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Old 01-08-2013, 07:42 AM   #1
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Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 23,183
My Ride: 330CiC, M5, X5, E93
Check your thermostat/engine temp - Report In

So occasionally I start a new thread and many times they take on a life of their own, we will see where this one goes?

Engine Cooling Temperature Issues

I have been around here and an number of other forums as well dealing with many other vehicles to include my own and I am starting to see a trend that appears to be going un-noticed quite often.

Engines running too cold due to soft failing thermostats.
Kind of opposite to what most of us usually worry about!

Unfortunately many of today's vehicles have either no engine temperature gauge or a temperature gauge that is not very accurate and or buffered to hide the actual engine temperature variations from the typical driver.

Also one problem is actually where the engine coolant sensor is located on the engine as it will sometimes cause concern due to the higher displayed temperate as compared to the actual thermostat opening temperature. More about this issue below.

Usually the only way to really check and verify the engine coolant temperature is to have a scan tool that will read and display real time data. Unfortunately many of the scan tools available do not always display real time data so many may be handicapped when it comes to checking the engine operating temperature.

Luckily for many in the BMW community we have the ability to check our engine coolant temperature built right into most of the cars. Using the OBC (On Board Computer which displays fuel economy, outside temperature, average speed, etc.) you can access the Hidden Menu and actually verify the engine coolant temp, and many other useful parameters.

So how do you access the Hidden OBC Menu?, check the 4th link below in my signature. I did not write this information, however, it is a very good guide on how to access this feature. There is one possible variation that has recently been brought up with the Engine Coolant Temperature, some cars may only have 3 digits displayed and may actually have a decimal point as mentioned in the link for the Hidden OBC Menu? Such as 88.7 vs 88 C. On my 2006 E46 Convertible my display is actually displayed as 4 digits and I have no decimal point, so there may be some variations out there on OBC display format??

The question is then what temperature should my engine run at?? Based upon a baseline from my E46, my temps seem to run consistently between 88-95C (starting to think 95C/203F is really the magic baseline after a bit more research??) , and in reality around town my car seems to really like 92-95C lately. Currently trying to also figure out what a upper temperature threshold or baseline may be during the Summer outside temps pushing 100F. Have not confirmed upper temps yet, however, 100-105C may be not unusual for the peak Summer temperature? Still trying to get some baseline on the upper window.

SPECIAL NOTE: Once the outside air temps get to 70F or higher, you may not be able to really confirm a soft thermostat as the engine will run slightly warmer once the ambient hits 70F. The only way to really confirm a soft thermostat is to quench the radiator with a garden hose to super cool the radiator and then watch the engine temp behavior. You may need to spray the radiator down more than once while checking the engine temp. But if you cannot tell for sure wait for a very cool Summer evening, or wait until the Sept/Oct temps start to drop a bit. Suggest you confirm as soft stat long before the Winter temps set in as I do not know too many people with heated garages with a lift that wants to take time during the dead of Winter to replace a thermostat when you are in a bind because the engine is running 20F too cold.

For what it is worth, I just looked at a new Wahler thermostat and it had 97C embossed in the upper edge of the plastic housing. 97C is 206F, which is just slight above my baseline that I have been measuring in my car. It may be possible that the thermostat heating element is always active to some level as the engine approaches operation temperature? Although the thermostat has 97C stamped on the housing, I do not believe the thermostat is always at this operation point as I would expect the engine coolant temp as measured where the sensor is located to be as much as 20-30F warmer than the thermostat operation temperature? Assuming 30F would be the upper limit, then this would end up right at the 113C max range the BMW documentation has stated! Interesting how things kind of add up.

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Note this value is what I am seeing on my 330cic, but E39 M5 temperatures will run at 79C, this is due to a the much cooler thermostat and the E39 M5 has the coolant sensor mounted directly on the thermostat housing and not at the rear of the cylinder head like most engines. The E46 M3 is a bit different, it has the coolant temperature sensor mounted in the rear of the cylinder head like the standard BMW I6 engines, but I believe they run a slightly colder thermostat than base 323/325/328/330. I do not have good solid data on the E46 M3, however, I would expect these engines to operate around 90C/194F nominal engine temperature.

One thing many may not be aware of is the standard E46 (and other vehicles of the same vintage using the inline 6 cylinder "323/325/328/330") have a special thermostat that has a built in heating element to force the thermostat to open earlier under certain more extreme driving conditions or higher temperatures. As I recall the DME has the ability to alter the engine coolant temperature by approximately 41F! Info that I have found stated the thermostat control range is: approx. 80C - 103C.

So because of this the engine temperature gauge in these cars is buffered and will stay at the 12 o'clock position over a range of about 68F. Info that I have found states the normal operating range of these engines is between 75C-113C or a 68F range!

This is where the bigger problem starts, how do we determine if our thermostat and coolant temps are in the proper range?

See this useful link regarding the Coolant Snitch an add on over temp alarm to warn the driver on an impending engine overheat. There is also a good description of the buffered temp gauge as well - http://www.zhpregistry.net/Tech/CoolantSnitch.aspx

Another useful tool that you could install in your car and actually set alarms on is the UltraGauge, see picture below.

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The UltraGauge is a small scan type tool that constantly provides real time engine data that the tool can access along with all sort of driving and fuel usage information. Additionally this tool also can read and clear generic trouble codes, not sure if this tool can display freeze frame data. I have been playing with one lately and it is a pretty slick device.


So for the price of a scan tool, you can actually have this always connected to the car, monitor coolant temp, fuel trims, MAF readings, Voltage and even set threshold alarms for each gauge. Cheaper than a coolant snitch and does way more but it is not tucked away and hidden.

I have no affiliation these persons or products, but many may find these products and the accompanied information useful.

Back to the comment about the engine coolant temps running in the 88-95C range and the thermostat may have a much lower opening parameter. This is due to the location of the engine coolant sensor location as compared to the thermostat location. I have not really checked at what temp the standard E46 thermostat is supposed to open at, but I am assuming it is likely a 185F/85C thermostat?? On many vehicles the engine coolant sensor is not located directly on the thermostat housing so you do not see coolant temps as low as the opening temperature of the thermostat. What you are reading usually is actually the coolant temperature at the output of the cylinder head in most vehicle, so coolant temperature readings may be displayed as much as 15-20 F higher than the actual thermostat spec. This is pretty typical and should not be alarming.

What I have been seeing is a trend for thermostat to soft fail to the low side, opening too early and causing the engine to run too cold. This usually only shows up in the colder Winter months if you actually watch for it and although many think they can rely on the DME or engine computer to trigger thermostat codes, you cannot rely on the DME to watch out after a bad thermostat. The tolerance window for the DME to trigger coolant codes is very wide and even if it does trigger a code and you clear it, the code may be VERY sporadic and not come back at for quite some time.

I have also seen situations where even freeze frame date for a thermostat or engine cooling temperature may show the engine coolant temperature in the low to mid 180F range and many even seasoned mechanics glance at this data and say 180F range, this is fine, however, it is may not be fine. You have to look at the freeze frame data and determine if in fact the captured temperate is in an acceptable range based upon vehicle speed, engine RPM and possibly calculated load. But if you do get a engine temp or thermostat code, take it seriously as the DME is very forgiving and will not easily trigger cooling or thermostat codes. If you have a code, you LIKELY have a problem!

Around some of the forums and with some vehicle models there has been a great emphasis on bad coolant temperature sensors and on some cars because of the low cost and ease of changing the coolant temperate sensor, this is always the first step of action and many are convinced that the coolant sensors are the problem. This is a VERY wrong approach. It is possible for coolant sensors to go bad, however, they are far simpler than a thermostat and do not fail as often as some would like to think. Additionally if you can confirm that the engine coolant sensor matches or closely matches the ambient temperature on a cold engine, you can confirmed at least the coolant sensor is not skewed from a baseline cold reading.

What I have found is today's thermostat do not stick closed as much as thermostats of years past. What I am seeing is a trend of soft failing thermostats that open too early causing the engine to run too cold and also cause a larger temperature fluctuation. What I believe to be the problem is the thermostat spring weakens over time and will all the thermostat to open too soon. Engines running constantly at lower temperatures can run richer and hurt fuel economy, do not heat up the crankcase and oil fast enough and hot enough to burn off excess moisture and water vapor in the crankcase causing premature sludge build up and possibly more chance for the CCV to freeze in colder climates, inability to cook off fuel in the crankcase leading to oil dilution and possibly premature engine wear, longer warm up times, may even lead to issues with automatic transmission where the the fluid does not warm up fast enough and in older transmissions may even make the cold shift engagement and slipping problems worse and so on.

Rough idle and poor mileage issues

Chronically cool running engines typically run rich which can cause additional carbon build up and lack of carbon burn off. Issue with rough idle and cold start misfire if the engine has been running cold for a long time sometimes can be a side effect of a cold running engine.

Additional carbon build up in the intake ports, on the back of the intake valves and on the O2 sensors can lead to difficult starts, cold start stalling and cold idle problems. Make sure your engine is functioning at the proper operating temperature otherwise you could suffer from a carbon deposit problems.

The reverse is also true, if you have a cold running engine that may be running rich, it may also be covering up lean conditions. Once you repair your cold running engine, you may then experience rough idle issues.

What I can say is depending on your specific situation if you have rough idle or cold start stalling I would recommend a few fuel treatments with Techron or BG Fuel Additive and drive the car for at least 2-3 full tanks of fuel (600-1000 miles) and see if any issues clear up with warmer running engine temps and fuel treatment. If by chance you have a scan tool that can read real time data, check your fuel trims and see if they are working back toward the "normal" range once the engine temps are back to where they should be. If the fuel trims are positive by more than 3%, then I would keep a close eye on them and consider looking for vacuum leaks.

Crankcase water vapor build up and/or CCV Freeze Up is typically caused when excess water vapor or an oil/water mixture (we will call mayonnaise) cannot be "cooked" or boiled out to the crankcase due to short drives, usually less than 20 minutes, in close to or below freezing ambient air temperatures.

The best approach to dealing with the "mayo" problem is management. When ambient overnight temperatures are near or below 40F, you should really check your oil and oil fill cap at least once per week, usually later in the week before the weekend hits so if you are having a "mayo" problem, you can plan an extended weekend trip that includes highway speeds and will last approximately 30-40 minutes or more. Also verify the engine thermostat is also working properly and bring then engine up to full operating temperature. Once you start checking your oil and the underside of your oil fill cap once a week, you can adjust your driving habits as needed to get the "mayo" issue under control. Just so everyone is aware, this is not just a BMW problem, this is a problem that plagues many manufactures and models and even if you own other cars or trucks you should them for moisture build up in the crankcase.

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This moisture can and will freeze and block the CCV's ability to drain oil and equalize pressures if not properly managed during very cold, sub freezing temperatures. Of the CCV is filled with "mayo", the oil/water mixture can freeze, possibly split the CCV housing, allow excessive crankcase pressures to build up to the point that the valve cover gasket and/or valve cover can become damaged and/or split. Then the oil in the crankcase can be siphoned or sucked directly into the intake depending on how bad the freeze up is and cause very heavy exhaust smoke or in more severe cases causing the oil to be sucked into the engine very quickly causing the engine to stall because of hydro lock and possibly cause serious, catastrophic and expensive engine damage. CCV freeze up is not a directly a result of a bad thermostat, however, a weak or bad thermostat along with short driving trips of less than 25 minutes in the Winter at ambient temps close to or below freezing can be a big contributor to water vapor build up in the crankcase. You have to constantly monitor and manage the water vapor build up in the crankcase during the colder months or you will have a big problem on your hand when the CCV freezes and likely cracks.

The CCV freeze up can also cause valve cover gasket failure and/cracked valve cover due to unexpected crankcase pressure differences. This mayonnaise is a yellow puffy looking sludge that will also form on the underside of the oil fill cap. Mayonnaise is usually in indicator of low coolant temps, short drives in cold weather and a CCV system that is not working correctly.

Since we have AGAIN seen a lot of issues with CCV freeze ups and yellow/brown mayo or goo on the underside of the oil fill cap in the sub freezing weather again this season, I thought I would add a number of links regarding CCV freeze ups and issues about the CCV oil drain system. One item that commonly gets overlooks during CCV replacement is the dipstick tube. The original dipstick tube is a double walled tube that can clog easily. You can remove and clean the base of the dipstick tube or replaced it at a big expense with a updated single wall dipstick tube.










So do yourself a favor while we are still in the midst of the Winter season, pull up you Hidden OBC Menu and verify your engine coolant temps are in the 88-95C range consistently and within the first 10 minutes of driving. I still need to graph my car to get an idea of how quickly these engines should hit the proper operating temperature in the colder weather, but as I recall, most of these cars should be very close to operating temp withing about 10 minutes of driving, not 10 minutes of idling.

Please report in on what you may find on your car as this may help others to get a better idea of what an expected baseline may be.

One problem is many times these soft failing thermostats are very hard to identify in the Summer months as the engines may run close to their operational temps even with a soft failing thermostat, so now is the time to check your thermostat!

To repeat the info that I have located around the web and in BMW documentation which I believe is accurate?? Here is a quick recap:

BMW states the "normal" operating temperature for these inline 6 cylinders with the heated thermostat to be 75-113C or 167-235F.

BMW states the "normal" range for the coolant gauge to stay at the 12 o'clock position is between 75-113C or 167-235F.

BMW states the "normal" operating range of the thermostat is 80-103C or 176-217F or about a 41F window. This is in somewhat in conflict to the lower limit of the thermostat as listed above, however, this is only a 8F difference, likely a tolerance window?

What we are seeing in real world conditions below about 70F outside temps is these engines should run between 88-95C at idle. We will have to wait until the Summer months hit to gather more data about idle temps in warmer weather.

Another problem area to address when replacing your thermostat or inspecting your cooling system is to closely inspect the temperature sensor in the lower radiator hose. If there is any moisture around the switch or on the top of the lower engine cover below the sensor, replace the O-ring. The O-ring on this temperature sender FAMOUS for leaking and usually leaking when the engine is cold. If you are ordering a thermostat, make sure you pick up a replacement O-ring for the lower radiator hose temperature sensor. Very easy to replace and it does not require tools to remove the sensor, just your fingers. I usually use a tooth pick to get under the old O-ring and help install the the new O-ring, you can cut the old O-ring off, but be careful not to nick the O-ring groove on the temperature switch. The O-ring is not listed as a serviceable part in the BMW parts catalog but it is BMW part #13621743299. See picture below of O-ring and temperature sender.

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Special note about filling cooling system expansion tank and properly bleeding the cooling system

BMW states the expansion tank level should be checked at 68F ambient temperature. So if you are getting a low coolant light at below freezing and/or checking and topping off the level in you expansion tank, I HIGHLY suggest you only top off the level to the lowest fill point in the expansion tank. Please NOTE this level is based upon the float in the expansion tank and the lower fill level will be about 5 inches below the top of the expansion tank. DO NOT FILL THE EXPANSION TANK TO THE TOP, if you do, the tank WILL burst in the first drive cycle and you WILL have to replace the tank due to over filling. The expansion tanks should be replaced every 6-7 years anyway as they are made out of plastic and they will become brittle and fragile due to all the thermo cycling that occurs under the hood.

BMW Coolant Fill.pdf

Proper bleeding of the E46 cooling system is also very important. If the cooling system is not properly bleed of excess air, you will have an air pocket in the cooling system and likely you will then have an over heating problem on your hand even if you have just recently repaired or replaced parts on your engines cooling system.

See this link for info on proper bleeding - http://forum.e46fanatics.com/showthread.php?t=914109

I am sure I may be back to edit this first post to include more information or to correct errors as I am SURE the E46 community will be more than happy to point out any errors that I may have made!!!!
Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temp, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose temp switch O-ring - BMW #13621743299

Last edited by jfoj; 11-16-2016 at 08:21 AM. Reason: Corrected info about M3 temperature
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