Does anyone know the bolt size for the 3.1L V6 Thermostat Housing Bolts?

Thanks!

 

It has been a while, so I don't recall off the top of my head. But knowing GM, I am guessing 10mm or 13mm. You should be able to get a socket or wrench on them to check.

Typically when I change a t-stat on a 3100 or 3400, I remove the throttle body and I get pretty good access to the housing. Some take out the exhaust cross over pipe.