underdog01

My 2007 s 550 with 109,500 won't reach normal engine temperature. I think it started around Christmas time, the car would not quite reach 80-85celcius. Just today went on a 200 mile round trip and the car never got warmer than 65c. The heater continued to blow warm air although not as warm as it normally does but that is due to the lack of engine temp I'm sure. The coolant is full and I don't have any leaks. Obviously it is not a coolant issue as the car won't get warm. If this car was a Chevy or Ford I would spend less than $5.00 and replace the thermostat. The car is acting as though the thermostat is stuck open. Do you feel that the thermostat is bad? I thought these cars had electronic thermostats and they don't work the same way. Is there any other suggestions you guys can make? Am I doing the car further harm by driving it? Thanks in advance for your replies.

Mike5215

Ha! Remember the days when you could hit a stuck thermostat with a hammer a few times and it would start working again? The only thing I would tell you is get it to a dealer or indie and see if there are any fault codes showing.

bha

Scan for codes and see if you get P0128 (either current or historical). I had a P0128 and cleared it, and it came back later on.

The thermostat in this car costs under $100 and comes as one giant piece.. thermostat housing, thermostat, electrical sensor/connector.

The entire housing is replaced and it doesn't take long. It has a spring clip rather than a hose clamp, so it's pretty easy to unbolt and re-attach. I think an idler pulley has to come off because one bolt is behind it, but it's easy to remove.

Thermostat is complex.. there is a sensor and it basically decides (or is told by the engine computer) when to open and shut. At idle and wide open throttle, it behaves differently than a regular thermostat to ensure the engine heats up faster, and stays warm at idle (without overheating). There is a 5 page WIS document on the web explaining it in excruciating detail if you want more info

My car had no problems running under temp, but when I replace it I started to get more heat in the winters.

I don't believe this code sets a check engine light. I never got one.

I would look into that. I think P0128 is specifically described as "engine not reaching operating temp" or something like that. The description matches what you are running into.

underdog01

Thanks bha, I'll look into that. My wife said the car tripped a code coming home earlier today. I will take it to an autoparts store tomorrow and see if they can give me a code. Thanks again.

alx

Your auto store with the generic obd2 scanner might not get the full picture.

It could be a thermostat or a faulty fan control. Car needs to be read with star.

underdog01

Thanks for your reply. I went to Autozone today and they hooked the car up to their OBDII scanner. Got two codes: p0128, and p0022. They did not have star, so I'm afraid your right alx, I'm not getting the full picture. p0128 does point to the thermostat and my symptoms seem to quantify this. The p0022 code is a cam position sensor (right bank over retard I think). Hopefully this is just the sensor and not a serious cam issue. Some are saying a $6,000+ repair. I just crapped my pants a little typing that.
Anyone here have any suggestions for me please. Oh pretty pretty please. Thanks.

bha

No need to panic. The first code is probably the thermostat (remember the sensor and thermostat are one part, so when you replace it everything gets changed)

Second error on most MB models is a simple cam "magnet" sensor. Not that hard to change (an hour or two at most if I recall correctly.. you can do it yourself)

Don't panic just yet.. I suspect under $100 for a thermostat plus a relatively inexpensive cam sensor will fix your problems.

Do some reading on the cam sensors.. they were defective and I think some C class owners were replacing them all when one threw an error code. Look into it as you may want to do them all at once.

Mike5215

I think I just had that can magnet thing done as part of a ticket that coincidentally was around $6000 but that included a strut and gauge cluster. If I remember the part was cheap but the labor was not. All CPO so no pain but definitely enough to reaffirm I can't hold on to this (beautiful) car much past the warranty expiration.

bha

I'm sure it's a $500 job at the dealer if not more...

$25 magnet
$50 in screws and bolts
$450 labour 3hrs @ $150/hr

If you open the hood and pull off the plastic cover, you can see these magnets. They are held in by Torx screws (3 screws I believe) and just unscrew.

I'm sure there may be something in the way (depending on which one you are removing) that has to be removed/reinstalled, but it can't be that complex.

I'd get a flashlight, magnetic retreival tool (for when you drop the little screws!) and a new camshaft magnet + 1 extra new screw. I'm sure it can't even take you 2 hours if you're reasonably handy and have the proper torx t-handle wrench (or torx screwdriver) all ready to go.

Any indy shop can swap this for you for a reasonable cost. No need to go to dealer.. these are incredibly common across MB models. It's about as universal as being able to mount a tire on a "Mercedes-specific" wheel.. not everyone can do it, but any good tire shop can do just as well as the dealer. Same kind of thing.

By the way the magnets used to run $20-25 at the dealer..should be the same price range now.

underdog01

Thanks again for your replies. After further checking I realize that it is the v6 c and e class's that would often require pulling the engine and replacing the sensor/balancer. Very good to hear. I just googled the error code, started reading, and must have slipped into shock.

My wife has a neck injury and the s class is the only car she has ever been in that she can actually take trips in. I'm talking anything more than an hour. We purchased the car with 98,000 and have driven 10,000 in the last 6 months(she has been mostly house bound for the last ten years). We could not get a warranty company to touch this car. I would hate to have to spend large amounts of money to keep this car running, but I would.

underdog01

One quick question. Shouldn't I replace the sensors and the magnets? There should be four of each right? I figure if I'm replacing the thermostat and at least one sensor/magnet, I might as well replace all four while I'm in there. I would appreciate it if someone could chime in whether or not this is over kill. Thanks so much!

underdog01

My bad, I realize the magnets and sensors are the same part. I just got confused because they were listed separately at genuinemercedesparts.com. They have the sensors priced at $21.60 each. I'm still trying to figure out if there are four of these and if I need to replace all four. Thanks in advance for your replies.

underdog01

Okay I replaced the thermostat tonight. Pretty easy fortunately and it seemed to cure what ailed me. I bought two cam sensors, I figured I would replace both on the left side while I replaced the thermostat. The oil cooler and the power steering reservoir are in the way. I figured the oil cooler would most definitely have a gasket I would need to replace. Needless to say, I didn't order an extra gasket for the oil cooler. I will order one and I think I will have to take the thermostat off again in order to get to one of the bolts for the oil cooler. So I'm going to have to order another gasket for the thermostat as well. In other words, everything I accomplished tonight I will have to do over once the gaskets come in.

Does anyone know of an easier way to do this? Thanks in advance for your replies.