Mystery coolant leak

[johnunit]

I've got a coolant leak. It's collecting on the front of the engine below the thermostat. I'm 99% sure it isn't the thermostat housing.
Weird part is that if I go for a drive coolant will have pooled in that spot below the thermostat. If I watch it idle, or even blip the throttle to a neighbour-friendly extent, I see no coolant exiting anywhere. Sometimes the coolant is also sprayed about the engine bay.

Where should I look? Any ideas on how to make it leak? I'm thinking it's something just busting loose at high rpm.

[1987cp]

Hm. I can tell you the obvious, that it could be from the water neck, the intake gaskets, or maybe from somewhere around the timing cover. Me, I'd be sure to quadruple-check the water neck since I had a constant water neck leak for several weeks after I first changed a thermostat - stupid thing seemed to just keep leaking no matter what I did!

I'm assuming your hoses are all in good shape and properly connected (I failed on this count just recently!) ... is any of the above something you've maybe had apart recently and might have goofed on re-sealing somehow?

[johnunit]

Hoses are a bit old. I guess that's the place to start. It was leaking the same way right before I parked it last year so it's not a product of any recent fiddling. I re-did the thermostat twice, once to hopefully fix this issue and a second time because the first time left it leaking quite obviously. It stays pretty dry now, even with the areas below and behind it yet.

[86VickyLX]

Pinhole in a hose, combined with pressure will do this. I had a heater hose that would only piss coolant when the engine was revved.

[johnunit]

Sounds possible. Sweet, I hope it is just hoses.
It's got one leak at the h-pipe I've gotta fix but this new exhaust makes it hard not to rev the piss out of it.

[johnunit]

I tracked it down. It was the thermostat gasket. It only happened when the thermostat was closed and the engine revved. A glob of sealant was blocking off much of the coolant bypass opening, so once the thermostat opened there wasn't enough pressure to make it leak.

I tried re-sealing it a few times with both a paper gasket and just blue rtv sealant. It leaked like crazy everytime, i'm not really sure why.
Assuming a clean and dry surface, might my luck be better using a thin coat of rtv to hold the gasket and t-stat in place?

[gadget73]

i usually install those dry, but the mating surfaces must be clean and flat. Try the self-stick gaskets with the sticky side towards the housing. That will hold the thermostat in place too so it won't shift and cause a leak.

[johnunit]

This is my only insured car and I can't find any places who have anything other than basic paper gaskets within busing distance.

I'm sorta stuck with goop, or paper. I could try some sort of home-made gasket I guess.

[86VickyLX]

Did you put the thermostat in the housing, and then the gasket? Or the other way around?

[johnunit]

T-stat in the groove, spring facing engine, then gasket over that, so t-stat is on the rad side of the gasket.

[86VickyLX]

Sounds right to me. Next I'd check for cracks.

[1987cp]

Use no gasket! Use no gasket!!! Personal preference, I know, but all of my failures related to water seals have been in locations where I'd used a gasket. Some people insist that you're to use a paper gasket and no goo .... maybe they've gotten it to work for them, but my experience is that they lie.


Seriously, though, I had your exact experience back in '98 or so. Well, actually worse, because it peed every time I drove the car even after several attempts to seal it up. Drove me bonkers for probably two weeks straight, even after sanding the back of the waterneck flatter and doing dumb things like adding radiator stop-leak, until I ended up (like a dolt) letting my mom talk me into paying someone else to fix my boo-boo, because I was a clueless dolt. They wanted an extra $50 to flush out the stop-leak, of course.


Anywhoo .....


First, use a rag or paper towel (or several) to make jolly sure there's no coolant lapping against the thermostat hole in the intake. These days I usually address this before removing the waterneck by siphoning a gallon or so out of the radiator. But, very important to make sure the mating surface can stay dry for several hours, so I almost always stick a rag or paper towel just inside the opening to mop up any coolant that looks like it'll threaten my new seal. I strongly suspect some of my early efforts may have suffered from contamination of my sealing material by adding coolant before the RTV was cured.


Next is the obvious, completely clean both the waterneck and the mating surface. Scrape, wire-brush (wire wheel if you've got one), wipe with a solvent such as brake cleaner or lacquer thinner.


Apply Ultra Black RTV everywhere that needs sealing. Use no gasket. Repeat, use no gasket! Go ahead and use a thin coat to glue the thermostat to the housing, as that eliminates one more annoyance as you put it in. RTV the water neck, RTV the intake ... RTV only the water neck ... for me, it hasn't seemed to matter so long as you end up with a few mm of RTV between the intake and the water neck.


More particular instructions usually say to apply RTV to this, apply RTV to that, let sit for X minutes ... I don't bother. I just apply sufficient RTV where it needs to be once I'm satisfied the mating surfaces are clean and dry, and loosely bolt the housing to the intake, snugging the bolts down till I'm satisfied the sealant is making good contact all around. Then I usually wait an hour or two and go ahead and tighten the bolts. Gluing the 'stat to the water neck beforehand does make this step easier.


Next step seems to be rather important: DO NOT operate the engine or top off the coolant until the RTV has cured for several hours! I usually end up letting it sit for at least 8 hours ... IIRC, the nominal instructions on the Ultra Black tube call for more like 24 hours. This is a good reason to do this on a weekend or other time when you can do without your car for a day.


Once the Ultra Black is cured, give the bolts another light twist, and you should be all set!











OR, if you aren't mounting a sensor in the top of your water neck, you can save a little trouble up front by getting an O-ring water neck from Spectre or Mr. Gasket. Very convenient to use no gasket AND no goo. It's annoying to have to track down replacement O-rings, though, and I own one O-ring water neck that up and warped for no apparent reason, so these days I've been making do with normal iron water necks. :shrugs:

[Lincolnmania]

i use a gasket and goop......some nice gmner sent me like 40 thermostat gaskets

[johnunit]

still fighting with it.

Got in two tries yesterday:
Gooped the housing surface with a thin coat of black RTV and stuck the thermostat and then gasket firmly in place, trying to smooth the goop out under the gasket. let that sit for about half an hour, then sinched that all down. No dice, leaked obviously as I re-filled the rad, didn't even have to start it up.

Tried basically Mike's method. gooped both sides about as thickly as I dared (maybe a quarter of an inch thick?), put them together and tightened it about halfway from where they made contact to full tight. came back about 1 1/2 hours later and tightened it down. waited maybe 5-6 hours to dry, then added in coolant. no leaks at first, but after running I saw one drip. Checking again after a 20 minute drive, I was leaving a trail and had lost a 3rd of my coolant.


In both cases I'm confident of a lack of contamination. It's also free of any cracks so far as I can tell. It's always seemingly leaking from the bottom at the sealing surfaces, except for the time it was spurting from beside the bypass. I used the paper towel in intake trick to get as much of the coolant as possible out, and both surfaces were clean and dry. Next step is probably to be even more careful with the prep process and give it overnight to dry after tightening it down before adding coolant.


On the plus side, the car makes heaps more power with the new exhaust. The butt-o-meter tells me the 20 HP the simulator predicted may be conservative. There's a more power everywhere, but the 3000rpmish range is just miles better. It drones like a pravneet but I don't have tailpipes on it (dumping right at the mufflers right now) so that should change with a full exhaust. I just wish I could thrash it more without the damned thing running dry.

[1987cp]

If my method doesn't work, and you're confident you didn't goof up, I'd strongly suspect a cracked water neck.

To be fair, I've very often gone ahead and tightened the bolts down right away and then waited several hours before filling the system. I don't think the procedure is very picky as long as everything gets adequately gooped and the surfaces are thoroughly cleaned beforehand.

Can always try reading Joel's instructions and see if it helps. His way appears to be basically what Scott and 86Vicky do, though he does include a nice pic of the coolant in the intake down below the level of the waterneck hole. http://sbftech.com/index.php/topic,29399.0.html


Could always try doing it again with Right Stuff instead of Ultra Black ... I've never bothered buying anything super-special, though. :shrugs: Maybe time to try an O-ring style neck?