UrS4boy

The oil temperature sender on our 20vt (3B, AAN, ABY and ADU) engines is down on the front of the engine in the oil pump and is connected to the instrument cluster/gauge by one wire. If there are oil temperature gauge problems, you need to suspect that a) the sender is flakey or b) the wire connection at the sender is flakey or c) the wire connection at the instrument cluster/gauge is flakey or d) a trace on the instrument cluster (or separate gauge) is flakey.

The oil temp sender is in the lower right corner of the photo here:



The oil pump is a gear pump which means the oil pressure is created by two rotating gear wheels as their teeth intermesh, causing pressure as the grear teeth try to compress the mostly incompressible fluid (the engine oil). If the pressure gets too high for some reason in the pump, the pressure pushes against the pressure release piston and spring, releasing pressurized oil back into the oil pan. Note: The ADU uses the 054115105D oil pump from the AAR five cylinder diesel engine instead of the more common 054115105E that the 3B, AAN, and ABY use.

Here is what the pump looks like with the gear pump parts assembled into the back of the pump body:



and then covered with the cover plate (note: temp sender isn't screwed all the way in yet):



We think the temperature sender (Audi PN 035919521B) is a 180ēC max VDO 92-027-081, as shown here:



The details of this sender are as follows:



More about VDO temp senders can be found HERE

The original un-annotated photos were from 4WheelDrifter (Stu) on the S2 forum.