Mechanics

WHAT MIGHT BE CAUSING COOLANT TO TRANSFER FROM THE RADIATOR TO THE OVERFLOW TANK AND NOT GO BACK?

2002 Dodge Caravan • 110,000 miles

The radiator cap has been replaced twice and the hose between the radiator and overflow tank has been replaced. There are no coolant leaks. Had a mechanic pressurize the radiator and perform a leak-down test to see if there was a cylinder head or intake manifold gasket leak-none. The temperature gauge reads normal. The coolant transfer isn't constant. It seems like the system really doesn't like 100% coolant in the radiator. When it drops enough to raise the overflow tank roughly 2 inches above the min line in the overflow tank, it seems to slow down. However, that may just be a coincidence. If I let the car come up to temp with the radiator cap off and rev the engine, the coolant drops in the radiator and then surges up when the throttle is released, which almost seems like trapped air. However, the front end of the car was raised to get the radiator cap to be the highest point and purge all air. The problem was discovered when sufficient coolant transferred to the overflow tank to cause the engine to overheat briefly. I also replaced the cooling fan relay since the mechanic mentioned they are problematic with this car.
Avatar
GEARHEAD100
May 6, 2012.



No, it is normal for the coolant to lower at high rpm and burp at idle.

You have a loss somewhere but you need dye in the system to determine the leak

Roy

Hi Roy,
I don't seem to be losing any fluid, it just moves from the radiator to the overflow tank.

Tiny
GEARHEAD100
May 6, 2012.
Ok, sorry. That is usually an indicator of a bad cap but you replaced it. Did you use a new one?

Roy

Roy,

I've tried 2 new Stant brand caps and 1 Murray. The Murray was low quality and I quickly got rid of it.

Tiny
GEARHEAD100
May 8, 2012.
Is the top of the radiator itself where the cap goes damaged in any way?

Roy

Not that I can tell. I used a pressure tester to pressurize the radiator and it held pressure. If the car sits for several hours after being driven, it still has pressure when I remove the cap. I used a depth micrometer to check the variation in depth from the top sealing surface to the bottom sealing surface in the radiator inlet and it only varied by a few thousanths of an inch.

Tiny
GEARHEAD100
May 8, 2012.