Overheating and coolant light ON
Thread Starter
Newbie
Joined: Jun 2011
Posts: 5
Likes: 0
From: Indiana
2005 ML500
Overheating and coolant light ON
My ML500 coolant light came on so I checked and topped off the coolant in reserve tank. Couple days later light comes back on and engine started to overheat so I decided it was time (135k miles) to replace coolant and thermostat, done...light still comes on. Now I'm looking at fan...it has ~12v @fan red&brown wires. I've seen fan 'twitch' but never actually run.
Given these fans seem to be ~ $1100, is there an easy test to validate its condition before ordering a new one??
Given these fans seem to be ~ $1100, is there an easy test to validate its condition before ordering a new one??
Thread Starter
Newbie
Joined: Jun 2011
Posts: 5
Likes: 0
From: Indiana
2005 ML500
There is no leak. I believe the issue is the fan but wanted to check here to see if there was a way to confirm before dropping $$$ only to find out it is some sensor or relay I don't know about. I've checked everything else I could find or that was eluded to on this site.
Senior Member
Joined: Mar 2002
Posts: 282
Likes: 5
From: Brisbane, Australia
2002 ML320, 2003 A160
The cooling system is sealed with a valve in the cap when the expanded coolant exceeds the capacity. If you topped up the coolant, then the light came back on, then you must be losing coolant somewhere. By definition, you have a leak.
Edit: So it's not a leak. Coolant is heating up and going somewhere, and it's not coming back. Whatever you want to call that, figure out where it's going and stop it. Attach a small PET bottle to the overflow pipe - if that fills up, replace the cap.
Other common causes of coolant loss are splits in the expansion tank where the hoses attach (under the tank) and failure of the water pump bearing at the front of the engine.
Edit: So it's not a leak. Coolant is heating up and going somewhere, and it's not coming back. Whatever you want to call that, figure out where it's going and stop it. Attach a small PET bottle to the overflow pipe - if that fills up, replace the cap.
Other common causes of coolant loss are splits in the expansion tank where the hoses attach (under the tank) and failure of the water pump bearing at the front of the engine.
Last edited by DrX; May 4, 2017 at 02:20 PM.
