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Engine Specific Info and Questions => IDI Engine => Topic started by: 92EcoDiesel Jetta on September 19, 2011, 05:13:44 pm
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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.
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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.
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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!
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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.
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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.
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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
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i would say its for either a TDI, or a 2.0 motronic..
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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
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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.
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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.
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For future reference, what are the resistance values for cold and for operating temperature?
Chris
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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.