I am working on my son's 1978 Delta 88 with the 350 Olds (R) motor.

It loses coolant down to a certain level then seems to hold its own. When I add coolant to fill the radiator, my son complains about the motor running roughly for a while, then it seems fine again.

I suspect I have coolant leaking into a cylinder when it's full causing this condition. After the coolant level drops a ways I have to assme that it isn't pushing as much coolant in and it's fine again.

There is no coolant leak externally that I can find. Also, no sign of coolant mixing with the oil. Also, no apparent overheating...

I imagaine that I probably have an intake gasket or a head gasket leak. I really don't want it to be the head gaskets

Is there a way to detect whether the leak is intake or head gaskets? In my fantasy world, I'd like to confirm it's an intake leak that I can fix without having to mess with removal of exhaust manifolds, messing with lifters/pushrods etc.

But obvioulsy if there isn't a trick to be sure it wouldn't be worth pulling the intake and not finishing the job while I was already part way there.

Any suggestions would be much appreciated!

 

Is it blowing white smoke out the tailpipe? A lot of smoke?

It would be a thick white cloud.

I had this problem with a 307, but it turned out that it was the heater control valve and heater core leaking very slightly.

The 68 350 lost some coonlat too, but that was the bottom of the water pump.

It will find a way out

 

Nope.. no noticeable smoke. I haven't been able to find any signs of external leaks.

The running rougher when the coolant is topped off makes me think the problem is more internal.

Thanks

 

My '84 307 is leaking somewhere too. If it was the heater core, where could it be detected? Or how?

 

If your heater core was leaking, white smoke and/or liquid coolant would be coming from your glovebox.

 

Okay then. I'm good to go. Thanks.

 

Does your son's 350 have an aluminum intake manifold on it? If so it could be leaking at the intake manifold due to the aluminum expanding and contracting at a different rate than the rest of the engine. This was a common problem with the 307s in the 80s.

 

Dutch, I love that custom Buick in the picture. I don't think that coolant level dropping some would neccessarily cause the leak to stop. In a pressurized system a leak is a leak in the entire system regardless.

 

Can you do a pressure test on the cooling system? Or...add dye to the cooling system and use the right light to check for leaks?

I won't say you don't have a problem, but my car does not like a FULL radiator. It will allways puke out about a pint, and runs about 2" low.

 

Don, you can get an additive called Zyglo that glows under black light. It is used to identify those hard to find leaks. Just clean off the engine, add the Zyglo and run the car for awhile. This stuff works pretty well, I have used it before. They make different additives for oil, antifreeze, transmission fluid etc.

 

Bad cap perhaps, mine did the same thing.

 

Yea that stuff does work, I use the inertia dynamics brand of dyes and light. I just thought the originall poster might have luck trying it.

About that cap, yea maybe I should replace it since its about 37 years old

 

I used to do zyglo/dye penetraint with a black light when I was in the aircraft business many years ago. I myself have a radiator with slight leaks thats also 37 years old. New is about $300. I also haven't been on the forum, since our ice storm left me without power for over 6 days.

 

Thanks for the guidance, guys...

Here recently the radiator began to leak. Now, I don't think it has been before. We park the car on cement and I didn't see any leakage on the ground prior to real recently.

I installed a new radiator yesterday. One thing I did notice was that the old cap was a 7# unit. The new cap I got with the radiator was a 16#.

I would have thought my recovery bottle would have been full if it was just pushing it out through the cap.

I'm wondering if the cap that was on there was an attempt by the PO to keep the radiator from building too much pressure and leaking. The more I look at the old coolant, I think there may have been some stop leak in there


Oh well, we'll try this for a little while and see what happens.

Thanks again everyone. I'll let you know how we make out...

 

16# cap should be fine. I'd also suggest either test it (yea right) or replace it.