So I first got the P0128 CEL message. After reading on this board, I was certain it was the common thermostat failure that everyone here was reporting. Was going to take it to the dealer but upon reading here, I noticed how easy it was to change this out, so I decided to do it my self and save some money.
Boy did I save some money

First off while on the thermostat I changed the V-Belt too.

Thermostat: 95 (220)
Coolant: 18
V-Belt 30 (80)
(650) for parts/labor from dealer. So I saved like 500 off the bat.


Just before starting the thermostat change out, the car decided to also get the dreaded chirping noise come up at the same time from the poly belt.
Wasn't sure which pulley was causing it so went ahead and changed both first.
Unfortunately, needed the parts immediately to finish so I bought these from dealer,They are like 50 less online but I couldn't wait, could have saved another 50.
Dealer thought it was the auto tensioner, but I'd rather risk 60 than 220 on a part. Even checked with dealer and they said they had changed the idler pulley under the service campaign. But after I read on here about a guy who dealer first changed the tensioner without success, then changed the pulley to fix the chirp, I wasn't going to jump for a tensioner. I really felt it was the pulley and was right after I changed it. So clearly those things are good for about 2 years

Guide Pulley 45 (65)
Idler Pulley 25 (60)
Dealer wanted 350 diagnose and to change both out. Saved me 220.

So I went ahead and also changed the air and cabin filters from autohauz. Believe it or not, I changed the cabin filter from the engine side, it was easy for me, didn't have to take out the glove box. Lol
Cabin filter: 27 (70)
Air filters: 29 (80)
Dealer wanted 200 for parts and labor. Saved my 150, thank you.


While I was at it, decided to upgrade the look. I changed the front grille
Got one on ebay for 125. Dealer wanted like 700 for parts and labor.
Grille 125 (700)
Save me 550 on that one. Easy change, but needed extra hand.


Car was due for it service 65K anyways. So changed the Oil at the dealer. Yes its cheaper. They offer this 89 dollar oil change with fluid top ups and carwash.
The oil and fleece alone are like 90 already, so might as well let them do that and wash the car also. But get this, they won't reset service light for that. Its not a full service by them so no. You can pay and have it done.
Saved my cash and just followed instructions in manual.
I also have a OBD II reader I picked up a year ago, for 30, came in handy to clear the CEL which the dealer will also charge to clear. LOL.


So after 1 crazy weekend
I had an oil Change,cabin filter, air filter. Reset service light, new thermostat, V-Belt, Idler Pulley, Guide Pulley, upgraded Chrome Grille, flushed coolant.
All for under 550 plus some intense work hours from me instead of the 2000.

I would have had to shell out like 2000 to get all this done at the dealer.
Feeling pretty good with myself, and best part is, I got to know the car a lot more.

Thanks to everyone on the forum.

 

Nice! Benz's aren't anymore difficult than an average toyota to work on but MB owners have this mentality that only dealers should work on them.

 

I have worked on my own Benzes for over 25 years and I feel that the mechanical side is very well thought out and easy to work on.

 

I have a ML 350 2006,with a code 128,how do change the thermostat ,how do you take hose out of thermostat housing?

 

Is there a DIY on the W164 Thermostat? I can't find it!