Sounds like the only thing you haven't tried is less torque.  It may work...years ago I couldn't make my new SBC in a 55 Ford 1/2 ton quit blowing exh. gaskets.  I replaced gaskets, torqued the hell out of them and they would be leaking in just a few miles.  Then I pulled them down to the factory recommended torque and no mor trouble.

You might try something like  7-10 pounds and see what happens.  Is that an OEM water neck?  If you've machined it, it might be a bit weak...like to the point where it is flexing very easily. 

You might also try Hylomar or RTV with no gasket.  That could aliviate any flexing of the bolt boses.

BB

PS:  Man that sure is a pretty engine compartment you have there.

Last edited by Bullet Bob (3/19/2015 11:43 AM)

Sounds like a Crack,check housing first....jj

As I recall?, There's ah little rib cast into the matting surface of the thermostat housing to apply added pressure to the center of the gasket. If you've machined that off flat, that may be most of your problem. In addition, like BB said if you've machined down that flange, thus making it thinner, It may be flexing more now as you tighten it?  Do you have an old housing laying around that you could do ah quick swap, and test?

on the factory housing there is a small raised rib about 10thds high that runs around the mating surface so perhaps the removed material is the issue. Also the thermostat sits in a machined groove this groove is only the thickness of the thermostat deep so make certain your thermostat is not sliding out of that groove I used to buy gaskets that had a sticky side so it would hold the damn thing in there so it wouldnt get pinched in there while reinstalling

I've used a few tubes of  The Right Stuff myself, and I've yet to hear of a leak or bad review on it. Your housing btw, looks amazing.

I don't think the stock housing was steel, was it?

Last edited by rpm (3/19/2015 2:24 PM)

A buddy of mine had this same issue. He solved it by installing 2 small bolts in the intake 90* from where the 2 Main Bolts go thru, by drilling the waterneck and tapping the intake. No more Leaks for him. 

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heres one option

put a piece of 220 sand paper on a granite counter top or a window pane next to the frame

clean the thermostat housing then color the gasket sealing surface with a black felt pen

rub the sealing surface of the housing on the sand paper for around 3 seconds

look at the housing . . if there is any black left, it is warped . . if it is warped, it is a pos . . get a real one OR sand it until it is flat.

clean the housing and intake with flammable brake cleaner. lacquer thinner or acetone . . then alcohol.

clean the bolt holes with a q tip using the cleaners above

they make a thin pos gasket and a thick one . . buy a thick one, fel pro has them as well as a few others.

use black permatex gasket maker or the right stuff . . do not use anything else.

when installing the t stat housing, be sure the thermostat is in the correct position because it will try to slide down and screw you.

put a dab of silicone inside the bolt holes with a q tip

put a little on the bolt threads

tighten bolts to around 10 ft lbs

let it dry at least 10 hours before use . . it will not leak . . ever, providing the intake surface is also flat.





 

Last edited by barnett468 (3/19/2015 4:37 PM)

rpm wrote:

That is a good tip to do Barnett BEFORE he machined it, which he said he did. Now it may have bent from reinstalling it, who knows. Following Kristang thru his build and posts, and seeing the quality of his work, I do believe he knows what he's doing.

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yes, but this process will still work on one that has been machined, however, i too vote for getting a new one made by a good mfg . . also, the sanding will instantly tell if it is warped, however, if it is flat, it could still be warping/bending under the tension of the bolts but then springing back to being flat after the tension is removed . . this is another possibility.

and yes the engine does look nice, and im sure he has good mechanical skills, and i dont mean anything bad by saying this, but if he knew what he was doing in this particular area, he would be able to find the problem and fix it on his own instead of asking here for help . . its that simple.

if everyone knew what they were doing in every area, there would be no need for mustang steves forum or any other car forum for that matter because they wouldn't have any questions to ask.

he could even go as far as to magnaflux the intake and sonoflux the t stat housing for cracks if he wanted.
 

Last edited by barnett468 (3/19/2015 5:18 PM)

Kristang wrote:

Thank you all very much for your suggestions! Last night I actually glued 2 gaskets together with a permatex water pump sealant. I then put a layer on the outsides of both gaskets and put it all back together again. I let it set up for 24 hours as directed, filled it and it immediately started leaking at the outer edge where the bypass is located. I backed the bolt out to see if indeed there was too much bolt tension causing the housing to flex. When I loosened the bolt the leak got worse. I also managed to pull the threads out of the top hole in the process of installing and removing so many times. Now I get to helicoil it!

Barnett, I like your thinking and process. I may just use your idea to see if it is no longer flat. I am wondering how important the raised line on the gasket surface of the housing really is. You'd think 2 flat machined surfaces with a paper gasket between them would seal! I still have not tried using silicone by itself, wonder if it is worth a try. I could also have a new raised line lazer welded to the surface.

This just seems like it should be so simple!

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the raised ring is certainly very helpful but absolutely unnecessary if the housing is not a flexy pos . . i have even sealed the cheap chrome plated chinese o ring ones by using a gasket and no o ring and my "technique" [which isnt special] . . two perfectly flat surfaces without sa gasket and just a thin coat of sealer will seal . . they have no option . . i can assure you that a cast iron housing aint gonna flex but obviously you dont want one on your extremely nice engine, lol.

if you do exactly as i suggest, it will not leak at the gasket . . it simply wont . . this being said, if the thing is chinese, it may leak at some point after . . might be an hour, might be a year . . also, it looks to me like the bypass pipe is metal . . if this is the case, i would make certain the o ring on the pipe is not leaking . . if you touch the bottom of the pipe where it goes into the housing with a kleenex and it is wet, that connection is leaking . . also, if it is a metal pipe, it is likely a chinese part . . also, o rings and gaskets do not like to seal on chrome plated parts if it is leaking it may never seal unless you jb weld it but dont do that.

the more gaskets you use, the more the housing will flex when you tighten it because the gasket will crush more where the bolts are on a weak housing.

definitely check to see if it is warped again . . information is power . . no tests = no results.

also, i ALWAYS just barely tighten the bolts then stick my finger in the hole and make 110% certain that the t stat moves around enough to tell that it is trapped within the machined area . . i started doing this a million years ago after i pinched a couple which caused a leak . . the cleveland and chevy top mount design is "almost" fool proof, lol.
 

Last edited by barnett468 (3/19/2015 6:28 PM)

Had one like this once, one of the holes in the manifold was not threaded as deep as it needed to be so I was not getting enough squeeze on the gasket. Last time I used a gasket.  Now I just use RTV. I run a 30 pound cap on the race car and just RTV with no leak.

I went back and colored the face of the housing with a marker, used a piece of 800 grit sandpaper on a piece of glass.  Definitely not flat, lowest point being outside edge next to bypass, right where it would leak.  I worked the housing on the glass with water and sanded it flat.

Helicoils are going in tomorrow.  Thinking about going with RTV only. 

Barnett, this is a Drake housing.  I drilled out the hole to accept the tube which is aircraft aluminum.  I bent it, flared it, and polished it, the had it tig welded on the back and stitch welded on the front.  I cut the back with a countersink to guarantee the weld would be good to the tube.

I have a feeling the machine shop did not cut the surface but rather flattened it on a belt sander with a fine grit paper.  I hope that by hand sanding it flat, this has fixed part of the issue.

Still on the fence about using a gasket.  I've tried 4 different gaskets.  I have not tried a cometic but by comments here, perhaps that would be a waste of money.

Thanks again everyone!

I have a chromed aluminum outlet that uses an O-ring instead of a gasket.  It doesn't leak.