OM642 - water pump and thermostat replacement - PeachParts Mercedes-Benz Forum

jay_bob · #1 03-10-2020, 09:18 AM

The next and hopefully last thing this car needs for a while....

Got all the other issues with the CAN bus, alternator, leaky oil filter, motor mounts, and stuck turbo actuator resolved.

But it was still not quite right. Noticed the temperature gauge struggling to get to 80 C and would drop rapidly at red lights. Classic symptom of a stuck open thermostat.

Engine seemed to be idling high and just generally not settled into its proper operation.

So I ordered up a new thermostat and water pump and replaced it this weekend. It has made a significant difference in the performance. Engine warms right up to 90C and holds there rock steady. Engine runs great now that it is out of its constant ‘warm up’ routine.

I used the dealer for parts since the genuine MB price wasn’t much more than online. They also made sure I had the one time use bolts on thermostat housing and pump housing. Pump was remanufactured and I had to pay $65 core charge.

How to:
First make sure your engine is overnight cold.
Pull bottom front and center lower covers.
Look on lower front left corner of radiator, there is a valve with a hose nipple on it. Slip a piece of tubing on and direct into a container that holds greater than 2 gallons. Open the radiator coolant reservoir cap and then open the valve on the radiator.

Remove the following off the front of the engine: (see W211 CAN Bus problems) for complete details:
Belt cover
Radiator fan (go ahead and pull it, it is super easy, gives you a ton more room to work)
Left side outlet muffler and silver turbo outlet tube
Triangle resonance pod on right side
Mixing chamber on right side
Belt cover bracket
Drive belt

By now the coolant should be done draining. Go ahead and shut the radiator valve and remove the drain tubing.

The thermostat is easy. Unplug the hose (uses the same type clip as the intercooler boost hoses) and move aside. Unplug thermostat preheater connector. 3 bolts, 2 short ones on top and one longer one on bottom.

The water pump has 6 bolts, all easy to spot. Gently back out all 6, pull pump off, new gasket, new pump back in. Have a drain pan ready under the pump, you will get a small gusher due to trapped fluid in the pump housing.

Put everything back together then fill system with new coolant. I did most from a funnel into the upper radiator hose and then finished off with filling from the reservoir. It took one gallon of coolant and one gallon of distilled. WIS tells you to vacuum fill it but I didn’t have the proper fitting for the tank neck. My HFT radiator tester has this dinky winged bracket and rubber cap that is just not up to the job.

Drove around and made sure the heat got hot then had to add a few ounces more water to bring it up full. Checked it the next couple days and had to probably add 8 oz more total above the initial 2 gallon refill.

dieselbenz1 · #2 03-11-2020, 06:45 AM

Were you going to replace the reserve tank also. I thought the silica needs refreshing to keep the coolant good for 15 more years.