C230 Coolant Level Mystery
 

1999 C230K (202.024) Transparent cooler reservoir with black top. I keep my coolant about 1/4" below black top so I can monitor level. Drove 400 mile trip (used heater for about 5 minutes) and level was 1/4" low when cooled off. Stayed that level for a week. Found no leaks. Drove 10 miles today and coolant was back up to the original top mark. Loosened reservoir cap and coolant came up even more (lots of air escaped). Where did this excess coolant come from or where has it been? I changed coolant 6 months ago. Could air have been trapped in system somewhere? Thermostat problems? How do you diagnose thermostats? I certainly don't want to "cook" this engine. Your input is greatly appreciated.

I don't really think you have a problem. I think you are analyzing the situation too much.

You probably had air trapped in the engine block or radiator as a consequence of changing anti freeze. I seem to recall that some engines have a bleeder valve on the side of the block. My guess is that an air pocket worked its way back to the radiator and consequently the situation you describe developed.

The coolant level rises when the engine is hot because the coolant expands and the higher temperature also builds pressure in the system. The cap will release at 1.2 or 1.4 bar. It should be marked.

Check your owners manual to see if the coolant level top line is hot or cold. Then make a mental note of the difference so you can check it either way.

Also, you should never remove the pressure cap when the temp is over 90. Coolant can blow out and you could be scalded. Even if below 90 carefully rotate the cap to the first detent while pressing down on the cap. Then slowly release the vertical force on the cap to slowly break the seal and release pressure.

Duke

Hey!guy's need help with my 1999 c230.leaking coolant in cylynder head .Im not sure if realy the head gasket?I jack up the car and start it.And its coming wright on the corner of block and head.Is their any other hose running in the back between trani and cylynder head?I have only 91,000miles on it.thank's!