Oil Temp Sender/gauge

wastintime · 03-02-2002, 11:58 AM

Hey everyone,
Well, my car isn't going anywhere so I'm working on little stuff until I get my new calipers.

Quick question about the oil temp senders. If anyone has a chance and doesn't mind doing this could you please disconnect your wire going to the oil temp sender and touch it to a piece of metal and tell me what happens.

I don't believe that there is anything wrong with my gauge because it was working before the temperature sender was broken, but I'd like to check.

I installed the temp sender for a VW Rabbit (it was only $10, and I'm not willing to pay for the correct sender, or to have my gauge recalibrated) and it seems to fit well, and oil is getting to it. I can't get it to give any readings though. This is what it looks like sans the adapter that allows it to fit:

I don't have the correct attachment for the wire to connect to it, I'm not even sure what is correct, but I have it set up with an alligator clip just to test it. I wouldn't see why it wouldn't work though.

I realize that the sender could just be completely incompatible with the gauge, but I was just wondering if anyone had any ideas why it gives the same reading if it is or isn't attached to the sender, and if it touches a piece of metal it goes to 0. Any ideas?

Thanks,
Andrew

cgarr · cgarr's Garage

I just got done working on mine and got it working. If you ground the wire at the sender it will peg the needle, the only thing your sender does is establishes a ground with varying resistence to ground, you can check this with an ohm meter, freeze it and you get less resistence, heat it up and you get more resistence, make sure your gauge is hooked up right and you dont have the wires reversed, if you do it will not move and you think it aint working, thats what I did,

I do have a new sender on order from Porsche for my 69 but I will not be using it because my original was just fine, it was $24.00 My parts book shows 69 was a different sender than the 68 and older for some reason.

Thanks

Craig G

wastintime · 03-02-2002, 04:41 PM

I know the gauge works, maybe the sender just provides too much resistance to give it a reading. Oh well, no big loss for $10. I'll keep playing with it, maybe I can make something work. I'm not sure how not to ground the wire at the sender, just attaching the wire seems to ground it out.

Morrie · 03-03-2002, 08:33 AM

STRANGE....

When I disconnect the wire for the guage on my 67 it pegs the needle on hot. When I short the wire to ground, it sets the needle all the way to cold.

Maybe this is the difference between the two senders (67 and 69). Possibly one has a positive temperature coefficent, one has a negative temperature coefficent.
They are both basically thermisters in a special package.

See which way your guage works then put a ohmmeter between the terminal of the sender and ground as the engine warms. Note the resistance change, whether it rises or drops as the engine warms, and what it settles out at when the engine is operating normally.

With this information, we can get this figured out....

Morrie

wastintime · 03-03-2002, 09:34 AM

Well, the problem is most likely that I'm not using the stock '67 sender, I'm trying to get a VW sender to work. I would have stayed stock, but I didn't have the $300 for one.

Disconnecting the wire does peg the needle on hot, and grounding it does peg the needle on cold. Hooking the wire up to the sender pegs it on hot as well though.

I took some readings with my ohmmeter and the resistance does drop as the engine warms. Since it should work the other way with the stock sender I have no idea if I can get this to work or not.

Actually this may sound like a crazy idea, but I wouldn't really be opposed to having the gauge work backwards. There are enough things on my car that I know are backwards or the wrong color, this would just be one more thing. I wonder if it's possible to adjust something to get useable readings. Obviously right now the coldest setting on this sender provides more resistance than the hottest setting the stock sender. Maybe I can play around with the guage (although I really don't want to) and see what happens. I'd heard you can get them rebuilt/recalibrated when you switch senders, but again, for the money it would cost it didn't really seem worth it.

Anyone ever tried tinkering with the guage?

pjv911 · pjv911's Garage

I like the name you picked " wastintime" thats priceless.

Yes the sensor you are using is wrong and so would one from a 911. It works on a different polarity. I would look around more for a stock sensor. I bet if you called the meistro he has a dozen used ones that are one step away from the dumpster or swept under the work bench. I bet I have one too in one of the three 1.6 engine cores I have. Im sure you will get one for less than $25.00 without problem.

Kurt Williams

Morrie · 03-03-2002, 02:52 PM

I have to agree with Kurt on this one. If the sender worked the same direction as your guage, we coulda done some pretty simple stuff with a couple bucks sepent at Radio Shack. With it working in reverse, I'm afraid you are stuck.

On the brighter side, it sounds like Kurt would sell you one for $25.00 if you asked nice!

Best,
Morrie

wastintime · 03-03-2002, 03:24 PM

Aw, I was kind of looking forward to the challenge of getting this to work... I still think I could get the gauge to read backwards if I knew how to calibrate it, but yeah, stock might be the way to go. I may play around with it for a little just for the fun of it.

Kurt, if you do have any please let me know because I have called around ( granted, I don't think I tried the Mestro) and couldn't find any anywhere, well none that weren't brand new and were going for almost $300.

Thanks.