OLE442

I replaced the heater control valve with a new OEM one, I replaced the radiator with a Dewitt aluminum radiator, new upper and lower radiator hoses and I still had a drip/leak coming from the AC/heater area underneath so I did the heater core bypass, Now, I still have a drip/leak from the AC/heater area underneath and from above it looks like a drip underneath the radiator overflow container. My car only has less than 50,000 miles but know it has many years on it. It's tight in that area and hard to see but is it logical to have an overflow container leak on this low mile Vette? I hate leaks. Experience.info appreciated!

Thanks,
OLE442

blk79nj

What year is the car? Mine leaked from the plastic overflow tank.

Also, your heater core will still leak, even if the shut off valve is closed. It's still under pressure when the engine is hot, just doesn't flow coolant.

OLE442

It's a 1976

I bypassed the heater core just after I put the new radiator in. The heater core and the heater bypass valve should not have an pressure.

After I put the radiator in and re-assembled the rest, none of the hoses or anything to deal with the actual new radiator itself leaked. But, it was dripping back near the heater core/heater control valve. I peeked inside the compartment and it looks like coolant is leaking under the overflow tank so I assume it's the tank. I felt around as best I could and didn't get any fluid on my hand. It's tight in there!!

I guess I'll raise it on the lift, remove the front tire and take the 3 screws out that appear to hold the tank in. I guess after 40 plus years, the plastic could be brittle and have a leak. I'm running out of culprits here....LOL!

Did I mention I hate leaks?

derekderek

overflow tanks are made to overflow if overfilled.

OLE442

The overflow tank is not over flowing.......

BLUE1972

If a hose is damaged internally it can leak at one end.

If a Freez Plug is corroded it can **** and drive you nuts trying to find it.

DAD111

You dont have to take the tire off - Car on the ground so you can reach and hold the tank when removing last bolt. Easy and cheep fix if thats the problem.

OLE442

Took the tank out and it does have a leak by the lower bolt/clip! Have one on order from ZIP!

doorgunner

Thanks for posting the results to help others with similar problems

OLE442

I received the tank from ZIP and installed it tonight. It went in OK but everything on these cars seems to be very packed into tight spaces....LOL! But I got 'er done with a little patience.

Now, I bypassed the heater core with a 1 foot length of 3/4 inch (I think) heater hose from NAPA. It seems like the hose is narrowing down(collapsing) quite a bit from the water pump to the manifold. Is that normal or do I need to get a longer or heavier duty piece of hose? I was also wondering if I should try to make the original hoses connect back and remove the bypass. There was/is no coolant leaking into the interior and is could be most likely that only the overflow tank was leaking in that area? I would like thoughts on this one. What are the odds the heater core could leak on this old of a car even though it's low mile?

Thanks for all your help,
OLE442

DAD111

Depends on if you need your heater or or not. Hook it back up to see if your heater core is good. That's a sharp turn for a non molded hose. Could get a longer PC and try that.

OLE442

I don't need my heater and will wait till next spring to deal with that. Spent too much on the car this year so I'll just wait to deal with whether the heater core is OK or not next year.

I did see on other online posts where some C3 owners just capped the water pump and manifold fittings on the motor. The hoses connect to the engine and then go to the heater core.

They used heater bypass caps. That would eliminate the heater bypass hose kinking. They used Dorman 493-100 (5/8inch) and Dorman 493-101 (3/4 inch) with hose clamps to block off those fittings.

Is that an acceptable temporary fix until next year?

Thanks, OLE442

bikesnbroadheads

I tested my heater core by plugging one of the hoses and made up a tee fitting with a schraeder valve and gauge on the other hose.. put 10 psi in it and it went to 0 psi in a hurry. took the hoses off the heater core and tied the 2 hoses together until I replaced the heater core. not a terrible project. any of the bypasses you mention will work but if you loop a hose between the manifold and water pump make sure it isn't against the hood. p.o of my 71 did that and it blistered the paint on the hood.

DAD111

You should be ok on that setup. Its nice to have coolant passing thru the motor before the thermostat opens with a bypass hooked up. At least you solved the leak all should be good.

OLE442

So, you're saying to leave the bypass hose on and not to block off the connections on the waterpump and manifold with the Dorman rubber covers?

DAD111

Yes you can leave the bypass hooked up. Maybe make it a little longer so its not kinked or touching the hood like someone else mentioned. .

Kacyc3

it circulates through the block to the water pump without any hoses connecting them. I removed my heater hoses and plugged the ports in the intake manifold and water pump 5+ years ago.

DAD111

There ya go - Its proven fact that you dont need the bypass.

540 vette

I have used those with no issues.

OLE442

So, I assume I could just leave the bypass hose between the water pump and the manifold on. It will still flow but is not perfectly round at the curve. Even if it were closed up completely, it would be doing the same thing as the Dorman caps? That would allow me to drive it until I check the heater core out for leaks.