Trying to stop thermostat housing leak?

SL1M3G1RL

MEMBER
1997 MAZDA MPV
3.0L
V6
4WD
AUTOMATIC
130,000 MILES

Hello, I'm trying to fix a thermostat housing leak that is currently causing a lot of coolant loss and overheating.

Here is a video of the leak:

https://youtube.com/shorts/XYpvcDuHCS8?feature=share.

I inherited the car from a friend recently and when I took apart the thermostat housing to examine it there was no gasket in the housing at all. The thermostat itself does have a gasket that fits snugly inside the housing but there is no gasket on the housing itself. I tested the thermostat and it's working well. So, I believe the problem is coming from the actual seal of the thermostat housing. I've tried searching the web for a thermostat housing gasket that would fit, including on OEM Mazda parts websites but every time the gasket that comes up is not one that would fit the thermostat housing. My thermostat housing is triangular and has 3 holes for bolts, and I can only find one that has two holes and a different internal size (for the circular part). I'm pretty sure the thermostat housing wasn't changed out for an aftermarket one. I'm just wondering at this point of I should buy Fel-Pro and try to make a gasket or use RTV/ gasket maker. I tried using thermostat housing gasket maker once before, but I think I applied it way too thinly because it definitely didn't stop the leak. Any input would be appreciated, thank you!

7 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,280 POSTS

Yep, that is leaking pretty good, thanks for the video. Could it be you have a cracked housing? The O ring style of gaskets work pretty good if the sealing surfaces are clean. Please check this guide out below and I have added the instructions for your car in the images below. If you still want to install a gasket you should be able to take the housing to an auto parts store and they will have one that will work.

https://www.2carpros.com/articles/replace-thermostat

Once the thermostat is apart you can upload images in your response so I can see what's going on to further help you.

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Tuesday, February 21st, 2023 AT 4:05 PM

SL1M3G1RL

MEMBER
30 POSTS

Hi Ken,

Thank you for your response. After talking to some people with more experience, I believe that the thermostat gasket is supposed to serve as the only gasket for the thermostat housing and there is not a separate one for the housing itself. I'm attaching a pic below; you can see where the thermostat gasket fits into the housing. I inspected the thermostat gasket, and it could definitely be replaced so I'll be installing a new one in the next couple days. I also took the housing apart again this morning and realized that I did not tighten the bolts enough when I put it together to make that video and confirm where the leak was coming from. I think that made the leak look a lot worse. Today I also soaked the housing bolts in vinegar and scrubbed them with a wire brush because I noticed that there was some gunk in the threads. I'm hoping that the combo of cleaning the bolts, getting a new thermostat gasket, and tightening the housing very well will solve my problem. The mating surfaces of the thermostat housing look pretty good to me. I don't see any cracks or chips.
Thank you,
Ella

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