Janousek Posted August 20, 2021 Share Posted August 20, 2021 I have a 40' Special that is running hot. I pulled the thermostat housing to check the bypass like others on here. This picture is what I have. Our 48' Buick has the same housing. Bob's Automobilia said this is the later part. I'm going to tap this hole and make it smaller. What would be a minimal hole that I should put in it. It's a 1/2" now and I feel that is enough to bypass a lot of coolant from the block. Radiator is recored Just ordered new waterpump. Going to remove the rear freeze plug and see what's in the block. Coolant isn't rusty. Car warms up fast in town. Seems to cool OK out on the road. Link to comment Share on other sites More sharing options...
sleeve-valve Posted August 21, 2021 Share Posted August 21, 2021 (edited) Take a look at this older thread. It links to an article that suggests 1/4 inch hole. Edit to add: My 39 Special started overheating a couple years ago, the thermostat was sticking shut. If only it could be that easy every time! Edited August 21, 2021 by sleeve-valve (see edit history) Link to comment Share on other sites More sharing options...
Janousek Posted August 22, 2021 Author Share Posted August 22, 2021 Thank you. I had came across that info somewhere. I've been pondering completely closing this and drilling a small hole in the thermostat. Seems dumb not to have all the coolant pass in a loop from the engine through the radiator. 1 Link to comment Share on other sites More sharing options...
Gary W Posted August 22, 2021 Share Posted August 22, 2021 2 hours ago, Janousek said: Seems dumb not to have all the coolant pass in a loop from the engine through the radiator. My '37 came with a freeze plug installed. No hole drilled, just a solid freeze plug. Frankly, I didn't know enough to even question it. When I installed the new thermostat, I drilled a hole through the thermostat flange, allowing a small amount of coolant to flow until the thermostat opened. It seems to work just fine. Over 2400 miles on her now, never ever gets above 180 and this has been a wicked hot summer. When you study the operation of the bypass system, the thermostat, the coolant flow when cold v. when hot..... it seems the hole in the thermostat pretty much accomplishes the same job. Heres the link to this discussion on my build: 1 Link to comment Share on other sites More sharing options...
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