cron1984 Posted October 29, 2022 Share Posted October 29, 2022 Good evening, Engine rebuild on my 38 olds 6 is almost complete and I’m in need of a rubber seal for the water pump bypass. I believe the part number is 408500 but I have no idea where to find one. I’ve checked most of the normal sites (fusick, etc) without luck. I came across something similar on eBay but the part number is different and it has a slightly different look. Flathead 6, 230 cubic inch. If anyone has any guidance/leads it would be greatly appreciated. Thank you. chris. Link to comment Share on other sites More sharing options...
NailheadBob Posted October 30, 2022 Share Posted October 30, 2022 (edited) I came up with different part number, group # 1.099 Seal, water pump by-pass rubber part # 408300, maybe other GM cars used same part. @Gary W maybe Gary if he stops by can shed some light on this. Bob EDIT: fits 1937 thru 1941 6 & 8 Oldsmobile Edited October 30, 2022 by NailheadBob Update (see edit history) Link to comment Share on other sites More sharing options...
Bloo Posted October 30, 2022 Share Posted October 30, 2022 I doubt other GM cars would use that except maybe LaSalle. Link to comment Share on other sites More sharing options...
cron1984 Posted October 30, 2022 Author Share Posted October 30, 2022 I hope Gary offers some guidance - His elaborate write up for his 37 Buick was the inspiration for me restoring my grandfather’s car! Once this thing is done I’ll share some details, but I can promise it won’t be as thorough as Gary’s thread. 2 Link to comment Share on other sites More sharing options...
Sunchaser Posted October 30, 2022 Share Posted October 30, 2022 The GMC part number for that is 408079, they were used in 1937 and 1938 1 Link to comment Share on other sites More sharing options...
Gary W Posted October 30, 2022 Share Posted October 30, 2022 A water pump bypass. My '37 Buick doesn't have a water pump bypass, but we do have a system where the cold water will bypass the radiator and continue circulating throughout the block to warm up faster: With the thermostat closed (cold water) the water pressure from the pump will overcome the spring pressure of the bypass valve and all the water is shunted not through the radiator but through the block. This condition is called "Recirculation" in the manual. When the water warms, the thermostat begins to open, allowing water to enter the radiator and thus there is no more pressure keeping the spring valve open. The spring pressure closes the bypass valve and normal radiator/block circulation begins. From the '37 manual. Here are a few photos of my water pump. I don't know if they will give you any information about your bypass. I tried to get a shot from all sides. 1 1 Link to comment Share on other sites More sharing options...
cron1984 Posted October 30, 2022 Author Share Posted October 30, 2022 Thanks for the input everyone. Finding one of these may be difficult- I’ll see if I can get creative or maybe the boys at work would be able to replicate it somehow. thank you again. 2 Link to comment Share on other sites More sharing options...
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