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    Thread: Coolant temp indication pegged low.

    1. Member sehaare's Avatar
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      06-09-2007 04:44 PM #1
      92 manual cabby. I've started a new thread to troubleshoot this problem separate before fixing the separate idle problem that initially appeared to be connected to this.
      Here's what I've got After doing a lot of maintenance under the hood my coolant temp gage in the dashboard is pegged low. a couple of things that might be applicable was that I flushed the coolant and replace all hoses and also I replaced the coolant level sensor (due to leaky seal)
      I just got done checking the sensor it initially read 1.5 Kohm with the car at ambient temp about 70 F +/- 5 F. Then when the car started to warm up it had dropped to about 600 ohm. So the sensor is not the problem. I checked the yellow/Red wire and had no voltage with to the brown wire or ground with the key in run.
      The other dashboard indications (fuel gage, low oil pressure etc)started up normal (including the coolant high temp/low level warning light in the middle of the gage coming on initially then going out).
      So I suspect a broken wire. looking at the schematics a good place to check the voltage would be at j120 the coolant level low control unit.
      Does anyone know where the coolant level low control unit is located?
      I should also mention that when i disconnect the coolant level sensor I do not get a warning light like I would have expected and also when I hooked up the old one with it not in any fluid I also don't get a warning light.
      I get a small voltage at between the two wires going to it. So it doesn't seem to be getting power either.
      So once again does anyone know where the coolant level low control unit is located?
      Any other suggestions appreciated. Before I start tracing out a wire.
      Thanks
      Steve
      Enjoy every sandwich - Warren Zevon

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    3. Member tolusina's Avatar
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      06-09-2007 05:56 PM #2
      Fresh, live readings using a Fluke 78 and a decade resistance box.
      Voltage on yellow/red, sensor disconnected, 9.95 VDC.
      Cold (approx 70° F) sensor resistance measured 1.2kΩ
      With decade box set to;
      300Ω (8.44 VDC on yellow/red), the needle point was at the left edge of the left bar.
      100Ω (6.43VDC), needle at 1/4 scale.
      65Ω (5.4VDC), needle to center of LED.
      35Ω (3.86VDC), LED lights, needle points to the left edge of the 2nd bar from the right.
      16Ω (2.3VDC), needle points to the left edge of the 1st bar from the right.
      11Ω (1.75VDC), needle points to the right edge of the 1st bar from the right.
      ---
      Does the car have a good, stock rating, 87° C thermostat? How many holes did you drill in it? A single, 1/8" hole is plenty.
      I'm thinking the engine isn't heating up enough causing both the gauge problem and the idle problem.
      DigiFant expects and needs a proper hot signal to run right, a cold rated thermostat prevents that. Keep the cold 'stats for CIS cars.
      ---
      Bentley schematic shows the Coolant Low Level Control Unit in location 18, http://dana.ucc.nau.edu/~kaw5/electrical.htm shows location 18 blank for '90 - '93, '83 - '89 shows location 18 as the spot.
      It's in location 16 on my '92.
      Look for the add on relay with two yellow/red wires to the same terminal.
      With the Coolant Low Level Control Unit unplugged, the gauge should function normally.
      ---
      On your schematic where you've located J120, see the black box with white text reading 18 to the right of J120? 18 is the location.



      Quote Originally Posted by kamzcab86
      I hate reading: "But I bought this car for $500 and don't want to put another dime into it."
      ____(hey, it's VW AND it's electrical, what's not to fail?) neoBentley+



    4. Member kamzcab86's Avatar
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      06-09-2007 10:40 PM #3
      Quote, originally posted by tolusina »
      Bentley schematic shows the Coolant Low Level Control Unit in location 18, http://dana.ucc.nau.edu/~kaw5/electrical.htm shows location 18 blank for '90 - '93, '83 - '89 shows location 18 as the spot.

      Oopsie... for got to copy/paste when I re-did the tables. Will add that back in on Monday. [IMG]http://*****************.com/smile/emthup.gif[/IMG] (FYI, ETKA shows the relay in position #18).
      Cabby-Info.com -- Your online guide to VW Cabriolets/Rabbit Convertibles
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    5. Member sehaare's Avatar
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      06-10-2007 01:09 AM #4
      Wow a fluke and a decade box I'm impressed, I haven't had those since I left the Navy.
      Now it's just a sears meter and radio shack resisters.
      Thanks for all of the good data, nothing makes troubleshooting a circuit easier than when you have some baseline data from a know good circuit.
      Right now based on not seeing any voltage on the yellow/red wire I feel that I have a broken wire. If I'm reading the schematics right it looks like I should be able to pull J120 (coolant Low LVL cntrl Unit) out and check for voltage at 8/G hopefully that designation will make more sense once I pull the unit. If I get the voltage there then either I have a broken wire or the unit itself is grounding out the circuit. Base on the fact that I was working around the wire I'd bet that it is broken.
      Looking at the circuit and your values if I put my two 100 ohm resistors in parallel (50 ohms) and use them to jumper 8/G to ground then I should see the meter move.

      I also first thought that the sensors weren't getting warmed up but there is a table of expected resistance VS temp for the Digi Temp Sensor and for the ambient temp the resistance matched up. I'll have to recheck and verify all of my values.
      Don't know about the thermostat, I didn't change it out but I didn't have any reports of overheating or not getting any heat. I have a brand new one from German Autoparts sitting on the work bench. I had planned on putting it in when I flushed but when I saw that the P/S pump had to be removed to get access to it I balked. I had already spent mega time replacing all the hoses (and that all turned out to be good). So as I ran out of time I passed on the replacing the thermostat.

      and finally, so that's what that "18" means. I confess that I wasn't even sure that the control unit was on the fuse panel vice being mounted somewhere else.

      I've got to travel out tomorrow for work and won't be back to at least mid week but I'll have plenty to work with when I do get back (I'll try and squeeze some in tomorrow as well).
      Thanks again Ron, and an assist goes to Kammie [IMG]http://*****************.com/smile/emthup.gif[/IMG] [IMG]http://*****************.com/smile/emthup.gif[/IMG]
      Enjoy every sandwich - Warren Zevon

    6. Member tolusina's Avatar
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      06-10-2007 02:07 AM #5
      Quote, originally posted by sehaare »
      Wow a fluke and a decade box......

      The Fluke 78 is still a currently available automotive specific meter, mine is 15, 20 years old.



      From http://us.fluke.com/usen/produ...tates

      The decade resistance box is a Heathkit I found at a surplus store, they had two, I only bought one, kick me, OK? I did buy both decade capacitance boxes.

      How long since you've heard "Heathkit"?


      Quote Originally Posted by kamzcab86
      I hate reading: "But I bought this car for $500 and don't want to put another dime into it."
      ____(hey, it's VW AND it's electrical, what's not to fail?) neoBentley+



    7. 06-10-2007 06:53 AM #6
      http://cgi.ebay.com/HEATHKIT-R...wItem
      http://cgi.ebay.com/Unbuilt-He...wItem

      There you go!


      Modified by itschuck2c at 3:56 AM 6-10-2007

    8. Member sehaare's Avatar
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      06-10-2007 10:10 AM #7
      I'm definitley old enough to remember heathkit. I had always thought about getting one of their O'scope kits but never got around to it.
      Here's the fluke model that I had used for 20 yrs in the navy working on everything from radars to nuclear reactors. Including 3.5 years as an electronics instructor.

      Give me this, an old tecktronics O'scope and a tech manual and there wasn't much that I couldn't fix.
      Enjoy every sandwich - Warren Zevon

    9. Member tolusina's Avatar
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      06-10-2007 02:35 PM #8
      Here's the model I have.......



      http://cgi.ebay.com/Vintage-He...wItem






      Quote Originally Posted by kamzcab86
      I hate reading: "But I bought this car for $500 and don't want to put another dime into it."
      ____(hey, it's VW AND it's electrical, what's not to fail?) neoBentley+



    10. Member sehaare's Avatar
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      06-12-2007 10:38 PM #9
      Got back early from my work road trip and took some more readings tonight. First Ron and Kammie are both right and the Coolant Low Level Control Unit is in position 16 vice 18 as the schematic shows. I verified it with part number 191 919 376A and Pin number G, S, 15, 31.
      I first checked for voltage at Pin 8 (where pin G plugs into) with the key in run. I got random voltages in the MV range.
      Next to prove that the problem was indeed upstream of Pin 8 - with the key in off, I checked for continuity between Pin 8 and the Y/R wire at the Coolant temp sensor and got 0.0 Ohms. So no broken wire there.
      So even as much as I dread pulling the fuse box, I think my next move is to pull plug B from the back of the fuse box and verify continuity to pin 8.
      I really hate the direction this is going.

      I also grilled the only person who has ever driven this car for more than 5 minutes and now she backs off her original statement that the Water temp gage worked before. Now she's not sure if she ever saw it move.

      Edit for change in plans. Edit again for correct pin number
      Rethinking the next step I'm going to pull the plug off of the cluster and check for continuity at Pin 4. Easier to get at and I'd probably end up there anyway. If I don't have continuity I'll just jumper from there to pin 8. If I do have continuity, then I have a couple of instrument clusters in the garage to scavange parts from.
      Modified by sehaare at 6:23 AM 6-13-2007

      Modified by sehaare at 6:24 AM 6-13-2007


      Modified by sehaare at 10:19 AM 6-14-2007
      Enjoy every sandwich - Warren Zevon

    11. Senior Member briano1234's Avatar
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      06-13-2007 11:27 AM #10
      Take the connector off the black coolant sensor.
      Jumper the two Pins together with a piece of wire.
      Remove the cluster.
      You will see that in the wiring diagrams the sensor bypasses the Coolant low level control unit, as at 8g it is tied back to pin t14/4 on the cluster. Measure on the large cluster connector t4 from Pin t4/2 to t4/4 for continuity..... or close to it. Turn the key on and it will be the same on a cold car as the car warms up the value will change too. This checks all the wiring back to the sender on the block.
      Some will argue with me that pulling the cluster is too much trouble, but I would rather sit in the drivers seat, and remove the cluster and check for continuity than to lay on my back and convort to positions that are not friendly to my knees or back playing with the fuse box and relays. If the Continuity dosen't ring true then I can back track, but I can also check the gauge at the same time and eliminate it.
      Place a 9v battery across the two brass terminals on the gauge back in the cluster far left and right, the gauge should move 3/4 of the way, if it don't it is the gauge that is bad. You can measure it for ohms as if it is infinite then it is bad....Either way. The middle nut is the LED.
      Take the two rivets off the gauge and see if the cat whisker wire is still attatched to the movement, it probably isn't. Try to reattach or clean the connection...
      I have done everything you have done, and come to the conclusion that its usually the gauge, I have had to replace 3 of them in 3 cabbies. The last one I fixed the whisker wire. The gauge unit out of a jetta or golf will work but it sit's a little cocked, and you have to trim the outer tin a tad.
      When I am rambling through the junk yards I take a 9v battery with some long leads and check the gauges to pick up spares....




      Modified by briano1234 at 11:31 AM 6-13-2007

    12. Member sehaare's Avatar
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      06-13-2007 03:58 PM #11
      Thanks for the help Briano.
      So you've had to replace 3 temp meters wow!
      I'm glad to see that they are that simple to replace. I've got two other cabby clusters in the garage. I've had clusters apart before because I had to swap in a 120 MPH speedo when I put in the 1.8L in my 81 because the car now went faster than the speedo [IMG]http://*****************.com/smile/emthup.gif[/IMG]
      I don't like pulling either the cluster or a fuse box on a 15 year old car because there is a whole lot of brittle wiring involved (plus the 92's dash is pretty much pristine). In fact one of the times that I pulled the cluster in my 81, part of the flexible wiring on the board lifted from the green board and I had to superglue it back into position so that it would make contact with the socket. [IMG]http://*****************.com/smile/emthdown.gif[/IMG] [IMG]http://*****************.com/smile/emthdown.gif[/IMG]

      As far as someone saying that pulling the cluster is too much trouble, I just look at that as a friendly difference of opinion . I've learned over the years that there is usually more than one way to go when troubleshooting electronics (unless you were one of my students or worked for me in the Navy then I was always right ). And everyone always believes that their way is the best or they wouldn't have suggested it.
      If you've noticed I've taken in everyone's input and kind of gone my own way as well. So far the hardest thing that I've had to do was pull a relay and push in a male spade lug so that I could check the voltage/resistance at that point. Now I'm to the part where I've really got to start working on parts that I can break

      I'll keep you guys updated on what I find. I know from personal experience there is nothing worse then spending a whole lot of time trying to help someone who then just goes away and never tells you if what you said fixed it.



      Modified by sehaare at 2:59 PM 6-13-2007
      Enjoy every sandwich - Warren Zevon

    13. Member sehaare's Avatar
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      06-15-2007 03:55 PM #12
      Ok update time.
      As I started to take the instrument cluster "surround" off I found missing screws and broke plastic on the "surround" - so much for my "pristine' dash. But I chalked it up to it the previous owner (PO which is usually short for POS) installing a stereo. When I got the surround off I saw that one of the screws that held the cluster in place was not original - this isn't looking good [IMG]http://*****************.com/smile/emthdown.gif[/IMG]
      I remove the two screws that hold the cluster in place and a large black zip tie pokes out from above the cluster- getting worse by the minute

      WTF so I pull the cluster out a little more and I see this.


      PO had broken the speedo cable and just wire tied it into place.



      Just ordered a new one from German Autoparts. Hopefully the gear won't come off in the tranny like it has for some others here.
      Here's what my dash looks like now

      I checked for continuity from Pin 4 on connector 14 to pin 8/G at the coolant low level control unit (still had a wire connected there) and got 0 ohms [IMG]http://*****************.com/smile/emthup.gif[/IMG] . I had already checked the ground connection on the temperature sensor, But just to close the loop and since I had it available I used a 100 ohm resistor to jumper the two leads on the temp sensor and checked resistance between pins 2 and 4 on plug 14. You guessed it 100 ohms. [IMG]http://*****************.com/smile/emthup.gif[/IMG] [IMG]http://*****************.com/smile/emthup.gif[/IMG]

      So I didn't break any wiring doing my initial work and now it's time to troubleshoot this.


      I checked the resistance between the two terminals on the back of my spare temp meter and got 50 ohms I checked it on the back of the car's meter and got something in the Mohm range. So I'm pretty sure that my meter is bad.
      Now I have to disassemble the cluster to check all the connections and verify my assumption then swap in my spare temperature meter.
      I'll let you know what I find
      Steve


      Modified by sehaare at 3:01 PM 6-15-2007
      Enjoy every sandwich - Warren Zevon

    14. Member sehaare's Avatar
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      06-15-2007 05:27 PM #13
      hopefully the final update----it's fixed.
      I took the instrument cluster apart and put the 9V Battery across the temp meter like Briano had suggested..........................and the needle moved - crap meter is good.
      So I put it all back together again. Just for the hell of it I took a resistance check across the meter terminal again and .............. I now got 50 ohm just like on my spare
      Sooooo, I hooked everything up again (with the 100 ohm resister installed like Ron suggested) and turned the key. The meter moved and indicated temp. I removed the jumper and connected the plug to the temp sensor and the meter went back to the low end as expected.
      I'm not sure what fixed it, (besides the obvious of fooling around with everything) I first thought that maybe the meter wasn't making good contact with the flexible circuit board, but that wouldn't explain the bad resistance across the meter since I was going right to the terminals. Maybe applying 9V directly to the meter shocked it enough to move (maybe mechanically stuck???),
      Oh well now I just need to leave the dash open until my new speedo cable comes.
      So now it's time to get dirty and do the half shaft and brakes.

      THEN I'll get back to trouble shooting the crappy idle (right now i need to do some mind numbing maintenance first where I don't have to think to hard)

      Thanks Briano and Ron


      Modified by sehaare at 4:50 PM 6-15-2007
      Enjoy every sandwich - Warren Zevon

    15. Member Moljinar's Avatar
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      06-15-2007 06:22 PM #14
      I'm kinda embarrassed. I've been fixing VDO clusters since the 70's and every bad reading gauge I've worked on simply needed the bolts to it tightened. They vibrate loose and the copper tarnishes just enough to make life nasty.
      I should've said something

    16. Member sehaare's Avatar
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      06-15-2007 06:49 PM #15
      It wouldn't have saved me much time, because I was only going to go into a dash that I hadn't broke into before, as a last resort. So I would have checked everything else first anyway.

      Now if you have a magic wand that fixes my rough idle on a DIGIFANT engine let me know.
      Steve

      Enjoy every sandwich - Warren Zevon

    17. 06-15-2007 07:18 PM #16
      Grounds...clean all the ground wires!!!! I posted this in your other thread. You would be amazed at what a clean ground wire cures..gauges to rough idles to flakey transmissions (electronic type). On any car with 10 plus years things get cruddy.

    18. Member sehaare's Avatar
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      06-15-2007 09:33 PM #17
      Good point. I did that to my 81 and even added a few ground straps. I'll have to find them on the 92 though.
      First time ever really doing any maintenance on this one and it is becoming a steep learning curve.
      Enjoy every sandwich - Warren Zevon

    19. Senior Member briano1234's Avatar
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      06-16-2007 08:57 AM #18
      Ruff idle on a digifart? Grounds, vacuum hoses, Blue CTS sensor, O2 sensor, idle adjustment screw o'ring......
      I have seen a bad heater servo cause the ruff idle... so while you are trouble shooting...... pinch the heater vac hose with a pair of hemostats.
      Grounds Grounds Grounds....

    20. Member Seamus68's Avatar
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      10-30-2007 05:15 PM #19
      Quote, originally posted by briano1234 »

      When I am rambling through the junk yards I take a 9v battery with some long leads and check the gauges to pick up spares....
      Modified by briano1234 at 11:31 AM 6-13-2007


      Do you have any pics of you putting the leads onto the cluster. I am not sure where the leads need to be placed

    21. Senior Member briano1234's Avatar
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      10-30-2007 11:19 PM #20
      yes put the black lead on one terminal and the red on the other, if the meter don't move reverse the leads if the meter still don't move then the gauge is bad,,, the center nut on the water gauge is the blinky light from hell.
      On a side note I have dissasembled the gauges, and when I got it apart the whisker wire was cold soldered to the stud. When I applied heat to it, the wire popped off, it wasn't even wound around the stud...
      After resoldering the wires everything worked great.

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