No change in level of coolant recovery reservoir

[ojb]

Hi,

I have (maybe) a problem with my cooling system. I have my Z for about 2000 mls now and I noticed that the level of coolant in the coolant recovery reservoir (front right) does not change.

In the service manual it is mentioned that under normal operating condition the level should rise to hot.

When I open the pressure cab when the engine is cold, there is enough coolant in the system.

I have a Jaguar which had a bad overheating problem which cost me several thousand dollars and therefore I am very afraid of any cooling issues.

Does anybody have a idea, if I have a problem and what it could be.

Thank you in advance.

Greetings from Munich, Bavaria.
Oli

[tomtom72]

Hi Oli,

The only real way to test a cooling system for leaks is to use a pressure tester. Ofcourse if you don't see any coolant dripping on the ground or traces anywhere it doesn't belong that's a good sign. The fact that your recovery tank remains at the cold level, when the car is cold, is not an idication of trouble. You would have to watch the recovery tank thru the full heating and cool down cycle to see the level change. Usually, if the system is full and air free the only time the level will change is when the motor is shut off after it has reached "normal operating temperature" and the T-stat has opened and then the motor is shut off. The coolant continues to absorbe residual heat from the motor but is not circulating and it expands due to heat absorption...the extra volume must go somewhere. That extra volume goes to the recovery tank and if the system is filled to the proper level the tank's dipstick will show the level at the "hot" mark. Once the motor cools the coolant contracts and the extra in the recovery tank is sucked back into the "high fill tank" to maintain the proper volume in the closed part of the system. The cap on the high fill tank acts as a two way valve, when cold it seals off the hose to the recovery tank due to no pressure in the closed part of the system. When the motor gets hot and is then shut off the pressure in the system goes up and the coolant flows to the recovery tank to relieve the extra pressure & volume. The cap should be changed when you change the T-stat.

If I understand you correctly, everytime you check the tank's level when the motor is cold the dipstick reads the coolant at the "cold" mark?? If so that is correct. If you have to add coolant every week to that tank to keep the level at the cold mark then you have a leak, maybe...needs a pressure test to locate same. To actually see the level rise to the "hot" mark with the motor running I would think the temp would have to be just before the point that both fans are on, 225* I think, or maybe higher, and the car would have to be stationary, no air flow thru the radiator so the coolant would be in the condition of heat saturation and start to expand in volume. The expansion would then open the fill tank cap via a pressure increase above 17 lbs/sq. in. and the "extra" volume would expand to the recovery tank. The only other way I know that you can see the level in the recovery tank change is if a hot motor is shut off and the fill tank cap is moved to the first detent...releasing the system pressure to the recovery tank...then you would see a "boil over" of sorts...in the recovery tank. I have never actually seen the level in my recovery tank change as I only check it as part of a "pre-flight" check list.


Tom

[ZR1 MK]

If you dont have a coolant sytem leak, you might need a new high fill cap. The cap is dual fuction. When system is full and cold and then heats after engine run, the coolant will expand past the cap and into the recovery tank. As coolant cools, it will return to the infill tank and remaining system.