W108 250SE Heat sensor unit

[Tassie Tiger]

I am seeking some clarification on the hose connections to the heat sensor unit on the fuel injection pump. The top hose goes to the temperature switch housing. The bottom hose runs to the inlet manifold and then into the thermostat housing area.
The warm up characteristics are fine, however, I have seen engine bay photographs where the hoses are connect same as mine but also reversed - ie. the bottom hose going to the temperature switch housing.
Which is correct?
Regards,
Tassie Tiger

[wbain5280]

It doesn't matter. The important thing is that the thermostat inside the housing works, the pin comes out when hot, and that the plunger under it all moves freely. It's for fuel enrichment and bypass air when cold cutting off when the engine is hot.

[Arthur Dalton]

The test for normal operation is to remove the air filter at the pump and start the car COLD
Put you finger over the filter port and it should suck in air .. As WB said, once it warms up, the suction should slowly shut off [ completely closed at 65C].
This is just a warm up enrichment device that is controlled by the sensor actuating pin inside the unit, dependent on the coolant temp running through the hoses...
Check the air filter for dirt while you have it off.
While on the subject of your FI pump, there is a little oil dip-stick in the back of the pump [ T handle] for the oil res... make sure that is full... for some reason, no one ever checks this and you do not want to be buying one of these pumps for simply letting it run low on lube...
The later pumps did away with this and are lubed from the crankcase.
Your pump is the last of the res design [ Bosch R18 pump]

[Tassie Tiger]

Thanks for your replies Warren and Arthur. The warm up device works fine and there is suction at the filter when the car is cold. It ceases when warmed up. I was curious about the hose connection and will leave mine as it is.
I checked the oil level in the IP some time ago and as I unscrewed the dip stick, oil came gushing out. No doubt this was due to fuel contamination with the oil causing the level to rise. It took over an hour to remove this oil with a syringe and tube. I topped up with engine oil up to the mark on the dipstick and level is still OK.
Regards,
Tassie Tiger