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The 7/16 inch hole in the water manifold is bugging me.

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  • Cool/Heat: The 7/16 inch hole in the water manifold is bugging me.

    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.

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  • #2
    All is well.
    That hole is a "bypass" hole. EVERY system needs a bypass, or else you have air pocket problems. Chevy, Ford, Chrysler, all off shore coolant systems have a bypass of some sort.
    Big Chevy...the small 90 degree hose that runs from the manifold to the water pump...a bypass. Small Chevy, one leg of the water pump to block has a second hole in it...a bypass.

    It has NO effect on the "amount" of water "in" or "passing thru" the radiator.
    It's actually sort of a built in...leak..!

    Actually, I don't know of anyone making it larger or smaller. Me, I'd let it be as it is.



    • #3
      I agree with Mike.
      Overheating can be caused by bad timing.
      Late timing sends a lot of heat into the coolant.
      A bad thermostat may not open when it should.
      A clogged radiator won't transfer heat to the air.
      A clogged cooling chamber in the block won't transfer heat to the coolant.
      This is rare, but I've seen fans installed backwards, so they don't pull much air.
      Also rare, but I've seen thermostats installed upside down.
      Last edited by TWChamp; 02-22-2019, 02:13 AM.


      • #4
        When I bought my 63 R1 Cruiser I drove it to the Orphan Drags in Brown County,IN. While I was there someone commented that the clutch fan's blade was on backwards. A PO had installed it that way and I'd never paid any attention to it. The engine ran hotter than I liked when idled. After I changed it, it helped the heating problem, but what helped the most was installing a fan shroud from SI.


        • #5
          I am a big FAN of adding a shroud, it did wonders for me.


          But mine is a Lark, so not sure how easy it would be to get one in a president. You may also have one already....


          • #6
            Do not make the hole larger. The hole's purpose is a to allow some amount of coolant to bypass the system during times when the thermostat is closed. If there were no hole, cavitation would result when the T-stat was closed. Also, if the hole were made bigger, the efficiency of the pump is reduced because of the increased bypass. As others have mentioned, it also helps to give air bubbles a path out of the system when doing a re-fill. There is a certain amount of science that goes into sizing those holes.
            Mike Sal


            • #7
              A coolant recovery tank will allow air to be purged from the cooling system. Air doesn't transfer heat very well. I agree; a lot of cooling problems are air flow thru the radiator related. I usually don't put a thermostat in unless the pemp won't get up to the 150 to 170 deg range and with Studebakers that would be unusual. I've put 2 Al+ radiators in 2 Hawks and they do seem to work well.


              • #8
                Here's an experience I had with the water manifold on the Plain Brown Wrapper. As most of you know, I bought the R3 engine new from Paxton Products in 1964. It came with the appropriate Avanti water manifold that all R3s had from the factory. From the time the engine was new, the warm-up sequence was strange: As the engine warmed up and the coolant temperature increased, the needle on the temp gauge would go much higher than a normal reading. It would go almost all the way up. Just when you're beginning to wonder if you should shut it down, the guage would suddenly drop back to normal (needle in the center of the gauge) and it would remain there for the rest of the time the engine was running. This happened every time the engine was warmed up from cold.From 1964 through 2010, the engine had been rebuilt twice. The block had been boiled out and cleaned twice. During those years, I had tried several different thermostats; we carefully checked for obstructions and debris inside the coolant passages, but found nothing. Finally, during assembly after the 2010 rebuild, I was cleaning and painting the water manifold. The thermostat had not been installed yet, and I happened to look down the hole below where the thermostat would be. I noticed that the bypass hole was mostly blocked by a casting flaw. I carefully knocked out the flashing that shouldn't have been there with a round punch; this increased the diameter of the bypass hole to approximately 7/16", as mentioned in an earlier entry in this thread.From that time on, the engine has warmed up normally--the temperature gauge stopped it's unusual dance and it has operated as it should. Obviously, the blocked bypass hole was not allowing enough hot coolant to reach the thermostat so it would open normally. Therefore, it required a higher coolant temperature than it should have to open the thermostat.So if your engine warm-up cycle is unusual, check that bypass hole to make sure it is the diameter the factory intended. George
                george krem


                • #9
                  Yes, in addition to what George discovered, if you install a thermostat in older cars that never came with one, nor a bypass, such as My Model A Ford, then I drill three 1/8" holes in the lip of the thermostat to allow coolant to flow by the wax pellet in the thermostat. This gives it a smooth opening as the engine comes up to temp. I also made my own bypass, which will later be the feed and return for a water heater under my floorboards. I'm not sure when Studebaker first used thermostats, so this may not apply to them.

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                  • #10
                    The bypass hole was originally 5/16" in the first 1951 V8's. A bulletin advised to enlargen it to 7/16". It's been that size ever since.
                    Another thing about wearing a mask......I don't have to shave before I leave the house!


                    • #11
                      What you are missing charlie, is that the majority of the water (coolant) is not coming from the 7/16 Hole, the hottest water flows as it rises from Front to Back in the block, Rear to Front in the Heads and then through those 2 water Manifold "Arms" from the Heads through the Thermostat to the Radiator, so as has been said, that hole is merely a Bi-pass and does not make the engine hotter, you just over-thunk it!
                      Second Generation Stude Driver,
                      Proud '54 Starliner Owner


                      • #12
                        As others mentioned, is the fan shroud in place?

                        I assume the temp gauge reading high is the symptom of overheating ?
                        I would carefully feel the face of the radiator when that is happening. Top, bottom, left and right. Also measure and record the temperatures with a point and shoot infrared thermometer.

                        Post the results here.


                        • #13
                          At first, i will replace all frozen plugs, and clean the engine Click image for larger version

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                          GT Hawk 62 V8
                          Lark 62 hardtop skytop 6 cyl
                          Silver Hawk 57 Hardtop 6 cyl
                          Transtar 57 V8
                          Starliner 54 V8


                          • #14