Sidneyhop454

Of course Im having the coolant overflow issue in my 70 bb and was thinking of adding an overflow tank to catch the runoff. Question is will the hose suck it back in to the system once it cools down? Any tips on setting this up correctly would be great.
Thanks!

flyeri

How much coolant are you putting in the system? The coolant level cold should be between 2-3 inches below the cap. Now for you question, it seems that I recall there is a particular cap needed to allow the coolant to be sucked back into the radiator as it cools.

Sidneyhop454

I was filling it mostly to the top of the tank. I wont add any more and see if it evens out to the few inches below the cap.

Easy Mike

Do you have an aluminum radiator or copper/brass? Factory air or AT? Do you have the assembly instruction manual (AIM)?

Sidneyhop454

Standard brass rad, factory air but not hooked up and manual trans. I do have the aim.

AzMotorhead

sambrand

ck the overflow line, I had the same problem and after frustrating days found there was a small hole in the overflow rubber line that would only leak when it was hot and the hose was soft and expanded. only way u could tell the hose was bad was taking it off and stretching it, then the hole was obvious. when the hot coolant was exiting the rad to the bottle the line would expand and the hole would open, trying to find the problem when the engine was cold was impossible.

edit, also be certain that the cap is in good working order, and that the pressure rating is correct for the rad, not all radiator caps are created equal

Sidneyhop454

The coolant is definitely leaking out of the overflow line. Also new rad cap.
As far as the level, its dumping out the entire contents of the overflow tank and then some. Is it possible theres an air pocket in the intake causing a lack of flow? I drilled a small hole in the thermostat to allow coolant to get through but not sure if theres more to do to prevent this?

sambrand

when the coolant heats it expands, when it reaches the psi of the overflow cap it allows coolant to escape into the catch can, as the coolant cools it contracts and the coolant is sucked back into the rad from the catch can. from what you descrine it seems the system is functioning properly so I wouldn't suspect anything on the pump or engine side. the coolant can should have a vent that allows air to enter and exit also preventing pressure from bursting things, if the overflow line has a loose clamp or pinhole siphoning action can easily account for total loss of all coolant passing the line. most intakes will indeed have a small amount of air trapped but unless its a good size bubble this doesn't affect coolant being pumped, if there was too much air the result is that the pump will cavitate and then engine will overheat. these bubbles tend to work themselves through the system on their own ending up venting into the overflow line where the catch tank vents this, a process known as "burping"
repair replace the area from the rad to the catch tank inspecting the nipples to connect the rubber line as well as the line itself for crack or pinholes, burping all air from the system is usally done by multiple heat cycles, filling the rad to where the coolant is visible when the car is idling you should see coolant being sloshed around and occasional bubbles coming out if there is air in the system such as a leaky water pump or rad hose, mind that if you shut off the engine while the cap is off you will have an overflow, aslo after a short time of running the car with the cap off should also result in coolant overflowing the rad, visual inspection of this process can help determine if theres some leak in the rad/engine side, but I suspect its between the rad and catch can.

also check your catch bottle for any cracks or leaks, as you said its a total loss in the can theres a good chance the bottle seam is cracked and as its warm that crack expands allowing leakage, ehn it cools the plastic will contract and you may not see a leak in the can

Sidneyhop454

ok, thanks for the tips.
Also I dont have an overflow tank (clear plastic container), Just the brass expansion tank that the rad cap is on. The neck of which has the overflow line that drains all the fluid out where I have it fished through the wheel well.

sambrand

oh, then if theres no recovery tank the system may simply be ditching excess coolant and you may be overfilling the rad, look for the level marks on the rad on non recovery systems the coolant level is usually around the 80 pernt full on the rad

Hammerhead Fred

With the brass expansion tank the tank should be only half full - the rest of the space is for fluid expansion.
Fill it too much and it will puke/overflow as the expanding fluid has no place to go (you cannot compress a fluid).

Sidneyhop454

Yes, it pukes the entire tank out and probably then some. The tank is empty by the time it cools down to check it.

MelWff

what is the pressure listed on the cap? 15 PSI?
what is the temperature reading on the gauge?

Sidneyhop454

Its a 16psi cap. The temp is around 190*, same as the thermostat installed.

Hammerhead Fred

So, once it's cool fill the system until the tank is just half full - you don't need more than that.

MelWff

Can you have the cap pressure tested?

Sidneyhop454

ok, but it still pukes it out until empty.

Sidneyhop454

Not sure how to go about it. Just guessing, apply 16lbs of weight on the spring portion?

C6_Racer_X

Go to Oreilly's or a similar store. They have "loaner" pressure testers. It's a hand operated pump attached to something the cap will fit on.

Pressure test the cap first. If it's good, pressure test the system in the car.

Your symptoms sound like either a bad cap, or possibly a failing head gasket allowing compression (and/or exhaust) to get into the cooling system. Is it blowing tiny bubbles into the radiator when it's running? If you attach the pressure tester to a cool/cold engine, does it immediately show pressure? Either of those are indications of a head gasket issue.