W204 Overheating Troubleshooting
11-18-2022, 01:05 AM
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C250
W204 Overheating Troubleshooting
I finally solved my overheating problems with multiple part failures with MBWorld forum help and thought I'd share the journey in case I can save someone else from my same mistakes.
Background:
I have lived in Japan 12 years. Cars are cheap here. I got a 2010 CGI C250 with 25,000 miles four years ago at auction for 4,500 USD. It was rated 4.5, with 5.0 being brand new. There are almost no DIY'ers here, and if you haven't taken a class you likely don't know how to pop the hood of your car. Parts are very expensive at dealers here.
I started getting the temp gauge over wavy lines on my dash about 6 months ago. I was also adding very slight amounts of coolant every week. I went to a garage and did a pressure check on the system that yielded no leaks with 15psi pressure. The guys at the garage said it could be the heater core. I learned about the thermostat's role and found the car always ran at 80degrees, and the upper radiator hose was always warm. I waited until I visited the states and bought a new thermostat housing, belt, and water pump for a 2012 SLK250 (has same engine code as mine). Unfortunately, the one I bought was for 103degrees and mine wants a 90 degree thermostat. I didn't pay enough attention on the nemigaparts.com site to the parts numbers. Came back to Japan and took out the old thermostat housing. It took 4 hours of wiggling and tugging since the spring was all broken. This led me to believe it was likely always broken since I owned it since it ran at a low temp. Sometimes when it was warming up, I would put it in drive and it would stall. It would just never warm up. The thermostat must have been stuck open. Car was still overheating so I went and bought a 90degree thermostat and installed. Car still overheating.
In the process of all this, I had drained coolant from the radiator, replaced, burped. I had turned the drain plug a bit much and jammed it in there. I ruined the entire plug area on the radiator trying to get it out, so needed to buy a new radiator. I bought a Mahle that was new but cheaper than OEM mercedes. Perfect fit. I will never again touch the cheap plastic drain plug and will get rid of coolant by removing hoses only.
Car was still overheating after 25 minutes of driving. Driving here in Japan is typically stop and go and you never pass 30km/h, so between sitting between traffic and lights, walkers often make more progress. My 5 mile drive to work takes me 80 minutes.
One morning I noticed the upper radiator hose was flat as a pancake. That was good. It meant there was no leak in the system and the thermostat was closed as it should be. Found out this meant the radiator cap had failed and was not releasing the vacuum created by cooling fluids. Replaced radiator cap, and no more flat hose.
Still overheating. I took the car to the Mercedes dealer. The guy said they could squeeze me in in about 2 months but he thought it was likely a bad engine. I was free to look at their newer models since I likely needed a new car. I have enough broken Japanese to share that if a car has a bad engine at 30,000 miles, I would never consider that brand again. I left.
I felt the heater core was not a problem because my floor mats were dry and no coolant smell. My heater blew blazing hot air on high and the a/c would work until the overheating warning light came on. I took the risk of continuing to troubleshoot by driving to work with the heater blasting to take the heat off the engine. Doing that and also watching it in the driveway, I found the warning light would immediately come on when the fan stopped spinning. The fan would also stop spinning when the A/C was on. This should not happen since there is only one fan in this engine. Since the fan worked sometimes, I didn't feel the need to mess with fuses or switches - it was likely a failing fan. I bought a new fan, opting for a Febi Bilstein rather than knock off. It was well made. It did not have the radiator shutter, but I did not want that since it is not very cold here. It also did not have the silver rectangular regulator box that my OEM did, but maybe that is built in. My OEM is 400 W. Replacement is 600W. A quick test of my battery with car off and car running showed my alternator working well, so I didn't worry. Fan works great. The amperage pull for the difference in 200W is minimal. Fan kicks on when car warms up to 95 and car temp sits at 92.5 consistently. Also stays on constantly with A/C. I will likely get better mileage than I did before since it is running at correct temperature.
All problems fixed. Hope this helps someone out there.
Background:
I have lived in Japan 12 years. Cars are cheap here. I got a 2010 CGI C250 with 25,000 miles four years ago at auction for 4,500 USD. It was rated 4.5, with 5.0 being brand new. There are almost no DIY'ers here, and if you haven't taken a class you likely don't know how to pop the hood of your car. Parts are very expensive at dealers here.
I started getting the temp gauge over wavy lines on my dash about 6 months ago. I was also adding very slight amounts of coolant every week. I went to a garage and did a pressure check on the system that yielded no leaks with 15psi pressure. The guys at the garage said it could be the heater core. I learned about the thermostat's role and found the car always ran at 80degrees, and the upper radiator hose was always warm. I waited until I visited the states and bought a new thermostat housing, belt, and water pump for a 2012 SLK250 (has same engine code as mine). Unfortunately, the one I bought was for 103degrees and mine wants a 90 degree thermostat. I didn't pay enough attention on the nemigaparts.com site to the parts numbers. Came back to Japan and took out the old thermostat housing. It took 4 hours of wiggling and tugging since the spring was all broken. This led me to believe it was likely always broken since I owned it since it ran at a low temp. Sometimes when it was warming up, I would put it in drive and it would stall. It would just never warm up. The thermostat must have been stuck open. Car was still overheating so I went and bought a 90degree thermostat and installed. Car still overheating.
In the process of all this, I had drained coolant from the radiator, replaced, burped. I had turned the drain plug a bit much and jammed it in there. I ruined the entire plug area on the radiator trying to get it out, so needed to buy a new radiator. I bought a Mahle that was new but cheaper than OEM mercedes. Perfect fit. I will never again touch the cheap plastic drain plug and will get rid of coolant by removing hoses only.
Car was still overheating after 25 minutes of driving. Driving here in Japan is typically stop and go and you never pass 30km/h, so between sitting between traffic and lights, walkers often make more progress. My 5 mile drive to work takes me 80 minutes.
One morning I noticed the upper radiator hose was flat as a pancake. That was good. It meant there was no leak in the system and the thermostat was closed as it should be. Found out this meant the radiator cap had failed and was not releasing the vacuum created by cooling fluids. Replaced radiator cap, and no more flat hose.
Still overheating. I took the car to the Mercedes dealer. The guy said they could squeeze me in in about 2 months but he thought it was likely a bad engine. I was free to look at their newer models since I likely needed a new car. I have enough broken Japanese to share that if a car has a bad engine at 30,000 miles, I would never consider that brand again. I left.
I felt the heater core was not a problem because my floor mats were dry and no coolant smell. My heater blew blazing hot air on high and the a/c would work until the overheating warning light came on. I took the risk of continuing to troubleshoot by driving to work with the heater blasting to take the heat off the engine. Doing that and also watching it in the driveway, I found the warning light would immediately come on when the fan stopped spinning. The fan would also stop spinning when the A/C was on. This should not happen since there is only one fan in this engine. Since the fan worked sometimes, I didn't feel the need to mess with fuses or switches - it was likely a failing fan. I bought a new fan, opting for a Febi Bilstein rather than knock off. It was well made. It did not have the radiator shutter, but I did not want that since it is not very cold here. It also did not have the silver rectangular regulator box that my OEM did, but maybe that is built in. My OEM is 400 W. Replacement is 600W. A quick test of my battery with car off and car running showed my alternator working well, so I didn't worry. Fan works great. The amperage pull for the difference in 200W is minimal. Fan kicks on when car warms up to 95 and car temp sits at 92.5 consistently. Also stays on constantly with A/C. I will likely get better mileage than I did before since it is running at correct temperature.
All problems fixed. Hope this helps someone out there.
