View Full Version : My first cooling problem

Mr. Snake Car
01-07-2007, 07:42 PM
Okay, okay. I know that most here like to discuss mods and preformance. Allow me, however, to take you back to the basics for a second to help me trouble shoot an overheating problem. Changed the coolant after I experienced my needle dangerously approaching the dreaded 'red 'H' Sat afternoon. In order to fully refill the raidator I filled the reservior (degas tank) and cranked the engine to circulate the fluid through in order to make room for more, thereby filling the cooling system to capacity (14.1qts). However, after I cranked the engine nothing happend to the fluid level. It was as if the pump wasn't working and the fluid was remaining static within the hoses, water jacket, etc. ANd of course this is my diagnosis but I was wondering if maybe I just didn't know how the degas tank worked and should look into the problem from a diferent persepctive given the unique nature of the system pressurization which includes the reservior. So, who knows or has dealt with their cooling system enough to shed some light here on my situation.

PS this is my first cooling system problem and actually only have a theoretical knowledge of it's function. No previous experience.


Ian -- gearing up for a future Knotts Berry Farm car show!!:bounce:

01-08-2007, 06:57 AM
For starters, what year is your cobra? Actually what you have stumbled upon can be common if the cooling system is drained and filled in the manner you have mentioned. Unfortunately the cooling system will not displaced trapped air in the heads. You need to bleed the cooling system.

Look for the black cross over tube which connects to both heads and to the main cooling return lines (one connects to the radiator and the other drops down to the thermostat). The bleed port may be in a different location depending on model year. (99/01 it is located just above the hose that connects to the thermostat). On the cross over tube there should be a round flat plug that has a square socket indentation in it which is the bleed port. The difficult part is oppening the port. Use an extension for a 1/4 inch socket (do not use the socket wrench without an extension on it since the metal in the wrench is much harder and will round out the square notch, I did that by mistake and learned a lesson).

Once you get out the bleed plug, that is where you need to add coolant mixture. It will help if you can find a plastic bottle that would screw into the port (with the other end of the bottle cut off) which will help to get the air out as well as can be used as a fill funnel. Once you fill with coolant, begin to squeeze the hoses and you will see the air bubbles come out. Continue to do this until you can no longer fill any more coolant. close up the bleed port (do not over tighten the bleed plug since you will need to take it off again). Set the heat control to high and turn on the fan to activate the heater so that the heater core can be purged of air and start the engine. Let the engine run a few minutes and shut it down. Once the motor cools down, open the bleed plug and repeat. At this time if you open the cap to the expansion tank fill it with coolant if the level has changed and close the cap once full. Continue to fill at the bleed port like you did the first time and close up the bleed port with the plug. The trick about the plastic bottle is that it can be overfilled without dumping coolant all over the engine. Much easier to see the air bubbles come out as well. Restart the engine with the heater on and this time wait for the fan to turn on. Wait and see if the fan shuts off and watch the temperature guage. If the fan is running more than a minute or two, shut off the engine and let cool and repeat the same deal again after the engine cools down. If the coolant level is at the fill mark on the expansion tank that should be fine. If the level is beyond its capacity, it will get displaced once heated and overflow from the cap can be expected.

What you are calling a degass bottle is termed expansion tank. Its basic design is to allow for coolant expansion so there is no overflow tank which is commom to other types of cooling system most of us are used to seeing.
The cap used is similar in operation in that it breathes. The problem is when it expells coolant it has no where to go but onto the engine and accessory drive belts.