[srd5948]

So few days back I started noticing the radiator fan running too loud, did research on the forum and found out that it's most common symptom of water pump or thermostat failure. In my case I was able to validate that water pump is running and functioning correctly by following the procedure mentioned in some of the threads.
My question is if the water pump is running ok, what are the chances that just the thermostat might be bad. Or is it something else might be causing this issue. I have only experienced this with A/C turned on. Any comments about the failure and cost to get it repaired?
I have taken car to dealership to get it fixed.
2011 E90 335i

[kkasson]

The pump tends to fail intermittently at first. Even if it was working when you tested it, there may be codes stored for pump speed deviation which will cause the fan to run. It may work for now but completely fail soon.

It may also be the thermostat, although they tend to fail in the open position and overcool the engine rather than overheat it.

It may also be working fine...having the AC on can cause the fan to run pretty hard. It may be that you just didn't notice it before, or perhaps a change in the weather is making the system work harder.

[Wilt]

The E9n thermostat is NOT like traditional thermostats...it does not have a mechanical temperature sensor which causes it to open and close. Instead, the E9n has a temperature sensor which the Engine Management Unit gets input from, and then the EMU commands the thermostat to regulate the flow according to what mode the EMU decides the engine needs to operate at...low emissions, max power, etc. So what the thermostat does under EMU command would be different at wide-open throttle acceleration, for example...NOT based upon the engine heat being sensed, but based upon the engine heat that the EMU wants to achieve!

The points of failure are multiple, not limited to the thermostat alone.

[F22_Raptor]

I'm in the same boat. My radiator fan runs loud as hell and is on almost all the time, even when it's 60F outside and I don't use the a/c. The highest temp I saw in the hidden menu was 97c, which isn't even that high.
I'm planning to get a water pump replacement kit from eeuro.com along with a new OFHG.
I suspect the failed OFHG let some oil mix into the coolant and fouled the thermostat over time.

[srd5948]

Thank you all for the comments !

[Efthreeoh]

Originally Posted by Wilt

The E9n thermostat is NOT like traditional thermostats...it does not have a mechanical temperature sensor which causes it to open and close. Instead, the E9n has a temperature sensor which the Engine Management Unit gets input from, and then the EMU commands the thermostat to regulate the flow according to what mode the EMU decides the engine needs to operate at...low emissions, max power, etc. So what the thermostat does under EMU command would be different at wide-open throttle acceleration, for example...NOT based upon the engine heat being sensed, but based upon the engine heat that the EMU wants to achieve!

The points of failure are multiple, not limited to the thermostat alone.

Not flaming ...

Based on the information on the N52 I have, you have the concept of the operation of the ECU corrct, but might be a bit off on the mechanical configuration of the T-stat. When I replaced my T-stat long ago, I looked at it pretty closely as this was the first engine I've had that actually had an electrical connection to the T-stat. From what I remember, the T-stat does have what looks like to be a traditional heat-spring loaded valve in it. But the T-stat also has a heating element that controls the opening and closing of the valve based on desired engine operating temperature. The heating element is what is prone to failure and is what causes the Service Engine Soon light to illuminate since cold start emissions are not able to be controlled if the T-stat is not working properly. It's possible that the heat-spring that I discussed is actually the heating element as well and does operate the valve directly. I never dissected the T-stat to find out. The Bentley repair manual states the T-stat is designed to fail in the "open" mode so that a T-stat failure will not cause an overheat condition. That tells me the valve in the T-stat remains open and closes upon heating of the valve control mechanism either by the ECU and/or coolant temperature.

However the N52 info I have says that the four temperature settings the ECU controls for engine operation you alluded to:

• 112°C ECO mode (economy)
• 105°C Normal mode
• 95°C High mode
• 80°C High + mapped thermostat mode

are controlled by coolant flow rate changes via the electric water pump rather than the T-stat. It would be interesting if anyone has actually dissected the T-stat to see how it is configured.

[Madnking]

my fan has been running like its late for work for a month now. I had it scanned for codes and nothing. 2012 n55 55k miles. one day ill bite the bullet and replace both thermos and pump. if the thermostat is bad will it throw a code?

[Stage5Lurker]

Originally Posted by Madnking

my fan has been running like its late for work for a month now. I had it scanned for codes and nothing. 2012 n55 55k miles. one day ill bite the bullet and replace both thermos and pump. if the thermostat is bad will it throw a code?

Expect failure soon! I am currently waiting on t-stat, pump, bolts and hoses in the mail.
I drove about 2.5 hours, one way, in 27 degree weather, and luckily right at the tail end of the trip my pump wouldn't stop buzzing loudly. I unplugged the battery to stop it. Next morning plugged it back in, to go wash the trip off, and as soon as I got onto the freeway, the car kindly informed me that it wasn't going on the freeway. LIMP MODE. I am currently at 49k. e92 n55. Long story short...Limp mode is coming....

[PhaseP]

Originally Posted by Efthreeoh

Not flaming ...

Based on the information on the N52 I have, you have the concept of the operation of the ECU corrct, but might be a bit off on the mechanical configuration of the T-stat. When I replaced my T-stat long ago, I looked at it pretty closely as this was the first engine I've had that actually had an electrical connection to the T-stat. From what I remember, the T-stat does have what looks like to be a traditional heat-spring loaded valve in it. But the T-stat also has a heating element that controls the opening and closing of the valve based on desired engine operating temperature. The heating element is what is prone to failure and is what causes the Service Engine Soon light to illuminate since cold start emissions are not able to be controlled if the T-stat is not working properly. It's possible that the heat-spring that I discussed is actually the heating element as well and does operate the valve directly. I never dissected the T-stat to find out. The Bentley repair manual states the T-stat is designed to fail in the "open" mode so that a T-stat failure will not cause an overheat condition. That tells me the valve in the T-stat remains open and closes upon heating of the valve control mechanism either by the ECU and/or coolant temperature.

However the N52 info I have says that the four temperature settings the ECU controls for engine operation you alluded to:

• 112°C ECO mode (economy)
• 105°C Normal mode
• 95°C High mode
• 80°C High + mapped thermostat mode

are controlled by coolant flow rate changes via the electric water pump rather than the T-stat. It would be interesting if anyone has actually dissected the T-stat to see how it is configured.

I had my old thermostat taken apart from this spring when I had replaced it. I took another look at it now. It has a traditional wax operated piston against a spring valve and operates just like any other traditional one from what I can deduce. Unfortunately being the original aluminum unit that was press shut, I hadn't disassembled it without damage and its wax had leaked out, rod got bent etc, rendering its operation not testable with heat.

The only difference from a traditional unit I could see is the additional heating element that is electrically operated. This element is placed at the base of the piston rod of the wax "motor". This allows to heat the wax and open the thermostat valve even when the coolant temperature is not up to the point of wax expansion temperature.
I think they put this because the thermostat is not right on the engine in these cars. And when ambient engine is low, engine coolant can reach high temperature before the thermostat section. So in such cases ECU can heat up the thermostat and open the valve without waiting the heat to overcome ambient temperature at the vicinity of the thermostat.

[PhaseP]

That said all the reports in this forum on the thermostat failure had been that it fails "stuck open", including mine. So if engine is heating expect water pump failing. In any case, it would make sense to replace both of them at the same time.

[PhaseP]

Here are some pictures of what is left of my disassembled taken apart old
original aluminum thermostat version, in case anyone is interested.

This one is to give some idea how it all comes together. The "washer" sitting on the mat was actually pressed/riveted on the top of the thermostat element pushing down on the small spring, during disassemble I removed it.
When thermostat heats up and opens, that washer closes the top hole which is the "by-pass" passage that goes to upper block. It allows by pass circulation when thermostat is closed. The big hose hole on the right section of the thermostat housing is where water pump is connected. And the smaller hole on the right of the right section goes to cabin heater core I believe. The water pump and the cabin heater is always connected regardless of thermostat valve position.

The left section of the thermostat housing has only one hole, which is connected to radiator return. Thermostat keeps it closed when cold.


This is a closer picture, note the thermostat is in "closed" position, a big plate/washer is pushing against the lower part of the thermostat housing, closing that section.


This is another view, which I moved that plate to "open" position to show what it would look like. (That big spring is not really pushing down on the picture, since I had cut it in half during disassembly, and only the half bottom of the spring is there.)


The opening of the thermostat valve, against that big spring happens because it has some wax inside the center section. The center section is drilled and is hallow with wax filled. A "pin", or "rod" or "piston" whatever the correct term is, is placed on that drilled hallow section which the wax pushes on. When heated the wax expands, a lot, and pushes down on that rod. In this case, the rod is stationary, attached permanently to the thermostat housing, which forces the center section of the thermostat valve to move up, against the spring pressure, and opening the valve. On the top part of it, this moving up shuts down the upper by-pass hole as well.
A picture of the "rod" and the center section of the thermostat valve (I moved up the thermostat valve manually)


The "rod" alone, the thermostat valve element completely removed:


This is the outside of the thermostat housing, note the electrical connection positioned at the base of that "rod"


The "rod" with the electrical connector attached to the base of it. Removed after chiseling out the press crimped aluminum ears around it. It is sealed with a small o-ring.


The electrical connector is a resistance as far as I can tell, and when voltage applied heats up that "rod". That "rod" being in direct contact with the wax, heats the wax up and causes the thermostat valve to open, even if the coolant around is not up to temperature. So either the heat from the coolant or the heat resistor heats up the wax and opens the valve. Take away the heating element, it is a traditional engine thermostat.

[Efthreeoh]

Originally Posted by PhaseP

I had my old thermostat taken apart from this spring when I had replaced it. I took another look at it now. It has a traditional wax operated piston against a spring valve and operates just like any other traditional one from what I can deduce. Unfortunately being the original aluminum unit that was press shut, I hadn't disassembled it without damage and its wax had leaked out, rod got bent etc, rendering its operation not testable with heat.

The only difference from a traditional unit I could see is the additional heating element that is electrically operated. This element is placed at the base of the piston rod of the wax "motor". This allows to heat the wax and open the thermostat valve even when the coolant temperature is not up to the point of wax expansion temperature.
I think they put this because the thermostat is not right on the engine in these cars. And when ambient engine is low, engine coolant can reach high temperature before the thermostat section. So in such cases ECU can heat up the thermostat and open the valve without waiting the heat to overcome ambient temperature at the vicinity of the thermostat.

Thanks for posting the information and pics of the T-stat. I never considered that one of the hoses coming out of it was a coolant bypass, which explains the "fails open" state that the Bentley service manual discusses. For some time now I've been contemplating how the electric T-stat could remain in a failed open status if it had a conventionally operated valve.

[PhaseP]

I believe what Bentley is saying if the electrical heating of the thermostat won't work to open the valve, it will eventually open mechanically by the heat of the coolant. They use term "fail-safe".

Regular traditional thermostats have this by-pass passage also from what I could find. The by-pass provides a small loop for the pump to circulate the coolant, between top and bottom of the engine block. Once thermostat opens bigger loop is used: engine top to radiator, radiator to thermostat to pump, pump to engine bottom. The small loops gets closed by the upper by-pass valve on the thermostat.

In summary, I cannot see any "fail-open" functionality of the thermostat. By default it will be closed. From what I can see, it can stay stuck open if the rod is bent or corrosion prevents movement of it. It can stay stuck closed if the wax leaks out, or again from corrosion etc it cannot move up.

Added later for clarification:
In the small loop there is nothing to "radiate" the heat away and cool down the engine within the loop. It only allows the coolant to circulate in the engine so that engine warms up uniformly and provides a path for the pump to pump the coolant around.