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Problem with VDO oil temerature dipstick
Purple Martin - March 31st, 2003 at 09:46 AM

Hi everyone,

A while ago I picked up a second hand VDO oil temerature dipstick and guage.

A couple of weekends ago I bench-tested them with a 12V battery and a kettle of water, and the guage reading had increased as the water got hotter and read about 100C when the water was boiling, so I know the sender and guage were working properly.

This weekend I installed them, and now something isn't working properly. When the ignition is turned on the guage needle instantly jumps right off the scale. I've checked and triple-checked the wiring so I'm as sure as I can be that I've got the right terminals wired to the right things, but clearly something is wrong somewhere.

Does anyone have any ideas what I should check next?

Thanks in advance!

kombikim - March 31st, 2003 at 09:58 AM

needle jumping of the scale means the guage is geting full 12volts from somewhere (hopefully not the sender) triple check or not the easist thing I can think of is take dipstick thingie out & connect with short wire & earth at dash to see what happens, there are 3 terminals on guage , sender, earth & ignition-power, The sender terminal or wire MAY be shorting to earth at or near the terminal on guage or dipstick

Purple Martin - March 31st, 2003 at 10:05 AM

When I pulled the wire off the sender the needle dropped back to zero, when I put the wire back on the sender it jumped back up to max. This was with the sender in place (dipstick tube). If there was a short at the terminals on the guage, taking the wire off the sender wouldn't make any difference, would it?

You said "The sender terminal or wire MAY be shorting to earth at or near the terminal on guage or dipstick"... did you mean shorting to 12V? I'm confused
:cry

Andy - March 31st, 2003 at 10:16 AM

Have a read here:
http://steve_vwworld.tripod.com/ht/dipstick.htm
I would try swapping the terminals over on the sender (dip stick). The +ve and -ve from the gauge MUST go to the +ve and -ve on the sender.
Just a thought.
Andy

Purple Martin - March 31st, 2003 at 10:20 AM

Thanks Andy, I'd already found that article and printed it out to use for the installation.

I'll try swapping the sender wires over - it's possible I've been stupid enough to get them the wrong way round.

kombikim - March 31st, 2003 at 10:30 AM

Hi
no I did mean short to earth an electrical temp guage is earthed, & has 12v power & works by measuring how many volts the sender unit lets through IT's earth from the variable resistance in the sender unit.
but go through what Andy said 1st, cause I haven't seen a dipstick sender unit, but I would say the + means it "takes" the positive "feeler" current sent by the guage

kombikim - March 31st, 2003 at 10:43 AM

did you understand what I said Andy? I know what I mean to say but not always how to say it- my brain is fried at work at the moment:(

Andy - March 31st, 2003 at 11:24 AM

I know what you mean KombiKim.
I'll know more when I look how mine is installed at home tonight.
:thumb

vw54 - March 31st, 2003 at 11:49 AM

yes yr getting a short circuit some where ... re check the wiring and connections.

Purple Martin - March 31st, 2003 at 01:40 PM

LUNCHTIME UPDATE

Well I just got back from lunch. Before I drove the bus to lunch, I switched the terminals on the sender. Hey presto - it works! I'd been so careful to mark the terminals when I bench-tested it, I've no idea how I managed to mark them the wrong way round. It's a bit embarrasing, but I've learnt something!

Thanks for all your suggestions.

Andy - March 31st, 2003 at 04:31 PM

:cool: