Ladies & Gentlemen,
As some of you know I have battled an overheating problem at idle with the 259 V8 in my ’55 President State Sedan. From the very beginning StudeRich and others have said to make sure the water pump is working OK. I have done quite a bit of due diligence and have decided to change out the water pump. I will make sure the impellers are about .015 from the race (or whatever it is called) in the manifold. It will be interesting when I get the water manifold off the engine what kind of clearance there currently is to see if that is a factor in the performance of the pump.
When I went back to look at some of the pictures taken during the rebuild I noticed how cruddy the pump and manifold were. If I had it to do again I would have put a new pump in when it was being rebuilt. I also noticed a small hole in the manifold below the thermostat but didn’t give it much thought at the time. I think it is called a bypass hole.
When a couple of thermostats were being tested for their opening temperature I was impressed with the open area that they would allow water to pass through. One had 1.5 square inches and the other 1.6. I then got online to calculate the area of that hole which I have learned through researching this site is 7/16”. That area is .15 square inches. It is pretty obvious to me that the limiting factor with how much water can get through the open thermostat to the radiator is that hole.
When that 7/16” hole is compared to the size of the passageways in the manifold it looks like only a fraction of the water is actually being pushed into the radiator. The rest of the water evidently is recycled without being cooled by the radiator. My initial thinking was I would drill that sucker out to ½” and let more water into the radiator. On second thought, I am thinking that someone must think that 7/16” is the magic number.
It reminds me of the tiny hole in the in-line restrictor in the partial flow oil filter system. I did not have it initially and the oil pressure dropped to zero and I knew something was wrong. Maybe enlarging the 7/16” hole would have the same effect on the water pressure. I thought I’d run this by the forum members and see if I should just let a sleeping dog lie.
Charlie D.


As some of you know I have battled an overheating problem at idle with the 259 V8 in my ’55 President State Sedan. From the very beginning StudeRich and others have said to make sure the water pump is working OK. I have done quite a bit of due diligence and have decided to change out the water pump. I will make sure the impellers are about .015 from the race (or whatever it is called) in the manifold. It will be interesting when I get the water manifold off the engine what kind of clearance there currently is to see if that is a factor in the performance of the pump.
When I went back to look at some of the pictures taken during the rebuild I noticed how cruddy the pump and manifold were. If I had it to do again I would have put a new pump in when it was being rebuilt. I also noticed a small hole in the manifold below the thermostat but didn’t give it much thought at the time. I think it is called a bypass hole.
When a couple of thermostats were being tested for their opening temperature I was impressed with the open area that they would allow water to pass through. One had 1.5 square inches and the other 1.6. I then got online to calculate the area of that hole which I have learned through researching this site is 7/16”. That area is .15 square inches. It is pretty obvious to me that the limiting factor with how much water can get through the open thermostat to the radiator is that hole.
When that 7/16” hole is compared to the size of the passageways in the manifold it looks like only a fraction of the water is actually being pushed into the radiator. The rest of the water evidently is recycled without being cooled by the radiator. My initial thinking was I would drill that sucker out to ½” and let more water into the radiator. On second thought, I am thinking that someone must think that 7/16” is the magic number.
It reminds me of the tiny hole in the in-line restrictor in the partial flow oil filter system. I did not have it initially and the oil pressure dropped to zero and I knew something was wrong. Maybe enlarging the 7/16” hole would have the same effect on the water pressure. I thought I’d run this by the forum members and see if I should just let a sleeping dog lie.
Charlie D.
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