Thermostat gasket

Just replaced the thermostat gasket cuz it was leaking a bit. Now its pouring out! The gasket which is a direct replacement isnt fitting as well as it should. anyone run in to this? Im about to just use liquid gasket but wanted to see if there is a better way first.

did you catch the edge of the thermostat between the two pieces? Just take apart and try again with a new gasket . make sure the thermostat is in the correct way. While at the auto parts store, borrow their coolant pressure tester. Put it on the overflow tank and put up to 15 psi in it to check for leaks. This will save you some coolant if it leaks again.

Action said:

did you catch the edge of the thermostat between the two pieces? Just take apart and try again with a new gasket . make sure the thermostat is in the correct way. While at the auto parts store, borrow their coolant pressure tester. Put it on the overflow tank and put up to 15 psi in it to check for leaks. This will save you some coolant if it leaks again.

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+1 that's easy to do. I think everyone of us that's ever replaced more than one or two T-stats has had this problem.

Bulldogger

I used to have to cheat on the old ford Windsor blocks, and use a couple beads of super glue to hold the gasket and t-stat in place. Both mating surfaces must be clean and level, use a file and run it across the surface a couple time to check for low spots. a wire wheel can do a lot of unrepairable damage to an aluminum thermostat housing.

Thanks guys. Super glue worked like a charm. Unfortunately it didnt fix the original leak I had. Im now thinking its the lower radiator hose spraying on the v belts and getting everywhere. Where can I find replacement lower radiator hose? I used the search function but it isnt as granular as on other forums. Any help is appreciated!

Go with Permatex gasket maker on both sides, let it set for a little bit and put them together. Problem solved. The thermostat gasket failed me too, getting the old one off was painful also.
I just replaced every cooling system hose in my 998. When I get home I'll get you a parts list if you still need it.

The truck uses a standard radiator cap so I would recommend going to Auto Zone or O'reilly and using their loaner tool coolant system pressure tester. Crank up to 15psi and find the leak(s)

I personally on any application calling for a cork or paper gasket use RTV silicone instead. They now make specific formulas for coolant, gear oil, Trans fluid besides the universal black, blue and high temp red.

Thermostat housings are easy to have hairline cracks if over tightened or not seated properly. Pull off, clean well, check for cracks and use some coolant rtv.

Here's the radiator hoses in the hmmwv, part numbers through Kascar:

Item #-----------------Description----------------------------------------------------------Price
23500084------------Hose 3/4 Id 5.5 inches long-------------------------------------$3.03
12339160------------Hummer, HMMWV Preformed Radiator Inlet Hose-------$8.17
12339155-1---------Hose, Nonmetallic Radiator, Water Crossover-------------$9.09 (need 2 of these)
12340046------------Hose, Surge Tank-------------------------------------------------$15.71
12339159------------Hummer, HMMWV Upper, Front Radiator Hose-----------$4.51
12339162------------HMMWV, Hummer, Front Lower Radiator Hose-----------$14.70

& the Thermostat for those who need it, don't buy the gasket, just use RTV:
14077122------------Thermostat, Flow Con Water Crossover 6.2----------------$14.41

When assembling take the hose off the outlet. Put some never sieze on both the outlet housing and the housing that the hose connects to. Place the new gasket on the part that connects to the hose. The never sieze will hold it in place. Stick your finger through the hole and place the thermostat its socket. Use your finger that is in the hole to hold the thermostat in it's socket while you bolt it up. This will keep the thermostat from falling down creating a gap for water to get out. Some times the super glue trick will hold the thermostat a little out of the socket creating a gap. This gap may allow water to excape. Using never sieze will prevent you from scraping the old gasket off the next time you have to take it apart. You can remove it with your fingers and reuse it in a emergency. If you mating surfaces are good and flat the gasket will not leak.

Took several months and several tries to figure out, but the crossover pipe (tube under crossover by the thermostat and top of water pump) fittings were two different sizes. Very slow drip which got worse when I replaced the hose and hadnt noticed the flange/connector pieces were different. Works great now.

Picture was from JUST getting ready to reinstall part at top when I looked at the hose again. If your hoses need replacing, replace all of them, consider checking the thread sealant too (I generally use PTFE tape but a lot of things work) and clean, replace/reinstall the fittings.

That hose was a pain to get off! The part number I listed above gave a generic hose that was a couple inches too long, had to trim. My two attachment points were the same size, perhaps they just grabbed what was available for yours?

Drip, drip, drip, drip...

Couple of weeks ago I noticed coolant dripping - again.

Bought up a bunch of constant-torque hose clamps and put ‘em on.

Drip, drip, drip, drip...

Wiped, everything down, ran truck around for an hour, parked back in garage, SEEMED to be coming from thermostat housing. Washed, wiped dry again, let idle for a while, yep, definitely coming from UNDER the thermostat.

Ordered new gasket, housing (remembered the old one was a bit corroded), 1000W electric block heater, disassembled everything this AM.

Got my first antifreeze shower, got soaked though field jacket, shop coveralls, hoodie, t-shirt, managed to drag bucket over from where it WAS collecting water to catch most of the rest of what was coming out and all of what did after I got the freeze plug to tilt wide open.

Not much corrosion inside, plug fit right in, wired to come out by the windshield washer bottle.

Am about to flip a coin about using the gasket. Did that last time, like the book said. Didn’t work. Got plenty of RTV (black, high oil/whatever resistant).

Good news is, where I replaced the connector hose fitting last time, it’s NOT leaking (yet... it’s a HMMWV, there’s still time), and coolant looks clean, no oil on top, oil looks good to (so far... it’s a HMMWV, there’s still time).

Thanks, Juan for posting. RTV it is. Right after my clothes dry.

one thing to remember you can ruin your machined aluminum surfaces if you use a powered wire brush to clean them, I like to use a razor blade and scotch brite you can also drag a file across the surface and see if its still flat I would just about guess you don't have a flat surface any more.

snowtrac nome said:

one thing to remember you can ruin your machined aluminum surfaces if you use a powered wire brush to clean them, I like to use a razor blade and scotch brite you can also drag a file across the surface and see if its still flat I would just about guess you don't have a flat surface any more.

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I shoulda took pictures. I clamped up a small mill angle plate using the bolt holes and tried sliding feeler gauges underneath. Got 5 thousandths no problem, which is likely w/in margin of tolerance for gasketed surfaces (about twice the thickness of my hair). The new outlet piece I put on a piece of marble and couldn’t see any light under it (that’s less than ten thousandths).

RTV is setting up now, bolts are just tight enough to start squeezing wet RTV out of the gaps.

Used the superglue trick to keep the thermostat centered.

I’ll know in an hour or so if it’s all working once I get the antifreeze back in and let things warm up.

Thanks.

I'm researching parts for my cooling system clean-up.

I see a few threads recommending that you omit the thermostat gasket and simply seal up the surfaces using RTV. How serious is this suggestion?
Do most owners do it this way? Does this apply to 6.2 and 6.5 engines?

My truck seems to have been re-powered with the 6.5L back in 2002 and I'm trying to make sure I get the proper parts.