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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 02-07-2010, 04:12 AM
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aca84 aca84 is offline
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Boiling Coolant

Hi Guys,

Before going further, I'd like to point out that in the last year, I've had the following components replaced as a precaution:

- thermostat
- water pump
- expansion tank
- various hoses and a belt.

I've also had to deal with a small radiator leak (which was the last coolant leak I've had to deal with). This was probably 10 months ago. Since then I've had to top up coolant slightly probably once every 3-4 months.

Anyhow today, I just came home from a 100Km (60 mile) journey (predominantly on the highway) and just before shutting off the car, I noticed a stranged gurgling noise eminating from the engine bay.

So I went and opened the hood to notice coolant overflowing from the expansion tank cap. The coolant was also boiling I imagine from the loud gurgling noise. There was a considerable amount which had leaked and was actually falling onto the driveway. The only source of the leak that I noticed was from the top of the expansion tank.

Throughout the journey, the temperature needle was at the 12 o'clock position and the car seemed to operating as per normal. What I'd like to know is if this a problem with the expansion tank (even just the cap?) or whether it could it be an issue with other components?

Thanks everyone in advance!

edit: Car has done 110 000Km (70,000 miles). Water pump, thermostat and expansion tank replaced at 57000 miles.

Last edited by aca84; 02-07-2010 at 04:56 AM.
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  #2  
Old 02-07-2010, 05:25 AM
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aca84 aca84 is offline
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Ok just a little update. It's been 1.5 hours now and after opening the cap, noticed that there was no coolant at all in the tank. So after filling up and starting the car for around 5mins the coolant temperature was reading 120 degrees (248F). The needle remained at 12 o'clock. << Info for troubleshooting purposes

Now as mentioned earlier, I've been topping up coolant every 3-4 months due to a small loss of coolant. I infact topped up coolant today before my 120 mile journey. I'm now wondering whether the problem was caused by me not tightening the cap properly as it removed very easily just now
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Old 02-07-2010, 06:24 AM
Waveho Waveho is offline
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It's possible that you overfilled with coolant? And did you use the proper coolant? The cap is designed to express fluid under extreme pressure, such as when overfull. Best way to make sure that it is at proper level is to open the cap in the morning before starting--top of the stick should be bobbing right at the lip of the cap opening, but not sticking too far up. Stone cold is a good time to bleed the system as well. Coolant should be either BMW coolant or silicate/phosphate-free coolant mixed with either de-ionized or distilled water only. A mixture of 60% coolant and 40% water is a good balance.
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  #4  
Old 02-07-2010, 06:54 AM
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bmw_n00b13 bmw_n00b13 is offline
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Did you replace the lid? If it's operating under spec it will cause a boil-over.
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  #5  
Old 02-07-2010, 12:12 PM
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Quote:
Originally Posted by Waveho View Post
It's possible that you overfilled with coolant? And did you use the proper coolant? The cap is designed to express fluid under extreme pressure, such as when overfull. Best way to make sure that it is at proper level is to open the cap in the morning before starting--top of the stick should be bobbing right at the lip of the cap opening, but not sticking too far up. Stone cold is a good time to bleed the system as well. Coolant should be either BMW coolant or silicate/phosphate-free coolant mixed with either de-ionized or distilled water only. A mixture of 60% coolant and 40% water is a good balance.
I only ever top up till the dipstick bobs up to the level of the cap. And yep, I only fill when cold (unless in emergency :P) As I've only ever had to top up a little amount every now and again, I've been using just distilled water... But now, along with a pressure test, I think I'll get the the whole system flushed and refilled.

Interesting to note though that I didn't have any issues 1/2 along my trip...so I'm hoping it's stupid me not having tightened the lid and it came loose over time.

Quote:
Originally Posted by bmw_n00b13 View Post
Did you replace the lid? If it's operating under spec it will cause a boil-over.
This is what I'm hoping! I could loosen the cap with my little finger last night
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  #6  
Old 02-07-2010, 04:05 PM
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bmw_n00b13 bmw_n00b13 is offline
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I didn't notice on the first post-120C is too high. Check your fan clutch, but I suspect there's a problem with the radiator or thermostat.
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  #7  
Old 02-07-2010, 04:24 PM
cn90 cn90 is online now
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With coolant boiling and it is 120 deg C, it is either:

1. Defective Reservoir Cap.

2. Head Gasket failure.

The mistake you made is that you tried to nickle an dime the radiator (I don't know how much the radiator costs in Australia but here in the US about US$200), even minor coolant loss from a leaking radiator can be disastrous as you just learned.

Info on 1998 528i cooling system is here:
http://www.bimmerboard.com/forums/posts/199986
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  #8  
Old 02-08-2010, 12:07 AM
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Quote:
Originally Posted by cn90 View Post
The mistake you made is that you tried to nickle an dime the radiator (I don't know how much the radiator costs in Australia but here in the US about US$200), even minor coolant loss from a leaking radiator can be disastrous as you just learned.

Info on 1998 528i cooling system is here:
http://www.bimmerboard.com/forums/posts/199986
+1

You shouldn't be filling and filling.... and trust me... you don't want to be... I got my new radiator for $100.... but even at twice this.... the problem with your solution is you are getting air into the system and even a perfect system .... in a perfect world... with the perfect coolant... air in this system and you will be blowing sh1t up left and right......

If you are losing fluid fix the leak.... at which point I will be more than happy to help you get rid of the air.... which I believe to be your issue....
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Old 02-08-2010, 02:02 AM
Beemaboy Beemaboy is offline
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There is something very wrong with either the temp sensor or the instrument cluster if the guage is dead centre at 120C! At 120C, your temp guage should be just over the 3/4 mark! It should start moving off centre at 115C, be inbetween 1/2 and 3/4 at about 118C. It will be in the red at 124C, which is when you engine starts to melt

Had exactly the same problem for months...turned out to be a cracked cylinder head...
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  #10  
Old 02-08-2010, 04:15 AM
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aca84 aca84 is offline
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bmw_n00b13, cn90, atrovarious and Beemaboy - Thank you all for your replies! I have addressed some of your concerns below.

With regards to the radiator, I was planning on replacing the unit at around the 120,000Km mark which is what I've read is a good time to replace it on these forums. I will certainly look at having this replaced when I have the coolant system checked over next week (I'm away on work till the weekend ).

With regards to the instrument cluster, the test 2 showed no issues with the temperature gauge the last time I checked. I recorded that coolant temperature around 1.5 hours after initially noticing the problem. Obviously I stopped the car for that 1.5 hours, refilled and started the car and left it running for around 5 mins and the temperature began at around 107 and climbed to 120 during that time (the car was stationary). But I maintain that the gauge did not budge from the 1/2 way mark Are the temperatures measured at two different locations? (for the analogue vs digital readouts?) The car was running perfectly so I hope I haven't caused any long term damage. What are tell tale signs of head gasket problems? And are there any tests that I should request the mechanic complete?

This morning, I checked the expansion tank, and it was bone dry again. Didn't notice any leaks so I hope it was due to having lost so much coolant last night via the cap that I'm having to really fill it up. Car wasn't started at all today (and probably won't be till I get back).

I checked the fan clutch in the morning, and it felt like "mollasses" as some have described it here, so that appears to be fine. However, on really warm days, I have had a fan in the engine bay sounding like a blower (irrespective of whether the air con is on or not) and increasing with RPM's. I recently purused these forums regarding that issue also and I gather that it may be normal operation on really warm days?

Keep any suggestions coming forth and I'll definitely keep updating my situation (especially after having it all checked out next week). Thanks once again!

Last edited by aca84; 02-08-2010 at 04:52 AM.
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Old 02-08-2010, 04:22 AM
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Quote:
Originally Posted by cn90 View Post
With coolant boiling and it is 120 deg C, it is either:

1. Defective Reservoir Cap.

2. Head Gasket failure.

The mistake you made is that you tried to nickle an dime the radiator (I don't know how much the radiator costs in Australia but here in the US about US$200), even minor coolant loss from a leaking radiator can be disastrous as you just learned.

Info on 1998 528i cooling system is here:
http://www.bimmerboard.com/forums/posts/199986
Can I just rearfirm, that the resevoir cap was on really loosely when I noticed the problem the first time, (and coolant was leaking only from the cap as far as I could tell). So I'm clinging on to hope the problem is due to number 1 (either cap being defective or me not having tightened it properly) and not 2!

Last edited by aca84; 02-08-2010 at 04:49 AM.
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  #12  
Old 02-08-2010, 05:33 AM
cn90 cn90 is online now
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Yes, a loose reservoir cap WILL cause a boil over.
Change your cap!
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Old 02-08-2010, 06:50 AM
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Quote:
Originally Posted by aca84 View Post
the coolant temperature was reading 120 degrees (248F).
In other threads, I'm trying to understand the function of the thermostat at operating temperature (not at startup).

My hypothesis is that the thermostat is "wide open" and does "nothing" to regulate temperature once it's set point is reached (within a few degrees anyway). We know what the set point is of the thermostat; we just need to know what the coolant temperature is to understand what the thermostat is doing at that temperature.

One unanswered question in those threads is the typical normal operating temperature of the coolant.

How did you figure out that the coolant was reading 120/248 degrees (C/F)?




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Old 02-08-2010, 07:07 AM
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I don't think it's too far-out there to guess that the thermostat opens at 90C for the 6s and 100 for the V8s.
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  #15  
Old 02-08-2010, 07:45 AM
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Quote:
Originally Posted by bluebee View Post
...My hypothesis is that the thermostat is "wide open" and does "nothing" to regulate temperature once it's set point is reached.....
Actually, car engineers design the cooling system like this: Let's say the engine heat production is 150,000 BTU/h.
Then the radiator is designed to remove heat at the rate of 200,000 BTU/h or so.

So the heat dissipation of the radiator always exceeds the heat production by the engine.

Look at it this way: let's say engine coolant temp is 100C and Las Vegas in July air temp is 40C, there is a 60C temp differential. Now, remove the thermostat in any car, and run it on the hottest day on earth, the car will run "cool", maybe around 80C coolant temp.

The best way to understand the function of the thermostat in the car is to look at this "experiment":

- Place a cooking oven (electric or natural gas) outdoor at the mercy of outdoor weather.

- Let's say you want to the heat of the oven to be 100C (oven temp is analogy to engine coolant temp)

- And let's say your only means of regulating the oven temp is the Oven Door itself.

- Think about the oven door as the thermostat. So during warmup phase, the door is closed. When temp reaches 100C, you open the door a bit to allow some heat to escape.

- Let' say temp keeps climbing (full throttle!), you open the oven door a bit more so heat can escape. But if you open the door wide open (such as a failed thermostat in the car), the oven will be cool.

- And of course ambient temp is also important in the operation of the "oven door".

So basically the car thermostat operation is a dynamic process: the "oven door" regulates temp to 100C based on:
- Heat production of the oven.
- How wide the oven door is open.
- Ambient temp and wind condition (heat dissipation).

HTH

Last edited by cn90; 02-09-2010 at 05:53 AM.
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Old 02-08-2010, 01:42 PM
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Bluebee, I retrieved the coolant temperature from the OBC after unlocking it (test 7). Personally, I've found the coolant temperature to hover somewhere between 100 to 110 or so when everything is running normally.
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Old 02-08-2010, 07:32 PM
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Quote:
Originally Posted by cn90 View Post
Actually, car engineers design the cooling system like this: Let's say the gnine heat produtcion is 150,000 BTU/h.
Then the radiator is designed to remove heat at the rate of 200,000 BTU/h or so.

So the heat dissipation of the radiator always exceeds the heat production by the engine.

Look at it this way: let's say engine coolant temp is 100C and Las Vegas in July air temp of 40C, there is a 60C temp defferential. Now, remove the thermostat in any car, and run it on the hottest day on earth, the car will run "cool", maybe around 80C coolant temp.

The best way to understand the function of the thermostat in the car is to look at this "experiment":

- Place a cooking oven (electric or natural gas) outdoor at the mercy of outdoor weather.

- Let's say you want to the heat of the oven to be 100C (oven temp is anaology to engine coolant temp)

- And let's say your only means of regulating the oven temp is the Oven Door itself.

- Think about the oven door as the thermostat. So during warmup phase, the door is closed. When temp reaches 100C, you open the door a bit to allow some heat to escape.

- Let' say temp keeps climbing (full throttle!), you open the oven door a bit more so heat can escape. But if you open the door wide open (such as a failed thermostat in the car), the oven will be cool.

- And of course ambient temp is also important in the operation of the "oven door".

So basically the car thermostat operation is a dynamic process: the "oven door" regulates temp to 100C based on:
- Heat production of the oven.
- How wide the oven door is open.
- Ambient temp and wind condition (heat dissipation).

HTH
What a great description of how that device works. I believe many people think that it is either fully open or fully closed. This makes it crystal clear.
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Old 02-08-2010, 09:22 PM
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Quote:
Originally Posted by occhis View Post
I believe many people think that it is either fully open or fully closed.
I'm trying desperately to understand the nominal operation of the thermostat.

I fully understood the oven analogy but that still doesn't tell me what the temperature of the coolant is under "normal operating temperatures".

Seems to me ... (assuming we're not talking about warmup) ...

a) If coolant temperature fluctuates both above and below the thermostat set point, then indeed the "open/close oven door regulation" mechanism fully applies.

However ...

b) If coolant temperature is always (or almost always) above the thermostat set point, then the thermostat is acting like a permanently open oven door.

All I'm trying to understand is the coolant temperature. Once I figure THAT out, then we know exactly what the thermostat is doing at that temperature.

I'll look up how to "unlock the cluster" so that I can better figure out my coolant temperature. Seems to me, that's the key to unlock the question whether the E39 thermostat is operating in mode (a) or (b).

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Old 02-08-2010, 09:38 PM
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Originally Posted by bmw_n00b13 View Post
the thermostat opens at 90C for the 6s and 100 for the V8s.
I assume we all know "how" a thermostat works, i.e., it opens above its set point and closes below its set point (hysteresis notwithstanding) ...

I also assume we know the set point of any particular thermostat (e.g., we can assume 90C for the I6 and 100C for the V8) ...

The question isn't "how" my thermostat works; nor is the question "when" does my thermostat open or close; the question is what is my cooling system temperature (well after warmup).

If I can figure out what the actual temperature is of my coolant dynamically, then I can easily tell whether the thermostat is operating in always-open mode or if it's operating in cn90-oven-door-regulation mode.

I'll concentrate on trying to figure out my (normal) engine coolant temperature since that's the only unknown here.

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Old 02-09-2010, 12:39 AM
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aca84 aca84 is offline
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Information for unlocking the OBC is here (I have the LOW OBC so don't get any coolant warning's on the display):

Unlocking the OBC (High and Low)

From my experience with the I6, I'd say the thermostat is fully open once the engine has warmed up.
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Old 02-09-2010, 06:07 AM
cn90 cn90 is online now
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bluebee,

Yes the thermostat opens completely at let's say 103C. But there is more to it.
The 103C coolant now flows to the UPPER radiator hose, through the radiator itself, and depending on outdoor temp (let's say it is minus 10C, yes it is -10C in Nebraska today!), the coolant will leave the LOWER radiator hose (back to the engine) at let's say 50C or so, now the engine receives "cool" 50C coolant ---> the engine is cooled down below 103C.

The thermostat now closes down a bit, maybe 50% ajar or so, reducing flow to the UPPER radiator hose to keep the temp at 103C +/- 5 C or so.

Anyway, another way to understand the thermostat is the house analogy. Let's say you want your house at 20C and outdoor is -40C (temp differential of 60C).
Let's say the furnace runs non-stop, producing heat and you want to cool the house down. Let's say temp now goes up to 40C in the house, you open the front door (which is the thermostat!) to cool the house down to your desired temp of 20C.

So, the thermostat open amount is a "dynamic" process and the amount of opening, whether it is 10%, 20%, 50% or 100% opened, depends on the engine coolant temp, which in turn is affected by the LOWER radiator hose feeding cooler return coolant, which is in turn affected by the radiator+outdoor temp+wind speed etc.

HTH.
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Old 02-10-2010, 06:19 AM
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Quote:
Originally Posted by cn90 View Post
the thermostat open amount is a "dynamic" process and the amount of opening, whether it is 10%, 20%, 50% or 100% opened, depends on the engine coolant temp
I understand all of what you say, in theory. In practice, what actually happens depends on the actual coolant temperature at the thermostat and the thermostat set point.

To that end, I figured out my dynamic coolant temperature; but I'm not sure WHERE that coolant temperature is measured (upper or lower) ... and I haven't yet figured out what my (presumably all OEM) 2002 BMW 525i thermostat set point is (nor my pressure cap overflow limit).

Once I figure those four things out, I'll better understand, in practice, what the thermostat is doing:
- What is my dynamic Koolaid KTMP (see picture below)
- Where in the system is that KTMP measured
- What temperature is my thermostat set point
- What bar/psi is my expansion tank pressure cap set to blow at

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  #23  
Old 02-10-2010, 07:58 AM
cn90 cn90 is online now
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bluebee,

In my car, the coolant temp (as shown in the cockpit) is measured using a temp sensor at the rear of the engine block, around cylinders #5-6 or so.
The other temp sensor mounted on the radiator (or LOWER radiator hose for cars made after 1999) is a different sensor which controls the operation of the Aux Fan (the Fan that sits behind the front bumper).

Last edited by cn90; 02-10-2010 at 08:08 AM.
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  #24  
Old 02-10-2010, 08:03 AM
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Originally Posted by cn90 View Post
temp sensor at the rear of the engine block, around cylinders #5-6 ... The other temp sensor mounted on the radiator
Is there a good way to get the "other" temperature sensor reading?
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  #25  
Old 02-10-2010, 08:11 AM
cn90 cn90 is online now
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A thought: get a meat thermometer, then drill a hole through a used plastic bleeder screw, then insert the meat thermometer through the screw, apply some silicone caulking.
Let it sit for a day. Then with engine cool, insert this meat thermometer and do a measurement with engine running.
And only remove this meat thermometer when the engine has cooled completely!
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