Dear fellow motoring enthusiasts:

I have a stock 2006 MC with 51k. A few days ago, the engine began to over heat when I stopped at stop lights. I drive a great deal on highways but I live in a city. The car does well around town for short trips but if the engine heats for a long time, then I hit stop and go traffic, it starts to overheat from the ~190 deg. average running temp to overheat light in about a min. or so.

I drained and refilled the coolant system (the heat works good) . I've pulled the thermostat and tested it (boiled water test) and it seems ok. I've even pulled the water pump and it seems fine (going so far as to open the pump and check the connection between the pulley and blade assembly). The tubes connecting the pump, engine, and radiator seem fine. I've flushed water through the engine coolant tubes and radiator and seem to get good flow. Also, there is none of the tell-tale milky colored foam in the dip-stick oil tube or engine oil filling cap that would indicate an leak in the head gasket. I'm kind of at a loss on this one.

Anyone have any suggestions? Thanks!

 

Sounds like you checked everything but the fan.....

 

Dear Modshack,

Oops! The fan was one of the first things I checked. The fan comes on a little after 190 deg. and I can hear it go from off... to low... then high.

 

the fan has 2 stages. check the power steering fan under the car and make sure it free spins and doesnt have a rock/squirrel wedged in it.

 

Might be a bad Temp sensor then....Common problem on my old Audi TT

 

UPDATE:

I think it's solved. After draining the system and refilling it (very carefully) we added some Bar's stop leak and the coolant system seems to be working again. Thank you all for your suggestions and help!

 

You probably have a leaking thremostat. Same thing happened to my 06 MCC.

 

How would a "leaking" thermostat cause overheating rather than not allowing the engine to heat enough?

Rich

 

If the problem is fixed awesome, but something I learned on both my old datsun and BMW E-30... Air in the cooling system. I would go to change out the coolant (old, not enough, etc) and unless I bounced the front-end a bit to get the air in the tank,radiator, to move, it would instantly overheat. clear the air and no problems. This would occur regardless if I had the car running while adding collant or not.