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good afternoon all, I am running the 98-02 f-body radiator and fans in my LS6 conversion and it seems to cool OK, it might get up to 210 or 215 on occasion but going down the highway it settles back down to 195 to 200. I am wondering if I am running the correct radiator cap because it does not seem to burp out the air after a fill and does not draw anything from the overflow tank. I am running a Stant cap that is supposed to be compatible with the radiator but should I try a stock GM one, would that make a difference? Is there anything else I should check out?
Sounds like your over flow tank hose may be leaking (air). This hose from the radiator to the overflow tank needs to be sealed. Check its connection (clamps) to both the radiator and tank as well as the hose itself.
Last edited by Jud Chapin; Oct 15, 2021 at 09:16 AM.
Please check to make sure that the radiator overflow tank suction hose is attached to the tank cap. This hose is located inside of the overflow tank and needs to be submerged under coolant for the system to work properly. Typically the line falls off of the cap nipple and lays in the bottom of the tank, or it is removed by a PO. Without the line in place, the radiator cannot draw coolant back into the radiator when the car cools down. It is Item #7 on the AIM sheet below.
Also, the OEM cap is a 15 psi cap. Check your Stant cap to see if it is the same. Below is a pic of the original cap from my '75.Let
Please check to make sure that the radiator overflow tank suction hose is attached to the tank cap. This hose is located inside of the overflow tank and needs to be submerged under coolant for the system to work properly. Typically the line falls off of the cap nipple and lays in the bottom of the tank, or it is removed by a PO. Without the line in place, the radiator cannot draw coolant back into the radiator when the car cools down. It is Item #7 on the AIM sheet below.
Also, the OEM cap is a 15 psi cap. Check your Stant cap to see if it is the same. Below is a pic of the original cap from my '75.Let
Let us know what you find.
Thanks fellow '73 and '75 owner! The hose from the radiator to the tank is new, as are the clamps, but I did not check the hose that is in the tank so I will check that as well. Since the radiator is from a 98-02 f-body I am using the cap that is compatible with it.
I confirmed the hose to the tank and the hose in the tanks are both secure, there is a hose clamp on the hose that attaches under the tank lid. I unhooked the hose from the radiator and gave it a good suck and got no air, just distilled water, so it is not plugged and there does not seem to be a leak that would let in air.
So a bit off topic but I do have a question. I understand how the radiator cap works when the radiator creates enough pressure to push coolant pass the radiator cap and the coolant goes into the overflow tank. But how does the coolant find its way back into the radiator once the pressure in the radiator is reduced and the radiator cap seals off the radiator neck?
So a bit off topic but I do have a question. I understand how the radiator cap works when the radiator creates enough pressure to push coolant pass the radiator cap and the coolant goes into the overflow tank. But how does the coolant find its way back into the radiator once the pressure in the radiator is reduced and the radiator cap seals off the radiator neck?
The little disc in the middle of cap acts as a check valve, it is held in place with a light spring, it does not allow the higher pressure in the radiator to escape but allows flow to reverse when the cooling radiator creates a small amount of vacuum. You can pull the disc away with your fingernail to kind of get a feel for it. The third graphic here shows how it works:
‘75 LS6 cooling question
