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Thermostat bypass mod.


Buick35

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 Jim Forshey used to keep all the old 1937-1938 Buick Torque tubes online available but he relinquished them to I think the 1936-1938 Club. I believe Matt Hinson has them now, but I couldn't locate them. Perhaps he can steer you in the right direction.

 Basically you  remove the shaft, spring and plate and replace it with a Welch plug with a 1/4 inch size hole drilled in the center of it. Trying to diagnose a problem I was having I did it on one for a 37 Special but went back to the original as the original one wasn't the problem. The modified one made it difficult for my car to get to a warm operating temperature.

 

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I modified the modification made to the bypass valve in my '38 Century last winter.  I removed the freeze plug that was added and replaced the steel tubing that disabled the spring with an appropriate piece of copper tubing.  The copper tube locks the OEM valve in the 'non-bypass' position just like the steel, but I don't want any more ferrous metal in the cooling system if I can avoid it.  The OEM valve (disk) leaves space around the circumference and doesn't touch the thermostat housing.  According to the shop manual, the area of the open space around the circumference is equivalent to a 1/4" diameter hole.  Coolant that gets by that gap bypasses the radiator, however, with the tube locking the valve it can't open any further so the volume of coolant allowed to bypass will never change.

 

At first glance, my bypass valve appears unmodified since the spring is still there...

Edited by EmTee (see edit history)
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3 hours ago, 1937-44 said:

 Jim Forshey used to keep all the old 1937-1938 Buick Torque tubes online available but he relinquished them to I think the 1936-1938 Club. I believe Matt Hinson has them now, but I couldn't locate them. Perhaps he can steer you in the right direction.

 Basically you  remove the shaft, spring and plate and replace it with a Welch plug with a 1/4 inch size hole drilled in the center of it. Trying to diagnose a problem I was having I did it on one for a 37 Special but went back to the original as the original one wasn't the problem. The modified one made it difficult for my car to get to a warm operating temperature.

 

I'm in Florida so that shouldn't be a problem.I also have an M.G.B.that was having trouble starting after it warmed up.I ended up removing the thermostat and installing a blanking sleeve in its place,I also installed a shroud.Now it has trouble teaching operating temperature but it always starts.

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Boy does this bring back memories

 

Late in the development of the 1985 3.0L V6 in Flint (Buick) we had terrible coolant temperature cycling high to low to high and on and on in colder ambients. The temp gauge would swing end to end. 

 

I got assigned the task to determine the cause and fix it.  Fast. Guessing it was the Winter of 84/85. We had new N cars in production.  
 

Long story short, the engine lacked any form of coolant bypass as designed. The bypass flow allows the thermostat to ‘see’ what the coolant in the engine is.  Without this flow, the coolant is stagnant until all heck happens within the engine and a boil occurs and the thermostat opens violently. Then the cold coolant in the previously stagnant radiator rushes into the engine and the thermostat slams shut and the fun starts all over again. 
 

We determined that a 1/4 inch diameter flow past/near the thermostat was the minimum flow to solved the issue but it also reduced engine cooling performance hot since this bypass flow coolant never went to the radiator. It also slowed down heater warm-up performance cold. 
 

Some engine designs allow this flow through the heater core and then out to the radiator but that will impact ac performance with hot coolant in the core next to the ac evaporator in the hvac box. And the N car could not take the hit in ac performance 
 

We then had to adjust the radiator size due to the new bypass flow not going to the radiator.  Off to Lockport NY and the Harrison Cooling Tunnels for hot work.  I did the cold work on I-75 night and day. 


The result was an added bypass flow circuit from the intake just under the thermostat to the front cover water pump inlet and one of those short little elbow hoses we all hate to work on.  But we also designed and sourced in just weeks a dealer fix for the problem for the early production cars. That was a bit of a Frankenstein but it worked and the dealers ordered them like crazy. 
 

We checked the 3.8L MFI (pre 3800) and found it had the same issue to a lesser extent so it got the fix too and we made many of the parts common. 
 

They also added coolant bypass testing to our Bill of Design and made sure the soon to come 3800 had no such problems. I was still in the Test Department back in the Experimental Lab and the Design guys were not to happy w my findings or their missing the issue. True to form I got promoted to help design the 3800 and was consulted on the cooling and bypass design. I was 26 and the senior engineer designing the system was over twice my age. 
 

They thought they would see what I was made of and had me design the entire brand new 3800 balance shaft system. Clean sheet. What a great job that was. 
 

And now you know how I spent the Winter of 84/85 in Flint 7 days a week 12 hrs a day for 3 months.  I was married in June of 84.  The boss was none too happy until she saw my paycheck. 
 

1/4 hole bypass is all you need. 

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40 minutes ago, Brian_Heil said:

They thought they would see what I was made of and had me design the entire brand new 3800 balance shaft system. Clean sheet. What a great job that was.

Well, I'll tell you that when i replaced the timing chain on my '90 Bonneville after 120,000 miles I saw the balance shaft system and was duly impressed.  That car was a runner - and even with 150K on the odometer I wouldn't have hesitated to get in and drive it cross-country.  That was a great car.  ;)

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Tested the heck out of that new narrow chain.  Most go 300k+.  They went 1200 hours on the dyno @ WOT. And we carried several over from one end of test to the next engine. 
 

No nylon sprocket teeth to fail and plug up the sump screen. 
 

There was an improvement to the chain tensioner/follower.  Not sure if the 1990 had that. 

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6 minutes ago, Brian_Heil said:

There was an improvement to the chain tensioner/follower.  Not sure if the 1990 had that

That was the issue with mine.  It was noisy (slap).  At the time I was unaware of the steel gear - I was worried about nylon tooth failure.  If I recall correctly I think the replacement tensioner was a different design.  Also had a '92 LeSabre that ran like a Swiss watch.  The Bonneville was more fun to drive though...  ;)

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20 hours ago, Brian_Heil said:

Boy does this bring back memories

 

Late in the development of the 1985 3.0L V6 in Flint (Buick) we had terrible coolant temperature cycling high to low to high and on and on in colder ambients. The temp gauge would swing end to end. 

 

I got assigned the task to determine the cause and fix it.  Fast. Guessing it was the Winter of 84/85. We had new N cars in production.  
 

Long story short, the engine lacked any form of coolant bypass as designed. The bypass flow allows the thermostat to ‘see’ what the coolant in the engine is.  Without this flow, the coolant is stagnant until all heck happens within the engine and a boil occurs and the thermostat opens violently. Then the cold coolant in the previously stagnant radiator rushes into the engine and the thermostat slams shut and the fun starts all over again. 
 

We determined that a 1/4 inch diameter flow past/near the thermostat was the minimum flow to solved the issue but it also reduced engine cooling performance hot since this bypass flow coolant never went to the radiator. It also slowed down heater warm-up performance cold. 
 

Some engine designs allow this flow through the heater core and then out to the radiator but that will impact ac performance with hot coolant in the core next to the ac evaporator in the hvac box. And the N car could not take the hit in ac performance 
 

We then had to adjust the radiator size due to the new bypass flow not going to the radiator.  Off to Lockport NY and the Harrison Cooling Tunnels for hot work.  I did the cold work on I-75 night and day. 


The result was an added bypass flow circuit from the intake just under the thermostat to the front cover water pump inlet and one of those short little elbow hoses we all hate to work on.  But we also designed and sourced in just weeks a dealer fix for the problem for the early production cars. That was a bit of a Frankenstein but it worked and the dealers ordered them like crazy. 
 

We checked the 3.8L MFI (pre 3800) and found it had the same issue to a lesser extent so it got the fix too and we made many of the parts common. 
 

They also added coolant bypass testing to our Bill of Design and made sure the soon to come 3800 had no such problems. I was still in the Test Department back in the Experimental Lab and the Design guys were not to happy w my findings or their missing the issue. True to form I got promoted to help design the 3800 and was consulted on the cooling and bypass design. I was 26 and the senior engineer designing the system was over twice my age. 
 

They thought they would see what I was made of and had me design the entire brand new 3800 balance shaft system. Clean sheet. What a great job that was. 
 

And now you know how I spent the Winter of 84/85 in Flint 7 days a week 12 hrs a day for 3 months.  I was married in June of 84.  The boss was none too happy until she saw my paycheck. 
 

1/4 hole bypass is all you need. 

I'm having second thoughts about the mod.I strongly believe that " if it ain't broke,don't fix it". Has anybody on the forum had a bypass valve failure causing a boil over? Just curiois.

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I have not personally experienced a failure, but apparently others have reported that the spring eventually weakens and allows increased bypass flow when it is not warranted (i.e., when the thermostat is open).  This allows too much coolant to bypass the radiator causing higher than normal coolant temps or boilover.  Locking the valve in the 'non-bypass' position still allows sufficient bypass for proper thermostat regulation via the 1/4" diameter equivalent area around the circumference of the bypass valve.  Refer to Brian Heil's first comment above regarding the requirement for coolant bypass.

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2 hours ago, Buick35 said:

I'm having second thoughts about the mod.I strongly believe that " if it ain't broke,don't fix it". Has anybody on the forum had a bypass valve failure causing a boil over? Just curiois.

Not personally, but based on experiences of other members of the 36-38 Buick Club, the spring often weakens causing an overheating problem. The springs were never expected to last this long. I suppose replacing the spring would be a valid fix but there does not seem to be any record of the stiffness of the original spring so replacement of the spring is not practical. The bypass valve modification simply eliminates the opportunity for problems with the bypass valve, and also essentially makes the change that Buick made a few years later, in I think... 1941, when the bypass valve was eliminated and replaced by a 1/4 hole in the housing.   

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Back in the early 1980's when I rebuilt the engine, the bypass system on my 1938 40-41 was in good shape so I cleaned it thoroughly and stretched the spring to restore its pressure resistance. All the parts are made of brass and I had to make a new brass cotter pin to hold the bottom disc in place. The coolant passages in the block were also thoroughly cleaned, new water pump, and the radiator re-cored. I also converted the system to 7lb. pressure by replacing the filler cap inlet with a modern type and run a 160 deg. thermostat. I use a 40-60 mix antifreeze (60% water).

 

Since then (40 years) I have never overheated and the car runs 170-180 on the road in 90 deg. temps and climbs to 190-200 when hot idling for extended periods but quickly comes back to <190 once on the road again. I do rigorously maintain the system by periodic flushing and changing coolant.  Perhaps the spring will eventually loose its strength but I only drive it <500 miles a year. When and if that happens, if I can't find a replacement spring, I will probably convert it to a fixed orifice.  I believe in running what the original engineers designed if possible. 

 

Steve D

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11 hours ago, Steve_bigD said:

...the car runs 170-180 on the road in 90 deg. temps and climbs to 190-200 when hot idling for extended periods but quickly comes back to <190 once on the road again.

This is essentially the behavior I'm seeing with my '38 Model 61.  The fan doesn't seem to be up to the task of moving sufficient air through the radiator at speeds less than about 25~30 mph.  I see on the forum that some people have added a custom fan shroud.

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Here is what I did to our 40' Buick.  Car has been in the wife's family since the early 80's.  Always ran hot.  I bought it last year, flushed the block, and it had a few year old radiator.  It still ran hot when I bought it.  I did the mod and it no longer runs hot.  I also put rubber seal strips around the front of the radiator so all the incoming air goes into the radiator.    

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Wait what? That is not the mod I have seen before. Buick's bulletin involved removing a spring loaded valve, and replacing it with a core plug with a hole drilled in the middle. Do you have no bypass at all now? I see you have a heater. Is that acting as the bypass?

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15 minutes ago, Bloo said:

Do you have no bypass at all now?

Hi Brad,

 

 I'm as confused as Bloo with the pipe plug in the welch plug as it would seem that would just eliminate the bypass altogether. These are pictures of a 1937 Special bypass. One on the left is unmolested whereas the on on the left is what I have always understood to be the recommended improvement with the 1/4 in hole.

 I have reinstalled an original in my car as the modified one made it run even cooler than an original one. My car generally runs around 170 -175 on a 90 degree day when moving and only climbs a little when idling.

 

Carl

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There has to be some bypass in order for the thermostat to operate properly.  Without any bypass the engine will get too hot before the thermostat opens.  My '38 shop manual states that the open area (i.e., gap) between the OD of the bypass valve and the ID of the housing is supposed to be an area equal to a 1/4" hole.  So, as I stated above, I simply disabled the spring by inserting a copper tube over the shaft (inside the spring) that holds the valve 'closed'.  What I did should be equivalent to removing the valve mechanism and replacing it with a core plug having a 1/4" hole drilled in it.

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When I got my '37, the bypass valve had a freeze plug installed with NO hole drilled in it.  

So basically the car runs as if the bypass valve is closed...  (engine fully warmed up, thermostat open, water being directed through the radiator)

 

What I did was simply drill a hole in the thermostat flange to allow water to circulate slowly, warm slowly and allow the thermostat to open at temperature for a full flow through the radiator.

 

With the freeze plug installed in place of the spring loaded valve, the water heats the thermostat, and once the thermostat opens the water enters the radiator and begins circulation.  (See "normal circulation" below)

 

I now have 2500 miles on her, out in these oppressive 90+ degree days and she hasn't ever gone over 180.  I get plenty of heat in the winter so I'm going to keep the setup as is.

 

 

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From the manual:

1. Recurculation:  What I call "warm up".  The spring loaded valve is open, thermostat is closed, water is cold, Water is circulating through the engine to warm up.

2. Normal Circulation:  This is basically how my car operates full time.  I have no spring loaded valve, just a freeze plug so ALL water is directed to the thermostat all the time.

I drilled a hole in the thermostat flange to allow enough circulation while the engine heats up. Then the thermostat opens, and you have "normal circulation"

 

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My bypass is 100% closed off.  All water circulates from the pump, through the block and up and into the radiator.  

Going over my restoration notes, I actually drilled two 1/8" holes through the thermostat flange. 

 

It's how I got the car, and it functions just fine.  It seems very logical to me as a way to eliminate the old spring valve.

 

She still warms up just fine, (maybe a little slower than normal?), but I have nothing to compare it to.

 

Have a great day!

Gary

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May I add a little to this conversation?    I do not know when but by 1950 Buick had integrated a bypass into the system that shunted water from just below the thermostat back to the pump suction.  Same spot , I believe, as the '37-'38.   This opening is about I/2 inch.  A short section of heater hose connects the thermostat housing to the pump suction. I have never had a problem. 

 

  My believe is that IF the radiator is right, most, if not all, cooling problems go away.  BUT, and that is a big BUT, radiators seem to have been designed with little excess capacity. To save money? probably.

 

  Ben

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11 hours ago, Ben Bruce aka First Born said:

BUT, and that is a big BUT, radiators seem to have been designed with little excess capacity.

Maybe, but my main observation with my '38 is that it seems to run right around 180 until forced to stop (idle).  Then the temp comes up a bit (maybe 190).  As soon as the car gets moving above 30~35 mph the temp goes back to 180 - this is in spite of the fact that the engine is generating more heat than it does at idle.  This says to me that the fan is not very good at pulling air through the core when the car isn't moving.  I've been thinking of trying a different fan or possibly fabricating a fan shroud.

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32 minutes ago, EmTee said:

Maybe, but my main observation with my '38 is that it seems to run right around 180 until forced to stop (idle).  Then the temp comes up a bit (maybe 190).  As soon as the car gets moving above 30~35 mph the temp goes back to 180 - this is in spite of the fact that the engine is generating more heat than it does at idle.  This says to me that the fan is not very good at pulling air through the core when the car isn't moving.  I've been thinking of trying a different fan or possibly fabricating a fan shroud.

You are not only changing fan speed but ram air speed and water pump speed (volume)

 

A house box fan in front of the grill at idle will answer your fan question. 

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Yes, more water and more air circulating at speed.  My point is the car seems happy there.  Conversely, if started cold, it will idle happily in the driveway and take some time to get to full temperature.  But, when forced to idle after already at temperature, the temp will increase.  Now, that seems logical for exactly the reasons you identified: less air through the core and fewer gph of water circulating.

 

That said, the experiment I haven't performed is letting the engine go idle after fully warm to see how long it takes for the temperature to come down (or whether it does) without additional air flow.

Edited by EmTee (see edit history)
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IMG_20220729_174956.jpg.eeee429c43e18cde196f3d930640c91a.jpgHere's how I did mine.I removed the bottom retainer plate and spring.I pushed the valve to the fully opened position and secured it in place with a cotter pin through the shaft. Please tell me if it should work or not since I haven't installed it yet.Thanks,Greg.

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One thing that seems to be getting lost in this conversation is what we are bypassing.

 

Drilling a hole in the thermostat is also a solution that comes up often in forum threads about newer cars. An example would be using small block Chevrolet "Vortec" heads on an earlier non-Vortec block, leaving you with no bypass. Similar situations exist on other engines.

 

A bypass hole (or holes), or the Buick bypass valve, or a bypass hose all bypass the radiator. Drilling a hole in the thermostat bypasses the thermostat. That doesn't necessarily mean one is bad and one is good, but they are different.

 

The bypass valve we have been discussing, as well as the 1/4" hole it gets replaced with always let hot coolant bypass the radiator. It ALWAYS does this. Since there is flow the thermostat gets hot water and opens before some other part of the engine gets boiling hot, as outlined in @Brian_Heil's post. That 1/4 inch hole is always open however. It shouldn't flow as much coolant once the thermostat is open, but always reduces cooling efficiency because some hot coolant can bypass the radiator. The thermostat, however, works as intended.

 

Speaking of the thermostat, you have probably seen factory holes in them. Tiny ones. In fact, the original Harrison bellows-type thermostats used in 1930s Buicks, Pontiacs, and others have a hole so small it is almost invisible. I have never seen a hole so tiny in a modern thermostat. This is for a different purpose. It is so you can fill an empty cooling system and get coolant all the way up to the thermostat before it ever opens. Otherwise the engine would have to overheat a little before you could get the rest of the coolant in. There is a downside though, a lot of water gets through the hole, more than you would think, and on modern stats the hole is bigger too. This prevents the thermostat from doing it's job as well as it could. Some modern thermostats have a "dingle ball", it is a little valve that opens to let the coolant in when you fill the system. Once the system is full and the coolant hits it, the valve closes and the thermostat works as normal. This is all completely unrelated to bypassing.

 

If you have no bypass at all and drill an 1/8" hole in the thermostat, that lets a lot of water through. I have heard drilling as many as three 1/8" holes recommended. That will solve the problem of getting hot water to the thermostat when the engine is cold, just like a bypass would. The trouble is the thermostat really won't have much control over engine temperature... at all. On the good side, you do not have any coolant bypassing the radiator, so you don't lose that portion of cooling capability.

 

Pick a side. ;)

 

Edited by Bloo (see edit history)
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2 hours ago, Buick35 said:

Where do I drill the 1/8" hole in the thermostat? Thanks

 

Assuming a modern type thermostat with a copper and wax pellet to move the valve, you would drill the hole in the flange somewhere around the outside.

 

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I wonder what Buick engineers were thinking when they decided to go with the radiator bypass as opposed to only bypassing the thermostat.  They apparently believed there was sufficient excess capacity in the radiator.  Maybe there was more concern about cold weather operation before ethylene glycol antifreeze became widely available?

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Could be.I'm in Florida so not too worried about that.I do think I'll go back to using anti-war though for the anti rust properties. My rebuilt water pump of less than a year old has what looks like a whitish powdery substance around the back plate gasket that looks like corrosion to me so I'm having my original one rebuilt,I should get it back soon.Thanks.I'll post a picture of the area in question later.

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12 hours ago, EmTee said:

I wonder what Buick engineers were thinking when they decided to go with the radiator bypass as opposed to only bypassing the thermostat.  They apparently believed there was sufficient excess capacity in the radiator.  Maybe there was more concern about cold weather operation before ethylene glycol antifreeze became widely available?

Probably because the thermostat wouldn't have much control over temperature. @Brian_Heil outlined how they approached it on the 3.8. They figured out what the minimum radiator bypass size was that would get the job done, and then adjusted the size of the radiator to make up the difference.

 

If you bypassed just the thermostat, people in Florida, SoCal, and Saudi Arabia might not notice, but they design these cars to work everywhere.

 

Edited by Bloo (see edit history)
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