Thermostat Housing Leak? - Mazda3 Forums : The #1 Mazda 3 Forum
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post #1 of 3 (permalink) Old 03-17-2019, 02:11 PM Thread Starter
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Location: Oklahoma
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Thermostat Housing Leak?

I noticed evidence of a leak during an oil change today. Dabbed it with my finger and, as I suspected, confirmed it is coolant. Went topside for a look and traced the wetness to the thermostat housing. The area is cramped and difficult to photograph. It appears the wetness is forming on the area which faces the passenger side of the vehicle. The liquid wends its way down the engine and breaks into two paths under the oil pan.

Any ideas or suggestions? I doubt the bolts (or the passenger side bolt) has loosened. My maintenance records show the thermostat was replaced under warranty in 2012 with 71K miles of service.

**EDIT - Did some quick checking after I posted, and it appears the culprit might be the thermostat housing seal is failing. Inspecting the area again shows the source to be around the passenger side housing bolt. The liquid is probably weeping through that point.

2006 Mazda 3 2.3L Hatchback 5-speed Automatic - 180K miles
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Last edited by VWandDodge; 03-17-2019 at 02:25 PM. Reason: Post inspection follow-up
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post #2 of 3 (permalink) Old 03-20-2019, 06:58 PM
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I didnt know what the Thermostat housing was til it was TOO late...Hahaha...I took the screws off thinking it was a piece of plastic...Little did I know it was not...haha..Got coolant all over the place...and when I did that I messed up the rubber seal...So I purchased a new seal from OReillys....and fixed the leak issue.

My 1st Mazda! - 2009 Hatchback - Golden Sand Metallic

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post #3 of 3 (permalink) Old 03-25-2019, 11:35 PM
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I would have a new housing/thermostat assembly on hand when you go to change the seal. I've seen plastic coolant parts with seal groves deteriorate and crack far to often to trust that one will just need a gasket once it starts leaking.
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