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

A bit more info.
The thermostat is in the cold water return from the radiator not the hot water out to the radiator. The thermostat has a heater which is controlled by the engine DME. The engine temp is kept hotter under light load and speed conditions. This is for emission reduction purposes. The M52TU and M54 engines have completely different cooling system flows compared to the earlier conventional cooling system M52 engines. They have minimal water flow through the block. Most of the water flow is through the head and is closely regulated by the engine DME controlling the heater in the thermostat. Under high load high speed conditions most of the water flow is through the radiator. This necessitates the need for an auxilliary water pump to ensure adequate water flow through the heater.
See these pdfs for more info:
http://www.ge39.com/files/m54x5.pdf
http://www.beisansystems.com/misc/SE...ROL_SYSTEM.pdf
edit: added this pdf see pages 16/17 for cooling system details http://www.bmwtech.ru/pdf/e46/ST034/9%20Engines.pdf

Hope this helps
RonR
99 528iT M52TU

Gary, who sells the modified expansion cap, explained this today:

Originally Posted by gary@germanautosolutions

I don't get on here as often as I would like, so I just stumbled across this thread.

There is a lot of good information here as well as a lot of misinformation.

When developing our coolant cap we risked possibly damaging two engines, an M52 e39 and an m54 e46. We tapped a pressure sensor into the air space at the top of the expansion tank and data logged system pressures from cold start up to full overheat (temp gauge pegged). To cause an overheating situation we removed the clutch fan and slid a full size sheet of cardboard between the radiator and AC evaporator to block the flow from the electric fan. We ran tests at proper fill levels, low fill levels and high fill levels.

We found the following:

1. The system runs below 1.0 bar at all normal operating temps.
2. A lower fill level results in lower pressure and a higher fill level results in higher pressure.
3. Overfilling the expansion tank beyond the proper cold fill level can result in system pressures over 2.0 bar, at which point the OEM cap will start to vent excess pressure.
4. Since the cooling system pressure, with a proper amount of coolant in the system (not overfilled), does not exceed 1.0 bar at any normal operating temperature, or even moderate overheating, the use of a 1.2 bar cap will not effect cooling system efficiency in any way.
5. 1.2 bar equates to a system temperature of approximately 126 deg C (260 deg F), which also equates to a fully pegged temp gauge.

For those that argue that the engine was engineered by BMW to use a 2.0 bar coolant cap and you shouldn't mess with it, consider this. BMW has used a 2.0 bar coolant cap on many models from 1982 to late 2000 something. These models have included iron block iron head engines, iron block aluminum head engines, and aluminum block aluminum head engines, in 4 cylinder, 6 cylinder, 8 cylinder and 10 cylinder configurations. Either they start from the coolant cap and design their engines from there, or the coolant cap is not an integral part of the engine design.

BMW has also moved away from the 2.0 bar system with most if not all current models using a 1.2 bar cap. I think the original thought process was to use a cap that was at the limit of the cooling system rated pressure to give the greatest amount of extreme overheat boil over protection. What they failed to take into account is that a 5 or 10 year old system has lost some of it's original strength, and that reaching a 2.0 bar pressure in these vehicles can cause things to go boom.

By the time my engine has overheated to the point that the bong and dash message have warned me, and my pegged temp gauge has warned me, I would rather pull over, shut off the engine, and let the 1.2 bar cap vent any excess pressure, rather than let the pressure rise until something expensive goes pop and I also need to call a tow truck. I also like the peace of mind that comes from knowing that if while in a hurry I overfill my expansion tank a little, that I don't run the risk of a catastrophic cooling system failure.

I would like to thank everyone again for all the support you have shown, and all the kind words you have expressed to German Auto Solutions. It's been a fun and busy first year with many good things in the works for the coming year.

Gary

JimLev kindly provided real world data ...

Originally Posted by JimLev

Here ya go. This is on my 2000 540 (M62tu engine) with the 2 bar cap. I do have a 1.4 bar cap but didn't use it as the cap doesn't effect the pressure.

I did this last fall, so the outside air temps were not in the 90's, no AC either.
I'll do it again this summer and see if it changes much.
It was posted and graphed on the other message board.
I heated the engine up in my driveway with the electric fan off to allow the engine to heat up quicker.
When the KTMP reached 103C I took the car out for a spirited drive, the temp never rose above 105C.

KTMP Reading/PSI Reading

• 40C/1.5 PSI = 0.10 bar
• 45C/2 PSI = 0.14 bar
• 50C/2.25 PSI = 0.16 bar
• 55C/2.5 PSI = 0.17 bar
• 60C/3.0 PSI = 0.21 bar
• 65C/3.25 PSI = 0.22 bar
• 70C/3.5 PSI = 0.24 bar
• 75C/4.0 PSI = 0.28 bar
• 80C/5 PSI = 0.35 bar
• 85C/6 PSI = 0.41 bar
• 90C/6.5 PSI = 0.45 bar
• 95C/7.5 PSI = 0.52 bar
• 100C/9.0 PSI = 0.62 bar
• 105C/16.5 PSI = 1.14 bar

When I returned from my drive I released some pressure via the cap. It was then down around 5 PSI. I went out for another drive, when I returned it was still at 5 PSI.
I'm going to modify the t-stat heater circuit to drop the temp which will drop the pressure.

Originally Posted by JimLev

The cap does not control the pressure. That is a function of the system temp.
The cap only vents the system when it reaches the cap pressure.
For the 540 tu engines that run at ~108°F the system pressure is around 17-18 PSI.

Note: 17 to 18 psi is about 1.2 bar (to one decimal place).

While researching the answer to this question:

Originally Posted by L0F

So there's a bit of discussion on what "normal" operating temp range is for our cars once warmed up. Most of the figures I've seen for my m52 have been ballparks ~88-95. We know when and at what temp they overheat at, but what I would like to know is the factory stated standard operating temperature. With out knowing this value it leaves a grey area between "running hot" and over heating. I don't like grey areas.

I revisited this M62 document which shows the characteristic "normal" temperatures for the V8:
- M62 Engine Details.pdf (585.3 KB, 514 views)

Characteristic map thermostat
The thermostat is integrated in the housing of the water pump. As on the M60, a conventional thermostat with integrated vent valve is installed on the E31 with M62 engine. This thermostat opens at 85 o C.

A new characteristic map-controlled thermostat is used on the vehicle series E38 and E39 with M62 engine.

Function of a conventional thermostat
The control of the engine cooling system with a conventional thermostat is determined by the coolant temperature only. This control system can be subdivided into three operating ranges:

Thermostat closed:
The coolant only flows in the engine. The radiator circuit is closed.
Thermostat open:
The entire volume of coolant flows via the radiator. This ensures the maximum cooling capacity available is utilized.
Thermostat control range:
A part of the coolant volume flows via the radiator. The thermostat sets a constant engine inlet temperature within the control range.

With the aid of the characteristic map thermostat, the coolant temperature can now be influenced specifically within this operating range (thermostat control range). In this way it is possible to set a higher coolant temperature in the partial load range of the engine. Higher operating temperatures in the partial load range achieve improved combustion, reflected in lower fuel consumption and pollutant emission. However, higher operating temperatures in the full load range would involve specific disadvantages (ignition timing (angle) reduction due to knocking). For this reason, lower coolant temperatures are set specifically in the full load range with the aid of the characteristic map thermostat.

I opened a separate thread to ask what the coolant flow is in the respective M52, M54, and M62 expansion tanks:
- Does anyone have a BMW description of HOW the E39 expansion tank actually works?

So did anyone ever actually answer at what temp range the m62 (not with electronically controlled thermostat) is supposed to run at? Also, any answer as where the needle stays, wether slightly to the left, slightly to the right, or dead center? The needle on my old 97 540i always sat a smidge to the left of dead center, and on my new (to me) 98 540i, the needle is a smidge to the right of dead center, with KTEMP readings of 105-107 C.

dont know about M62 but my M54's keep it 93C - 95C

Originally Posted by mrpumpk1n

So did anyone ever actually answer at what temp range the m62 (not with electronically controlled thermostat) is supposed to run at?.

I'm confused, but I don't know any other engine but the M54 that I have.
But, isn't the M62 covered in post #79?

My 92 E36 318iS Coupe had a 200kpa/2.0 bar pressure cap. My E39 M52TU has a 200kpa cap. It seems most BMWs from that time have a 200kpa radiator pressure cap irrespective of which engine. There are bound to be some exceptions that prove the rule though. M series engines perhaps???
From Realoem.com
http://www.realoem.com/bmw/showparts...61&hg=17&fg=05
The M54 and M52TU engines should have a 97degC thermostat according to the TIS. The M52 has a 92degC thermostat. The M62 and M62TU engines don't get a mention as far as thermostats go. MMMMM?

RonR
99 528iT M52TU

Is the pressure cap rated at 29psi absolute or gauge, because that is a huge difference.

Its gauge pressure. ie: pressure above atmospheric.

RonR

unlocked OBC shows coolant temp at 92C, this is after about 20 minutes on the highway the highest i have seen is 94C. 528i M52tu

Originally Posted by kapetajr

92C

Wow. That's one of the lowest. They must have run the older E39 I6 engines considerably cooler than the newer ones.

97-98 m52b28's (Not TU's) use a 92 degree mechanical thermostat produced by wahler. Mine's typically been around 94 while on the highway this winter. It's also very cold in Chicago, 16 degrees f right now, so the heat blasting is a must.

In town the car seems to run hotter, highest temp I've seen was 101 and that was from idling for some time.

My electric fan died on me so while I'm waiting for the new one to come in, I've been driving without a working fan for the past few days while closely watching test #7. During normal highway driving I get around 104C, local roads/light traffic 108C-110C. The highest I've seen was 116C and this is where the temp needle starts to move right. 114C is still right on 12 o'clock, 115C does not show up at all for some reason, the next one 116C is where I saw the needle move slightly to the right from the 12 o'clock position.

After another coolant catastrophe, I just took my car for a test drive and recorded the following temperatures:

Detail
528i UK model
Manual says its a M52 B28 engine (Not TU)
August 1998 production

Temperatures
Read from unlocked debug test on the dash (test 7)

Warming up, I got 75C just as the needle reached mid-point. the needle stayed rock steady in the middle throughout

Went to 98C - 100C while getting out of town in moderate traffic/lights etc

Reached 102C max while on dual carriageway, doing 50 - 70 mph. Most of the time it was 100C - 101C.

Wellied it and hit the big button several times. This didn't seem to affect the general temperature.

I conclude that right or wrong, my car is operating in the 98C to 102C range under normal warmed up driving conditions.

My manual says that the thermostat opens at 92C.

For my 97 540, without the ac, the coolant will be steady at 105C, no matter I am at the highway or stuck in traffic. After the car had been driven long enough, roughly 2 hours, the VC fan will start to kick in and lower it to 95C.
But with the ac on, the temp will stay between 87-95C, it is running at much lower temp with the AC on, as the AC fan will move the air. Plus the hot air from the ac condenser will get the VC fan kick in as well. Whenever the coolant temp is below 90C, I can hear the roar of the fan.