So, I unlocked the OBC and decided to monitor my KTMP temperature test 7.0 while I was cruising at 70 MPH. The ambient temp at this time of year in the Northeast was around 25-26F, to my surprise the reading of my engine cooling temp was always around 83-84C. This is a little too cool with nowadays engine if you ask me.
I then continued to monitor through out the stop and go traffic doing about 30-45 MPH on local road, and during this time the KTMP dropped even further down to around 80-81C.
Once I had arrived home I decided to let the car idle in the driveway, and after about 10 minutes the KTMP temperature shot to 97-98C then of course the fan kicked in and cool it off.
I don't know what M52 engine cooling temperature specs is and if mine is normal or not, But I would love to hear from other with their M52 engines.
Here is a quick note to unlock your low OBC
Press and hold your trip reset button until test--xxx then let go
quick press to cycle to test 19 then let go
quick press when you see "off" display
quick press to cycle to test 7 then stop.
The OBC should display your KTMP temperature in Celsius if my memory serves me correctly.
Last edited by 16valex; 01-16-2011 at 11:38 AM.
When was the last time you change your thermostat?
1999 E39 Touring Sport and 3 pedals
I had similar "issues" as you and the t-stat replacement really seemed to help.
About three years ago, but if you go by the gauge then you won't see any discrepancy whatsoever, the gauge is right smack in the middle after 10 minutes.
I remember your thread Evan.
I also have M54 engine on my 02. M54 thermostat is equipped with a heater to better control the thermostat's open and close, while M52 engine is totally mechanical.
I agree that it could be the thermostat, but I wanted to see others here have to say on their M52 and it's temperature's behavior.
Last edited by 16valex; 01-16-2011 at 02:23 PM. Reason: Automerged Doublepost
My coolant temps are much more stable now. I really didn't have the temperature spiking that you talked about though.
I am going to send you a quick PM.
Do you have the lower engine cover installed?
1999 E39 Touring Sport and 3 pedals
I just recently picked up my e39, it is an M54 but I thought my experience relates to your question.
Prior to my doing a cooling overhaul, the car always ran at 80-86*C. After doing the cooling overhaul, which included a new t-stat, the car runs at 92-95*C. I definitely think my t-stat was well on its way to being stuck open.
Do you have the correct thermostat? I just changed mine and it was too cold, 87 C I think was installed and the one I ordered using the OEM P/N was 92 C.
Thanks Evan, and good to hear your is fixed.
Thanks for the re-enforcement. I'll be changing out the thermostat soon.
Yes I do, I think my thermostat is opened too early.
I forgot what I put in there three years ago, it could be the wrong one though. But I will definitely change it out soon. It just doesn't seem right operating at 80C. I think it should be around 94-95C is more like it.
Last edited by 16valex; 01-16-2011 at 08:05 PM. Reason: Automerged Doublepost
So, I decide to do the thermostat.
Called the local dealer 55 bucks. Nah! That's ripped off.
Called NAPA from Evan's tip.
NAPA has one for $29.95. It's an Altrom made in France! 92 degree Celsius. BTW, this is BMW specs for M52 engines.
Swapped it out. The old one was a BMW and it was rated at 92 degree Celsius.
So after all that bleeding bussiness, then went for a ride.
Unlocked OBC and test number 7 is displayed.
The whole time driving from local roads and or highway. Engine cooling temp is now 92-93C Just the way it meant to be.
So if you have a 97 or 98 528I, you should unlock OBC and read your KTMP, don't rely on just the gauge.
Just as an FYI for this useful thread: The gauge needle is buffered between 85 and 115 Celsius if I remember correctly. So it means you won't know of a full 30 degree change by looking at the cluster alone because the needle will be at the dead center. You DO need to unlock the OBC if you suspect your car is not within normal operating temperature. Mine stays at around 94 C most of the time. When idling it can go up to 100, and highway cruising at 91 or 92. It doesn't have to be at 92 the whole time. There is a bit of play on that.
That's one of the worst design decisions that BMW made with the E39 (and several other models), a buffered temperature gauge. I don't have words to describe how insanely stupid that is. Our E34 has a normal, useful gauge.
Last edited by crdiscoverer; 01-19-2011 at 02:44 PM.
Resident Third World Country Advisor
Nice to hear a happy ending that is cooling system related around here!
Also, for the M54 - the electronically controlled t-stat: if you suspect it failed in the open position, and the OBC reading point to it, actually a code is released, no SES light. Checking the codes will reveal if the t-stat is stuck open.
Looking for a DIY? Parts? Check this out, it might be your ticket
Stable: e92is, e53 N62, e46M54B25, Tribby & e39 M54B30 R.I.P.
Correct, for M52 as long as it's in the 90's you should be ok. Athough ambient temp does plays a roll in your engine cooling temp but should not be too much 2-3 degrees max.
Yes, that is true, and don't forget M54 engine cooling temperature is much higher. It's 97 C I believe.
Thanks Evan. Your tip saves me 25 bucks, and time.
Last edited by 16valex; 01-19-2011 at 03:07 PM. Reason: Automerged Doublepost
So ever since I replaced my thermostat with the correct rating (the old one was "too cold") my gas mileage seems to be improved. Before my MPG would bottom out around 16 mpg due to city driving, it seems to be 18mpg now.
97 M52 101k kms...my 18year old is just getting broken in.......but MPGs are in the toilet 10-12 MPG...Test #7 and I barely get up to 74C on my way home...after 30min of driving like I stole it I can only see 84C... gets as cold as 65C when at highway speed...
PO has dealer invoice for new radiator , expansion tank, clamps and hoses BUT not a new thermostat..huh?
No chance it's anything other than a stuck open thermostat?....how about clutch fan that is always engaged?
thanks for your time and opinion
A fan clutch permanently fully engaged would be roughly similar to ambient temperature below freezing with a properly operating clutch. Yet one would still expect coolant temp to rise to the normal range.
If not a stuck thermostat is the only plausible explanation would be a faulty temp sensor. Given the other symptoms though, a stuck thermostat is the far more likely cause.
Regards
RDL
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