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Just purchased a 2004 Vintage Speedster.  The combo gauge oil temperature indicator barely registers when oil is hot. We measured the oil temp at 180F using a dipstick motorcycle probe. 

For information, with the wire disconnected at the sensor on the engine, the resistance to ground is around 175 ohms at the 180 degrees of the sensor. When cold the resistance measures over 400 ohms.

To see what signal the gauge wants, we attached a 0-100 ohm pot to the input and to ground (at sensor wire at the engine) of the gauge (sensor wire still disconnected from the sensor).  At 20 ohms the needle is at maximum. At a little less than 100 ohms the needle barely moves.  

So how do we get these to balance? 

Is the sensor putting out the right resistance? If not what is it?

Is the gauge not working correctly?

Is it possible the gauge is a 6 volt gauge?

Something is not right.

Can anyone help?

Thanks

Last edited by Theron
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Geez......  I go to the gym and my beeper goes off.

Wait....   I don't HAVE a beeper any more!

The short answer is that the gauge is fine - you've just got the wrong/mismatched sending unit.

Fortunately, Luis in Seattle did an in-depth study for us on proper sending units, so go here and you should be all set.  Scroll down a bit to his post:

https://www.speedsterowners.co...4#566654706113875654

Gordon

Last edited by Gordon Nichols

My car is the same year and we had the same problem. We just started experimenting with a variable resistor (pot) on the back of the gauge until we got it close. We measured the resistance across the pot and put resistors matching that resistance on the back of the gauge permanently. In my case when the car is just started and cold the needle is at the center but it gets into the critical hot zone accurately so we let it be. Being that these are crappy Chinese gauges I am not sure the VDO sending unit will match perfectly; maybe it would be a good idea to send the gauge to be reworked at North Hollywood Speedometer; I had to do that with the tachometer which came not working when the car was delivered new straight from the shop; was replaced by VS and malfunctioned again.

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