slimpee

So i've poked around and read a few threads about the P0128 code. I replaced the air hose and cleared the code a few days ago. It popped up again today so I guess the problem hasn't gone away. I'm fine with replacing the tstat but my car seems to be operating pretty reliably at around 80 degrees, sometimes a bit more, sometimes a bit less. Wouldn't it run cooler or hotter if the tstat were bad?

Like I said, i'm fine replacing the tstat but i'm kinda concerned that it's a wiring issue or something.

Thoughts?

pcy

Thermostat could be sticking intermittently. Eventually it will be stuck, permanently.
Most of the times, these thermostats get stuck in open position. If it were to get stuck in closed position, engine will be in trouble very quickly.

If I were you, I'd buy a thermostat online and replace it at the earliest convenience.

Glyn M Ruck

80 degrees is too cold. That's why you are getting a 128. The standard thermostat starts opening at 87 deg C & is fully open at 90 deg C. That should be the operating temp.

Replace your stat.

funnyent

As pcy states the thermostat is probably sticking. My code come up last month but engine temp was sort of warm at first, and then after another week it was very low. I'd go ahead and replace it; it won't take more than an hour tops.

slimpee

Thanks. I called the dealer and asked about price. He quoted me $58 plus a few more for rings. I told him i would just order it online and then he came down to $38 plus shipping. I still told him i'd order it online.

Is Wahler the tstat oem?

pcy

Yes, Wahler is OEM.

Khan28

I'm not getting any CEL or codes but in the cold weather (Below 0 Celsius) my engine temperature only goes up to about 75 or 80. Only in warmer weather will it go to the 85-87 mark. Should I replace mine? What about the temperature sensor? The coolant level is good and the coolant looks very clean.

ncmudbug

I just bought a new thermostat from rmeuropean but I didn't see a gasket listed for the housing. Isn't there one?

VVF

I bought Wahler from Autohaus a year ago, it had two o-rings. One like a normal ring, and one ring with square profile. You may want to check parts dot com for the o-rings...

ncmudbug

Thanks for the reply, VVF. Yup, I should get the o-rings. I guess I'm set!

slimpee

I think you guys are right. I drove my car tonight probably 10 mins, let it sit for an hour or so, and then 10 mins home and it never got above 80 so I think you're right, the tstat is stuck at least partially open. Is it bad to drive for the next week or so until the new unit arrives?

Ps. It's probably in the high 20s-freezing here

ncmudbug

I have the same problem. My car will eventually get up to 80 (which is just shy of 180F which is a reasonable temperature). Elsewhere Glyn advises babying your car till it gets good and warm - something I've been doing mostly because of my rather old habits to not stress a car till it's warm.

I have no doubt that it's important but I've wondered just why it's important now, though. It used to be because you needed to get the oil up to temperature so it would be a bit thinner and lubricate better but it seems that would be less important with oil that is 0 weight when cold. I wonder if it's to get to the heavier weight of the oil since 0w40 would act like 40 weight when it's hot. Maybe someone can clue us in on why it's still important.

In the meantime, I would follow Glyn's advice.

Moviela

It is for fuel conservation (CAFE) and emission rules.

Glyn M Ruck

The oil flow story is a bit of a red herring. Most cars have positive displacement oil pumps so flow is constant unless cavitation or leakage occurs. Most wear takes place at cold temperatures & engines are less efficient running cold as Movie states.

The biggest reason to warm up a vehicle before making maximum power demands is to normalise all engine clearances & thus achieve proper hydrodynamic lubrication where appropriate.

ncmudbug

Thanks Movie & Glyn!

Khan28

Is the Wahler unit a fail safe type thermostat? I guess if I go ahead and change the thermostat I might as well change the coolant instead of reusing the old coolant.

Glyn M Ruck

The genuine Benz stat is designed to fail open.

VVF

AutohausAZ lists Wahler as OEM: http://www.autohausaz.com/search/pro...200@Thermostat

Khan28

That Wahler unit shows 100c temperature? Shouldn't it be 90c?

Glyn M Ruck

I don't understand that. Even the "so called" winter thermostats were somewhere in the 90~93 deg C range.

samaritrey

I did a quick search and could only find ones that were 100c

VVF

You can try contacting guys at parts com and asking them... Or a dealer?

Glyn M Ruck

Anybody here with a car that runs at 100 deg C?

Edit: Interestingly I note that conventional thermostats as fitted to M271 & M112 engines by Wahler are listed as 87 deg C stats. The Electronic thermostats as fitted to the M272/273 engines are listed as 100 deg C.