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1988 260E
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Discussion Starter #1
Hello all!
I have a 2006 c280 with the m272 engine. about three months ago I replaced the radiator, thermostat and the engine cooling fan. At the time the fan would not come on causing almost overheating. I has worked well since then.

About two weeks ago the fan would run very loud starting shortly after starting the car. Searching the internet found that this is often due to loosing communications with the engine control computer.

When connecting my Icarsoft scanner to the car, It shows the the engine computer is telling the fan to come on at 89%. So the fan is doing what it is told.

The temp gauge on the dash shows about 90.

The scanner shows that the computer senses the engine temp at 104 degrees C. or 219F. that is quite warm! The car does not show any signs of actually getting hot. as a matter of fact, my laser thermometer only shows the outside of the thermostat housing as 170F.

Does this sound like the temp sensor on the back of the engine? I ordered one but not sure how to get into it to install. Looks like a pain job and want to explore any other possibilities first.

Thanks in advance.

Joe
 

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About two weeks ago the fan would run very loud starting shortly after starting the car.
Are you sure it is the radiator fan making the noise? Have you had someone else start the car and verified that is where the noise is coming from? When you say it is "running loudly", is it abnormally loud? Like louder than you have ever heard it? Or is it just running at high speed? Does it continue to run loudly or settle down after a minute or two?

The scanner shows that the computer senses the engine temp at 104 degrees C. or 219F. that is quite warm! The car does not show any signs of actually getting hot. as a matter of fact, my laser thermometer only shows the outside of the thermostat housing as 170F.
Are you saying that the car says it is 104C immediately after a cold start? If so that would certainly indicate a temperature sensor problem. If that reading is after it has warmed up then it is a perfectly normal temperature. Your thermostat is set to open at 100C and since they are a mechanical device they aren't spot on accurate. They don't last forever and are super easy to replace (although messy!).

Does this sound like the temp sensor on the back of the engine? I ordered one but not sure how to get into it to install. Looks like a pain job and want to explore any other possibilities first.
The coolant sensor on the block is easy to replace. Just unscrew the bolt, pull out the old and push in the new. Be ready and try to swap it quick as you will lose a little coolant in the process. I attached the procedure for you.
 

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Discussion Starter #3
Are you sure it is the radiator fan making the noise? Have you had someone else start the car and verified that is where the noise is coming from? When you say it is "running loudly", is it abnormally loud? Like louder than you have ever heard it? Or is it just running at high speed? Does it continue to run loudly or settle down after a minute or two?



Are you saying that the car says it is 104C immediately after a cold start? If so that would certainly indicate a temperature sensor problem. If that reading is after it has warmed up then it is a perfectly normal temperature. Your thermostat is set to open at 100C and since they are a mechanical device they aren't spot on accurate. They don't last forever and are super easy to replace (although messy!).



The coolant sensor on the block is easy to replace. Just unscrew the bolt, pull out the old and push in the new. Be ready and try to swap it quick as you will lose a little coolant in the process. I attached the procedure for you.

Thank you for the reply Planethill,

Yes it is the coolant suction fan. It runs fast (sounds like jet engine) whenever the car is running and at normal temp 90C according to temp gauge on dash. I thought it was running full speed as I have read it does that if the fan controller looses communication with engine computer. It continues to run until car is switched off. It also does not come on until the temp starts rising.

The car does not show 104 immediately. takes a few Minutes to get there as if it warming normally. I did not realize that the thermostat opened at 100C. I am used to dealing in F and that is 212F. I usually work on cars where it opens around 90C ,( 195F). So that 4 degrees it not far off.

Do you know what temp the fan is supposed to come on?

I actually have that same set of instructions for removal of the temp sensor. What the picture does not show (unless I am reading the diagram wrong) is the firewall is about an 2 inches from the sensor. There is also another device not shown in the picture directly above the sensor (not sure at this point what it is) this is about an inch thick. This leaves me an inch of space to get my hands through and then I have to come back toward front of car to get to the back of the head.

I would love to know that I read the digram wrong so please give let me know. It appears the sensor is mounted on the rear of the drivers side head,

Thanks so much for the help!
 

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I did not realize that the thermostat opened at 100C. I am used to dealing in F and that is 212F. I usually work on cars where it opens around 90C ,( 195F). So that 4 degrees it not far off.
Actually, I may be wrong. It IS 90C on some C-Class models. I just checked my sons C230 and it is a 90C thermostat. However my other two vehicles, a ML and GLK, both have the M272 and it is 100C. Post your full VIN to be certain. You may simply have a "lazy" thermostat.
 

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Discussion Starter #5
Actually, I may be wrong. It IS 90C on some C-Class models. I just checked my sons C230 and it is a 90C thermostat. However my other two vehicles, a ML and GLK, both have the M272 and it is 100C. Post your full VIN to be certain. You may simply have a "lazy" thermostat.
WDBRF54H66A857556

Next question (thank you for your time), if the gauge on the dash reads 90 (half way between the 80 and 100) why would the ECU see 104? Do both readings come from same sensor?
 

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Ahhh. Now we are getting somewhere! This is why having the VIN is so important. Look at you with your heated washer fluid!

There isn't one document that explains everything, but there are clues scattered throughout several systems. They are all attached, perfect bathroom reading material. 😊

The correct thermostat is 100C for your car. Now, the difference is that your thermostat is electronically controlled, that's why there is a connector on it (you can actually test it with a volt meter). The ECU commands it to open/close, regardless of the coolant temp flowing through it. That means it is important that the temperature sensor is working correctly or everything else could be off. Even though it is electronically controlled, it will go full open at 110C independently as an emergency fail safe.

There is only the one coolant sensor, and I verified that you have the correct remove/replace document. I am not sure what the "two inch" device that is in the way, is though. After you remove the air cleaner assembly, the sensor should be fully exposed. Did you completely remove the rear cover from the throttle body? You can test the sensor with a voltmeter before replacing it (see attached doc).

There is a heating system shutoff valve on your engine. When cold, it should close to help the engine warm up faster. It isn't clear, but it looks like you may also have an electric coolant circulation pump for the heater. Although both of these are not directly involved, if not working properly coolant could circulate wrong (or not at all) and your temps might not be exactly correct.

Is the outside temperature correct on your instrument cluster? Believe it or not, it also has hand in all of this as well as the intake air sensor. The coolant thermostat you replaced reacts differently above and below outside temps of 12C (about 53.5F). It is all connected! Read on!

"To prevent critical temperatures, the increased coolant temperature range is reduced under the following conditions to around 90°C (with outside temperature below 12°C) or to around 80°C (with outside temperature over 12°C):
  • Engine speed greater than 3000 rpm
  • Engine load more than 30%
  • Intake air temperature more than around 38°C <<< That would be the MAF sensor
  • sporty driver detected <<< 😆
SO! Unlike most vehicles where the coolant temperature is fairly constant, it looks like your vehicle changes the coolant set-point continuously from 80C-100C based on data from several different sensors and data points.

I would say that if you have no codes, you have heat in the cabin, and coolant isn't boiling over, it's working as designed. Crazy as it may be!

In addition to all the reading material below, I also included a PDF of your datacard for your records.
 

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Back to your original issue, the loud, continuous fan.

Is your A/C system operating correctly? Did you recently re-charge the freon? The A/C system can also command the fan to run full blast via the front SAM, as it also cools the A/C condenser. Refrigerant pressure that is too high will cause it to run at 100%. See attached.
 

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Discussion Starter #8
Back to your original issue, the loud, continuous fan.

Is your A/C system operating correctly? Did you recently re-charge the freon? The A/C system can also command the fan to run full blast via the front SAM, as it also cools the A/C condenser. Refrigerant pressure that is too high will cause it to run at 100%. See attached.

WOW! Thank you very much. I have some homework to do..

As far as "Normal", we have had the car for almost 4 years and this is the first this has happened. By "Loud" I can hear the car coming from way down the street. (not quite 1/4 mile).

The other things involved might mean something but since we live in Georgia USA, we have had two rounds of all 4 complete seasons in the last two weeks. (you probably think I am joking). Yesterday it was 72F around here and a couple days ago we had 1 1/2 of snow.

I will start studying immediately. Thank you very much for the information!
 

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Back to your original issue, the loud, continuous fan.

Is your A/C system operating correctly? Did you recently re-charge the freon? The A/C system can also command the fan to run full blast via the front SAM, as it also cools the A/C condenser. Refrigerant pressure that is too high will cause it to run at 100%. See attached.

P.S. the heat and AC work quite well and the noise occurs with heat and air controls completely off.:)
 

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And there are no other codes? Even codes that may appear to have nothing to do with this issue?
 

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And there are no other codes? Even codes that may appear to have nothing to do with this issue?
Planethill, The only code was for the flapper in the intake manifold. Another chore for the future.

But there were no other codes.
 

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Planethill, The only code was for the flapper in the intake manifold. Another chore for the future.

But there were no other codes.
Cool. Just making sure, as often something will appear unrelated but isn't!

BTW, I did the swirl flap fix on my ML350 (also M272). It was fairly easy, but time consuming as you have to remove the entire intake manifold to get to the broken link. (I replaced it with one of the all metal kits from ebay). It took me the better part of a Saturday to do. You don't need any special tools, knowledge or heavy lifting... there is just a lot of junk to remove so you can actually get to the problem! You will need new gaskets though.

The irony is that the actual fixing of the broken flap linkage takes about 3 minutes. All the other hours are spent taking everything off and then putting it all back on. Ugh!
 

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Planethill, thank you for your patience!

I hope you enjoy reading long posts and I really appreciate you reading this one if you would.

More info. The car is used by my wife for her daily commute to work. Roughly 30 miles but a lot of stop and go so it takes over an hour.

Yesterday she called me on the way home to tell me the car was over heating. Dash was all red and needle up to 120.

She pulled over immediately, shut the car down and called me. The fan continued to run. The car was shut down a minute at most. When she turned the key back on, the needle on the dash was at 90 like it always is and the car was fine.

Hard to believe the engine could cool down 25 degrees that fast. She drove the car to her nail salon and back to the house and it behaved normally with the exception of the fan noise.

This morning I went out to the garage and started the car and let it idle. I made the following observations.

When the dash temp gauge reached 60, the computer said the coolant temp was 53.8. the fan on signal was at 0% and was not turning.
When the dash temp gauge reached 70, the computer said the coolant temp was 63.6. The fan on signal was at 0% and not turning
When the dash temp gauge reached 80, the computer said the coolant temp was 72.59. The fan on signal was at 0% and not turning.
When the dash temp gauge reached 90, the computer said the coolant temp was 83.0. The fan on signal was at 0% and not turning.

The dash temp gauge is marked in 20 degree increments. So I guessed at 90 because it was directly between the marked 80 and the dash for 100.

I say this because things happened here and I do not have specific temps from the gauge as I could see little movement.

At the 90 degree mark the computer said 83 degrees. Up until this point the dash gauge was always 7 degrees warmer than the coolant.

The dash gauge did eventually climb but very slowly to the 100 degree mark. by the time it reached this mark, the computer said the coolant temp was 115.29. During this time the gauge went from reading 7 degrees high, to almost 16 degrees low.

When the computer said the coolant temp was 95.81 the fan started turning at 12% and steadily rose to 89% at a rate of 20% a minute.

When the computer said the coolant temp was 103.3 The fan was running 100.05%. I started using my laser thermometer ( in Fahrenheit) to check the thermostat are both at the block and on the thermostat body. It was at 155F or 68C.

When the computer said the coolant temp was 107, the thermometer said 158f or 70C.
When the computer said the coolant temp was 108.5, the thermometer said 160f or 71C.
Soon the dash temp gauge climbed to 118 degrees and this matched the computer at 118.28. the thermometer on the thermostat housing was now at 165F or 73C.
Eventually the dash gauge read 120, the computer read 120 as well. the thermometer still read 165f or 73C.

The engine showed no signs of actually getting hot.

There was a DTC showing the thermostat had an open circuit. That may be from me unplugging it.
 

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This is the back of the head as viewed from left side (drivers in america). The sensor is located under the device in the rear of the head with the vacuum line running to it.
 

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This is the same area viewed from the front of the car with my hand in it. The tip of my fingers barely reach the connector for the sensor. Have no idea how to get a tool in there. Someone suggested removing MAS.
 

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FYI Any one watching this thread. The device on the end of the valve cover blocking access to the temp sensor is the "vacuum pump". It runs off the cam to provide vacuum to the break booster. It is known to leak oil and appears to be doing so in my case. I have order a seal kit for it so it will be removed to be resealed. I think the temp sensor would be easier to access while it is removed. I will let you know how it goes.
 

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You might also see if it's easier getting to the sensor from underneath. Sometimes it's much easier on the arms/fingers (but harder on the back!).
 
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