temperature dash light ?

1992 / 400E -- while returning from 2,000 m. road trip, dash temperature light came on.....temperature gauge "does not" show overheat / and / drove 600+ miles w/ no overheating.
I have checked / topped off coolant (took VERY small amount) and it does not appear to be losing any coolant at all....now, 4 weeks later and dash light still on ??? Local M/B dealer want a minimum of $84.00 hr. to determine problem ?? Any thoughts ????

[vinamg]

How is your coolant level now?
There is a sensor in the expansion tank. The coolant level needs to drop below it in order for the light to turn on. If your coolant level is good, then you need to check the sensor. This is very rare. You probably are loosing coolant. Loosing small amount of coolant is usually a sign of a bad water pump. This will only get worse. Check the wheep hole for signs of coolant or crust.

Vinamg

the coolant level is right at the proper fill line (after I put a few drops in it upon return home).....4 weeks later, right at the line and I can see no leakage. Is there any way to "check" the sensor ? thx !!

[vinamg]

If you are absolutely sure that the coolant level is fine and the light comes on you should remove the sensor and check it. Check if it moves freely. If you have ohmmeter check for open-close loop.
If the problem persists you should replace it.

Vinamg

thanks alot for the sensor reco. /// it's a start !!!!