i have a 34 dodge truck with a 350 small block mild cam. problem motor does not over heat but pushes coolant out of over flow tank only at higher rpms. for instance im driving down the road at 60 mph 2000 rpms i get on it say 3000 rpms to pass a car . after i let off it blows coolant out over flow. temp dosent get over 180 degrees. i have put a 7lbs 11lbs and a 16lbs radiator caps on all with same problem. any ideas? i have also checked the oil no coolant in it its nice and clean.
just a guess, does the lower rad hose have a coiled wire in it, to keep it from sucking flat? Cheap to try it.
Is it a down flow radiator, or cross flow? Down flow radiators top tank acts like an expansion tank, and will spew coolant out until it get to its right level.... Sp if you top the tank off it will do what your describing until it rests about the half way mark.... that's half way the top tank, not the radiator...
Is there a problem with the radiator nech where the cap fits? ,preventing cap from seating correctly and holding pressure? There are 2 neck depths 1" and the more common 3/4" ,cap match the neck?
Leaking head gasket? At high cylinder pressures exhaust gets pushed into the cooling system, and it has to go somewhere... Had a OT car do that, just fine when driving slow, but put the pedal to the metal and have the entire engine bay sprayed with coolant from the radiator overflow.
Just my 2c. Sounds like a fluid level problem to me. What difference does pressure make? The fluid level is the same. In order for the coolant to exit the system it must get past the cap. As it heats up, the coolant expands, when it gets to the cap, it flows out. If you keep refilling the system it will keep overflowing. I have a down flow radiator. When I first started driving the car, I filled the tank to the top. Once hot, coolant leaked out. But I didn't add any and the system has not leaked since. The radiator is not "full", but the car does not over heat either.
how full do you keep over flow tank before start up? what mix of coolant? what type of fan, if electric pusher/puller with shroud? high speed water pump? use bypass hose from intake manifold to water pump? condition/pressure radiator cap? run a hood?
I would say that the cap is the wrong style and is not sealing to the radiator, or the radiator neck is damaged and not allowing it to seal.
so tonight i checked radiator cap for fitment. all good there but bought a new rad. cap 22lbs and installed. toped off rad. and drove yes i lost some fluid at first but only about a quart . i guess we will see what happens!
I've run in to the cap issue as well. Exact same problem as you describe. New rad and new cap. Cap didn't seal. Replaced the cap and is fine.
Try a AC RC 33 made for a recovery tank .Once avery thing is equilizad it will be normal just check your tank level
Quit topping the fluid!! Let the thing seek it's level, and LEAVE IT ALONE. Use a puke can and watch your temp gauge. After it quits spitting out the excess, all will be fine.-MIKE
No. The tank catches the coolant that is released by the cap when it expands beyond the capacity of the radiator due to heat. When the coolant in the radiator cools off, it contracts and creates a vacuum, which sucks the coolant from the puke tank back into the radiator. Make sure the overflow hose is submersed in fluid, to eliminate an air gap, otherwise all it will suck is air.
Is fluid going back into the over flow tank? I had mud wasps pack mud into my over flow hose when it was off putting in a new water pump. When I put everything back together it, would spit coolant out. After replacing pump again, cap, hoses, and having radiator cleaned, a friend asked if I checked the over flow hose. Who would of thought that it could have happened. Good luck, I am now working on a 37 Dodge, and hoping for no problems, but we know that ain't going to happen.
If it's a stainless overflow tank like everyone runs, make sure you have the hose on the right inlet and not the outlet.
Being paranoid, I am kind of with G-Son on this, leaking head gasket or similiar. Have you tried running it without the cap on the rad and observing if you see some bubbles. On a reall small leak you won't always see oil/water cross contamination or even have any issues until the car starts running consistantly to the higher side of its temperature range. I did have one wierd problem years ago. I had a seal leak on the water pump shaft. It would pressure up the system when running and push water out the overflow (pre catch can era) and not leak at the pump, then when you shut the car off the pump would leak a minor amount from the small hole on the shaft casting until the pressure dropped then stop leaking.
okay so i have gone up to a 22lbs rad cap and thought problem was fixed. wrong!!! so tonight put a pressure tester on rad. pumped it up to 22 lbs and it slowly bleds off. so next i pulled all spark plugs and numb 6 was wet. next i pulled the head and checked gaskets. all seamed to be good, but on inspection noticed more like oil in the intake runner for the number 6 cylinder. does this sound right for a cracked head or could it be the intake.
The tank will never stay full. Its an expansion area. top it off, and it will puke antifreeze out till it settles... If you have a cracked head, you would see air bubbles coming out while running at operating temps with the cap off.... But you still have to let the fluid level settle.... Normal range is about an inch over core tubes.... Not full
machine shop confirmed that i had a cracked head on the number six cylinder. the crack was between the valves causing me to have to much preasure in radiator. thanks for all the feed back
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