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Thread: Temperature warning light (NO gauge questions).

  1. #1
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    Default Temperature warning light (NO gauge questions).

    I have an '87 Vanagon Westy that has a tempremental overheating light. If I drive somewhere, stop somewhere, then start it up again, the light will start flashing just after it does its little test phase. Often it will stop if I let it run or drive for a little while, shut off the ignition then start it again. Occasionally it will come on for no good reason when I'm on the freeway. My coolant is topped off so that's not a problem. I do have a slight crack in one of the heads, but it is minor at this stage and not causing any major leakage. Any advice? Do you think this is a problem with the sensor inside the tank (is this how the light works?) Thanks in advance for advice.

    wkarrfalt
    junior member

    [ 09-01-2001: Message edited by: Capt. Mike ]
    Wayne K.
    '87 Westy

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  3. #2
    Join Date
    Apr 2001
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    Hiya

    I have a similar problem with my 82 Transporter (well that's what its called in the UK !) The light comes on intermittantly and has no relationship to the coolant level / engine temp. From looking at the wiring diagram I think that the light is purely a coolant shortage light. I think it works by measuring the resistance between two probes in the expansion tank. When the coolant falls below the level of these probes the resistance increases and the light goes on. So first thing i did was to clean up the probe and check the relevant earth connection (under the coil in mine), I also checked and re-wired the plug because it was looking pretty grotty. However, still no joy. Thinking some more about how the probe works I figured that even when the probes are submerged in coolant (I'm not sure what the conductivity of coolant is, but i imagine it's not that great) the resitance would be pretty high. Therefore there must be some little circuity thing that amplifies this resistance change to a level significant enough to switch on the light. I've used some fairly similar amplifiers to pick up changes in strain gauges (I'm doing an engineering degree!) and they were fairly tempremental so it wouldn't surprise me if this bit was at fault. However, I'm afraid I haven't got a clue where this bit of circuit is, and short of wripping apart my dashboard I'm stumped. Anyone got an further hints ?

    Neil (Cambridge, UK)

    [This message has been edited by Capt. Mike (edited 04-07-2001).]

  4. #3
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    Although the circuitry is different between an '87 and the UK version (I'm assuming the '82 UK water-cooled is similar to the US '83 -- we didn't get the water-cooled until '83½.), the principle is the same. The power is live and goes through the control unit, then the sender, thence to ground. The sender is the variable at completing the circuit. I'm assuming the UK version of the Bentley has the appropriate wiring diagrams.

    If a unit can ground between control unit or sensor, it will falsely activate the light. The may show up intermittently in temperature or vibration conditions. The instrument panel circuits on the Vanagon are printed, so you could have a crack in the printed circuit even if the wiring looks good.

    The low coolant sensor is typically in the tank and activates the low coolant light. It's shown in the '83 US & '87 US wiring diagrams as a hydraulically operated switch. Yeah, I said ??, too.

    But the same light may be used by the coolant temp sender and activated by the coolant temp send unit as well. So you could have the light activated by two difference kinds of problems.

    wkarrfalt -- read the warnings elsewhere on the site about continuing to run a cracked head. There is an expensive risk involved.

  5. #4
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    Thanks for the help !

    Was indeed a cracked line in the instrument printed circuit which was closing and opening the circuit with vibration. Fixed it now !

    Neil

  6. #5
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    Greetings,
    My coolant light on my '84 is acting up as well. I found the connector to the expansion tank wet with coolant. I suspect it is cracked as the light flashes until the engine reached full running temp., then remains off until the next drive. If the sensor is a hydraulically operated switch then that might explain why it goes off when its hot. The Bentley shows a two pronged switch but I can only locate a "one pin" as a replacement. Any observations are always welcome.
    Cheers, Steve

    [ 08-15-2001: Message edited by: Steve Williams ]

    [ 08-22-2001: Message edited by: Steve Williams ]

  7. #6
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    I had the flashing coolant light syndrome a couple of years ago in my '85, but it's pretty much gone away. Here's my theory:
    The coolant in the expansion tank completes a circuit with the two probes. If the conductivity of the coolant isn't quite high enough (e.g. different type of coolant than delivered from the factory), or the level of the coolant is too low, the circuit is interpreted as "open" and it causes the light to flash. You can confirm this by disconnecting the connector at the tank with the engine running--the light will flash. If you connect the two contacts of the connector together (with a wire stub). The light will stop flashing. If I have the false indication problem again, I'm going to try putting a large resistor in parallel with the probe to slightly reduce the resistance without defeating the purpose of the probe. If necessary, I'll reduce the value of the resistor by trial and error until it works properly (could use a potentiometer, for that matter). Note that I haven't had to try this yet...

  8. #7
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    I made this query of the coolant experts at Penray. Here's their response:
    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Sounds reasonable to me, the cicuit being completed by the conductivity of the coolant. Coolants do have differing conductivities but they do all conduct. Even organic acid based coolants use salts that are conducting.<HR></BLOCKQUOTE>

  9. #8
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    In my 90 Westy I am going to replace my Temp II sensor (the one near the thermostat).

    I have never done this before so my question: If I remove the sensor will there be gush of coolant? I am hoping it might be kind of isolated so that I can minimize the coolant refill and bleeding chore.

    If anyone has experience replacing this sensor I would certainly appreciate knowing more.

    By the way, I am changing this sensor to hopefully solve a too rich problem when the engine is warm. The engine has no power, blows black smoke and idles terribly-when warm.
    Laurence Smith

  10. #9
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    Mar 2001
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    I'm having a problem with the Temperature gauge on my 1987 Vanagon GL. The light comes on all the time even when the engine is cold. My van never overheats and the coolant is topped off at the reserve. I've had the coolant temperature gauge sensor at the thermostat replaced along with the coolant level sensor at the expansion tank. However, neither of these stopped the light from coming on. My mechanic thinks it might be a faulty gauge. Is there anything else that I can check before trying to replace the temp. gauge in the dash? Lastly does anyone know how low the coolant must become in the expansion tank before the temp. light comes on? I ask this because my expansion tank is only filled about 2/3 although
    my reserve is at the max. I hope these are not stupid questions as I am still learning. Thanks for your help.

    John

  11. #10
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    Besides overheating, light also comes on to indicate low level in the primary expansion (the pressurized one) tank. It appears to works on the priniciple of the coolant providing the final circuit for light activation. That tank should be full at all times. If not, the cap is probably defective. The sensor may be corroded or otherwise coated or damaged so as to work properly.

    Capt. Mike

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