Radiator fans running all of the time

[AntMB]

Hello, on my E270, today I've noticed the radiator fans are running constantly after start.

This happens with air con and all heating off. Engine temp is normal, coolant level is normal.

I've scanned for fault codes, everything is ok. Any suggestions? Perhaps the fan temp sender is faulty?

Thanks.

 

[Uky]

This normally happends if the fan control unit looses its CAN-bus connection with the engine (or AC) controller.
In order to protect the engine, it puts the radiator fan(s) in max speed. But this condition should
normally result in error codes! Anyway: Check cables/connections for bad connections, corrosion or misaligned
contact elements in the plugs/sockets.)

There has been cases where workshops have simply replaced controllers since error messages
indicated lost connection and this has been misinterpreted as hardware (controller) fault. Many electrical problems
are mechanical and I advice anyone who asks to make the checks themselfes. A particularly nasty
problem that has showed up is the use of "Z-joints". That is: In order to save money, auto makers
have introduced the habit of joints inside cable harnesses, eg. in order to share a GND connection.
And yes - there has been several cases of this, resulting in various problems not
always easy to fix.

Another IMHO stupid decision has been the introduction of very thin wires in harnesses used for sensors that does
not carry high currents. When such a harness is carelessly bent for any reason, then thin wires are streched
beyond breaking point creating open circuits. This results in erroneous sensor readings.

 

[MrGreedy]

If the fan starts around 10 seconds after engine start, it could also be low air con pressure or a duff air con pressure sensor.

Do you have iCarsoft? can you interrogate the air con system pressure when the car is of and running and what readings do you get?

 

[AntMB]

Thanks for the suggestions so far, I do have iCarsoft. I will take a look at that.

In the meanwhile, I've been in the car again, started, so many seconds later, fans on. I then noticed the temp guage shot up to 90c straight away. It then went up to 120c then back down to 90c.

So, likely the temp sensor? What do you think guys?

 

[Supernoodle]

Thanks for the suggestions so far, I do have iCarsoft. I will take a look at that.

In the meanwhile, I've been in the car again, started, so many seconds later, fans on. I then noticed the temp guage shot up to 90c straight away. It then went up to 120c then back down to 90c.

So, likely the temp sensor? What do you think guys?

Certainly sounds like a suspect. You should be able to see the actual temp sensor values on icarsoft.

fan control unit looses its CAN-bus connection

Norm is PWM for a fan, with diagnostic signal grounding to allow fan controller to report errors back to ECU.
LIN may be too, that's cheap and more than fast enough, but CAN would make that a very expensive controller.

 

[AntMB]

The coolant temperature sensor is in the thermostat housing, actually, I still have the old stat housing which I replaced 5 years ago, I'll try swapping that sensor over when I get a chance.

 

[AntMB]

Certainly sounds like a suspect. You should be able to see the actual temp sensor values on icarsoft.


Norm is PWM for a fan, with diagnostic signal grounding to allow fan controller to report errors back to ECU.
LIN may be too, that's cheap and more than fast enough, but CAN would make that a very expensive controller.

What is LIN?

 

[Supernoodle]

What is LIN?

Local Interconnect Network. It's a 12v serial communication system. One master device (eg ECU) controls one or more slaves (eg glow controller and alternator). The slaves only send data in response to a request from their master.

That's different to CAN where every device is a master, ie they just send data without being specifically requested.

 

[badgx]

Check fan relay, might be sticky?

 

[AntMB]

Check fan relay, might be sticky?

Wouldn't muck the temp readings up though, so that's why I'm pointing to the temp sensor.

 

[AntMB]

So this evening, put the key in, ignition on, but not start, and the temp reading shot right up to 90c right away. Start was rough, so that points to the temp sensor, as the fuel settings wouldn't be correct, as the engine is in fact cold, but the computer thinks it's at running temp.

I'll try the other sensor Sunday.

Had a scan of the aircon pressure as suggested earlier on, it's reading 3 bar.

 

[AntMB]

I tried the other sensor a moment ago, I just plugged it in hanging in free air, still in it's stat housing - temp fine and fans remained off, so that's proved that.

So I've tried to remove my good sensor from the old housing, it's not budging, doesn't want to come out, so the one in the car will be the same - I risk breaking the socket of the sensor, so looks like a complete housing change with a new one!

 

[AntMB]

Ok, so parts supplier issue - I like Topran stuff, often they are OEM, I've been stung by that scam from Autodoc where they alter your order to give you a part from a manufacturer called Stark.....a google suggests they're a Chinese manufactuer which they own and I'm not the first to have been done by this.

Main dealers, out of stock completely, long lead times so long that they don't even know when they'll have them.

 

[Supernoodle]

I replaced the duff stat on my E220 with Mahle part. You should be able to source one of those in easily.

 

[AntMB]

Where did you get yours from? Euros don't show one, GSF only says premium, though I got mine there last time around and it was a Calorstat, which are usually good, but I didn't know what they were supplying until I got it.

 

[Supernoodle]

It was from Partsinmotion, or rather specifically their eBay store partsinmotion.

Looks like they don't sell that one any more, but notice there are others that seem to have the same part. They list by Mahle part number so doesn't come up if you search for E270. Don't know if this is the same as yours

Thermostat, coolant for MERCEDES-BENZ MAHLE TI 27 92 | eBay

Engine: 2685ccm 125kW 170HP (Diesel). Year: 1999-07-01 - 2003-03-31. Engine: 2685ccm 120kW 163HP (Diesel). Year: 2000-02-01 - 2003-03-31. Engine: 2148ccm 105kW 143HP (Diesel). Year: 1999-07-01 - 2002-12-31.

www.ebay.co.uk

 

[AntMB]

A late update, I managed to replace just the temp sensor. In the original Mercedes one, I couldn't remove the sensor at all, but I noticed the one in this Calorstat could rotate, so I tried removing it, which I was able to, so I replaced the sensor, which was a result.

So after which, everything is back to how it should be, fans and temp all good.