using Hondabond sealant with no gasket.

Hondabond High-Temp Silicone Liquid Gasket 1.9 fl oz https://a.co/d/cO19rvl

Be sure to let it cure completely before adding coolant.

[R. Button]

just a couple of suggestions... The thermostat - you need to be sure the thermostat stays in the housing! By that I mean your holding the housing vertical and as you go to put it on the intake manifold the thermostat can slip down and when you tighten it up, it will leak. The thermostat is now caught between the housing and the intake manifold! I do use the gasket to make sure it sticks to the thermostat housing there by helping to hold the thermostat in place.
Just wondering if you recently installed the intake manifold? If so it's possible the leak is coming from the front corner of the intake manifold, leaking down to make it look like the thermostat housing is leaking. Just a maybe.
A minor additional comment, nothing to do with the leak but the thermostat may have a tiny hole in the outer edge of the thermostat. Make sure that is at the top of the thermostat when you install the housing. It's the air bleed to keep from getting air pockets in the cooling system.

[rponfick]

When I had this problem a number of years back, I discovered that it was not the thermo. housing being the problem, but the intake manifold. I had an Edelbrock manifold and the flat surface machined on the manifold left very little sealing surface for the thermo housing. I contacted Edelbrock, and an engineer there agreed with me and said they would reengineer the manifolds and add more surface to the sealing area. Then I got a personal call from Vic himself saying there was nothing wrong with his product.
The bean counters won out, and I had to struggle with the problem on my own. Examine both of these surfaces on your application, and see how much coverage you have. Just keep working at it.

Ralph

[BrewCityCobra]

What water neck are you using? I had a cheaper off brand and could never get it to seal. Went with the Ford OEM and that did the trick. One other tip is to dab the t-stat with some gasket sealer and allow it to set up for about 45 mins to hold it in place, if it does not sit flush when you connect the neck to the manifold it will cause it to leak.

This is the neck I ended up buying and had zero leaks once I installed it. Unfortunately the price has gone up over $50 in the past couple years.

https://www.cjponyparts.com/ford-racing-thermostat-housing-90-degree-302-351w-1979-1995/p/M8592M90/?gclid=Cj0KCQjwn9CgBhDjARIsAD15h0C_dY-rUQdFuFh3cyQQRNpl1Qhu0IpNKjTdfDFqNX3vAIocjDSDv-gaAvL2EALw_wcB

Edit: Summit has one for a little cheaper price

https://www.summitracing.com/parts/fms-m-8592-m90

I have the below setup which is a 90 degree unit that Forte included. It does look awfully close to the one you have suggested so I might be good on that front.

That said, I'm not sure I used the gasket sealer trick so maybe that is the key.

181713

[BrewCityCobra]

I finally cured my leaking thermo housing by using no gasket, and used Permatex " Right Stuff" sealer instead. Also on the water pump-no gaskets either. No leaks in 10 years!

That might be the trick! I'll have to look into that.

[BrewCityCobra]

Appreciate all the input. Sounds like there are two major ways forward 1) try to re-do the gasket (e.g., without a physical gasket but using a gasketing compound), and if that doesn't work 2) think about possibly purchasing a better housing. It seems like my housing should be OK so I'm guessing the gasket install is probably the issue and worth a try first. I'l probably try some form of gasket maker (e.g., either Permatex form-a-gasket or Permatex Right Stuff) and just have to decide if I want to get another paper gasket or not.

[CraigS]

I used Right Stuff once and it worked fine. 3 months later I wanted to use it again on something else and the can was clogged and no way to unclogg it. So the extra expense seemed worth it at first but later I figured that was a one and done experiment.

[Mike.Bray]

I used this one (https://www.summitracing.com/parts/csi-9111c).

Pricey but looks nice, uses O-rings for leak-proof sealing, and the neck can be rotated to any position you want. No messy gaskets or sealant to fool with, just install it and be done.

[danmas]

Revising a necro thread as I now clearly have the same problem so many of you have had. The paper gasket just isnt doing it for me. Considering RTX. Or perhaps the stuff that Papa suggested (although his link is dead). This is current on Amazon: https://www.amazon.com/Genuine-Honda-Hondabond-08717-1194-applications/dp/B00STVCWYY

[Mike.Bray]

The one I referenced above uses O-Rings to seal and never leaks. No messy goop required.

[Papa]

This is what I used that finally worked:

https://a.co/d/eMMwzy8

[danmas]

The one I referenced above uses O-Rings to seal and never leaks. No messy goop required.

Yep, In general I am fix it once and be done kind of guy. That said, $120 bones for a part I have already. That and I would need to either find a black one or powder coat it. Right now I have a paper towel stuffed under it. I think today is a "Im not gonna play in the shop day." Just not feeling it.

[gbranham]

Revising a necro thread as I now clearly have the same problem so many of you have had. The paper gasket just isnt doing it for me. Considering RTX. Or perhaps the stuff that Papa suggested (although his link is dead). This is current on Amazon: https://www.amazon.com/Genuine-Honda-Hondabond-08717-1194-applications/dp/B00STVCWYY

O-Ring setups are nice, as Mike mentioned. As an alternative, and since you already have the water neck you want, consider doing away with the paper gasket entirely, and just use RTV. I did on my current build for the first time, and I've had zero leaks. I usually struggle with paper gaskets and leaks on SBFs. I think Rich actually mentioned this as a solution. I put a thin bead on the manifold, and a thin bead on the water neck, let it sit for 10 minutes, then joined them up with the bolts barely finger tight. Let it sit overnight, then torqued the bolts appropriately. Works well.

Greg

[rich grsc]

Make sure the bolts aren't too long. Had a buddy with a leaking housing even though the bolts where extremely tight, so I went to help. The lower bolt was too long, so even thought it was torqued down, it was bottomed out and not clamping the housing

[BB767]

I finally cured my leaking thermo housing by using no gasket, and used Permatex " Right Stuff" sealer instead. Also on the water pump-no gaskets either. No leaks in 10 years!

DITTO THIS!

I really wanted to keep it the way Ford did it and use the gaskets. Also tried gaskets and sealer. After trying two different thermostat housings and three different water pumps with leaks from all of them I was advised to do as cobrajj did. Not a drop since. Just do it.