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Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 26635
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1990 Corvette: can see the coolant on the driveway

Resolved Question:

I have a 1990 Corvette which has a engine cooling problem. I have a slow leak where I have to add 1/2 to 3/4 gal water daily. I can see the coolant on the driveway. I have good circulation from the radiator. But, the water that flows to the overflow resevoir does not get "sucked" back into the system. The overflow resevoir remains at constant "hot" level. When I pump out water from the resevoir back to the cool level, run the engine for awhile, it fills back to "hot" level & remains. I have had freezer plugs replaced on both sides of the block.
Submitted: 9 years ago.
Category: Car
Expert:  Amedee replied 9 years ago.

Sounds like you have two smaller problems contributing to one big one.

First, you have a small coolant leak. This leak will have to be pinpointed and then fixed. If its hard to find, you might need to get in there with a mirror to take a close look. If it is still hard to pinpoint, another good idea is to pressure check the cooling system. This will put the cooling system under pressure so it will start leaking. This will make it easy to identify where it is leaking from.

Your second problem is a bad radiator cap. If there is a small leak, (as your coolant level drops in the radiator) when you stop the engine and let it cool down, the cooling system will draw a vacuum and if the radiator cap is working properly, it will let this vacuum travel to the reservoir and will suck the excess fluid from the reservoir to the cooling system.
Customer: replied 9 years ago.
I have a new radiator cap. Could it be faulty, or is there something else which could prevent a vacuum? The line from the overflow reservoir back to the cooling tank (where I put the water)appears to be ok.
Expert:  Amedee replied 9 years ago.
As long as the TWO seals on the radiator cap are not ripped or cracked the cap should be ok. Just be sure that the seat where the cap sits is nice and smooth.

If you bought a cheap cap, I would replace it with a STANT radiator cap.

You might want to try blowing thought the line that goes from the radiator to the reservoir with the other end plugged up to see if there are any leaks in it.

Also, be sure that the line in the reservoir goes all the way to the bottom.
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