I have a 1946 flathead, 21" tall radiator, high flow water pump from speedway. when I drive it under hard acceleration the water is pouring from my overflow pipe. not that much if I drive gently, but still a bit. so when the radiator get low on water it over heat badly. I have a 7lbs pressurise cap, try to run 180degrees thermostat or nothing. nothing changes. Did a compression test all cylinders are good, tested block for cracks too. Any idea of what to do next?
Pull off the bottom radiator hoses... Loosen the top hoses and rotate them 180 dgrees... Take off the radiator cap... Stuff a full flowing 5/8 inch garden hose in each rotated top hose... The radiator should handle the flow readily, if water backs up and overflows through the filler neck, you have plugged tubes if it's an old stock radiator, or not enough tubes if it's a new radiator. Restricted flow through the core could lift the 7# cap.
How good is your radiator? Maybe the high flows are pushing too much water to the top of the tank before it can flow down. 4lb cap.
did a test for exhaust gasses, all looks good. Have no water leak in the head gasket either... If I rev hard in parking nothing happen, it is just when driving.. radiator is new, had a old school radiator guy look at it and it say all was good its a good radiator. not sure how many core is it tho. was going to try 13lbs cap and ad an overflow tank.... could a be an head gasket, even if their is no visible symptoms?
Make sure you have the right pressure cap and that it is sealing good. What kind of temps are you running at speed and around town? Butch
it run around 175/180 when not going hard with fan on (town or highway), as soon as I look water it goes up to 200.
You are going to cause yourself a world of hurt by upping the rad cap pressure. Those long top rad hoses WILL collapse flat with a pressurized cap. -any pressured cap. The constant strain of cycling between collapsed and round will quickly destroy the hose's structural integrity and it will fail. The hose will collapse both while operating the vehicle as well as after you have shut it down. Once you shut the engine down the rad/system goes into a negative pressure as the water cools. This will suck the top hoses flat as the pressured rad cap will not allow any of the previous lost air/coolant to re-enter the rad. While operating the engine, the action of the water pumps will cavitate the system and suck the rad hoses flat. Ford didn't use a pressure cap until about 49 or 50. Placing an 'anti-collapsing' spring inside the rad hoses may help but the hoses will still be stressed as they are made for a non pressurized system and are not heavy-multi ply and are not designed to take any pressure at all. Remember, for every action there is an equal and opposite reaction and cool down suction (at the rad cap) is the opposite reaction of warm up pressure relief. just my humble opinion.. moe .
Your issue is with the radiator, if its a used radiator it could be plugged, if its a cheapo" I got a deal one" then most likely it has small tubes and poor flow. So the question is what are you using for a radiator or what was it intended to be used on?
I have aluminum top hoses. My radiator was custom made by a good radiator shop, not on a cheap side at all. had it checked yesterday by a old school radiaotor who know flathead and he said that my radiator was good...
I was going to say the same as #6.... Take the radiator to a known good shop,...it may need to be recored, if it's restricted too much. 4TTRUK
I had a 37 flathead and it overheated at highway speeds,but not at low speed. A dirt track racer told me my water flow was to high and did not cooldown in the radiator. Told me to remove water pumps and cut back on the fins to slow it down. Tried to restrict flow by other means. Did not work. Did his trick and it worked. Try it on a pair of old pumps first. Good Luck Bill
Your radiator is only good if it physically flows all the water it's getting from the pump. The test I suggested is simple, quick, and costs nothing and you are in L.A, so you don't have a weather problem like up here, why not do it and eliminate or identify a possible problem? You could also just remove the radiator cap and watch the water in the top tank. I would drain it down to just above the tubes in the core assuming it's not a cross flow. Then start up the engine and increase the rpm's gradually while watching what's happening in the top tank. If the water flow into the top tank seems strong and the level over the core stays steady, you should be good. Some previous info posted here is not true or accurate. Be careful of what advise you follow. You don't mention if your radiator is copper brass (which will handle a 20 lb. cap) and transfers heat better, or aluminum (many of which will handle a 30 lb. cap) which is stronger. In either case a 13 lb. cap would be fine and a recovery type radiator cap will pull any coolant back from the overflow tank (which is vented). The 13 lbs. would only also be reached if the cooling system is restricted somewhere, can't handle the flow, and the pump is capable of building that much pressure. While I have looked in the past for typical figures for pump pressure and volume, I have come up empty on a pressure figure. Rubber radiator hoses will not be affected in any event. Of course the 13 lbs. can also be exceeded by a completely filled system when the temperature rises and causes expansion of the water, or worse when the engine is putting more heat into the coolant than the radiator and cooling airflow can dissipate and the coolant temperature rises above the boiling point for that pressure radiator cap, creates steam which due to it's large volume needs to escape.
I wouldnt cut the impellers on your pumps. Thats just a band aid cure for another problem. Flatheads run notoriously warm and 200 is not a worrysome temp. Id try another cap first, same pressure, and rule that out. Definitely do a retorque on your heads regardless. Thats a must on flatheads.
A 21 inch rad isnt all that big either. So your forcing a larger volume of water through a smaller space. It has to go somewhere. Upping the cap pressure in my opinion is not a fix but might help the overflow. Over long runs you will probably overheat quicker.
I used 1/2" top hoses on my A/59A to slow the flow rate down. It worked, so I put restrictors in the top hoses. That worked for my problem; hope you can cure yours. Davo.
See you are still in the inquiry stage so lets get a little more specific, a 42-48 radiator core is in the area of 21" high by 20" wide by 3 " thick so your new radiator should be that approximate size with at least 3 rows of tubes. If it is the next question is to check the flow so this goes back to the suggestion of 28dreyer, pop the cap and observe the water flow as you increase the engine rpm, If the water flows thru unimpeded and doesnt buildup in the tank then the radiators ok and there is something else to check. If the water builds up and it is a new radiator first check the size of the tubes. If the radiator tubes are too small they restrict the water being flowed by the pumps. You should have a tube size about 1/8" opening x 5/8" wide and minimum of three rows deep. You can check the tube diameter using a 1/8" piece of welding rod to determine size. If a piece of welding slides into the tube thats the size , if it doesnt then the tubes are small. What are your results?
I was assuming the 21 inch radiator was including the upper and lower tanks. A cut down rad, based on the avitar. If it only the core messurement then your in better shape.