What is the coolant temperature of an E39 (I6 or V8) under normal operating condition

I have a fundamental question about my E39 thermostat operation at normal operating condition.

We all understand (in theory) "how" a thermostat works (i.e., it opens above the set point and closes below the set point, hysteresis & bleed holes notwithstanding).

The fundamental question I have is whether that set point is constantly broached during normal operation, or if that set point is typically exceeded during normal operation of my E39 (well after warmup).

It's impossible to understand typical E39 thermostat operation without knowing the temperature of the coolant ... so I ask, specifically:

After warmup, what is the typical coolant temperature (in degrees) of your E39?

Helpful additional information might be:
- How did you measure that temperature (unlocked cluster, carsoft, thermometer, other)?
- Year/Engine of E39 (e.g., 1999-to-2003 have electrical thermostats; others mechanical, Behr or OEM)?
- Where does your temperature gauge point (in normal operation)?
- What is your thermostat set point? (e.g., 88°C/190°F, 90°C/194°F, 92°C/198°F, 97°C/207°F, 100°C/212°F or?)?
- What is your overflow tank cap release point? (e.g., 200/2.0Bar/30PSI or 140/1.4Bar/20PSI or?)?
- What is your coolant ethylene glycol percentage? (e.g., 50:50)?
- What is the condition of your radiator & fan & waterpump, etc. (e.g., new, old, zionsville, airbubble, leaking)?
- What were the test conditions (i.e., ambient temperature, load, altitude, traffic, etc.)?
etc.

NOTE: Related threads:
- Boiling coolant
- New thermostat question
- Solution to exploding radiators
- Missing coolant temperature gauge
- Test 7 coolant temperature on 540i
- Where do we look on the E39 for cracks

7/98 using the unlocked cluster, it reads 105 to 110 (that's when the fan kicks on) C.

I'm reading around 97C--varies from 93 to 97C

Yep...if you've unlocked your OBC...you can run TEST #7 and monitor your engine coolant as you drive around town.

If anyone needs instructions on how to unlock your OBC...I have instructions (with a brief explanation of the TESTs) for both the HIGH instrument cluster and the LOW instrument cluster posted on my CarDomain site. Just scroll down to which ever cluster you have and click on the pages...they will explode into a larger view...and if you run your cursor up/down the left/right side...arrows will appear that allow you to go back or forward to the previous or next page: http://www.cardomain.com/ride/3134093/6

Originally Posted by QSilver7

Yep...if you've unlocked your OBC...you can run TEST #7 and monitor your engine coolant as you drive around town.

If anyone needs instructions on how to unlock your OBC...I have instructions (with a brief explanation of the TESTs) for both the HIGH instrument cluster and the LOW instrument cluster posted on my CarDomain site. Just scroll down to which ever cluster you have and click on the pages...they will explode into a larger view...and if you run your cursor up/down the left/right side...arrows will appear that allow you to go back or forward to the previous or next page: http://www.cardomain.com/ride/3134093/6

From what I've read, this is not coolant temperature. This is the engine core temperature. You'll notice that your coolant dummy gauge gets up to operating temperature way before the OBC reads ~105^C. I'm not sure where this temp is taken from. It's not oil temp either though, because there is a test for that, but it doesn't display anything because there isn't an oil temp sensor on our cars like the 4.6 X5's have.

Originally Posted by washburn33

From what I've read, this is not coolant temperature. This is the engine core temperature. .

If that is true...then someone needs to tell BMW to rewrite the info...because it clearly states in the documents that it's coolant temp (you DID go the link I gave to read what the various tests were, right?).

See TEST 7 - HIGH Cluster:

See TEST 7 - LOW Cluster:

Originally Posted by QSilver7

I have instructionsfor both the HIGH instrument cluster and the LOW instrument cluster

I'll print them out and test 'em and report back.

This may be a dumb question ... but ...

How do I know whether I have the high or low instrument cluster in my 2002 525i (no navigation)?

Q:

Nice looking site! Can you net-net it for me -- what are the biggest benes from unlocking?

Originally Posted by Edgy36-39

Q:

Nice looking site! Can you net-net it for me -- what are the biggest benes from unlocking?

I don't know what net-net means?

The benefit of unlocking the OBC is to be able to check or view the information that the various TESTs reveal. For instance, TEST #9 gives the battery voltage (when ignition is in position 1 or 2)...and reveals the charging systems voltage when the engine is runnning. Or TEST #2 which is an instrument cluster test that shows if the lights and gauges work...or TEST #13 that let's you check if all 4 tones of the GONG is working.

You will read it repeatedly when people post questions about their car's not starting...and they don't know what's wrong because the lights come on and the radio works...but when they turn the ignition...all they hear is click, click, click. Well if you do TEST 9 (takes all of a few seconds) you can check your battery's voltage...if it is below 11.89volts...then the battery is at 0% state of charge...and may only require a jump or for the battery to be charged up.

And as in this thread...if your car is starting to overheat...or you're having an overheating situation...you can open TEST 7 and watch the coolant's temperature...and you can see if it's getting ready to overheat long before the needle moves to the red area in the gauge.

Here's a video of TEST #13...the GONG test. The 1st sound is the HOUR MEMO's 3 beeps, the 2nd sound is the ICE WARNING/OUTSIDE TEMP gong, the 3rd sound is the LOW FUEL/LIMIT MPH gong, and the 4th is the CHECK CONTROL gong sounds:

Originally Posted by QSilver7

And as in this thread...if your car is starting to overheat...or you're having an overheating situation...you can open TEST 7 and watch the coolant's temperature...and you can see if it's getting ready to overheat long before the needle moves to the red area in the gauge.

This is concerning a problem I may be having at the moment : What is the upper limit for coolant temperature? I've been advised on these forums that 115 to 120 is really the upper limit before trouble ensues.

Originally Posted by bluebee

I'll print them out and test 'em and report back.

This may be a dumb question ... but ...

How do I know whether I have the high or low instrument cluster in my 2002 525i (no navigation)?

What you have pictured there is indeed a high cluster
High:


Low cluster doesnt have that digital readout, instead it has the picture of the car to signify which doors are open etc...

Originally Posted by GrahamDesigns

What you have pictured there is indeed a high cluster

Thanks. Someone else also said I had the high cluster 'cuz of the two buttons (high) versus one (low).

So, for others, I guess you can tell which cluster you have by:

HIGH:
- Two buttons, 20-digit readout at the bottom, oil service to the left
LOW:
- One button, no 20-digit readout (car picture instead), oil service on right

(I'm amazed you guys just know a myriad of little things that I have no clue of ... ).

PS: Now my quest is to find out:
- The set point of my (presumably OEM) thermostat
- The blow point of my (presumably OEM) pressure cap

Then, I can figure out what's happening with the thermostat under normal operation.

Originally Posted by QSilver7

Yep...if you've unlocked your OBC...you can run TEST #7 and monitor your engine coolant as you drive around town.

If anyone needs instructions on how to unlock your OBC...I have instructions (with a brief explanation of the TESTs) for both the HIGH instrument cluster and the LOW instrument cluster posted on my CarDomain site. Just scroll down to which ever cluster you have and click on the pages...they will explode into a larger view...and if you run your cursor up/down the left/right side...arrows will appear that allow you to go back or forward to the previous or next page: http://www.cardomain.com/ride/3134093/6

Hey QSilver,

Thanks! Do you know if I can unlock my 1998 528i OBC using your instructions?

Thanks!

Where do you guys get this "core temperature" stuff? The "KTMP" is a German acronym for "Kühlmittel Temperatur", which translates to "Cooling Agent Temperature", which, in this case, is a mix of ethylene gycol and water.

BTW, the analog cluster gauge is buffered, so that it only stays at 12:00 unless the engine REALLY overheats. Then, it dives for the red. This keeps worrywarts from watching a fluctuating needle. The temp sensor has dual elements: one feeds the DME, and the other feeds the buffer circuit that drives the analog gauge.

The V8 runs at a considerably higher temp than the six, as noted above. The DME controls the thermostat to the extent that it can open it more when the engine is under a heavy load, to provide more coolant flow.

The slow speed of your electric fan kicks in at 196d F or 91d C.

The high speed kicks in at 219d F or 104d C.

Measured at the radiator outlet.

All per Bentley.

Like I said, this is just what I read. Your explanation seems to make much more sense.

Originally Posted by edjack

Where do you guys get this "core temperature" stuff? The "KTMP" is a German acronym for "Kühlmittel Temperatur", which translates to "Cooling Agent Temperature", which, in this case, is a mix of ethylene gycol and water.

BTW, the analog cluster gauge is buffered, so that it only stays at 12:00 unless the engine REALLY overheats. Then, it dives for the red. This keeps worrywarts from watching a fluctuating needle. The temp sensor has dual elements: one feeds the DME, and the other feeds the buffer circuit that drives the analog gauge.

The V8 runs at a considerably higher temp than the six, as noted above. The DME controls the thermostat to the extent that it can open it more when the engine is under a heavy load, to provide more coolant flow.

bluebee,

Your owner's manual has drawings of both clusters. If that's yours in the pic, it's high: it has the text message readout at the bottom center.

Originally Posted by cn90

Hey QSilver,

Thanks! Do you know if I can unlock my 1998 528i OBC using your instructions?

Thanks!

Yes, there are instructions at the link I posted for both the HIGH cluster and the LOW cluster. Just scroll down past the HIGH cluster instructions and you'll see the 1st page for the low instrument cluster and how to unlock it. It's a bit different since there's only 1 button on the instrument cluster...but still not difficult.

Here's a video uploaded by Edwin of the Netherlands...that shows how quickly and easy it is to unlock the OBC if you have the high cluster.

When the cluster is locked...just like it states in the written instructions at the link I posted above...if you try to open a LOCKED test...you will be taken directly to TEST 19 (which is the test that unlocks the OBC). So that is why when E goes to TEST 3...he can unlock his OBC...his cluster is locked and TEST 3 can't be used until the OBC is unlocked...so when he attemps to open it...he's taken directly to TEST 19:

Thanks to QSilver's instructions, I was able to read my 2002 525i "high" cluster all day today (Test No. 07) at low and medium speeds (up to about 65mph), from about 100 feet above sea level in Silicon Valley to over 2300 feet above sea level in the Santa Cruz mountains flanking the valley, and in ambient temperatures from about 54°F to 59°F with a light mist in the air.

During all that time, my "Kühlmittel Temperatur" Koolaid temperature fluctuated from as low as 84°Cto a high of 98°C, but mostly bell-curved around 88°C to 92°C.

As noted, during this entire fluctuation, the "buffered" analog gauge read just a hair shy of the noon position.

Specifically:
- Measured how? (answer = unlocked cluster)
- E39 Year/Engine? (answer = 2002 525iM54 2.5liter)
- Gauge position? (answer = just a hair shy of noon)
- Thermostat set point (I think it's OEM but I do not know the set point)
- Pressure-cap release point? (I think it's OEM but I do not know the set point)
- What is your coolant ethylene glycol percentage? (unknown)
- Radiator & fan & waterpump condition (85k miles)
- Test conditions (54°F to 59°F, light load, 100' to 2300')

Now that I know the warmed-up Koolaid temperature, once I figure out the set point of the thermostat, I can tell what the thermostat is actually doing!

Pressure cap info is known…..I think it's like 8 bar or something. Of course I can't remember it now…..

Edit: It's where I thought it was. 2 bar, not 8 (what was I thinking)
02 Radiator cap 2,0BAR 1 17111742231 $17.82 +core

Originally Posted by bmw_n00b13

Pressure cap is 2 bar
02 Radiatorcap 2,0BAR 1 17111742231 $17.82 +core

I wonder why I didn't see that as I searched RealOEM first before asking!

Since 1 bar is 14.5 psi, that must mean I have a 29 psi pressure cap.

Now all I need to find is the Thermostat temperature setting. Again, I don't see it in the realoem diagrams! ... nor in any of the listings on the net.

I'll check my paper Bentleys (still packed after the big move).

If you know the Thermostat temperature setting, that would complete the puzzle.

Yeah, I checked the realoem listings. It might not be listed for the 530 engine, but as far as I know they're the same. I was pretty sure it was there, which helped me find it.

Originally Posted by bmw_n00b13

Yeah, I checked the realoem listings

Weird that I didn't find it in RealOEM but no matter.
Thanks to you and cn90 and others I now have the basic datapoints to better understand what the thermostat is actually doing in my driving.

- 2002 I6 pressure cap is 2.0 bar (29 psi)
- Thermostat set point is 92°C (198°F)
- KTMP yesterday fluctuated from 84°C to 98°C (183°F to 208°F) but bellcurved between 88°C and 92°C at altitudes of 100' to 2300' and temperatures between 54°F and 59°F in misty air.

That means my thermostat is operating as cn90 said, in open-a-little-close-a-little mode constantly around the 92°C set point (hysteresis and bleeder holes aside).

Funny. I thought the thermostat operated in mostly-open mode; but this data seems to point to mostly-closed mode.

What might change this analysis is whether the KTMP is typically higher or lower than the temperaure AT the thermostat itself.

Any idea whether the KTMP is typically higher or lower than the thermostat coolant temperature?

The radiator test pressure is 1.5 bar = 21.75 psi

The cap test pressure is 2.0 bar = 29.0 psi