LudemJo

So, I am looking over the MSD distributor in preparation to run through some checks of ignition timing, and I look over and my top radiator hose is flat as a pancake!?! The engine was stone cold, and hadn't been run today at all. I opened the radiator cap and heard the vacuum release and the hose returned to normal shape. The overflow tank was at the hot level, so it almost seemed that the radiator was not able to pull fluid from the overflow tank as it cooled. So, a new radiator cap, or ????

John

MakoJoe

I would check the overflow hose for blockage first then if it is good replace the radiator cap.

Sounds like you see it and the spring or the hose is not allowing the return of the coolent into the radiator.

jnealg

when I bought mine the PO didnt have a return hose. I noticed an antifreeze smell one day and the car was over heating.
Turns out the rad was pumping into the reservoir but not getting anything back. The reservoir was overflowing and the rad was purt near empty.

I couldnt find a replacement cap with a return line so I just stuck a vacuum line on and called it good. several months later all is still good. If I run across an orig at a swap meet I will snag it then.

MakoJoe

Did a little more research and looks like the Corvette Cooling system requires a 16 Lb Radiator cap in the model years from 1971 till 1998 for both big block and small block engines. Found a cool Mr Gasket cap that has a thermometer built into it for $25.00 bucks. Hmm might have to get me one of them

LudemJo

Thanks MakoJoe. I may look into that Mr. Gasket cap as well. It would be nice to have a backup coolant temperature gauge...

John

mds3013

Radiator cap needs to have a one way check valve. This is located in the center bottom of the cap and is an upside down brass cup. When a cooling system is brought up to temperature the ck. valve closes off and will not allow any coolant to flow into the recovery tank. When the system cools down the extra space caused by expansion will produce a vacuum on the system. The ck. valve opens and allows coolant from the recovery tank to be drawn back into the radiator and releases the vacuum. I think you have the wrong radiator cap or the ck. valve is defective. Look at the AC Delco RC-33 radiator cap. mike...

http://www.ebay.com/itm/GM-AC-DELCO-RC-33-RADIATOR-CAP-1973-TO-1978-CORVETTE-CAMARO-AND-OTHER-GM-CARS-/281153565510?pt=Vintage_Car_Truck_Parts_Accessories&hash=item41760ef346&vxp=mtr

noonie

there are two types of caps with either a spring relief valve or a weighted (no spring) relief valve.
The spring type seem to hold up better over time.

BKarol

My owners & chassis manual, specification guide calls for 15lb not 16lb. You should check your manual for the correct one.