SES help: P0128, coolant temp below range - The Unofficial BMW M5 Messageboard (m5board.com)

R748 · 6th October 2006, 05:18

I've had this code come up twice now, the first time I reset it thinking it was just a sensor blip. It didn't come back for over a week, but the same week I suffered a coolant leak due to a broken hose clip. That was fixed and system flushed with fresh coolant, etc, see coolant all over the floor

Now this code is back again this week, so my guess is that the coolant leak and the first occurance of P0128 was just a strange coincidence. Lucky me

So the question is, what do you guys think this may be? A bad thermostat or just a bad coolant temp sensor? Could it be something else? My car is a 2001 with 50K miles. My water temp guage needle sits just left of the 12'oclock position now that the amblient tempreatures have cooled. I would say somewhere betwen the first dot and the 12'oclock position. No other driveability issues or problems that I can detect.

rbrowns29a · 6th October 2006, 07:07

Ditto on this question. My 2001 with 75K miles has been throwing this code intermittently for the last 3 weeks, ever since it started cooling down from the 90's to the 80's here. I can reset it and it will come back in a few days or if I just leave it alone it will reset itself in a few days and then pop up later.

My oil temp used to hover just below 210. Now with the engine warmed up my oil temp is around 170. Nothing in the car has been worked on recently.

I much less worried about a low temp warning compared to a high temp so this is more a nuisance than anything else. I haven't noticed any difference in the way the car is driving.

greg · 6th October 2006, 07:20

I think your instincts are right - thermostat stuck open, or bad sensor. I'd suspect the former, but I would replace whatever is cheap and easy first and if that doesn't work, do the other. They might be cheap and easy enough to just do both anyway.

M5Pageco · 6th October 2006, 08:59

My car is in the shop for this now. (2000 71Kmiles) It seems to throw all kinds of weird codes, cause the engine never gets out of the "warm-up" stage. It messes the software or programming all up. They are replacing my thermostat, sensor and housing, with 4+ hrs of labor. (About $800.00)
I have a question...when you saw the coolant leak, what color was it? Does it kind of look dark? or like oil?
Thanks all!

kees · 6th October 2006, 10:57

Air in the coolant system can cause low temperature readings as well. Make sure it is properly flushed of air.

neilm12 · 6th October 2006, 16:57

When I first got my M5 the coolant temp was just clearing the first dot. I took it to the dealer and they fitted a new thermostat. Now it sits ever so slightly to the left of the vertical most of the time (goes vertical when driving hard).

Oil temp is about 82 celsius, or between the first dot and the middle. Goes to just under the middle when driving hard. Never goes past the middle point.

I would change the thermostat first as this is a relatively quick job and a regulat job on my previous BMWs.

rdm190 · 6th October 2006, 17:08

Quote:

Originally Posted by neilm12

When I first got my M5 the coolant temp was just clearing the first dot. I took it to the dealer and they fitted a new thermostat. Now it sits ever so slightly to the left of the vertical most of the time (goes vertical when driving hard).

Oil temp is about 82 celsius, or between the first dot and the middle. Goes to just under the middle when driving hard. Never goes past the middle point.

I would change the thermostat first as this is a relatively quick job and a regulat job on my previous BMWs.

To get to the thermostat on the S62 the entire upper intalke has to be torn down. Dealer told me $789 for the job. Then they covered it under CPO

Beamer_usa · 6th October 2006, 18:22

Had the same problem with my old 540, the thermostat was stuck open. fairly easy fix - Good Luck!

R748 · 7th October 2006, 02:33

Thanks for all the replies, so I'll get the thermostat changed. The procedure is somewhat involved on the M5, since it requires draining the coolant and then removing the upper sections of the air intake system on both sides, before the thermostat housing can even be accessed. So the labor is over 3 hours. Although, I'm sure a good mechanic could do it in under 3.

Quote:

Originally Posted by M5Pageco

I have a question...when you saw the coolant leak, what color was it? Does it kind of look dark? or like oil?
Thanks all!

It was a very light blueish color. There was a slighly oily consistency. Since it went into my concreate garage floor, it was hard to tell the color except in those terms. But it was definitely NOT dark like motor oil. It was almost like water, just a bit more oily.

Has anyone tried a non-BMW thermostat? I'm just wondering if a better alternative is available to the OEM unit, which appears to fail a lot. This is based on some reading on this and other E39 boards.

TeXJ · 3rd November 2006, 00:23

Anybody have a how to on replaceing the thermostat? I have the same code, P0128. My temp guage doesn't move past the first "dot" on the guage. The car drives normal, just he check engine light is on.