need help with coolant temp sensor resistance

[92EcoDiesel Jetta]

My coolant temp  gauge is reading extremely low at the 1/4 mark. I checked the coolant hose at the flange with an IR thermometer on a hot engine and it reads 194 F. I am trying to determine, if the sensor, or wiring or gauge is bad. With a hot engine idling for a few minutes and 194F per the IR thermometer, the sensor is measuring 160 ohms. Can someone measure their sensor resistance with a DVM on a hot engine as a check? I'd hate to spend $30 on a new sensor if it is not bad.

[cyrus #1]

I don't have the resistance handy at the moment, although I did see a chart floating around somewhere.  However, as a quick and dirty test you can disconnect the harness from the sensor and ground the yellow w/ red stripe wire.  This should simulate a high engine temperature and make the gauge move to the top of the scale.

Have you noticed any other odd issues?  Is your fuel gauge behaving normally?  There is also a voltage stabilizer that can fail and cause these types of issues.  Typically the fuel gauge would be doing the same thing though.

[92EcoDiesel Jetta]

No other odd issues that I noticed. Fuel gauge is behaving normally. I will try shorting the yellow/red wire to ground and see what the gauge do. If you can dig up a link to that table it'd be appreciated. Thanks!

[745 turbogreasel]

Check your Bentley for sender resistance @ temp, then run down to Radio Shack, and buy a resister of  however many Ohms.
Substitute the resistor for your sender, and see what you get.

I think mine was 1050 Ohm @ mid gauge, but Volvo used a few different senders by year.

[92EcoDiesel Jetta]

I grounded the yel/red wire and the gauge pegged to the max. Did the same thing when I jumpered the connector terminals to each other (also grounds the yel/red wire).

My 85-92 Bentley does not not have anything on the resistance /temp relationship of the sensor in the cooling system section. Maybe I missed it? If you find it please post the info. At this point I suspect the sensor. I think they are original sensors from when I bought the car. The one for the glow plug is NFG (open circuited so it was getting max glow plug time and since modified to be manually controlled) . I'll just order new sensors.

[92EcoDiesel Jetta]

Autohausaz shows 2 coolant temp sensors. I have the black one. Anyone know what the blue one is for?

https://www.autohausaz.com/search/product.aspx?sid=1w3j1knwvjcdrnecbe5ajs55&makeid=800026@VW&modelid=1283486@JETTA GL TDI &year=1992&cid=sensor@sensor&gid=2188@Coolant Temperature Sensor

[R.O.R-2.0]

i would say its for either a TDI, or a 2.0 motronic..

[Luckypabst]

I would begin by just checking for a change in resistance with change in temperature to see that the sensor is working. I think most failures would show up as no change as the sensor heats up.

In your case, I would check wiring connections and power supply first if I suspected an inaccurate gauge reading. Apples to oranges for sure but my Vanagon had a temperamental temp gauge, until I turned one of the contactor nuts on the backside just enough to break up any tarnish on the connection.

Chris

[92EcoDiesel Jetta]

I would begin by just checking for a change in resistance with change in temperature to see that the sensor is working. I think most failures would show up as no change as the sensor heats up.

In your case, I would check wiring connections and power supply first if I suspected an inaccurate gauge reading. Apples to oranges for sure but my Vanagon had a temperamental temp gauge, until I turned one of the contactor nuts on the backside just enough to break up any tarnish on the connection.

Chris

I did all that already. I am down to a bad sensor. If someone can measure theirs at operating temp so I can confirm my sensor is bad that'd be great.

[92EcoDiesel Jetta]

The old (bad) sensor resistance is roughly 2x higher than the new one for any given temp. Installed the new sensor and just went for a drive and temp gauge reading is back to normal. 

[Luckypabst]

For future reference, what are the resistance values for cold and for operating temperature?

Chris

[92EcoDiesel Jetta]

For future reference, what are the resistance values for cold and for operating temperature?

Chris

1.1k ohms @ approx 72 F
108 ohms @ approx 170F measured by an IR thermometer of big coolant hose off the flange where sensor resides.