In Reply to: Re: thermostat question posted by Tim Daley(MI) on December 01, 2018 at 08:22:28:
While I agree that an orignal-quality thermostat should not need modification to work properly, in our modern age of imported aftermarket parts it is entirely possible that a thermostat would need a bleed hole drilled in it.
I installed a "will-fit" thermostat in an 8N with the same results as the OP. It turns out that the original application (foreign car) had a bleed hole elsewhere in the thermostat housing, and to get it to work in the 8N I had to drill one in the body of the thermostat near the opening for the plate. It works great now.
I would not be too concerned about the size of the hole. If it is a little large, it will slow warm-up ever so slightly. If too small, it might not allow enough flow to break the air-lock, but it would need to be tiny to do that. I think I used about a 3/32" drill bit on mine, but 1/8" would have been fine.