Leaking thermostat housing

[Tryoung]

I winterized my engine for the first time myself in the fall (with a lot of knowledge from this forum and the Moyer manual – thanks!). As part of that process I removed the thermostat and cleaned and tested it over the winter. This spring I put the thermostat back in, along with a new gasket from Moyer Marine. The installation seemed uneventful. With the boat now in the water, I have water leaking like a sieve around the thermostat housing.

Are there any non-obvious (or idiot-proof!) steps in getting the thermostat sealed correctly? It didn’t leak before I removed it, and from the looks of it hadn’t been removed for several years. The old gasket was stuck to the head and thermostat housing. I *thought* I did a good job of cleaning the old gasket off and left a clean surface for the new gasket to seal. If I take the housing off again to check it, will I need a new gasket or can I use the gasket I have?

Thanks,
Tim

[Dave Neptune]

Sealed?

Tryoung, did you use a sealer? Check closely around the studs and be sure you don get the edge of the T'stat caught out of its "seat".

On old engines as these I suggest you use Permatex #2, it's mess but it seals and oily surfaces won't bother it like "silicone" grades.

Dave Neptune

[Tryoung]

Thanks Dave. I'll check for for the thermostat out of its seat, but I don't think that was it since the fit of the housing on the gasket looked even and tight. As to the permatex, I put it on both sides of the gasket? Even if the oil doesn't bother it, would I want to clean the surfaces first, maybe with a little acetone?

Thanks,
Tim

[roadnsky]

How many foot pounds did you torque the 2 head nuts down to?
I always start out at 25fp and if there's any leaking, then work up to 30 and then to 35 if I have to go that tight.
If they're not tightened enough, then water will find a seam to seep out of.
As Dave said you also need a sealer or it'll likely leak for sure. Get it around those studs too.
I'm also a fan of Permatex

[Dave Neptune]

Clean

Tryoung, you can scrape with a good flat scraper (small wood chisels work well)or even with a razor blade. Pay close attention to the bits left around the studs. Wiping down with acetone or lacquer thinner won't hurt, but if it is good and clean the wiping down really isn't necessary with non-silicones such as P#2.''

Yes I would get a new gasket and they are pretty standard in most auto parts houses.

Dave Neptune

[roadnsky]

As to the permatex, I put it on both sides of the gasket?

Tim-
The "suggested" use is to only coat the bottom surface of the T-Stat gasket so you can re-use after removal.
(See the attached PDF)

Coating both sides is fine too though.

[hanleyclifford]

Just to add to the above points: Those studs are primarily "head bolts" and the thermostat is only along for the ride. Make sure the body of the stud itself is clean and lightly oiled and that the threads on top are clean and lightly oiled. In this way false torque readings will be avoided.

[Tryoung]

Thanks for all of the advice!

I plan to try the permatex tonight. I picked up some permatex and a new gasket at an autoparts store. I hadn't used a torque wrench on it before, but I'll get one to use on the nuts.

Thanks,
Tim

[Dave Neptune]

One more thing

Tim, when you get it started pay close attention if it leaks again. The t'stat housing can be sealed as far as the gasket is concerned and you can still get a leak from the studs. Water can literally run past the threads in the block and up the sealed hole in the housing and run out of the nuts on top holding the housing. This could of been your leak in the first place. Sorry I did not think of it sooner.

If the studs are loose clean them and reinstall with the #2.

Dave Neptune

[Tryoung]

Thanks Dave. I'll check the studs carefully. That wasn't the problem when I tested it on Monday. Water was obviously shooting out of the gap between housing and the head. On the order of about a cup of water every ten seconds. Both at the front of the engine, shooting water toward the front spark plug, and in back of the housing, shooting toward the back of the engine.

This has certainly been a surprise for me. Of all of the things I've done on this engine, I never would have guessed that sealing the thermostat housing with a new gasket would be difficult!

Thanks,
Tim

[edwardc]

With that much water, it sure sounds like the thermostat is not sitting centered in it's recessed mounting lip, preventing the housing from sitting properly on the head.. Perhaps some grit got under it during install?

A couple of questions:

1) Is this an original style double-action thermostat (circular plate on the top that engages the circular boss in the housing), or is it an aftermarket single-action thermostat installed with a spacer and a modified housing? From the picture, the nuts look like ones that come with the modified housing. If so, is the spacer installed too? I can't tell from the pic.

2) Any chance the thermostat is installed upside down? (Sorry, I just had to ask)

[Tryoung]

Dry as a bone!

I installed a new gasket with Permatex on the head side of the gasket (and a little around the base of the studs) and it is dry as a bone! It seems that last Fall I didn't clean off the old gasket as well as I thought. I found more bits and pieces of it last night on the head side of the mating surfaces.

Neil, you weren't kidding when you said that the permatex is messy. Nasty black gunk gets everywhere! But it certainly seemed to work and I'll definitly be keeping it in the on-board tool box.

I borrowed a torque wrench from an auto parts store, but I couldn't get it to fit. The wrench was for 1/2"-drive sockets and the 9/16" nut 1/2"-drive socket added enough height to the wrench that the handle hit the top of the engine access door frame. I'll have to see if I can come up with a different setup that fits. In the mean time I cleaned the studs, added a little oil, and tightened the nuts down with my best guesstimate of 25 fp -- which is about as tight as I can get it with my little 6" rachet wrench.

Edward, The thermostat only fits one way, and its the same one that's been there since before I owned the boat, so I *presume* that it is correct. The diameter of the thermostat lip fits perfectly inside the seat of the housing. I don't know what the dual-action thermostat looks like, though I doubt I have it. I am attaching photos of the one I have. Testing it last winter, it opened at 160 deg F.

A sincere thanks to each of you for your advice - on this issue and the many others that you have knowingly and unknowingly (in the case of my reading older posts from you and others) helped me with! I am amazed at how comfortable I am in working with this little engine compared with when I got my boat a few years ago. That change is entirely due to this website.

Thanks,
Tim

[edwardc]

What you have there, to quote Neil, is the "Holy Grail" of thermostats, the original Holley 3-spring dual-action thermostat. Take good care of that puppy. They are no longer made, and the replacement dual-action 'stats are increasingly hard to find and also expensive. This is what prompted Don to develop the more economical single-action conversion kit.

The thermostat initially starts to open at 140 degrees. This allows cooling water to begin to flow through the block. As it heats more, it opens farther, until at 180 degrees the flat disk on the top side is completely pressed against the circular boss inside the housing, cutting off all flow through the bypass loop and forcing all coolant through the block. Thus, in normal operation, the late model engine temperature is allowed to vary between 140 and 180.

[roadnsky]

...From the picture, the nuts look like ones that come with the modified housing. If so, is the spacer installed too? I can't tell from the pic...

Ed-
That pic is of MY Therm setup (albeit an old pic) not Tim's.
And yes, I do have the spacer installed.

...I borrowed a torque wrench from an auto parts store, but I couldn't get it to fit. The wrench was for 1/2"-drive sockets and the 9/16" nut 1/2"-drive socket added enough height to the wrench that the handle hit the top of the engine access door frame. I'll have to see if I can come up with a different setup that fits. In the mean time I cleaned the studs, added a little oil, and tightened the nuts down with my best guesstimate of 25 fp -- which is about as tight as I can get it with my little 6" rachet wrench.

Tim-
There IS actually a scientific procedure for figuring out torque values if you don't have a torque wrench. It's explained here
Neil may be along later with drawings or pics of his own to better explain...

[Tryoung]

What you have there, to quote Neil, is the "Holy Grail" of thermostats, the original Holley 3-spring dual-action thermostat. Take good care of that puppy.

Really! Wow! I had no idea that I was so privledged! After reading many times how hard they are to find I would have never guessed that my little A4 had one! I'll definitly take extra care of it!

There IS actually a scientific procedure for figuring out torque values if you don't have a torque wrench. It's explained here
Neil may be along later with drawings or pics of his own to better explain...

LOL! Mine was about a one-and-a-half, though my calibration is likely different!

I hope Neil doesn't post pics!

Thanks,
Tim