Temp Sender

[wemtd]

Does anyone know if all 120°C VDO temp senders deliver the same resistance=temperature readout (ie. any one will work for my dash gague) ?

 

p.

[catsv7]

I don't know if all VDO senders have the same temperature/resistance relationship.

 

However, I used a VDO 323095 Temperature Sender to measure oil temperature and sent the signal through a switch to my water temp gauge (2002 Caterham). I needed to add a resistor inline to make the displayed temperature correct. So this approach might be an option for you.

[toedrag]

I tested a bunch of temp senders a while back, and the resistances vary dramatically from model to model and even among duplicates of the same model - all from the same manufacturer.

 

Resistances are non-linear, and while these below aren't VDO, the behavior is similar to what you'll find with VDO:

 

http://www471.pair.com/stalkerv/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=27648&g2_serialNumber=3

 

If you get lucky and find a compatible sender that has the same curve as what you have today but is only offset by a static resistance, adding a discrete resistor inline could work. If the curve is different, however, choosing a resistor becomes a task of picking the range of temps where it's most accurate, ignoring values outside that range.

[speedwagon]

Am going to make a few guesses, There are a vast number of thermister manufactures and very few are likely to be in good ole USA. The quality will vary all over the place. Automotive gauges being made to sell, the accuracy is going to be below the desires of most of us. And the buyer will usually not be discerning enough to know whither his gauge is off by 10% at 200 and most certainly not notice a much greater inaccuracy at 100. What I use to check my gauges is a digital infrared thermometer. (mine happens to be a harbor fright from chairman mao's junk store) Point the dot at the sender and get a readout. to check it's accuracy point it boiling water on the stove and correct for elevation to calibrate. The tool is also very good for checking exhaust pipe temperature differences. You can see an almost instant change when the fan turns on and a low performing or lean cylinder shows up readily. So will a poor electrical connection if it is conducting current and there is voltage drop. Cheap tool for what use you get out of it, originally bought my first one years ago for about 500 when doing electrical/mechanical troubleshooting. john