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jeff

Straight 8 thermostat bypass question

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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

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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

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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 by Dynaflash8 (see edit history)

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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

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