My newly acquired 72 Coupe SB has a slight problem. When run up to operating temperature for 20 minutes or longer, radiator fluid is lost at the overflow hose. This has happened (3) times now. The car does not overheat when driving. My thoughts are that the previous owner overfilled the radiator, or that the cap is bad.

Anyone have this type of problem and can give me some help??? Also, it has been a while since I flushed a radiator / cooling system. Can someone give me the quick rundown?

Thanks,
Dino

 

I would try replacing the cap first.

Cheap and easy.

As for the flush - NAPA has flush kits with instructions that are easy to follow.

 

do you keep putting more water back in?

if so, chances are its overfilled and is just leveling itself off.

 

my 70 does not have an overflow tank. it's just a tube to the ground. the radiator fluid stays about two inches from the top. no overflow ,or overheat problems...

 

I did have that problem, and I chased it around like a dog chasing his tail before I finally figured out I was simply overfilling the radiator!

This may or may not be your problem, but the first thing to do is check your user's manual or service manual. With the 1968 model year (again, 72 might be differerent, check the manual) the service manual (and owners manual) specifically says to fill the radiator within 3" of the filler opening. Now if you stick a ruler in there and measure 3 inches, it looks like the radiator is half empty! What I'm saying is, factory spec is a lot lower than a normal eyeball just fill it near the top might do.

So, hopefully that is your problem. It was a real PIA for me, I'd be sitting at a stoplight and start spewing coolant on the street, or come back from a drive and shut off the engine and start spewing coolant all over the driveway. I tried all kinds of things to stop the engine from "overheating." My mechanic told me to attach an overflow container and stop worrying about it (great advice) , but I had to figure out the overfill problem on my own.

 

Thanks for all of the info. I have not added any coolant to the car since it started happening. My thoughts were that it was overfilled also. I hoped that after the first two times, it would just level off. I may just replace the cap and look into adding an overflow bottle.

Thanks,
Dino

 

Im glad I read this thread cus Ive recently replaced the rad/upper rad hose/ and put in an electric fan. The car is running a ton cooler than before but I was still losing so coolant from the cap so I was adding alittle to "top it off". Must have been topping it off to overfilling it.

 

I have a '68 with the TH400 and copper brass radiator. I had a similar problem right after I purchased mine. After shutting engine off, it would puck up antifreeze for a short while, then stop. I replaced the rad cap (15#) and flushed the system, then refilled with a perfect balance of 50/50 mix to obtain a 262 boiling point. After that, even when going through a parage for 1 hour at 5 mph or less, it would not puck up. I think in your case, make sure the mixture is correct and the cap is doing its job....

P.S. I also agree with the previous statement that the fluid needs to be at least 3 inches below the top of the filler neck.

Gonzo

 

A new radiator cap, a professional radiator flush, and proper coolant solved the same problem for me.