yes, sorry for late response.

 

So the “new” over flow tank arrived. The cap is stripped but with plumbers tape i believe it’s tight enough (hopefully). What a pain getting the old one out and new one in!
I was excited that the new one has the lip to hold the battery in place, vs my zip ties on the old one. Well now I know why the lip was broken on the old one- because the battery doesn’t fit! Apparently rather than get a slimmer battery that fit, the previous owner chiseled the lip off the reservoir tank!!!! So now it’s off to auto zone for a battery.... this reservoir tank better not leak! (Actually the little metal tube that GM in their wisdom doesn’t make anymore)

 

Final (?) update- I’m an idiot- i measured and my battery fit perfectly. So it’s all back together. I need a little bit of coolant to bring the reservoir tank to the proper level, now just the waiting and watching for leaks game. I’ve got to make sure it’s ok before a 5-hour round trip ride to relatives on July 4th!
Can anyone comment on how important it is the reservoir tank cap is super tight? And anything better than plumbers tape?

 

I don't think the tank itself has to seal tight. As long as there is coolant above the reservoir hose inlet of the tank, a vacuum will be created in the radiator to return any coolant back to the radiator as the system cools down. In other words, I think the coolant in reservoir tank creates the seal for the tank that allows a vacuum to build in the radiator as long the rest of the cooling system is sealed.

You know I'm wondering, have you tried to see if your old cap fits this tank any better? They should interchange I think.

 

Yeah the old cap doesn’t fit any better. I put a little more plumbers tape on it and it’s pretty snug. Thanks for your help!

 

Well jumped in the camaro to bring it over to the shop for control arms, and the low coolant light came on. Sure enough the radiator was low, so I added a bit, maybe a pint. I thought I’d put the proper amount in the new reservoir tank, maybe not. I’ll monitor it, but I have a sinking feeling it isn’t drawing coolant back from the reservoir tank as it cools down. It’s at the shop now, should I ask them to do a pressure test? What does that entail?

 

These pages from the 1994 service manual describe pressure testing the radiator. This tester will also test the radiator cap, so if you have them test the radiator, I would also test the cap.

 

Thanks. I will ask them to do that. Could a faulty cap cause the radiator to not draw coolant back?

 

you also may be losing coolant while your driving (as its heating/pressuring up) at such a slow rate you dont see the leak. if its not drawing the coolant back into the radiator then the coolant level in overflow tank will get higher. it has to be going somewhere.

 

I would think it could, but I can't say for sure. If the cap didn't sealed right, there would be no vacuum created in the radiator as the system cooled to pull any coolant back from the reservoir.