Thermostat housing leak
 

So I have been battling a leak at my thermostat for quite a long time. Last year I took the housing to a piece of sandpaper that was stuck to a piece of glass, so that is perfectly smooth. I then tried taking the housing to to the intake with sandpaper stuck to it and tried to make sure the intake was true. Hard to do with such little space. Well it was still leaking after I did all of this, even though it took a while to show up.

I pulled the housing today and the housing still looks really good, but the intake doesn't look all that great. My thought was to pull the intake and take intake and housing to a machine shop and see of they could true them both up and then make sure to cut in the groove for the thermostat to sit in to make sure it doesn't sit up too high.

Any thoughts on this? Is there a decent way to true it up on the car without removing intake?

Here is some pictures of the intake and a picture of the still clean housing.

Thanks,
Karl

You should be able to get the thermostat gasket sealing surface on the intake flat enough by using a large flat file that's nice and sharp.

As long as it hasn't sat on the bottom of a lake for an extended period of time it should clean up fairly quickly.

Cutting that surface on a mill and boring that groove for the thermostat to seat down at a machine shop will cost you more than simply finding another intake that's in better shape.

Dress it down with a flat file and get it done.

Don't over tighten the housing either .... find out what the torque spec is and use that. Sometimes on odd shaped parts, over tightening can actually cause them to warp in a way that will make them leak worse ... specially aluminum parts.

If that is all pitting that I see on the intake side ..specially on the front bolt ... you are going to have to clean that up a lot to make it seal.

Yep ... go out and purchase a new, quality, flat file, smoke some pot and spend a couple of hours listening to your favorite music and patiently file that intake flat and smooth again :)

Remove it again , clean up both sides and then wipe both sides down with Actone, enough to to get into any corrosion pores in the manifold side or the T stat side.

It all must be 100 % free of antifreeze !

Next get some blue silicone gasket maker and apply a bead to the intake side and let it set up for 20 minutes.
After 20 minutes bolt on the water outlet and let it cure over night.

You need to apply a big enough bead of sealer to have come out the sides a good amount , then the next day you can trim it back with a single edge blade and your golden!

The file trick works great. The pot smoking is optional, but I would use Ultra Grey Permatex...

Thanks guys, I will try what you all suggested. There is just so little room to do this in the car, but I'll try removing the alternator to get more room and make sure I am going flat and true. This is the original intake, and would like to keep it especially with the date code being correct.

Steve, when the engine was rebuilt back in 96 and the engine re-builder I think did that, because he used a black RTV or similar. It oozed to the inside also, and a few years ago when I pulled my radiator, you could see it coming through some of the rows. That just has me leary of using anything like that again. Battling how this thing likes to run a little hot and I often wonder if he used that stuff anywhere else and if it could be blocking any passages in the block.

Thanks,
Karl

This stuff works great for applications like yours:

Permatex 22071 Water Pump and Thermostat RTV Silicone

https://www.google.com/url?sa=t&rct=...UXZq_FJtv7ms-A

coat both surfaces with dykem or color with marker and do the file trick, when both surface have no coloring on them they should be flat enough for a good seal..

So I started on the intake with a file, a couple of passes took the real light stuff off. I think it was more staining, but there has always been some deep corrosion going on towards the passenger side.

I pulled the EGR ported Vacuum switch, fuel line and alternator just to give me more room. I am going to color it with a marker and get a small piece of glass to put self adhesive sand paper on so that way I go across the whole surface at the same time. Otherwise I am worried with a file that I might push down too much as I cross in certain spots and will end up getting rid of the corrosion, but will create a low spot.

Get a Teflon gasket from Tin Indian Performance. No need for sealers and they don't leak and are reuseable.

The specific Permatex gasket sealer would be your first choice, but the Ultra Gray will be too a close second to call. Reason we recommend Ultra Gray is that it really likes to stick to itself, and I've never seen it come off inside an engine and migrate. Same goes for Ultra Black and The Right Stuff, but the list ends there. I've fished clear, red, and blue out of all sorts of places inside engines we've taken down.

Always a good idea to wait 24 hours to let any silicone set up. I've seen guys get away with slapping engines together and firing them up, but the waiting period really insures the silicone is fully bonded to the parts and to itself.

I do like the Teflon gaskets, but the Ultra Gray will do the job even if surfaces are heavily pitted and tore up.

Also make sure your bolts aren't just a hair too long

I used Permatex's The Right Stuff on my son's S10 thermostat housing that had a bad nick in one surface, and it has worked great. Use it instead of any other gasket, and I would always let it dry overnight before I added any fluid. Also, make sure you use it inside and outside the bolt holes.

And, as mentioned above, screw both bolts in all the way without the housing in place and measure how much thread is exposed. Measure that against the housing thickness to make sure your bolts aren't bottoming out.

Have you pressure tested the system? All too often I have seen the gasket blamed for a leak when it is actually the hose that is leaking. The fluid is seeping between the hose and the housing. The cheap screw clamps don't help the situation. You need the spring loaded type of clamp. Just a suggestion.

Cast iron or aluminum thermostat housing? I've never had anything but trouble with the aluminum housings.

this stuff is really good.
http://www.valco-cp.com/Hylomar.htm

Yes, I have done that. I can actually see it seeping from the gasket area. That area that it does seep from has a lot of pitting/corrosion. I have also checked the bolt lengths and those are good.

As an update: I sanded it down after taking the alternator off and fuel line to the carb and removed my ported vacuum switches, so I would have more room to get to it. I used a large DA sander to be able to cover the whole area at once. It took quite a bit to get it all gone. So much that now the thermostat doesn't sit in the lip anymore on one side. I tried putting the thermostat housing back on without gasket or thermostat and I could fit a .013 feeler gauge under the middle of it on both the front and back. If you considered the sides where the bolts go.I put the housing on a piece of glass and tried checking that I had a hard time even getting a .0015 under it. So the housing is good and true.

I could send mine to a place in Michigan that can build the intake up and then machine it down and cut the lip into it so you wouldn't even be able to tell it was done. But HFR had an intake that had a date the next day from mine, so we worked out a deal. I'll post pictures tomorrow of my finished intake.

It is the original Aluminum housing. But that is actually good and true. I sanded that down last year on a sheet of glass with DA paper stuck to the glass.

I have tried that also, and have always had good luck, this one just didn't want to seal up.

This. I like to do a light assembly after coating both sides of gasket with Ultra black/grey. I put on the water neck, start threading the bolts, and give the neck a little wiggle with the slop of the bolt holes to help rtv distribution. Then I delicately finger tight the bolts to keep even contact. I wait until the next day and then do final torque.

I have used JB Weld on a water crossover surface with severe pitting, and then used a file to true it up. But for the most part, rtv should be able to take care of business.

Intake after sanding
 

So here is a picture of the intake after I sanded all of the corrosion out of it.

Looks great.

Looks are decieving
 

Thanks, but when I put the housing on it, I get a .013 gap between the bolt holes on both sides, so something isn't true. Also the thermostat doesn't sit in the lip anymore.

That's what rtv is for...

I've got another intake on its' way that is dated the next day than what mine is. I will see how that one fits. With this one now, I wouldn't trust it with the thermostat sitting up out of the lip.

I would block sand that thing back flat and use a cone shaped bit in a dremel to cut the recess back in.

Wish you was closer, I like fixing stuff like that.

Good idea. One thing that might work even better than a cone would be one of those small Dremel grinding wheels, since the side of the wheel could lay it flat on that ledge and grind it down flatly all around the hole.

Yes it would, The little cut off wheels would really get it done in a hurry.
I've got an inch thick piece of glass that's about 4" X 6". Using it with emery cloth would fix the OP's intake up in a snap.

And small world, I've got a brother down there in Lawrenceville

So it has been a while, (too long) and time for an update. I picked up another intake and it took awhile to get it all cleaned up. I had to do the sandpaper on a sheet of glass, that cleaned up a majority of the pitting on the intake. I didn't go too low that I lost the groove for the thermostat to sit in and took a grinder and was able to grind in the seat for the thermostat to sit in. I then did more glass with sand paper and got almost 90-95% clean. I ground the seat in more too make sure the thermostat was siting down in the groove. I torqued down the housing without a gasket and had about a .003 gap on the backside of the assembly. I figured a gasket would take care of that, so installed housing with a teflon gasket from Tin Indian Performance and torqued the housing down. Installed the intake after painting and then noticed my ported vacuum switch was causing a vacuum leak at it's base, so was on the search for a replacement one before I could fill the coolant back up. Finally got one about 2 weeks ago and last weekend got it installed and filled the coolant. I pumped it up with my coolant pressure tester and the damn thing started loosing pressure. I found the cap for the back-flushing tee a little loose so I tightened that and pumped up some more and still a slow drop in pressure. Looking all over the intake to make sure it wasn't that and finally saw a little bead at the front and rear of the thermostat housing again and yes I made sure it wasn't the hose. I finally said enough was enough and bought a new housing from inline tube because I saw it on eBay and had the same P/N and the "3" on it as mine did, I am assuming the "3" is for '73. It came in Friday and I put the two housings together flange to flange and held it up to the light and could see light through it. So now which one is bad? I took the new one and held it against our kitchen window glass and it was solid, held my old one up and there was very slight rocking even though I sanded it on a sheet of sand paper adhered to a piece of glass, just must not have been able to hold it perfectly true. So I was pretty confident that was the cause of the leak, but still used the Permatex Ultra Black and coated both sides of the teflon gasket and installed housing finger tight for an hour, then came back and torqued it to 30 ft lbs in 3 stages. I know I didn't need to but it doesn't take that much more time, I did 15, 25 and then 30. I let it sit until tonight to give it 24 hours to fully cure, filled it with antifreeze and pumped it up. As I sit here typing, it has been an hour and it hasn't dropped.

The reproduction housing from inline tube I believe is what fixed it. I may have been able to get away with just the housing and no Permatex Ultra Black, but I didn't feel like taking a chance. The new housing looks just like the original except two right angles are very crisp sharp edges where the original is slightly rounded, easily fixed with a file.

Thanks for everyone's help and input and sorry or such a long post.
Karl

Thanks for the update!

If that doesn't work: Use Permatex's The Right Stuff and finally be done with this. It will fill-in any pits or mis-matches and seal. I used it on my son's S10 thermostat housing that had a bad nick in one surface, and it has worked great. Use it instead of any other gasket, and I would always let it dry overnight before I added any fluid. Also, make sure you use it inside and outside the bolt holes.

I stopped using gaskets just right stuff silicone let sit overnight no more leaks a lot o them looked like the coolant was seeping thru gasket

Just as an aside: I generally don't use any sealer just new quality gaskets. I often see with cooling system stuff that there is some weeping the first one or two heat cycles before the parts set up watertight. If you had the parts that flat it's possible it was still going to be OK.

Good to know those points. We will see how it goes once I get it running and out for some drives.

We repair this area on the intakes all the time when doing our 100% stock-appearing builds.

Fairly easy if not totally destroyed. We've fixed ones worse than yours in the photo. (See below)

The gasket surface gets machined first then the thermostat register, all is like new when done.

Thanks, Gary in N.Y.

P.S. Here's a BBC we recently repaired, don't have the finished shot but it cleaned up nicely and not a sign of any leak.

Fingers crossed on the coolant leak repair.

If it returns, i would look for cracks from freezing

I would be interested in having my original intake repaired. What do you do if it has been sanded down too much or so much corrosion that machining it down takes a lot off? What do you guys charge for a job like this? You can PM me the info if you want. Do you mate the housing with intake so yo know it is all true and leak free?

Thanks,
Karl

Hi Karl, if it can be repaired it runs somewhere between $100.00 and $200.00, depending on the setup time more than the machining. Most end up in the $150.00 range.

After establishing a "clean" flat area for the housing/gasket you then machine the register depth for the t'stat!

Some intakes lend themselves better to clamping than others.

Thanks, Gary in N.Y.

P.S. Here's another shot of a repair underway, it's about 1/2 way finished here. You can actually see how bad it really is, the "smooth" looking areas are machined!

http://i16.photobucket.com/albums/b2...psjffbkuwk.jpg

I use a dremel tool with a 1" wire wheel to clean the intake surface. then go over it with 80 grit--you don't want a smooth as glass surface. same with housing. then I use the fel pro blue gasket. just a little skin of sealer on the housing side and let it tack up before installing the bolts. oh yeah, and make sure the surfaces are 100% clean. use lacquer thinner or similar. cannot have any coolant contaminating the gasket or it will leak. never an issue..alum or iron housing.

Use the 13 dollar neoprene reusable gasket from Mr. Gasket that they keep on the shelves at advance auto etc. I have been using one for years on just about every kind of engine besides Ford 😂 And have never lost a drop at the thermostat housing. It's metal with an orange neoprene core.

I have never seen that before. Interesting Do you put it on dry or use anything on it?

It goes on dry. It's reusable too. My Advance has it out on the performance aisle. It's listed for a Chevrolet but it works fine for a Pontiac. I have been using this one I have now for over a year with three thermostat replacements on it. Part number is 738g and it's only 8 bucks on Amazon

Mr. Gasket 738G Water Outlet Gasket https://www.amazon.com/dp/B000CMF20O..._DQPdzbXENPBCE

Alright, I just ordered one from Amazon to have around for future in case I need it. hopefully not though.

Thanks,
Karl

Doesn't fit my Pontiac
 

So it came in yesterday and I tried it on my housing and the holes are too far apart on the Mr. Gasket part. I suppose I could try to machine out the holes in the Mr. Gasket part, because those don't need to be sealed. My bolt holes, the one is blind and the other goes all the way through to the bottom of the intake, neither go into the coolant. I am pretty sure, I will double check later today. Only concern would be not having that built up seal around bolt holes could cause housing to warp by pulling down on mounting ears.

That is not for Pontiac . use the correct gasket .

I know it isn't for Pontiac, but it was stated that it worked on Pontiac, so I thought I would try it. I wish they would make one like this for Pontiac.

https://www.summitracing.com/parts/s...s/make/pontiac

This one says it does.

Glad to know this, Thanks! Hope it helps the OP.

Thing is, is that I can't believe it's not the same 738G part.