When I bought my 77 Vette last April, it didn't have a plastic coolant tank on it. I ordered one recently from Eckler's, and installed it. It came with no instructions, so I just guessed at how it hooked up. I ran one hose from one of the fittings on top of the plastic bottle to the hose fitting on top of the radiator. On this same fitting on the plastic bottle, I attached a 6-8 inch hose inside the plastic bottle. It goes almost to the bottom. The other fitting on top of the plastic bottle appears to be an overflow, so I didn't attach anything to it.
Once everything was hooked up, I filled the radiator to the top, then filled the plastic bottle approximately half way. Here's the problem: everytime I drive 50-100 miles and check under the hood, the plastic tank is completely empty, and there is coolant on the underside of my hood, directly above the fan. It's done this 8-10 times, and I can't figure out where the coolant is coming from. It's like the fan is slinging it onto the underside of the hood, but there's no coolant anywhere else. The car never overheats, but the radiator coolant level does drop down 4-5 inches and then stays there. The plastic bottle itself is not leaking, and I have brand new radiator hoses top and bottom. I crawled underneath and cannot find a coolant leak anywhere. The plastic bottle shows no sign of coolant coming out the overflow fitting on the top. Could I be overfilling the radiator or something?? The car ran fine without the plastic bottle, I was just trying to get it back to original, as I think these models came with the plastic reclaim tank. It's a 77 Vette/350 motor. Anyone run into this problem before?? Sorry the post is so long. Just trying to cover everything. Thanks,
Kenny

 

You are overfilling the overflow tank and you need a overflow hose from the top of the overflow cap to direct the overflow. Ypur coolant is expanding hot and then coming out the top of the bottle on turns, braking, and acceleration.

When cold, you should have about 1" in the overflow bottle. Hot, about 3".

See the pic for the overflow hose. It is in front of the hose from the radiator but ends above the control arm. Also, you can see the fluid level. That is with my car sitting for about an hour. It is a little lower, full cold.

 

Thanks Steve. Will give it a try. Should the radiator on these cars be filled completely to the top??

 

Yes, if you have a coolant recovery tank, the radiator should be full. Here is how I do it:
1. Fill radiator. Leave cap off.
2. Start engine. Level will drop, top off.
3. Keep squeezing upper hose to get air out, top off.
4. When thermostat opens, upper hose will get hot and level may drop a little more, top off.
5. Put cap on radiator and let car run for a while. Make sure coolant reservoir is about half full (car is hot now).
6. Shut car off and let cool. This will draw fluid into the radiator from the reservoir.

I find that it takes 2-3 heat/cool cycles to purge all the air out of the system. after that, the level in the overflow tank stabilizes.

 

Steve has it correct. You definetly need a short hose on the oveflow to direcxt any excess down and away.

 

Sounds like you have it plumbed properly.

Sounds like your cap me be bad or not the correct one.
Make sure it is of the overflow type. There are 2 types of these, a drop center and a spring center.
Use the spring center one and 16lb test without the pressure release lever.



I always fill the overflow tank full the first time and it will level to around 1/2 full after a few heat/cool cycles.