2001 s600 Coolant Temp Sensor issues
 

I recently replaced my coolant temp sensor and it doesn't stay in place, so it leaks coolant. Is there some kind of clip to hold it in place? There is just an o-ring trying to keep it in place, but it's not doing so well. Thanks in advance for some helpful advice.

There must be something to hold the fitting onto the O-ring. Did you dismantle the system to replace the sensor? If so, what was holding it in place when you disassembled?

I would have NEVER thought that there would be an O-ring fitting to hold pressure in the cooling system. THEN I had to remove the radiator on my '03 S600 and found out different. There the upper hose (return to radiator from the block which is actually in the middle of the driver's side of radiator and NOT actually at the top) is a plastic fitting that fits over a the plastic radiator. The O-ring seals the fitting between the two plastic parts and is held in place by a metal clip that holds the hose fitting from sliding off the radiator fitting. Every radiator I have ever seen has a rubber hose held in place by a clamp. This system SEEMS a little precarious but has not leaked since I changed the radiator.

Your fitting has to have some kind of clamp, or more likely-clip, to hold the fittings together. Look a little closer.

Keith

The o ring is seated outside of the thermostat housing and the coolant temp sensor slides into that. I don't think there was any clip on it when I removed it. I suppose there may have been a clip placed on the inside of the housing that fell off when I removed the sensor, but I didn't notice any loose parts when I took the housing apart. Also, the sensor is new, and it did not have a clip in the box with it, just the o ring. I did notice that on some online parts stores show a clip next to the sensor and o ring in the product image. I guess I'll take the housing off and open it up to look for a spot for a clip.

a c clip holds it in place