High 900rpm idle with fan on before engine fully warm - BMW M5 Forum and M6 Forums
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post #1 of 26 Old 14th May 2019, 10:04 PM Thread Starter
Phil.S
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High 900rpm idle with fan on before engine fully warm

I have seen lots of posts about this issue, some saying it is normal but can't seem to find a definite answer.
Brief history is I have owned my 2005 e60 m5 for over a year and have never noticed it before, I recently got stuck in stationary traffic and noticed the revs creeping up to over 1000 with a " hot cat" smell so switched off and all seemed ok after car cooled down.
Now though I have noticed the idle rpms sit at 900 on and off, this seems to be when the engine fan is running which I guess makes sense but I have noticed that the fan will come on before the car is even warm (oil temp around 75 degrees)
I replaced the temp sensor on the radiator return hose but problem still there.
I have seen posts on charcoal filter, MAFs and other issues but not sure why any would make the fan come on early?
Any help appreciated.
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post #2 of 26 Old 15th May 2019, 05:01 AM
J.R ///M5
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Do you have AC on? Fan kicks in when AC refrigerant pressure reaches over 9bars.

BMW E61 ///M5 -07


Ex. BMW E39 ///M5 -01

Current mods: Short shifter, Custom clutch stop, Alpha-N + Power tuning by Evolve, AP coilovers, HEL brake lines.

Last edited by J.R ///M5; 15th May 2019 at 06:48 AM.
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post #3 of 26 Old 15th May 2019, 09:41 AM Thread Starter
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Hi, no the AC was not on. I am going to start the car from cold and see how long it takes the radiator hose to warm up, this may give me an idea whether the thermostat is stuck open, if anyone could do the same so I can compare that would be very helpful. Thanks.
Update:- started the car from cold- started a stopwatch. Fan started at about 1min 30sec, hose started to feel slightly warm just after that but not hot.
Idle rpm fell to around 700 even after fan on so may not be connected?
Is it normal for the fan to start that early, perhaps it runs constantly but speed varies with temp?

Last edited by Phil.S; 15th May 2019 at 11:16 AM.
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post #4 of 26 Old 15th May 2019, 12:33 PM
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I don't know if this help, but you can check your coolant temp from instrument cluster secret menu so you have a clue whats the temp. What i know about the fan function is that the speed is influenced by coolant temp and pressure in AC-system.

What comes to idle raise to 900rpm i noticed last winter when my battery was low on charge, car charged the battery more frequently and allmost everytime when i was on traffic lights. After i charged my battery the rpm raise went away. I think this is one factor which will cause the idle raise. Other thing is that when the engine is cold there is cat heating procedure. This will also raise the rpm but it goes away when engine reached 78-79C operatign temp. I bet there is more reasons for the idle raise but i don't have clue what...

BMW E61 ///M5 -07


Ex. BMW E39 ///M5 -01

Current mods: Short shifter, Custom clutch stop, Alpha-N + Power tuning by Evolve, AP coilovers, HEL brake lines.

Last edited by J.R ///M5; 15th May 2019 at 12:53 PM.
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post #5 of 26 Old 15th May 2019, 03:17 PM Thread Starter
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Thanks for the suggestions, I have had some recent issues with the battery not appearing to charge fully and recently changed the battery and had it coded and registered. I have put a trickle charger on it and will try it again in 24 hours, perhaps I have an issue with the charging system, not the battery itself. I have just worked out how to access the hidden menu so I can get an idea of coolant temp and charging voltage. Thanks again for the ideas. Phil.
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post #6 of 26 Old 16th May 2019, 01:00 PM Thread Starter
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I have checked the voltage and coolant temp with hidden menu:-
Voltage is steady at 14v while car is running so seems ok.
Coolant temp ranges from 77c to 80c, this sounds low so I am thinking thermostat but I cannot find any confirmation that it is low, can anyone confirm normal running temp for the e60 m5 when engine is fully warm? Thanks.
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post #7 of 26 Old 16th May 2019, 04:22 PM
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Quote:
Originally Posted by Phil.S View Post
I have checked the voltage and coolant temp with hidden menu:-
Voltage is steady at 14v while car is running so seems ok.
Coolant temp ranges from 77c to 80c, this sounds low so I am thinking thermostat but I cannot find any confirmation that it is low, can anyone confirm normal running temp for the e60 m5 when engine is fully warm? Thanks.
You should see 78-79C temps in highway cruising speeds if your thermostat is good. When mine failed it showed 75C on highway and when winter was coming and climate got colder it finally showed error code.

City driving showed over 80C temps with bad thermostat, so highway driving is your solution.

So if you are under 78-79C, you should change thermostat and while you are under the plenum change dual temp sensor also.

BMW E61 ///M5 -07


Ex. BMW E39 ///M5 -01

Current mods: Short shifter, Custom clutch stop, Alpha-N + Power tuning by Evolve, AP coilovers, HEL brake lines.

Last edited by J.R ///M5; 16th May 2019 at 04:26 PM.
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post #8 of 26 Old 17th May 2019, 12:27 PM Thread Starter
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Thanks again, took the car out just now, outside temp 13.5c by hidden menu. (Bit cooler than yesterday)
At 70 mph cruising coolant temp was 74-75c
At 30 mph 76-77c.
So pretty sure thermostat is no good, I have ordered a thermostat and temp sensor for the thermostat housing.
Many thanks for your advice!
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post #9 of 26 Old 17th May 2019, 04:08 PM
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Quote:
Originally Posted by Phil.S View Post
Thanks again, took the car out just now, outside temp 13.5c by hidden menu. (Bit cooler than yesterday)
At 70 mph cruising coolant temp was 74-75c
At 30 mph 76-77c.
So pretty sure thermostat is no good, I have ordered a thermostat and temp sensor for the thermostat housing.
Many thanks for your advice!
Yes, your thermostat is bad. Remember to change the dual temp sensor also while your plenum is out. It's not expensive part and it's located in the engine V-section.

Good thermostat will keep the engine in 78-79C when cruising on highway even the outside temp is under -20C😀

BMW E61 ///M5 -07


Ex. BMW E39 ///M5 -01

Current mods: Short shifter, Custom clutch stop, Alpha-N + Power tuning by Evolve, AP coilovers, HEL brake lines.
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post #10 of 26 Old 17th May 2019, 06:29 PM Thread Starter
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Yeah I have ordered the second temperature sensor and also the thermostat housing o-rings with the new thermostat. I have also ordered a flexible 1/4" drive extension as this will be my first time taking off the plenums. Not sure if this will help the idle issue but we will see, I think my next step is the charcoal fuel filter as I sometimes get the "woosh" noise when releasing the fuel filler cap, I will check the fuel vacuum valves while I have the plenums off. Thanks again for the help.
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