I recently had the cooling system serviced and over the past several weeks I have noticed the level in the overflow tank remains the same (doesn't go up or down like it normally does when a hot engine is turned off and then cools). I took off the radiator cap and the coolant level was about 1/4" below the neck. Always before when I removed the cap the coolant level would be in the neck. I checked the overflow line to the overflow tank and it's clear, also checked the pickup tube in the overflow tank and it's clear. I thought that if the cooling system was "starving" for return coolant during the cooling down period the lower radiator hose would be collapsed but it is not. So, it would seem something is breaking the vacuum of a cooling engine not to collapse the lower hose.
Any ideas? Could it be the radiator cap?
Thanks,
Jim
Tulsa
'89 two door v6 auto
A

As long as you have a full expansion tank[recovery tank],and the hose and cap from it are OK, I'd replace the radiator cap as a cheap test. Sounds like it's stuck or leaking pressure.