Thermostat change on M273 engine
 

on my way to work this morning my check engine light came on. the common p0128 error, indicating a failing thermostat. relatively cheap part. my question is this..i noticed on the older 550 engines, attached to the thermostat is a nice, easily movable radiator hose..attached to my m273 engine, is some stupid clunky huge metal tube, that makes any work in that area basically impossible. What purpose does it serve? can i just get rid of that and use the old style radiator hose?

I'm gonna need pictures. Both the M273 in my '08 S550 and the M272 in my wife's '10 E350 have a rubber hose with a metal end that all but disappears when it is clicked into the thermostat housing.

https://cimg6.ibsrv.net/gimg/www.mbw...623c7ca482.jpg
underneath the oil filter..attached to my thermostat housing is this stupid metal pipe...upon further research it has something to do with 4matic

Ahhh ok. That would be why I don't have it.

No you don't want to get rid of that and it has the new style clip connector on both ends.. Also, it would be a great time to replace the gaskets on the oil cooler and inspect the condition of the belt tensioner which also needs to removed.

That metal hose is the 4matic version of an upper radiator hose

Easy to remove, I believe there is one screw on the right side, then two hose clamps that come off. They are the clip type, not regular clamps. Pull out the clip and the hose comes off. Key to putting it back together is reinstall the clip on the hose FIRST, then push the hose on. That way you know it is on properly when it clicks. You can't put the hose on THEN the clip, because you won't be sure that it is on completely.

Once that hose is off I think there were 2 or 3 screws holding the thermostat housing, along with an electrical connector.

If you have all the tools it's less than 30 minutes work from what I recall (although I did it about 5 years ago so don't remember exactly)

I didn't drain any coolant, since the hose and thermostat are so high up they were quite empty. Make SURE you do this on a cold engine though. I believe a small amount of coolant spilled but if you have a rag or two underneath it isn't a problem. Check coolant level once the job is complete.

Back then was the time to do that, but I get it. When I changed the gaskets on the oil cooler it made sense to change the thermostat as well.

I have replaced the thermostat last year after my oil cooler gasket failed and put all the coolant into the engine and then almost overheated my car on the freeway. Oil level shot right up.

The thermostat rubber had actually gotten wrinkled because of the oil going through it, and although I was not getting any codes or issues with the heat, I went ahead and changed it.

*** Definitely make sure oil cooler gasket is replaced if you haven't already. It almost cost me the M273 engine .

did you replace the thermostat personally? or had your dealer or shop do the work? how did you know something was wrong if not getting codes or heat issues?

I replaced it myself. I never let the dealer do any work in my car unless they have to do an online programming module or wheel alignment.

My car started overheating and fans were blowing at full speed. The temp started going up close to the red dot.
I immediately pulled over on the side of the freeway. Fans were still at full speed which means:
1) either there is no coolant in the radiator and the fans can't cool off anything, or
2) the water pump has failed to circulate the coolant from the radiator to the engine causing the coolant in the engine to get hotter than operating temperature which triggers the fans to work at full speed by default.

(Either way I had to pull over )
Pulled the dipstick out, saw the oil level was way over the high mark ; by 2 inches.
Got a rag and laid it over the coolant reservoir and loosened the cap enough where just a bit of air was releasing. Once the air was out the cooling system, pulled the cap out and sure enough there was no coolant in the reservoir.
I was 10 min away from home so I added some more water and would turn the engine off at every stop. Had to pull the start button out and put the key in the ignition. Using the key, I could turn off the car and let it roll into a light or traffic and turn it back on without having to use the brake pedal if I was still rolling.

It was a messed up situation but when I got home and did some troubleshooting I realized; Coolant was in the oil, but the coolant tank also had oil marks in it.
Verdict:
1) when the coolant would get to normal temperature, the water cooling system would create enough pressure and start sipping through the gasket (that connects the oil cooler to the engine block) and leak into the hole next to it which was the oil passthrough hole.
2) If I started the engine when cold (when the cooling system had no pressure), the oil (which had a higher pressure) would sip through the same gasket and put the oil into the coolant port; so I never noticed my cooler tank ever empty when I would check it in the morning at random intervals.

For a $25 gasket, M273 almost overheated. I am sure if my mother or gf were driving it..I would be looking for an engine now.

haha i recently showed my girlfriend how to use the temperature gauge in her c350, unfortunately i doubt she realizes how important it is..the only thing i noticed on my 550 besides the check engine light was that the air would only blow lukewarm at the highest heat setting. coincidentally the morning the CEL came on i had an appt to have the trans mounts replaced and couldn't be bothered with doing the therm myself..a decision ill no doubt regret..have you done the water pump on your m273 yet? id assume so if its a 2007,,

One other thing you may want to take a look at is the temperature control valve at the back of the engine. It's plastic and after 10 years and over 180,000 miles the connector for the hose broke off dumping all of the coolant out of the car, good thing I had just pulled into a parking spot.

is that the same as the part ive heard refered to as the heater control valve? seen those replaced before, another relatively cheap and accessible part.

That's the one.

to build on this question, does anyone know if its possible to remove the radiator fan/shroud without having to drain the cooling system or need to remove this metal pipe? if so, please explain

no no, im only talking about the radiator fan/shroud..for when the time comes that im going to need to replace the alternator(which i think is coming soon) it looks pretty much impossible to get the alternator out without at least the fan being removed

yeah, the WIS says that the radiator fan has to come out...does that crossmember thing that the grille and the hood latches rest in have to be removed too?