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MG MGA - Thermostat Housing Leak

Just had a nose under the bonnet and spotted a small leak from the thermostat housing. Normally it would not warrant a post on this problem, just take the housing off, inspect, new gasket and reassemble. But what caught my eye was a blob of fluid sitting adjacent to the nut of one the housing studs - source of the leak?

It would seem that under pressure, the water has migrated up the stud hole and out the top. Is this unusual?

Steve


Steve Gyles

Steve,
Don’t think I’ve ever noticed a leak like that one. Usually the gasket seals off the three studs from any water. Should be just a bad gasket. Looks like you don’t need to change your thermostat seasonally.
David Werblow

It most likely is the gasket, an easy fix with either a new one or some hylomar or something similar. Other possibilities are a slighly oversize thread on the stud allowing the coolant to seep through, which hylomar will also fix or, less likely, a crack around the thread.
Hope its a simple fix
Colyn
Colyn Firth

Think I'd try tightening the hose clip firt Steve; just in case. Travelling at close to the speed of light can cause strange things to happen!
Lindsay Sampford

As already stated, probably a gasket problem. However, it could be corrosion in the thermostat housing with water passing through to the stud, above the gasket level.

Mick
M F Anderson

But just run your hand under the hose first, leaks are not always coming from the obvious source.
Lindsay Sampford

I agree with Lindsay. Antifreeze is on top of the nut, net to the stud. The paint in that area looks to be very thick and intact. Looks like a hose leak to me.
Chuck Schaefer

Not unusual either way! Hope it's the hose 'cause it's easy fixed. Otherwise, most likely bad gasket or mating surface between thermostat and stud. Worst case, less likely, cracked or porous thermostat housing. Had exact same "stud leak" on my midget many years ago, was due to corroded surface on housing. A bit of sanding and some gasket sealant did the job.
Neil McGurk

No, the end of the hose is totally dry. I have just had a closer inspection and spotted a small drop of water easing out of the stud washer (see image).

The car has been laid up for 10 days while I have been away so I probably would not have noticed it in daily use with it evaporating off.

Dismantled and repainted the engine 3 months ago. Just one of those bedding in things during the early days. It's the source of the leak on this occasion that surprises me.

Steve


Steve Gyles

The hose was worth a look, I didn't want you taking the housing off for nothing, and I know from my own experience how fluids can get all over the place under the bonnet and lead you right up the garden! Doesn't Barney say something about sealing the studs that screw into threaded holes that are drilled right the way through into the water way?
Lindsay Sampford

Here it is, 5th para. down. http://mgaguru.com/mgtech/care/cf109.htm
Lindsay Sampford

Thanks Lindsay. Off to the garage now. I will report back later. Good opportunity to put the summer thermostat in, or is that tempting fate?!!!!

Steve
Steve Gyles

Yes, Lindsay got it. Two of the three thermostat studs go through into the water jacket. Remove the studs, put a touch of thread sealant on them, and reassemble (with a new gasket).
Barney Gaylord

The cork gasket had seriously disintegrated on the inside. It looks like it allowed water to migrate up the housing stud hole. The studs were rock solid in their threaded holes. I have fitted a different composite gasket. Looking back, I wonder at the wisdom of using cork in this environment, but that's what came with the supplier with the thermostat.

Waiting now for the paint to dry.

Steve
Steve Gyles

I do not think that it is your housing that is leaking. I belive that the problem is your radiator hose and clamp. The reason for this is the stain on the side of the housing leading from the hose back to the bolt. When the hose leaks, the side of the housing become wet making it look like a gasket or bolt problem.

Jim
JP Jim

Jim

The car has been stationary for 10 days. The water appears to have been leaking during that time by gravity. If the hose had been leaking it would have dripped down in the area of the temperature sensor or along the underside of the housing tube, not across the upper surface of the tube, down and then up the bolt hole casting to the top side of the washer.

There was not any staining, nor any signs of fluid blow back caused by the fan when the engine is running. I had a good for that. I think it must be a camera flash reflection you are looking at.

Cheers

Steve

Steve Gyles

Those cork gaskets are pretty flimsy Steve, definitely a "use once" item, I found, when I removed a freshly installed housing to substitute a different thermostat. I had to replace the gasket again but used a paper one the second time.
Lindsay Sampford

Just done a test run and let the engine cool down. Good news and bad news. Good news is that the leak from the original stud (No.1 in attached image) has stopped. Bad news is that No.2 stud is leaking from the top. Bearing in mind that I replaced the gasket and flattened the thermostat base on a sheet of glass with grinding paste ( it was slightly uneven - new item!) I am minded to agree that Lindsay and Barney have it right. Could someone please confirm which stud holes are drilled through the water jacket. For simplicity please refer to my number system. An afternoon job - again!

Steve


Steve Gyles

Can't remember for sure Steve, but I think it's No. 1 and 2. If you remove the studs it's easy because you can see daylight through them, but removing the studs is not always easy! What kind of gasket did you use this time?
Lindsay Sampford

Thanks Lindsay. The current gasket is a multifunction BMC item. You select the appropriate stud line-up and trim off the excess. It looks like some sort of impregnated card. Image of two of the cut off bits attached.

Steve


Steve Gyles

Just gone from bad to worse. The No.2 stud has just sheared. I doubt whether any water was leaking up its threads. Rock solid.

Despondent. Thrown the spanners on the floor and gone to watch the Cheltenham Gold Cup.

Steve
Steve Gyles

I have an inch of the stud left. Tried heat with my butane torch but the heat dissipates too quickly. Before I cut it off flush and drill it out I am thinking of welding a nut to the shaft. Worth a try? Any other thoughts?

Steve
Steve Gyles

Second question. What size thread for tapping into the block? Not sure I have the right size.

Steve
Steve Gyles

Steve -
Welding a nut on is your best chance. Use plenty of heat, then let cool completely. The heat expands the stud and crushes the whatever that is holding it; enough heat (red stud) crushes the hot stud itself in the cold casting, so it winds up smaller than it started out, hence loose.
The things are always prone to leaks - the sealing surface is very narrow between the Tstat counterbore and the stud holes. The OE cork gaskets were of much better quality than anything else, and worked just OK if everything was as new. "Fits Nothing" gaskets are simple trash. I've taken to using Loctite Gasket Eliminator (515 I think) on them, with no gasket at all & with lots of antiseize on the studs. Permatex #2 on the threads into the casting.

FRM
Fletcher R Millmore

Sorry to hear of your misfortune Steve, you have my sympathy, I've been there a few times. If you still have have something to get hold of, it might be worth plugging away with the heat for bit. A welded nut might help if you can get a decent weld, are there any threads left to screw it on to? I usually adopt a softly softly approach to these things, not too much force in one go, but heat then try to turn clock wise, then anti-clockwise, then more heat etc etc. A good long soak with WD40 is sometimes more effective than you think it is going to be. Heat the casting that the stud screws in to, several expansions and contractions will eventually crack the bond. I have had several thermostat housing studs sheer off over the years, in both "B" series and "A" series heads, and I have never yet had to drill one out, maybe I've just been lucky but I think patience pays in the end.
Lindsay Sampford

How annoying is that Steve? It always seems to be the minor things, that you could probably ignore for years, that seem to end up causing the most trouble when you try to fix them!
When I had the same problem many years ago I used lots of easing oil (WD40 or thinner) alternated by heating the casting with a propane torch. After a few (very smokey) repeats the stud came out. I believe I borrowed a stud gripping tool, cant remember what you call it but it fits over the broken stud and looks like a big socket spanner. You use a ring spanner or a socket spanner on it to unscrew the stud, the more you turn the spanner the harder the tool grips on the stud.
Let us know how you get on once you have calmed down!
Best of luck
Colyn
Does anyone think we should start a book on guessing the exact time and date that Steve gets the stud out?
(Maybe we should also guess the exact words Steve used when the stud sheared!!)
Colyn Firth

Colyn

'Blast'.

1953 hours.

Got it out using Lindsay's and your method. I think I have also found the reason of the leaks out of both studs. There are small splinters of metal missing between the 2 studs and the thermostat hole. The metal is aged so it's not a case of it happening during my stud removal. See picture.

Happy to listen to best ways to address this.

Steve


Steve Gyles

Glad you got it out Steve, and at least it was worth doing, that problem was only going to get worse. As for the cure, it's either building up that hole with new metal, in which case it would be head off which seams a shame, or is there a high tech adhesive filler that could be used, plastic metal or something?
Lindsay Sampford

Steve, some adhesives here that might work http://www.repairproducts.co.uk/page41.htm
Lindsay Sampford

Lindsay

Yes, I was thinking of JB Weld. Despite the fractures I would have thought it is a relative stress free area. I just need an epoxy that is water proof, can take the heat and withstand 7 psi. I can only imagine that a DPO caused the fractures during stud removal/insertion. It was not me. Never had them out before.

Steve
Steve Gyles

Hopefully Fletcher or Barney will come up with an answer in a few minutes!
Lindsay Sampford

Araldite will do the job, no problem. So would JB Weld. You may even get away with just using a standard gasket sealer Loctite 5910 or 5926.

For a belt and braces(and semi permanent) job, I would fill the holes with araldite or JB weld and assemble the cover with polythene or cling film between it and the head (but no gasket) remove the cover after the epoxy has set and dress any excess off the head before reassembly with gasket. It wont need it, but for peace of mind you could use some gasket sealer too!

The permanent solution of course would be to weld and grind the head.
Neil McGurk

Now you see what I mean when I said the seal area is very narrow, yours is absent! Partly corrosion and partly years of chiseling Tstats out. If the water elbow looks the same it is even worse, but that's easier to reface, even with careful filing.
Anything like JB weld is not likely to stay put; I've found it doesn't like feathered edges, and the casting is full of glycol and water. If you use it you will certainly have to redo it every time you have the stat out.
A good gasket could work, if you could find one. The good ones are very fine ground cork in a rubbery binder. A thin coat of Permatex #2 or 515 on the tstat counterbore (under the stat) is strongly recommended, since part of the problem is that AF creeps under the stat, then up the narrow bit. A ring of insulated electrical wire, maybe .025-.030, like the stuff in phone lines, laid carefully around the stat perimeter under a gasket will significantly improve sealing. 515 or #2 might do it, without a gasket. And my least favorite substance in the world, RTV sealant, might be a good thing here, applied carefully and sparingly to surfaces cleaned as well as possible.
Correct fix is crazy hard - surface cut on the Tstat area, recut the counterbore.
Some Volvo, c1968, used a neat grooved O ring seal that fit over the tstat edge, but that requires a deeper counterbore. No idea if such is available or what else might use it, but I think I've seen them recently.

FRM
Fletcher R Millmore

Thanks FRM and Neil

I will be (ad)dressing the problem this morning. Seems to me that filling with a JB Weld-type compound would be quite acceptable, especially if I also use Wellseal non-setting gasket glue between the repair and the gasket. It would then be held firmly in place by the tightened down T cover. That said, I would agree that it would be easy to come loose, especially on subsequent thermostat removals, since the repair is so small. The photograph I posted exaggerates the size of the damage. Total circumference damage is 1.5 cm.

Steve
Steve Gyles

How often do you need to service the thermostat? I don't touch mine unless I suspect it of being faulty, hopefully your repair should last until you want to service the head. I wonder if a drop of silicone sealant on the stud might stop any coolant that gets past the repair?
Lindsay Sampford

Lindsay

My thoughts entirely. Prior to this problem I have only had the housing off 3 times in 10 years.

I can see a good old fashioned bodge coming on here with a blob of sealant. I can see the post in xx years time when the new owner changes a thermostat, suffers a leak and castigates me as a DPO!

Steve
Steve Gyles

The entire top sealing surface looks to be of questionable condition. That doesn't include the missing "bits". It is not so far gone, that a bit of high quality silicone RTV sealant, such as Ultimate Gray, shouldn't fix. Clean up the surface well with a wire brush followed by some solvents before applying the RTV. After assembly, let the RTV cure for 24 hrs before filling with coolant.

Don't forget to resurface the aluminum cover.

Sure there are other possible engineered solutions. I really don't think they are warranted.
Chuck Schaefer

Chuck

I agree. I was surprised how poor the whole surface is. It does not appear to have been machined to the same standard of other mating surfaces. Is this the norm on other owners' engines?

I rebuilt the damaged area with epoxy metal and skimmed the rest of the surface. I then ground back with a small wet stone. The attached photo shows the other areas that were filled. Surprisingly, the stud that originally leaked and was the cause of this thread has a good solid surround, so I guess water migrated up the stud as Barney and Lindsay suggested.
Steve


Steve Gyles

That looks a good job Steve. Your photo really shows how little land there is between the stud and the coolant. It's a wonder we all aren't pissing coolant out of the thermostat housing! I'll tell you what, I aint gonna touch mine!
Lindsay Sampford

Lindsay

The gasket of course has a wider shoulder on the thermostat side of each hole, it overlaps the thermostat. Also, the cover has a wider shoulder to bear down on that part of the gasket and the thermostat to keep it in place. I am inclined to follow your advice and put a 'washer' of silicon sealant around the base of each stud to properly seal the stud shaft.

Thinking back over the years, I have often suspected a small leakage/weapage in the general area of the front of the engine, as shown by splash marks blown back by the fan. But because I rarely let the car stand for more than a day or two, I have never witnessed the pooling of liquid before.

I have to leave the epoxy to cure for 24 hours so it will be Monday before I test the repair. I ran a tap down the threads to clean them up. Barney said to put a drop of thread sealant on each stud. I have Loctite 641 Retaining Compound. Is this a sealant also?

Steve
Steve Gyles

Steve -
The 641 will certainly seal, but it could prove a problem if you have to remove a (broken) stud - retaining compounds tend to be very strong. I use Permatex #2 on all such threads into water.
Your whole point on the width of the stat/gasket/top is exactly correct. If you prevent liquid from leaking under the stat, then no liquid will ever even get to the damaged area; that's why I said to put glop on the counterbore face under the stat. And the wire ring I mentioned is a double seal at the perimeter, after the stat bead.
Nice fix work!

FRM
Fletcher R Millmore

FRM

I understand you fully now and agree. many thanks.

Steve
Steve Gyles

I'm with you now Fletcher, so the aluminium elbow is meant to seal,via the gasket, against the thermostat rather than against the head! It all makes sense now, I couldn't see why sealing the thermostat in the counterbore was important before. Having said that,my thermostat has a washer under it that came with the head gasket set, which fits exactly in the counterbore. I assumed that's what the washer was for but on looking at the exploded view of the cylinder head, I don't see it shown, but I believe it to be part No. 1G1365, it is refered to as a thermostat gasket on this website. http://www.mlproduktservice.com/1755.html
Lindsay Sampford

Lindsay -
Right, the stat bottom seals against the counterbore, and the top seals against the gasket/cover. The bead on the stat is to take up tolerances and provide "spring". It is good practice to set the stat in the c'bore and check that the bead is slightly above the head face, since otherwise the water goes under the stat even easier. The beads get crushed in use, so reused ones may leak, and corrosion in the c'bore also gives leaks. The squishy top gasket usually covers all sorts of ill fitting bits, but if it doesn't, you need to go back to design and figure it out.

Getting interesting now.
I have seen the thin ring gaskets, but not very often, and long ago. It is clearly shown in the MGA 1500 & Magnette parts list. Not shown by Moss at all. I have just looked at the collected remnants of 46 years of gasket sets, plus a couple of unopened gasket sets, and I don't find a single one of these. I never throw anything away, and I don't recall putting one in over at least 30 years. I certainly have not removed one from an engine since at latest the early 70s.
Presumably these were deleted at some point, possibly involving a change in the c'bore depth. This would be dealt with via the squishy gasket, until a little too much corrosion and abuse takes hold. At that point, one might expect that earlier heads might leak more easily than later ones.

FRM
Fletcher R Millmore

Wow. I have learnt about stats today. Never knew all that.

Stat
Steve Gyles

Cured. No leaks. I did not have a rubber ring gasket of the correct size. I put a ring of sealant in the recess and Wellseal on the underside of the gasket.

Steve
Steve Gyles

Looks to be an excellent repair Steve, I cant see you ever having to look at it again.
Glad it wasnt an oil leak after all the hard work you put into cleaning up and painting the engine.
Colyn
Colyn Firth

I found this thread in the archives, which was very helpful, so thank you.
It made me realise why there are so few postings these days - whatever problem occurs on an MGA, the chances are someone has been there before, so it is probably in the archives already!
I have exactly the same type of leak Steve had, so everyone's input made very interesting reading.
I originally started the work as I had a leak from the top rubber hose and when I removed it, I noticed the housing in a very poor state - see picture. Someone has taken a bite out of it!
But when I replaced it and put it all back, I had the tiniest of leaks from the rear stud head. I probably have had it for a long time and just hadnt noticed it; it was very slight and would probably evaporate quickly.
But now that I know it's there, I cant leave it even though I doubt it will do any harm.
I have a small chip out of the face of the head, like the splinters Steve found, but just the one, and very much smaller. So I will just use Holymar and hopefully that will do the job.



Graham V

Two of the three studs go through into the water jacket. Get the studs out, and put some thread sealer on the threads before assembly, so water does not leak through the threads.
Barney Gaylord

When a housing is that corroded, it's better to replace it as well as the gasket. I suspect that if tightened to cure a further leak in the future the remaining tube will simply collapse.

I have had to chisel the remains of similarly corroded housings because they were so firmly attached to the studs. As Barney says, thread sealer is the magic prevention for this.

Dominic Clancy

Thanks Barney and Dominic

Barney, I will do as you say, thank you.

Dominic, yes thanks, I agree. I wasn't planning to put that damaged housing back. I have a replacement
Graham V

I've had this on my MGB. The coolant is escaping up the threads which are open to the water jacket. Not wanting to remove the thermostat housing I applied sealant to the the surface on top of the housing, used plain washers (not spring) and nyloc nuts. Worked for me, dry for a couple of years now.
Paul Hollingworth

Paul
How lazy can you get 😀

But joking aside, I did as Barney said. It really didn't take long and it is all leak free now (thanks Barney)

Graham V

I wanted to avoid the hassle Steve the original poster had in removing the studs. What's the difference between relying on sealant in the threads or under the nut. In my experience the Klingersil gasket is the best (available from Moss). If only my heater tap would stop leaking. Luckily its much worse in the off position than the on.
Paul Hollingworth

I was only teasing! Just ignore me
😀
Graham V

I was onLy teasing.
😀
Graham V

I hope the repair holds. The head is not the most robust part of the machinery - I would guess Peter Burgess will have a long list of faults he has found in other areas. The obvious lesson for the thermostat is to avoid tempting fate. In our climate, the engine functions well without one - absence which reduces the interval when the cap has to come off.
There is a better reason for running without a thermostat - the balance of advantage is for debate. My 1588 runs thermo - statless pretty well throughout the year when there is no salt on the roads. It's not the only one.
Roger Walker

On 16 May 2022, Paul Hollingworth wrote:
"I wanted to avoid the hassle ... in removing the studs. What's the difference between relying on sealant in the threads or under the nut. In my experience the Klingersil gasket is the best (available from Moss)".

When you allow fluid to pool around the studs inside the housing holes, the studs will rust (and the cover will also corrode). Rust expands to cram the holes full of debris. Next time you want to remove the cover it wont come off. Then you end up destroying things, have to buy a new cover and new studs, and may have to drill out broken studs.

The factory did not use thread sealant, but they did use a cork gasket with small holes around the studs. When bolts are tightened the cork squashes and constricts on the studs to make seal there. Fluid could then get into the lower threads. but would not leak higher up around the studs or at the top. I like the cork gasket (and thread sealant).
Barney Gaylord

On a related theme.

A product I have had excellent results with in freeing corroded studs/bolts/nuts is INOX mx3. Developed for the electrical/heavy engineering/agricultural/fishing industries.

Put on to this by an old school mechanic some years ago. It really does penetrate through corroded/galled threads and lubricates their removal.

I have used it to free seized thermostat housing studs, manifold studs/exhaust pipe nuts/suspension parts and lawnmower blade mounting bolts and nuts.

Based in Queensland here, they have a very good website worth a visit. It has details of their UK distributor. Also descriptions of their related products.

Regards
Roger
R Taylor

This thread was discussed between 18/03/2010 and 13/06/2022

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