Air in cooling system

I have and issue with my 2006 Jaguar S type 3.0L with air entering the cooling system, resulting is a false coolant level alarm. The coolant level does rise in the reservoir but none is lost and returns to normal level once cool. I have vented the cooling system through the bleed screw several times . There appears to be air entering the cooling system from somewhere. Suspecting a failed head gasket I have carried out a compression test on all cylinders and all within spec. I carried out a cylinder pressure test with air and does not appear to be any leakage. Also there is not a smell of combustion gases from the coolant reservoir.

Would appreciate any comments
Keith
2006 Jaguar S Type 3.0

 

May not be entering so much as just has not bled fully.

 

Hmm, is this a new problem out of the blue? Or did it start after some repair? How much have you driven the car since bleeding the system?

Have you pressure tested the cooling system? Make sure to pressure test the cap, too, in case it is venting too early or too late. Carefully inspect the surface where the cap seals up. If not in good condition, the cap won't seal properly even though it tests fine. My pickup was giving me fits until I thought to check there.

If concerned about a possible head gasket issue, you can test for the presence of combustion gases in the cooling system. You can get little test strips to dip in the coolant. They change color if exhaust is present. There's another tool that looks a little like a turkey baster, and has a chamber that holds a special test fluid. You draw in some air from the top of the reservoir. If exhaust is present, the test fluid changes color. Or just take the car to a shop with a pre-OBD tailpipe emissions sniffer, and have them test for the presence of exhaust gas.