jeff Posted July 18, 2018 Share Posted July 18, 2018 As a pre-war Buick owner ('38 Special), I have been advised to restrict the spring loaded thermostat bypass mechanism to limit the flow bypassing the radiator. The claim is that the post-war version of this straight eight engine has a different "fixed" bypass arrangement, and that this later design is more effective. Can anyone confirm the design of the bypass in the later Buick straight eights? Jeff Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted July 18, 2018 Share Posted July 18, 2018 Jeff, the bypass on the 1950 and later is heater hose size. Comes off the bottom o the thermostat housing into the suction of the pump. A 1 inch or so piece of heater hose connects. Ben 1 Link to comment Share on other sites More sharing options...
Dynaflash8 Posted July 19, 2018 Share Posted July 19, 2018 (edited) Actually, it is the exact opposite. Many years ago an article was published in the BUGLE from a 1938 owner, if fact, that the best thing to do was take the bypass valve completely out of the thermostat housing. In 1948 Buick did away with it altogether from the factory. I was recently advised by a major Buick restorer to take it out of my '41. I'm sorry I did it as that didn't make any difference. The '48 style is a little more open than a '36-'47 housing I think, but the difference is miniscule. Both of my '39s run find with the valve in place. We've found crap in the block and plan to flush the engine out, but the shop is afraid to take out the engine plug and I think I am too. But right there at the back of the engine is where most of the crap settles. Back before permanent anti-freeze people used alcohol and had to drain it every year and the plugs were in use. That ended over 60 years ago. If you can't get a new thermostat housing, at minimum, I recommend you take the valve out. What is there for, anyway, is for quick warm up in the mornings. Edited July 19, 2018 by Dynaflash8 (see edit history) Link to comment Share on other sites More sharing options...
jeff Posted July 19, 2018 Author Share Posted July 19, 2018 Thanks for the feedback! Ben, a 1" heater hose probably has a 1/2 or 5/8 ID. Agree? If so, that lines up pretty closely with the equivalent orifice diameter of the closed bypass valve, which is 1/2 inch. (it has an annular clearance when closed, the shop manual says it's equal to 1/2" diameter orifice.) So, when your thermostat is closed, the pump is circulating water through the head with this 1/2" restriction at it's inlet. That will be the same as what I rig up. Dynaflash - I totally agree with your comments on crud in the block. I have flushed mine twice over the years, but I am sure there is still junk in there - maybe crusted to the point where flow is restricted. My symptom is this... Good temperature control on the hottest days (93 F recently) while moving at 50 to 55 mph. (Special, with a 3.9 rear, radiator rodded out, 160 thermostat) Temperature will read about 190 under these conditions. A bit less on a more moderate day. When I come to a town and sit at a few traffic lights, the temperature will creep up - pretty close to max. Stopping for gas on the recent 93 degree day caused some coolant loss as it briefly boiled. The related issue is fuel percolation when the underhood temperature creeps up like this. I recently re-routed the fuel line to help this issue. I would love to go back in time and see how well these cars performed under these conditions. My best reference is a friend's '39 Packard and another friend's '37 Dodge - both are more capable under these kinds of conditions. Great feedback - thanks again! Jeff Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted July 20, 2018 Share Posted July 20, 2018 Jeff, not 1" hose. Probably 5/8 ID, 1" LONG. Ben 1 Link to comment Share on other sites More sharing options...
jeff Posted July 20, 2018 Author Share Posted July 20, 2018 Thanks! Link to comment Share on other sites More sharing options...
Rick.J Posted May 7, 2022 Share Posted May 7, 2022 Hi everyone I have a 1934 Buick straight 8 I just recently replaced the water pump and noticed the housing for the thermostat there was a bypass under the thermostat nothing was holding it in except corrosion I slightly tapped on the bypass valve and it fell out not sure if there was supposed to be a nut on the bottom of this bypass valve and also don't know if I actually need it in the car or if I should just leave it out. Link to comment Share on other sites More sharing options...
pont35cpe Posted May 7, 2022 Share Posted May 7, 2022 There is a fix that has been discussed here before. Remove the bypass guts/stud, and press in an appropriate sized freeze plug, drill a 1/4" hole in it. 1 Link to comment Share on other sites More sharing options...
Rick.J Posted May 7, 2022 Share Posted May 7, 2022 Will do that's the next project I got to take on then Link to comment Share on other sites More sharing options...
pont35cpe Posted May 7, 2022 Share Posted May 7, 2022 Just now, Rick.J said: Will do that's the next project I got to take on then It is a rather simple fix, i did mine. If i recall correctly, freeze plug is 1"dia. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted May 7, 2022 Share Posted May 7, 2022 3 hours ago, Rick.J said: Hi everyone I have a 1934 Buick straight 8 I just recently replaced the water pump and noticed the housing for the thermostat there was a bypass under the thermostat nothing was holding it in except corrosion I slightly tapped on the bypass valve and it fell out not sure if there was supposed to be a nut on the bottom of this bypass valve and also don't know if I actually need it in the car or if I should just leave it out. The bypass is NEEDED , otherwise there is no circulation until the thermostat opens . No circulation means no hot coolant gets to the thermostat to cause it to open. Ben 1 Link to comment Share on other sites More sharing options...
1937-44 Posted May 8, 2022 Share Posted May 8, 2022 I have a 1937 Buick Special and had an overheating issue on a car I've owned for46 years that had never overheated (including the 100 degree temperature in NC). I removed the guts of the bypass put in the freeze plug but it didn't fix the problem. Before pulling the radiator I investigated further and found the lower radiator hose was collapsing (seems the newer hose I replaced the old one with was thinner). I put a spring in the lower hose now I can't get the darn thing over 165 degrees no matter what the temperature. It might be needed on the 320 engine but I don't think the conversion is necessary on the early 248 if everything is working properly. I'm going to be putting my old bypass back in. Carl 1 Link to comment Share on other sites More sharing options...
Bloo Posted May 8, 2022 Share Posted May 8, 2022 The freeze plug is a Buick factory fix, and has a hole in it so there is still some bypass. Maybe it is for the 320 only(?), not sure about that. Link to comment Share on other sites More sharing options...
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