ODD Surge Tank Problem

[nate_o23]

I have a 85 sub with a 6.2 that has a small leak in the radiator which requires me to top off the radiator from time to time. One thing I have noticed is that the level of coolant in my surge tank never goes down. My understanding of the cooling system is that if the radiator is low, as it cools it creates a vacuum which opens a valve in the rad cap which sucks in fluid from the surge tank. This is not happening in my sub. I have replaced the rad cap and that didnt make a difference. Any other ideas?? Thanks

[trbankii]

My guess is that the hole in the radiator is keeping the system from having enough vacuum to pull anything back in from the surge tank. As things heat up, the pressure forces fluid out of the hole. As things cool down, it sucks air back in the hole rather than overcoming the radiator cap valve to pull fluid in from the surge tank.

I've had that exact problem on other vehicles. You check the surge/overflow tank and don't see a problem. You open the radiator cap and are amazed to see the fins without any coolant...

[ZZ]

My radiator had a slow leak like that. I used a small tube of the powdered Stop Leak in it and it hasn't leaked a drop since. I made sure it was fully warmed up and then drove it 30 minutes afterwards to keep the heater core flowing & etc.