Can any of you technical experts help me with a problem of overheating (E280/M104/24V with A/C), only apparent during the recent hot weather?

I’ve read somewhere that the auxiliary cooling fans work independently. One starting at 100 degrees and the other (i.e. both) at 115 degrees.

Whilst idling in traffic in very hot conditions, A/C on, the engine temp goes really hot – right up to nearly red then (finally) both auxiliary fans cut in together and the temp soon drops to normal….only to repeat this every five minutes or so. It’s all getting a bit too hot for my liking and I don’t remember it doing this last year. I think maybe the 100 degree switch / relay (or whatever) isn’t working.

On the front of the engine, next to the thermostat housing there are two sensors. The front one with one wire I know works the temperature gauge. The other one has a square plug with four wires. When I unplug this, both fans come on after a slight delay.

Does this sensor monitor both 100 and 115 temperatures? If so, am I right to assume it need replacing, or is a relay at fault?

Is there any way I can test the sensor before buying a new one? I don’t want to burn anything out shorting out the wires!

Anyone help?

Thanks