Cooling fan running and coolant hot message
Thread Starter
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
Cooling fan running and coolant hot message
Just a few minutes ago my radiator cooling fan came on high speed while I was at idle at a stop light. I also got a coolant icon as a vehicle status message.
However the temp guage looked about normal or maybe a little lower than usual - I usually run about 90C. The vehicle does not seem overly hot - if anything it’s a little cooler than normal.
I was driving in a lot of start/stop traffic when this happened. Ambient temp is about 62F.
I parked and turned off the vehicle right away. The radiator fan stayed on about a minute after the vehicle was shut down.
Upon restart, the fan cranked up to high almost immediately and stayed on. A/C is off. However, the temp guage is still in the normal range (a little lower due to cooling for a few minutes.)
When I turned the vehicle off again, the fan again ran for about a minute then stopped.
I am out of town, and don’t have my scanner with me so I can’t check for codes.
- No check engine light.
- no coolant low message
- the belt looks good
- coolant level - observed from the side - looks good
i need to get home - about 170 miles. My intuition tells me that this is some sort of sensor issue - specially since the coolant temp guage is in normal range. However the inconsistent info has me concerned about such a long drive.
any recommendations about what might be the issue or what to check?
However the temp guage looked about normal or maybe a little lower than usual - I usually run about 90C. The vehicle does not seem overly hot - if anything it’s a little cooler than normal.
I was driving in a lot of start/stop traffic when this happened. Ambient temp is about 62F.
I parked and turned off the vehicle right away. The radiator fan stayed on about a minute after the vehicle was shut down.
Upon restart, the fan cranked up to high almost immediately and stayed on. A/C is off. However, the temp guage is still in the normal range (a little lower due to cooling for a few minutes.)
When I turned the vehicle off again, the fan again ran for about a minute then stopped.
I am out of town, and don’t have my scanner with me so I can’t check for codes.
- No check engine light.
- no coolant low message
- the belt looks good
- coolant level - observed from the side - looks good
i need to get home - about 170 miles. My intuition tells me that this is some sort of sensor issue - specially since the coolant temp guage is in normal range. However the inconsistent info has me concerned about such a long drive.
any recommendations about what might be the issue or what to check?
Thread Starter
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
A little more info.
I just did a short test ride. The fan is still running full speed upon start - and continues running full speed until about 90 seconds after turning off the vehicle.
the coolant message icon will come up periodically, then the message center will return to a normal display.
The owners manual says that the icon may mean that the fan is malfunctioning - which is what seems to be happening. I’m thinking I probably can get home ok since the trip is about 99% Highway.
I just did a short test ride. The fan is still running full speed upon start - and continues running full speed until about 90 seconds after turning off the vehicle.
the coolant message icon will come up periodically, then the message center will return to a normal display.
The owners manual says that the icon may mean that the fan is malfunctioning - which is what seems to be happening. I’m thinking I probably can get home ok since the trip is about 99% Highway.
Thread Starter
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
Final bit of additional info.
I disconnected the fan, and cranked the vehicle, then turned the vehicle back off. (Was thinking that might reset the issue somehow.)
Upon reconnecting the fan (with the vehicle off) the fan came on (I assume it was doing the same 90 second run out.).
Next, I immediately cranked the vehicle - and the fan stopped.
Will do a test run later to see if it holds.
I disconnected the fan, and cranked the vehicle, then turned the vehicle back off. (Was thinking that might reset the issue somehow.)
Upon reconnecting the fan (with the vehicle off) the fan came on (I assume it was doing the same 90 second run out.).
Next, I immediately cranked the vehicle - and the fan stopped.
Will do a test run later to see if it holds.
MBWorld Fanatic!
Joined: Jun 2014
Posts: 1,086
Likes: 443
From: Melbourne, Australia
2010 ML550 VIN WDC1641722A564750, 2010 B180
Maybe buy yourself a cheap scan tool. You'd think even a cheapo one would help you out since you're away with coolant temperature. I agree with you - it sounds like a sensor issue rather than anything else based on what you've described. 90 degress on the dash is normal - noting the thermostat opens at 100 degrees C.
