What are all these water sensors for? - 5.0 Megasquirt - PeachParts Mercedes-Benz Forum

GGR · #1 10-04-2009, 02:32 PM

Hi all,

I am planning to Megasquirt my euro 5.0 M117 engine. For that purpose I have fitted an in take manifold out of a 4.5 Djet engine. I have now four water sensors:

- one in the back of the right cylinder bank with one contact and a green wire; is that for the temp gage in the instrument cluster?

- one on top of the water pump, in the neck linking the water pump core to the front of the intake manifold, with one contact, I don't know what it is for;

- two on the water bridge in the front of the Djet manifold. Both have two contacts. The smallest must be the water sensor for the Djet system. I wonder what the bigger one is for...

Thanks in advance for the help!

Tomguy · #2 10-04-2009, 02:59 PM

The first probably is. Doesnt sound familiar to me since 108 4.5's have an old style mechanical one in the head.

The single prong big sensor is the 212* fan switch.
The big one up front is the thermo-time switch for the CSV.
The small one is a temp sensor for the D-Jet ECU.

GGR · #3 10-04-2009, 03:28 PM

Thanks! Megasquirt doesn't need an additional cold start injector so I guess I can get rid of the big thermo contact in the manifold. Megasquirt can also take care of the fan, and my car doesn't have any (apart from the mechanical one) for now so that sensor can also go.

The one for the temp gage brings another question. This Megasquirted 5.0 engine will go into a W111 Coupe currently equipped with a 3.5 engine. I guess the gage sensor is the same as on the 4.5s. Does that mean I should keep the sensor currently on the 3.5 to get a correct temp reading? How does a mechanical sensor work? They are both in the same location in the back of the right head.

Tomguy · #4 10-04-2009, 07:40 PM

It's gas pressure in a capillary tube that, when warmed, makes the gauge go up.