Memorializing what I found today. The thermostat original OEM is 66 1/2 mm diameter but it fits in a milled out female area in the housing on the engine block, at least for the 96 and beyond models, at 69 mm. The net effect is the thermostat left to right up and down is loose by several millimeters. Also, when you mate the thermostat housing on to the engine block in this location there is several millimeter gap inward that houses is the thermostat. If the thermostat has no seal around it it will vibrate left right up-and-down, but also if there is no gasket or seal in front of or behind it, it will jiggle forward and aft by several millimeters in each direction. Needless to say, the gasket needs a rubber seal around it that wraps over front and back, a cross section would look like a C. What I found out today is that seal when wrapped around the OEM thermostat is 71 mm total. The seal without the thermostat in it is exactly 68 mm and fits Inside perfectly. When you put the thermostat in it due to the interior dimension of the seal itself it stretches to 71 mm. This presented a conundrum. I spent time with my Dremel tool literally milling the OEM thermostat down to millimeters in order to have the assembly fit within the female housing on the head. this way the thermostat housing meets directly up to the head with the gasket in between and you don’t need to force it. What happened in my case was a prior mechanic jammed the thermostat in there with the seal around it and used the four bolts to seal the assembly which cut the seal and resulted in the photos above. done properly, what I did tonight, is the thermostat with seal should mate inside the female housing before you put the thermostat cover housing and gasket on it. Hope this makes sense. If you send your car off to get a new thermostat done by a mechanic I guarantee you he didn’t take these extra steps.
The first photo shows the thermostat with seal does not fit properly. The second photo shows this more clearly. The third photo shows the seal itself fits perfectly inside the female housing on the header.
as is clear to me, my car had a clutch job done with the prior owner at 10,000 miles and I suspect they replaced the thermostat with an OEM thermostat but the seal did not fit. They jammed one in there that failed. This explains why I have some new OEM hoses in the coolant system and some original OEM hoses. My belief is the one that blew forward of the engine between the firewall was original 1997.
The first photo shows the thermostat with seal does not fit properly. The second photo shows this more clearly. The third photo shows the seal itself fits perfectly inside the female housing on the header.
as is clear to me, my car had a clutch job done with the prior owner at 10,000 miles and I suspect they replaced the thermostat with an OEM thermostat but the seal did not fit. They jammed one in there that failed. This explains why I have some new OEM hoses in the coolant system and some original OEM hoses. My belief is the one that blew forward of the engine between the firewall was original 1997.
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