Testing of Oil pressure/temp gauge/sender

[lmcchesney]

I used the wiring diagram from the VDO site. 12v into +, grd to (-) side and G to sender pole. Used the (-) to ground to the sender case as well. Heated the sender in boiling water. Made the connections but the gauge did not register.

I made a similar hookup to the dual pole pressure sender. Made up a pressure chamber by using a brass "T" with air compressor into one fitting, mechanical pressure gauge in another fitting and the sender into the last fitting. 12v to + side of gauge, "G" of gauge to "G" of sender and ground to neg terminal of 12v supply and case of sender. Turn compresser on to 30psi but no registaring of the VDO gauge.
Does anyone know where I went wrong?
Thanks,
L. McC

[914GT]

Hmmm ... are you using the same jumper leads for each setup? Maybe you've got a bad lead or alligator clip? Check the gauges w/o the senders attached by jumpering across the terminals, should get full scale deflection or put a pot across it and vary it to watch the needle move.

[lapuwali]

Clarifying, if you jumper G to +, you should get full deflection one way, jumpering G to -, you should get full deflection the other way. You should get max temp/press with + to G, and min temp/press with - to G.

If the gauges check out, then use a multimeter on the senders instead of the gauge (across the sender housing and the pole) when heating or applying pressure, with the meter on the ohms setting. For std. VDO, you should see about 10 ohms for min readings and 180ohms for max readings. +/- 10 ohms or so.

If you get both checking out, one last check is to use resistors to jumper from - to G on the gauge, 10, 90, and 180 ohms (min, mid, max). It's possible you have mismatched gauges and senders. 10-180ohms is the std. VDO range, but there are other ranges that VDO supplies. The std. GM ranges, for example are 240-33 (reversed from VDO), but VDO sells gauges for that range, in addition to their own range.

If you bought from egauges.com, this is actually likely. I have had them send me mismatched orders more than once.

[lmcchesney]

Success!
Thanks Lapuwali. They are European wired. Thus, black is grd and brown is positive.
Placed the temp sensor into boiling water and gauge reads 100°C.
Hooked the pressure gauge up to my pressure chamber and the gauge coorelates with mechanical gauge bar for bar. I have two pressure gauges. One measures to 10 bar and the other to 5. It seems that the 5 bar would be best suited for the pressure range of the engine. Both guages work though. Thus I have a second pressure gauge to sell.
Thanks again for your help.
L. McC

[lapuwali]

Yes, the 5 bar gauge is better for a Type IV. 5 bar is a bit over 70psi, and you're not generally going to see more than 60psi. Normal operating pressure at cruise should be 2-3 bar.

[Dave at Pelican Parts]

"European wired"?? On all VWs and Porsches that I know of (except the really early ones!), brown is ground and black is "hot"... No 914 ever left the factory with a brown wire used as a source of +12V.

Are we talking some sort of British iron, here?

--DD

[lapuwali]

Germans are just backwards when it comes to electricity. Black is ground everywhere else I know of except on German cars (and perhaps only on Porsche/VW). On British stuff, brown isn't typically "hot". Red or white is typically hot (red = unswitched, white = switched). Brown is usually reserved for signal lighting (brake lights, turn signals, etc).

IMHO, brown is also a terrible color to choose for wiring, since ALL wiring tends to look brown after awhile from dirt and color fading.

[lmcchesney]

I agree. Brown is a poor long term color identifier.
The gauge/sender is Volvo.
L. McC