I have a 190 W201 1.8E petrol saloon with a five speed manual gearbox registered in 1991. The VIN number tells me it's the base Australian version - so none of the electrically operated options except a passenger side electric mirror. No sunroof. A previous owner did have an aftermarket airconditioning system retro-fitted it functions with a simple on off button when the regular slide O - Max internal blower is operated.

The car runs fine BUT ... the temperature guage never rises above 80 C and when I put the heater on I only get lukewarm air coming from the demister and passenger / driver air vents.
Apparently the thermostat should start opening at 87 C. The car seemed overcooled. So I bought a new thermostat and bled / topped up the system whilst the engine was running. There seemed a slight improvement in that the thermostat seemed to make a single click noise as the temperature rose to about 85 C. The fan came on shortly after this but the indicated temperature never rose much beyond 85 C. The warmth from the internal heater vents didn't improve beyond tepid. The vacuum operated heat exchanger leading to the heater core operates as it should. Both pipes leading to and from the heater core are warm at about 85 C. There doesn't appear to be air in the system.

In between the oil filler and thermostat housing there is a bank of three temperature sensors. The Haynes manual isn't any help with this. I'm getting conflicting advice online regarding what each one does. I could use some help (see pictures). I think the three-pin sensor nearest the front of the engine is related to switching on / engaging the electric fan. I think this sensor is either the wrong temperature or has gone wrong and is causing the fan to come on too early. I've ordered another three-pin sensor (although only one pin is used) with the part number
006 545 91 24 it's supposed to come into play at 100 C which sounds like it might be the answer to my problem.

I don't know what the other two sensors do. The middle sensor looks to have a two pin connection with a wire take off to connect to the three pin sensor. That said I can't find any two pin sensors from the usual suppliers. Initial attempts to remove the connection plug resulted in one of the plastic retaining lugs breakng off at the merest touch - so I wasn't keen to pursue any further investigation risking damage to fragile old plastic. Any idea what its function is?
The rearmost sensor looks to be a four pin connection - judging from pictures and references online. Again, I chickened out of pulling the plug off to confirm because I don't want to risk breaking anything if I don't have to. Any idea what its function is?

Cheers in advance for any help.

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Thermostat support broke ... lemmie find that thread ....

https://www.peachparts.com/shopforum/tech-help/372866-thermostat-normally-open.html?highlight=thermostat

It's not the thermostat. I bought a new one. It's something else on the temperature sensor side of things, I reckon.

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does your auxillary water pump turn on? That might be the problem

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1990 190E 3.0L