coolant in a 12

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    I took my ’33 836 out for a 25 mile run, mostly at 45-55mph. It’s HOT here today, around 90*+ and sunny, so the roadway airtemps are over 100*.

    The engine temps only climbed above the 1/2-way mark on the gauge when running 55 with a slight tailwind.. this is a vast improvement over the overheating I was experiencing at Rochester Mn. I’d like to load up the car and pull some long hills to see how much hotter it will get, the halfway point on the temp gauge is a laser-thermometer measured 155-160*. When the gauge is at the top, the water is at 210*. Right now I was unable to get much above 1/2 way.

    So the one or two tablespoons of rust flakes that blew out with the reverse flushing seems to have been the culprit.

    The method I used to reverse flush the radiator is quite simple. Remove the upper radiator hose from the engine outlet fitting, leaving it attached to the top radiator inlet pipe. Extend the radiator hose with a long length of PVC pipe and elbows if needed, Glue the elbows if used, and put the open end in a trash can. A clean trashcan if you want to inspect what is flushed out. A 5-gallon pail will work, but the engine holds at least this amount of water, so you will overflow the bucket with each flush of the cooling system.

    Then hook up a blow-gun to your air hose/air compressor, and wrap a rag around the end of the blow gun, making a golf-ball sized ‘plug/adapter’ on the end of the gun.. insert this rag plug and blow gun into the water outlet where you disconnected the upper radiator hose. Push firmly st seal the rag to the pipe.

    With the cooling system full of water, fill the engine with compressed air through the water outlet, this huge bubble of air will force the water down through the head, the water jacket, through the water pump, into and through the bottom tank of the radiator, forcing the water backwards through the radiator and pushing all the crud sitting in the top tank and covering the radiator tubes out the upper hose and into the trash can.. Refill the cooling system and repeat several times.

    You must have a sealed radiator cap installed. And V-12 engines will need the other upper radiator hose to be removed, and the outlet covered with either duct tape or heavy plastic tape, then the radiator hose reinstalled.. You want to introduce the compressed air into a sealed engine cooling system with the only outlet the top radiator hose. I didn’t bother capping or sealing the overflow tube, it’s rate of leakage with this flushing system is negligable.

    V-12 owners, don’t forget to remove the tape sealing the water outlet on the other head before starting the engine !!

    Greg L


    Still waiting for the long muffler to arrive, the resonator is already here. I drained the antifreeze, refilled with water and flushed three times. Did not get more than a few flakes out, so it is clean. Then filled with water, made certain the radiator shutters were wide open and drove 10 miles in 95 degree heat. I checked the temp. several times and it stayed at 181 degrees just as before. I can now check these off and wait for the muffler. Doug


    Just took the 12 out for a test drive after getting the new exhaust system installed. This included a resonator, a five foot muffler and the 2 1/4 inch pipe the whole lenth. The temp. was in the 80’s not the 90’s as before. I got 165 degrees after 10 miles and 172 after 14 miles and the 1000 ft. 11% driveway up to the house. This MAY have been my heat problem, but I will try another trip on a hotter day . Doug


    The rest of the story…..or should I say the end of the story in my cooling case. The cooling problem was First the timing was off when checked with a timing light, second the radiator shutters were not opening all the way. Third, the exhaust was possibly too restricted. I just took the car on a VMCCA tour and the temp. stayed at 171 . I still have many things to do but the running hot is behind me. Thanks to all you guys for your help. Doug


    I’m glad you are running cooler! At first glance, changing from 2″ to 2 1/2″ pipe may seem insignificant, but it actually increased the cross sectional area of the exhaust passage by 50%. John


    Thanks John, And there is nothing like knowing that it is done right. Doug



    I’m not an engineer like you are, but I calculate the cross section incremental increase from 2″ pipe to 2.5″ pipe as 25%, not 50%.

    The round cross section formula (= that for the area of a circle) is, I think, 2 x pi (3.1416) x r(radius) which would give 6.2832 sq in for 2″ pipe, and 7.854 sq in for 2.5″ pipe, for an increase of 25%. This is still very much worth doing, in my opinion, but if my calcs are correct, the additional exhaust evacuation potential is 25%.

    It would seem we are still limited by the exhaust flange diameter and the ability to make a radius bend to go from vertical (downpipe) to horizontal pipe (under car) direction, even though the horizontal pipe may ‘grow’ to 2.5 inches, which would seem to reduce the 25% improvement a bit. Does anyone have any suggestions for using the maximum possible diameter for the downpipe using a factory flange?




    You may be correct, but for the wrong reason. The correct mensuration formula for the area of a circle is pi x r squared (2pi x r = circumference). John is correct, a 2-1/2″ is larger in area than a 2″ pipe by about 50%.

    However, Doug’s posts only talk about a 2-1/4″ system, which would be about 27% larger than a 2″ system.

    Regarding your concern for the header pipe size. This is a twelve with each bank’s pipe coming to a siamese joint just before the first muffler. Each pipe only needs to be 1-3/4″ diameter to be half of a 2-1/4″ system.



    Yep-I looked back and see the correct system is 2-1/4, not 2-1/2.-thanks Bob. It sure is interesting and important to mindful that such a modest 1/4″ increase of diameter at this size pipe represents a 25%+ addition in cross area.”


    Bob is right on the formulae for calculating area and circumference of a circle. My sixth-grade teacher would have me in a corner wearing a dunce cap! Thanks, Bob!

    Any ideas on the most practical location to enhance an 8-cylinder’s pipe size?


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