Why after checking for correct liquid levels does coolant leak from 1966 Corvette pressurized coolant reservoir overflow line after engine is shut down for 5 minutes or so?

Answer 1

When you mentioned you had checked for correct coolant levels what do you mean or think is correct? If you are filling the coolant level to the top of the radiator neck when the engine is cold (then you are overfiling the radiator - keep in mind your vehicle does not have a coolant recovery tank), once the engine heats up the coolant will expand and if the radiator was filled to the top of the radiator the expanding coolant will overcome the cap pressure (listed in psi on the top of the cap)I would recommend leaving the coolant level down approximately 1 inch from the overflow hose. If you are not overfilling the coolant level then it could be caused by a defective radiator cap. The pressure rating on the cap can be used to test the relief valve by using a radaitor/cap pressure tester (your local parts store more than likey has one that is available for customer use. Bottom line is a typical radiator should have a rating of 14 or 15 pounds. When they test the cap it should hold whatever the rating is on the cap. You will notice when the cap is tested it will quickly go t the rated pressure and slightly above then it should release the excess and remain at the prescibed poundage rating on the cap. If it does not hold replace the radiator cap. When you replace the cap I highly recmmend that you order one from your local GM dealer, due to the mettaurgy of the radiator (usually aluminum) if you put on a normal radiator cap you may end up with a problem with electrolysis which could cause pin holes in your radiator, heater core and even possibly in heavier metal parts. Again I would highly recommend that you replace it with OEM parts. Do not rely on the individual behind the counter at a non dealer parts house. He or she may not have the technical training and it couldcost you a $1,000.00 radiator. As I indicated earlier it is important to insure the radiator cap is working properly since 1 # of pressure increases the boiling point of water 3 degrees (at sea level). For example a 15 # radiator cap X 3 degrees would equate to raising the boiling point 45 degrees (3 X 15 = 45), add the 45 degrees to 212 degrees (the boiling point of water) and you end up with a boiling point of 257 degrees. When a car has a 190 degree thermostat it is designed to keep the car at approx 190 degrees as long as the car is running which will allow the water pump to circulate the coolant through the radiator which will allow the heat to disipate from the cooling system. When you turn an engine off the coolant temperature will raise 20 to 50 degrees, if it is already at 1190 degrees when running and it raises 30 degrees the temp of the water now exceeds the boiling point of water at sea level (if the radiator cap is not working the pressure would be the same as atmosheric presure) in other words the temp would be 190 + 30 = 220 degrees or 8 degrees above boiling and the coolant will boil and overflow. To diagnose your problem determine the proper coolant level, insure the cap holds the proper pressure and if there are stil problems you may have a radiator of coolant circulation problem with the engine. I did not discuss the fact that properly mixed oolant will also raise the boiling point of the coolant but the mi is more than likely not the issue unless you have pure anti-freeze. Good Luck Rich lennon@triton.iccc.cc.ia.us