Safe to assume sender is DOA?

[Danny_Ocean]

My oil temp guage isn't registering. It "jumps" a little when you first turn on the ignition, but stays @ zero while you drive. Today, I shorted the sender wire to ground and the guage pegged to "max".

Is is safe to assume the sender is bad? I'd like to be sure before I disassemble the A/C to get to it.

[Jim Sims]

"I'd like to be sure before I disassemble the A/C to get to it."

The oil temperature sender is on the rearward facing part of the engine; it can be accessed without removing the A/C compressor.

[Zeke]

I'd think about checking some more wires first. I'm not sure why it would send a signal when grounded, but instrument grounds are impoertant in that they must be able to ground very small amounts of current. Sometimes a little corrosion can inhibit that.

You can tell I'm no EE, but the grounds on the whole car should be cleaned periodically.

[randywebb]

you can also run a long wire on the outside of the car from gauge to sender - if it works then you have a bad wire

[jstobo]

The Oil Temp gauge sould be fine. It should read full scale when the sender point is grounded and read zero when cable is disconnected.(Curiously the oil pressure gauge is opposite). So the problem is from the sender to the gauge. Could be wiring or the sender. If you shorted the sender wire at the sender and the gauge read full max then the wiring is okay and the sender is probabaly bad. Be sure you get the sender that matches the range of your gauge. Good Luck.

[jstobo]

The Oil Temp gauge sould be fine. It should read full scale when the sender point is grounded and read zero when cable is disconnected.(Curiously the oil pressure gauge is opposite). So the problem is from the sender to the gauge. Could be wiring or the sender. If you shorted the sender wire at the sender and the gauge read full max then the wiring is okay and the sender is probabaly bad. Be sure you get the sender that matches the range of your gauge. Good Luck.

[Danny_Ocean]

Originally posted by Jim Sims
"I'd like to be sure before I disassemble the A/C to get to it."

The oil temperature sender is on the rearward facing part of the engine; it can be accessed without removing the A/C compressor.

Not sure about your car, but the brackets holding the A/C compressor on mine are definitely in the way...unless there's another way to access? I'm not 100% certain I have stock A/C brackets, either.

[Danny_Ocean]

Originally posted by jstobo
If you shorted the sender wire at the sender and the gauge read full max then the wiring is okay and the sender is probabaly bad.

That's what I thought...same test procedure as an American car. If the wiring was bad, there would be no path for the grounding test to affect the gauge.

However, I didn't want to assume because these "Porsh-a" mechanicals are always throwing me a curve.

[Early_S_Man]

I ran a test in the summer of 2002 on a new ['69 - '73] early VDO sender in a pan of old, rancid cooking oil on a hotplate in a cast iron skillet ... using a thermocouple probe and Fluke 52 thermometer, and measured the resistance at 10°F intervals from 70°F to 300°F.

If you substitute a 1000 Ohm potentiometer for your sensor ... you could test your gauge by sweeping the range, and temporarily disconnecting the pot. to measure the resistance that produces readings at your gauge marked points ... I wouldn't worry too much about the 300°F to 340°F range!

Temp - °F -- Sensor Ohms:

70° -- 1148 Ohms
75° -- 1000 Ohms
80° -- 918 Ohms
90° -- 756 Ohms
100° -- 607 Ohms
110° -- 504 Ohms
120° -- 424 Ohms
130° -- 357 Ohms
140° -- 301 Ohms
150° -- 260 Ohms
160° -- 219 Ohms
170° -- 189 Ohms
180° -- 162 Ohms
190° -- 142 Ohms
200° -- 122 Ohms
210° -- 108 Ohms
220° -- 92.4 Ohms
230° -- 82.2 Ohms
240° -- 73.2 Ohms
250° -- 64.2 Ohms
260° -- 57.6 Ohms
270° -- 51.2 Ohms
280° -- 43.8 Ohms
290° -- 39.6 Ohms
300° -- 35.4 Ohms