My car has 160,000 miles, I've done the cooling system twice. Both times the system was easy to bleed and required no thought or observations.

 

You are correct, sir. Just do the job(s) professionally per my guide and you'll never experience a problem in your entire lifetime.

 

Fair observations.

Point # 11. Your BMW doesn't necessarily like to run at 97C - The EPA likes it running at 97C. I like mine running at 93C which it does by using a European market replacement t-stat.

The "black box" as you referred to it, is a variable based upon the total history of the car and the efficient operation of all related components. Many simply raise the front end and rev the engine during bleeding to ensure circulation through the secondary coolant branch that feeds the heater core and heater valve.

BMW recognized many deficiencies on the e46 and fixed them for the next gen - in the e9x bleeding is an automated sequence performed by the DME and the electric waterpump.

Welcome to the forum.

 

The "black box" as you referred to it, is a variable based upon the total history of the car and the efficient operation of all related components.

^This. Every car is unique to a degree, but the "standard" bleeding procedure has proven to work for the majority of cases and is a good starting point.

You seem to be an exception, and I'm sorry for your struggles with the cooling system. Good luck getting it resolved.

 

Mine is running even highier.see below.
Any suggestions?

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I totally agree with #5. The heater control valve is open in the default position. If you worried about the heater control valve, just unplug it while bleeding the cooling system. There is too much bad information propagated about turning on the heater in these cars.

The confusion or constant statements about turning the heater on for bleeding may be a carry over from models with the Coolant Pump integrated into the heater control valve for running the heater when the car is turned off. I think??? the M3 may have this feature or it may be optional depending on if the car has the NAV option, I know the E39 M5 has this option and some of the other models may have this feature with a small electric coolant pump integrated into the heater control valve. A quick review appears that this Coolant Pump integrated into the heater control valve is used primarily in European model E46 and only in the US E46 M3 and it may be an option on the US E46 M3, so not all of them may have this feature.

Search the M3 in Realoem.com and you will see there is an option for the heater control valve with pump.

http://www.realoem.com/bmw/enUS/showparts?id=BL93-USA-08-2001-E46-BMW-M3&diagId=64_0890

The standard US E46's do not have this option. It may be that cars with NAV may have this as a feature, maybe only the M3 with NAV, I have not really tracked this across the models.

 

There was one time I forgot to do the heater on step and had issues getting heat, re-bled with it on and problem solved.

 

I had a similar issue to yourself that you described in point number 1. The "typical" coolant flush process gave me an issue when I redid the cooling system and the car would get up to the point of over heating. Luckily I never drove it until I resolved the problem was fixed so it would never get hot enough for long enough to create any problems with the HG or to warp the head.

I appreciate that you gave data points as well. I went with the Behr thermostat. My car tends to run at between 198 and 204 deg F while in moderate traffic. Usually around 201 F (94 C). As for highway it tends to run at about 194 to 200 deg F or about 90 to 92 C.

Anyways, welcome and great first post.

 

This is indeed a full cooling system overhaul. :thumbup:
Looks like the hard coolant pipes came out in one piece. This doesn't happen often...


I have not replaced yet anything downstream of the heater control valve, since these components are unlikely to cause a significant leak that will get me stranded when one of them fails.
The heating also doesn't get a lot of use around here...

 

I use the standard bleeding procedure and it works fine. Some have also used the alternative method where you rev the engine to 4-5K rpm for 20 secs and then turn off the engine. Start with the system closed and cold. Add coolant as needed...repeat until the level is stable. Make sure you end with the level between min and max since there's no mark for 'over max.'

 

since there's no mark for 'over max.'

Or dmax.

 

BMW-North, I appreciate learning that there are different temperature thermostats available for the E46. The idea of running the engine at a cooler temperature is appealing to me. I would be curious to know how the DME in my car would handle a lower-temperature thermostat. I suspect that it would not be a big deal. The radiator fan would be triggered less frequently, for one thing.

I compared the thermostat of my 2010 Accord with my 2002 325i. I put them in a pot of water and slowly heated the water. Here are the numbers I observed:

Honda (normally runs at 83C)
start opening 82 - 84C (179.6 - 183.2 F)
fully open 95 - 97C (203 - 206.6 F)

BMW (normally runs at 97C)
start opening 95-97 (203 - 206.6 F)
fully open 99-100 (210.2 - 212 F)

What is interesting to me is that the operating temperature I am most likely to see while driving is also the temperature at which the thermostat just starts to visibly open. My understanding is that the thermostat valve constantly moves up or down slightly in response to the temperature change, and that a thermostat is not just an "on-off" valve that stays fully open once a temperature threshold is crossed.

Of course, the "pot of water test" does not take into account the coolant pressure that may be exerted on the thermostat valve due to the water pump. All such bench-top testing can only be an approximation of real-world conditions.

Megalocnus, you are right, the hard plastic pipes were a pain to remove. They broke off. I dug out the remnants very carefully with a screw driver, taking care only to dig into the plastic portions, not touching the aluminum surface of head/block passages.

Ever since I performed vacuum bleeding of the coolant, my BMW has been working just fine. I was pleased at how many subsequent "monkey motion" steps it saved: Waiting for engine to cool down, checking the coolant, reving the engine, checking the heater, squeezing the hoses, raising the front end, repeatedly adding coolant. I was literally done bleeding with that one step, other than adding a cup or so of coolant the next day. No overheating, no problems. I am enjoying a car that drives and handles nicely.

 

emineid,

You need to be careful about testing thermostats in boiling water and thinking you know how they function. There is a lot more to what is going on then some people initially think.

The biggest problems with thermostats is the main springs get weak over time and they open too early. This is referred to as a "soft" failure.

Most modern vehicles operate at around 205F/96C, keep in mind you may find a thermostat with a 185F/85C value stamped on the thermostat, but find the engine runs around 205F/96C. This is due to where the temperature sensor on most engines is located. Most engines have the coolant/engine temperature sensor located in the rear of the cylinder head where the coolant starts to return to the radiator. So the typical engine operating temperature is 10-15F or 11-14C higher than the thermostat rating in most cases.

I would bet your Honda may be running too cool, but I do not have specifics about your car and I have no idea if it is stock or modified. Again, most engines run/operate in the 205F/96C range and I would doubt the Honda is supposed to be operating at 83C.

While you and others think that running a colder thermostat in the E46 may be a good idea, I would not do this for a number of reasons. Part of the efficiency and wear levels are based on the 205F/96C temps the engine is designed to operate at. While there was a cooler thermostat offered in Europe, the engine also has a different DME tune and it is possible that the engine could run slightly Rich depending on the DME fuel Map. While the engine should operate at a 14.7-1 Air/Fuel ratio, the DME can and will shift this ratio to a Richer mixture as the engine coolant temperatures drop. So an offset is put in place on many of the DME/ECU fuel Maps. I do not know exactly where the fuel Map shifts in the DME, but it is something to think about.

I am not convinced that operating the engine cooler will do anything positive for you or anyone else. Look at number of E46 produced and how long they typically last. The BIGGEST heat contributor and problem for these cars is not the engine coolant temperature, it is the way the exhaust manifold with the integrated catalytic converters are designed. With the catalytic converters effectively mounted on the side of the engine and not under the car, the excessive heat from the catalytic converters will cook everything under the hood and the first 20-30 minutes when the engine is turned off and the engine heat soaks under the hood is the absolute worst case scenario for under hood temperatures on these car.

Just some things to consider and think about before you jump down a Rabbit Hole.

BTW, I have the ability to vacuum fill engine cooling systems and use this quite often. I have still had problems using the vacuum fill method, but this usually means there is an additional problem that has not been corrected.

 

Good observations. BMWs run hot on purpose for economy. They cool down when load is demanded for performance. Dynamic cooling. Older cars typically couldn't have this fine control on temps so they'd just run cooler.

And you are right, localized hot spots can cause a crack on one side of the head, headgasket, etc. This is why don't do lazy bleeds and as I've always said, do more than a few bleeds. All my E46/E36 cooling jobs have had platinum plus success using my furious touches combined with professional BMW factory methods.

Always go pro!

 

emineid the DME logic along with the IHKA logic is coded with threshold values. If you are familiar with the Temp Gauge Buffer adjustment you will note that the hex file loaded in the firmware has values which cause actions to occur. The t-stat on our cars is mainly mechanical and is forced open by DME only during extreme circumstance as a safegaurd for related components. The DME thresholds will accommodate the different t-stat mechanical values.

I will concede as Mango and JFOJ pointed out that there is a trade off to running a cooler engine - that being fuel economy and emission burn off. The statement "BMW's run hot for fuel economy" might not be accurate as they don't run this hot in the rest of the world. If you read the descriptive narrative of BMW Cooling logic put out a decade ago you will note the many references to environmental regulatory requirements (EPA) and the selling (marketing) of the "green theme". Personally speaking, having lived in Europe for many years I'll take the lower engine temps, power and longer part life (reduced extreme thermal cycles) and pay a little more for fuel.

9 years ago I had an ET explode - I swore it would never occur again and it has not. I've been running a cooler t-stat in my 330i e46 for a number of years without any noticeable decrease in fuel efficiency (I average around 7.9 - 8.1 l/100km) - opening a can of worms now, but I combined the t-stat with a water pump that pushes more volume I hoped to address the Achilles heal of this car which is the cooling system and the damage caused by overheating.

Not all will agree, and that's fine - it's their car. I don't force people to do what I do nor do I infer it is the best or only approach. The cooling system on the e46 is a fabulous characteristically mapped design that can adapt to various climates and options - I chose to take advantage of that for my own preference (a cooler operating car) - The e46 cooling system had some weaknesses and those were purposely changed after the e46 to address many of the issues that are the biggest topics on here.

 

Not sure why this is so important for 10+ year old cars, replace the expansion and CAP tank every 8-10 years and do not over fill the cooling system.

The problem is sometimes these issues come up, then there is a mad dash of insanity to jump through un-necessary hoops.

I will say, I do not like the fact that my 4.8L E70 X5 runs at 230F! I would prefer it to operated at 205F So I have a solution for that.

There is a BIG difference between 230F and 205F! The valve seals are NOT happy with 230F and they do not last very long.

 

jfoj, it is interesting that you mention how the wax element of the thermostat does not "see" the same temperature as the coolant temp sensor in the rear of the engine. In the M54 engine, the coolant is hottest as it exits the coin-size hole in the back of the recess that the thermostat fits into. When the thermostat is closed (cold), the wax element "sees" this hottest coolant temperature. That coolant had a direct passage from the back of the engine where the temp sensor is, and did not have a chance to cool off yet. So when the thermostat is closed, the thermostat sees the same (or perhaps slightly higher) temperature as that reported by the coolant temp sensor.

As the thermostat starts to open (at approximately 95-97C), there is a small amount of lower temperature fluid in the return hose from the radiator that mixes with the hot coolant from the head. The wax element "sees" this mixture. At normal operating temperatures, a substantial portion of the coolant to the thermostat still comes from the cylinder head, rather than the radiator. I would estimate that at normal operating temperatures (96-97C, say), the thermostat still sees essentially the same temperature as the coolant temp sensor in the back of the engine. The engine typically operates right at the temperature when the thermostat starts to open just a little bit. Of course, the verification of this hypothesis would require either a good thought experiment or actual temperature probes in the thermostat and other areas of the coolant system

Not sure I can visualize "softening" of the thermostat spring. These springs don't seem to be made of steel that would anneal or "soften" noticeably. The spring that was on the thermostat I took out of my BMW (age unknown) seems just as strong as a new one. Also, even if the spring "softens," it is still pushing against essentially incompressible solid/liquid wax, not a "spring-like" element, so as long as the spring is strong enough not to produce a slack, I am just not visualizing the "soft failure" that you are mentioning, unless the thermostat is simply stuck in open position.

My completely stock Honda Accord does indeed run at 83C, and a brand new OEM Honda Accord thermostat that I bought just do to comparison experiments does start to open at 82-84C in my experiment. Honda's published data shows it should open between 76 and 80C, and be fully open at 90C. My wife's Camry runs at 85C. So the E46 runs at a hotter temperature that is not necessarily representative of all cars.

As for the under-hood catalytic converter cooking things, it seems more of a fire hazard than actual contributor to coolant system failure. The coolant runs essentially at the temperature of boiling water. The valves and the head combustion chamber surfaces experience essentially your oven temperatures. The catalytic converter sees essentially self cleaning oven temperatures. The combustion chamber sees the temperature of the surface of the sun. You can wave your hand inside a hot engine compartment and not get burned, since air is a good insulator. The kind of overheating that gets one stranded starts with the heat in the combustion chamber that somehow fails to transfer adequately via the radiator.

I really like the idea of running a cooler thermostat AND higher coolant flow rate on the BMW to increase the margin of safety. It seems like a sort of "defense in depth" where you are relying less on any single critical element to stay within range.

I would like to really understand why the E46 cooling system goes bad that one percent (figuratively speaking) of the time. I agree that 99 percent of the time, the stock 97C thermostat should be perfectly adequate. I would allow that the majority (?) of the time, the standard methods of coolant bleeding is probably adequate. What happens to push the state of the coolant system to go from "good" to "bad?" The rupture of the expansion tank has often been mentioned. I would be curious to know if there are avoidable "internal state" of the engine that would cause such a rupture. From my experience, avoiding "excessive" air in the coolant system is one such step.

 

I like some of the points you made above. IMHO the e46 runs so hot that when a reliant component (i.e. aux fan, wp etc) even starts to minimally fail the expansion tank commonly blows as it seems to be a weak point. Better it blow than many other areas but still there is little tolerance since the engine is already running so hot. One would hope that the cap give way as that's the intended design but I've seen first hand that doesn't always happen. The ET explosions are typically a symptom of a failing or failed component elsewhere.

I have no data to support this but since I've swapped t-stat and put in the high performance waterpump I haven't changed a cooling system component including the ET. Reduced stress from lower thermal cycles might increase the longevity of the parts - scientifically at least, so why not practically?

I also pasted this from the BMW tech docs which describes one of the safeguard logic gates for energizing the t-stat wax element. It also answers JFOJ in regard to the service station function of the heater valve.

Engine map cooling
Map cooling is used by the DME MS 43.0 for the M54 engines. This can create very high coolant temperatures which could be damaging to the climate control system. If the heater core temperature exceeds 80C, the water valve is closed until the temperature drops
below 80C.

If the temperature at the heater core increases above 93C (i.e. water valve faulty), the IHKR will signal the DME (via K-bus/Kombi/CAN) to energized the map cooling thermostat.

Service Station Feature
The service station feature prevents the vehicle occupants from getting a blast of hot air after the vehicle is restarted following a short stop. The water valve is powered closed by the IHKR control unit for three minutes after shut-off. This prevents the heater core from
being flooded with hot coolant.

 

VERY interesting thread. Some random thoughts by a monkey with a keyboard....

I cooling system is on its last legs. Ordered everything but the radiator and hard lines. Went back and realized what an idiot I was for not ordering a radiator (expected them to be much more expensive) and ordered one as well. Everything is here except the radiator.

Over the weekend we went to DFW for a family event (3 hours away). I knew I'd been losing coolant and before returning I went to check the ET and my radiator cap broke! The top came off and the part with o-rings stayed in the ET. I screwed the cap back on and prayed. Less than an hour in, my low coolant light came on so I turned my Dynavin N6 to the OBC mode and watched the coolant temps. They hovered at 200° +/-. Thankfully, everything hung in there and when I got home, I installed the new radiator cap. Given the fact the cooling system is a weak point, I was concerned.

As jfoj said, the system is designed around a certain temp. I'm not sure I want to mess with that. Too many things in the engine affected by temp and I don't intent to reverse engineer the system. Since the engine is stock (nothing to raise the thermal load), I don't see an issue. In my previous E46, I bought it with 30k on the clock. Quickly had to replace the WP and never again. Never replaced the T-stat. Replaced all the soft lines, radiator, and ET though. Got rid of it just shy of 200k. The cooling system is a weak point, but I wouldn't call it fragile.

By and large, whatever you do to the cooling system, assuming you haven't taxed it with a greater thermal load, such as FI, the t-stat is going to control the temp. Again, I don't see an issue. And comparing with other cars is a false flag. Remember, a pressurized system will not boil until much higher than 212°F. Operating at 200°F isn't a real problem I think. If the system (from fuel swirl in the cylinder to gaskets to...) is designed for a particular temp, I don't see a reason to change (again, unless we've adjusted the thermal load).

I guess this is all a long-winded way of saying, perhaps we're over-thinking here?

I will say, the discussion about ET explosion is interesting however.

So, FWIW from a monkey with a keyboard.

 

Have any of you looked into the actual operating pressure of the cooling system? I believe that the catastrophic failure of parts in the e36 and e46 cooling systems has to do with the 2.0 bar radiator caps.

The operating temperature determines the operating pressure, which can be calculated based on the volume of the system, temperature, and volume left in the ET when full.

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10. The expansion tank is much maligned as the cause of the coolant system failure. However, the exact sequence of events is not always clear. Does the crack in the expansion tank cause loss of coolant and runaway temperature leading to engine overheating? Or does local overheating in the head cause "departure from nucleate boiling" leading to pressure spikes that rupture the expansion tank? This remains an open question without further experiments to validate.

good observations emineid! I agree the ET may prematurely fail due to overheating... last year I changed fluids and hastily took off before properly bleeding and the engine overheated for about 2 minutes before i shut it down.... 3 months later the ET developed a slow leak, probably a snall crack in the vertical seam due to the overheating event... (2001 330i orig owner 78K miles, all original components except ET, VCG, OFHG, and pulleys/belts).

 

i just want to point out for the bleeding/re-fill procedure to add the coolant very very slowly. if you add it quickly, some coolant may trap air underneath that would have otherwise had a path to escape. if you add it very slowly you should really only have air pockets in any up-side-down 'U' sections. then starting the car and giving it a few quick revs should push a lot of the pockets around so that they can collect again at the bleed screw. i'd repeat this step until no more air comes out.
i also noticed that at any point when the bleed screw is open, the ET should be filled to the brim, otherwise air will actually go into the bleed screw.

you can run and rev the engine with the ET open provided it is cold.
also when i bleed the system, i open the bleed screw very slightly and i keep the ET filled to the brim and not let it drop.
when all is done of course you need to reduce the ET back to the proper level, the float should be near the maximum point but should not be totally maxed out, ie. if you pull up on the float it should still go just a tiny bit further up.

 

Huh? None of this is necessary.