help with new temp gauge

i got all new electronic gauges from VDO. all work fine except the temp gauge. if i take the wire from gauge to the temp sending unit and ground it to chassis it pegs to the max. so that means the gauge is working, correct? but when i hook it up to sending unit it doesn’t budge. i got a new sending unit from Qtec. the little one near the firewall with one wire connection. still the same thing. was i supposed to do anything to the new sender other than just take out old and screw in the new one? i even tried replacing the connector plug to sender and still doesn’t work. i ran a brand new wire to gauge, and still doesn’t move. i used 18ga wire which seemed to be what was there. someone please help, i’m going crazy with this. i was thinking just run the wire from the sensor in t-stat housing to the gauge, think that would work?

Not sure if this will help at all but I’m in the process of adding on an oil pressure gauge to my scoobe-doo. And in the instructions it says that you are suppose to hook the power/ sending wire up to the sensor and that the sensor will ground itself when you screw it into the engine. Then it goes on saying that if you are not hooking it up directly to the engine or are using plumber tape you might need to add a ground wire to the unit, so that it will have a strong ground. I am not connecting mine to the engine so that I won’t get as much vibration reading so I added a ground wire onto the male part for the sensor (I still have yet to install this all due to time). Hope this helped you out at all.

yeah maybe its not getting grounded good enough. i’ll try adding a ground wire and try that. i think it will just make the gauge peg to the max, but i’ll try it.

The sensor should ground itself to the block. When you installed it, did you just screw it in or use some type of sealer or tape? That would prevent it from grounding and cause your gauge to not work.

i tried to clean the threads a little with piece of curled up cardboard, then just screwed the new one in.

You should try adding a ground wire to it to see if it works. Attach the ground wire to the portion of the sensor that contacts the block.

is it possible that the new sending unit i got was bad? i tried the grounding wire thing and still nothing. returned gauge for another one and still same problem. how do the mechanical temp gauges work?

Where did you try adding the ground wire? When adding the ground, it needs to be attached to the outside part of the sending unit. Where the threads are that go in the block. Not the tip where the sending wire connects too.

What temp range did you get?
Do you have the part number for the gauge kit?

i got the sender from Quadratec for the 91 wrangler. i tried the ground wire squished between the sender bottom and block then to firewall. the gauge is an electrical VDO 0-250 deg from jegs

That’s your problem. Your using the wrong sending unit. When ordering a sending unit for an aftermarket gauge, you “have” to get the one for that gauge. You can’t use the stock factory unit that runs a stock gauge. The voltage that the factory sending unit outputs could be different than the one that the VDO sending unit puts out.

give me a bit and i’ll find you the correct sending unit to order.

ahhhhhhh, that makes sense.

The VDO universal thread size sending unit for $24 part # 323900 is what you need.

Now I wouldn’t disconnect the stock gauge. It’s nice to have as a backup in case you have a problem with the VDO gauge.

I would remove the stock unit and check to see what thread size it is. You could do that at the hardware store with the small pipe thread adapters they have. EX: 90 deg elbow’s.

Once you find the thread size, figure out a way to connect a T fitting to which you could run both sending units at the same time. You can find a system using some elbows to put the T fitting in a spot that you can fit both sending units.

Dont know what you have for room around the temp sensor, but something like this is what I did on my old ranger:

Used one of these to come out of the block:

3/8 X 2" long

One of these on the end and then the sending units attached one to each side: