CptnTonus

I recently replaced the thermostat in my '92 LS400 (225k). Everything went smoothly, it's not exactly a difficult procedure. I drove the car around all day without any problems. I parked it overnight, came out the next morning, and there's a HUGE puddle under the car--it's coolant. I check the level in the resevior, it's normal, so I kept driving the car.

The car only seems to leak coolant after it's been sitting for multiple hours, like overnight. After I drive the car I can see little specks of water that get flung around the engine bay, but nothing serious. The car doesn't overheat at all, and the coolant level doesn't really change in the resevior.

Anyway, I took off the plastic water neck to the t-stat housing, RTV'd it, and put it back on. It seems like there's a slight gap between the water neck and the t-stat housing, and that's the only place I can think that it would be leaking from. When it was RTV'd it helped with the leak, but it still does leak a little bit after it's been sitting for a few hours. Is it common for that plastic water neck to get warped or something? It's hard to tell where the leak is dripping from because it all just leaks into that huge plastic pan under the engine compartment, then slowly drips from there.

PureDrifter

iTrader: (10)

gasket around the thermostat opening.

CptnTonus

Are you referring to the O-ring that goes around the thermostat? I replaced that when I replaced the thermostat.

avalon42

iTrader: (1)

You can get a coolant system pressure tester and use it to test where the coolant leak is. I think you may need to clamp down on your hoses more.

You may not see any overheating in your car, but the water is pressurized from being in the hot engine. Its gonna release at the weakest point.

CptnTonus

The hoses are tight, and sealing as far as I can tell. The strangest thing about this whole issue is that it doesn't leak unless the car has been sitting for multiple hours.

damon

Likely culprit is that pain in the *** coolant line that runs under the intake manifold. Sorry, but I do not know the specifics.

Mine gave up the ghost when I changed the Timing Belt.

CptnTonus

Hmm, ok, well I'll see if I can do some investigating into that. Thanks.

thebeeguy

Did you ever find the problem? Mine is doing this now as well. Already changed the Timing belt/waterpump/etc. This was like 3 months ago. Just yesterday it developed the same leak you are describing. i can leave the engine running for a half hour and not a drop. i can park the car for hours while I'm at work and not a drop. but when i park it over night and come out the next morning, theres a small puddle underneath the car. Its coming from the little hole in the cover thats right behind the crank pulley. The only thing that I can think of leaking inside that cover area is the water pump. But it doesnt make sense that it would only leak when its sitting over night, and not while the engine is on or anything...

FabX

Mine just overheated from this mysterious water leak. Will search for it tomorrow.

python

iTrader: (4)

all of u need to have a pressure check done, my housing cracked and i had to replace it, its plastic...go figure

sonicman

Did you figure out where this was from? My car is doing the exact same thing as you describe...

CptnTonus

I sold the car a long time ago, but I never did come to any conclusions about the leak. Eventually I came to the realization that the leaking fluid on the ground was probably condensation run-off from the A/C, it was pooling up in the underbelly tray and then spilling out eventually. I stopped seeing specks of coolant in the engine bay, and I basically forgot about it altogether. Sorry I couldn't be of more help.

Och

iTrader: (3)

Was the thermostat and O-ring OEM or aftermarket? I once bought the tstat from the dealer, but they didnt have a gasket, so i bought an aftermarket gasket, and it would leak. Then I found OEM gasket, and the leak stopped - the OEM gasket is considerably thicker.

Also, RTV doesnt work, it doesnt stick to the plastic housing.

shadowless

its not that it doesnt work.... rtv just sucks. dont buy that cheeseburger next time your hungry or dont tip that stripper that extra dollar for a dance lol j/k instead spend the extra saved bucks on some real sealant like toyota FIPG and save your self the heart ache that rtv will cause you. not saying its the fix but it doesnt help.

MRLexus90

Resurrecting this post to provide a comprehensive solution.

I had the same problem on my 90 LS400. Pressure tested the system cold with---this is critical or you could blow seals---up to, and not more than, 12psi. Look for leakage all throughout the cooling system while you have it pressurized, but in particular with this issue for seeping from the water neck. In my case, I installed a new thermostat and OEM O-ring seal, and still had a mysterious leak dripping from the bottom of the harmonic balancer timing belt cover's weep hole, specks of dried, sticky coolant flung around the front of the engine bay by the fan, and needing to add coolant/distilled water to the reservoir every week to bring it up to level.

Solution: Warped plastic water neck. Replaced with one from the parts store for ~$10, problem solved. Hope this helps others