My 2001 300M is behaving oddly. Occasionally it will gradually overheat after I have driven around for 15 or so minutes. Yes, occasionally. I took it to my mechanic who changed the thermostat and hoses. I then drove it on a trip on the interstate and over a mountain (140 miles ) It was fine with no signs of overheating. Then the next day when I drove to work in the city, the stop and go traffic had it overheating near the end of the trip. I've been able to keep it from going in the red by using the heater. After this happened most of the days, but not all, I took it back to the shop. He reported that the fans were working correctly and the only thing he could come up with is a weak water pump. He stated that when it did get hot, he was able to bring the temp down just by rev'ing the engine a little.Does that sound right? Any other ideas and how to test?
Ok when a water pump is not working of is going out it leaks water or coolant but not because the thermostat is new mean it works trust me that happend to me. Try this leave the thermostat out and test your car. But more important ones you put any liquid in to the radiator make sure you take all the air off from the engine because if you don't it will seem that its full and when the the car runs the water Level will drop and affect your engine.
The only reason to replace a water-pump on such a new car is if the weep-hole on the bottom of the water-pump in-put shaft casting is leaking. If your upper radiator hose if hot when the dash temperature reached 195 degree's there is nothing wrong with the water-pump. Cooling systems plug when brand X antifreeze is mixed with the standard equipment, long life type. *Did your mechanic do an inexpensive *cooling system pressure test to look for external and internal coolant leaks? Is the radiator filled to the very top when the engine is stone cold? Is the plastic coolant recovery bottle at least 3/4 full when the radiator cap has been removed? Have you checked to see of the electric cooling fans are operating behind the radiator when the dash temperature reaches 205 degrees? It's less expensive to change the thermostat and radiator pressure cap than a non-leaking water-pump. An 11 year old car is do to have the cooling system drained flushed and *cleaned before having Fresh factory recommended ZEREX G-05 antifreeze added.
If he said the temp fell by revving the engine one of two things either the water pump is going out the bearing is failing and faster RPMS is pushing the water pump inside to spin faster and the bearing is starting to catch and work and spon the propeller OR the radiator is plugged or needs to be replaced. If the radiator is going bad it could be restricting water and more RPMS once again is pushing the water through the radiator to cool it. The other thing it could be is a radiator cap if it is not holding pressure then it will cause the water inside to boil slightly and make it hotter also. I would by a new cap and do the water pump. Those are the two cheapest. If that doesn't fix it then do a radiator.
Sounds precisely like your water pump. I had the identical predicament with a cavalier. The pump shoud be around $30 to $50 or so. Price to alter? Quite often around $one hundred to $150. Might be extra so don't quote me on that. Every keep has their own hourly cost.
