Engine Light on and no Water Temp Gauge

[PaulPJ]

Hi All, I drove to supermarket this morning and when I switched the engine off the fan was running which I thought was strange. When I left to come home I noticed I had no water temperature gauge and the engine was revving high and then I saw the Engine Management light was on. I drove straight home and dumped it in the drive, any one got any thoughts as what could be wrong and how to resolve. Many thanks

 

[markjay]

Check the coolant level (when the engine cools down).

Having no reading on the remp gauge can be the result of the sender no longer being immersed in coolant. If there's a volume of air in the coolant system, the temp sender won't work.

And of course you should get the fault codes read with STAR.

 

[PaulPJ]

Hi Markjay, I will leave the car and hour and then check coolant level and update you, thank you.

 

[PaulPJ]

Hi Markjay, the expansion tank was half full so I put a bit of water in, started it up and I had a temperature gauge and the fan was not running. I backed out, drove 100 yards and temp gauge stopped and fan came on again. Not sure what to do now.

 

[Petrolheed]

It could be that there is air in the system, topping up the expansion tank may not have fully filled the system. Check the level again, top up if necessary, then start engine, to see if the level remains, or drops. When did you last check the coolant level. Either way. it would seem there is an underlying problem if the coolant level has dropped.

 

[PaulPJ]

Hi Petrolhead, coolant level was checked about 3 weeks ago. Paul

 

[Petrolheed]

It must be loosing coolant somewhere. Check for damage/leaks to hoses and the clamp connections, or any signs of leakage.

 

[ashenfie]

You need to get the error code read to understand the issue. I would keep a close eye on the water level in the mean time. Definitely don't drive if the water level appears low.

 

[alecmascot]

Hi Markjay, the expansion tank was half full so I put a bit of water in, started it up and I had a temperature gauge and the fan was not running. I backed out, drove 100 yards and temp gauge stopped and fan came on again. Not sure what to do now.

Sounds like the water level is fine. The fan will come on if there is no reading from the temperature sensor.
It would seem that there is an intermittent connection to the sensor, or that it is faulty.
My first action would be to replace the sensor. If you siphon off all the water from the header tank then you should loose only a tiny amount. Put it in a clean container so you can put it back. The sensor is often part of the thermostat assy.
Let me check for a location on an M271 engine.
What year is your car ?

 

[PaulPJ]

Hi Alecmascot, it was first registered Dec 2008. Thanks for your help, Paul

 

[alecmascot]

Item 146 A0999053800

 

[PaulPJ]

Hi Alecmascot, thank you for your help. Looking at this diagram and looking at my engine I think it plugs into hose 130 just below where the expansion tank feeds into hose 130 and should I get a 149 too. Please can you confirm my assumptions if you would be so kind. Paul

 

[alecmascot]

I think that's right. It is good practice to replace the o-ring as well.

This is for an older C230 but I think the Temp Sensor location is the same.

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I do not think you will need to drain the coolant if you empty the header tank.
Have some mixed coolant ready to top-up afterwards,

 

[PaulPJ]

Thank you very very much for your help Alecmascot. Mercedes in Southampton have one put by for me to collect assuming my wife will run me over there shortly

 

[PaulPJ]

Thanks to Alecmascot the task took me 20 minutes and all now resolved. The Engine Management light went out on its own.

 

[Petrolheed]

Great news, what puzzled me was the loss of coolant, I've never had to top up the coolant unless doing some work on it, or flushing.

 

[Petrolheed]

While I'm on here, maybe someone could chip in and let me know how to create a new post, I'd like to post a question, thanks in advance.

 

[steveq]

While I'm on here, maybe someone could chip in and let me know how to create a new post, I'd like to post a question, thanks in advance.

When you are logged in go into the Forum where you want to create your thread. At the top of the screen on the right hand side there is a 'Post New Thread' button.

 

[PaulPJ]

Hi Petrolheed, I hadn't lost any water at all, it was just that the water temperature sensor had died. A quick trip to Mercedes in Southampton to purchase another and it was resolved. It actually took longer to syphon out the contents of the expansion tank than it did to swap sensors.

 

[DSM10000]

Without a temperature signal some ECU's will assume a cold engine and add more fuel hence the higher rpm.