Temp Gauge goes straight to hot when ignition turned on

[Malminor]

Hello, Newbie first post .
My 1.9 petrol auto 1983 temp gauge goes straight to hot with the flashing light as soon as the ignition is turned on from cold,
when running it remains in the same position, I have looked at the wiring / sensors that I can see and they are connected,
I have a wiring diagram but the wiring in the engine bay just disappears into the loom
I have an issue with a seized blower motor that I need to fix, could a blown fuse cause the temp gauge to play up.
I am considering fitting a capillary water temp gauge as a back up (old school)
any advice would be very much appreciated

[Paul Southworth]

I had a similar problem, it turned out the sensor was faulty. If you search the forum for temperature gauge sensor you may find an answer. Good luck these problems can be difficult to sort out. My guess though the sensor may need renewing. A genuine VW one is not too expensive and better and more reliable than one from GSF or euro parts.

[marlinowner]

The gauge will go straight to the top and put the warning light on if the wire to the sender is grounded. This could be due to a faulty sender, or because the wire has shorted somewhere. Disconnect the wire from the sender. If gauge then reads cold the sender is faulty, if it still reads hot then you will have to look for a short circuit between the gauge and the sender. Only other possibility would be a fault in coolant level warning circuit, you can eliminate that by removing "relay" marked either 42 or 43.

[Dazco]

Check coolant level in the tank on the left side back of engine bay. Should be FULL. There is a sensor in there that detects low coolant level . If full, it could be the sensor that needs replacing.
https://www.brickwerks.co.uk/index.php/ ... olant.html" onclick="window.open(this.href);return false;

[Mocki]

Check coolant level in the tank on the left side back of engine bay. Should be FULL. There is a sensor in there that detects low coolant level . If full, it could be the sensor that needs replacing.
https://www.brickwerks.co.uk/index.php/ ... olant.html" onclick="window.open(this.href);return false;

The op described the gauge going to the hot end and the light flashing, so it isn't a low coolant warning, it's over temperature warning, and as its doing when the engine is cold, it's a faulty sender , or damaged wire .

Take the connection off of the temp sender in the thermostat housing ( single spade terminal) and if the gauge and temp light go out its the sender gone south..... Or if no change its a damaged wire grounding out , check just above the exhaust header in the lhd side of the engine bay just before the black box it all goes into .

[Malminor]

Many thanks for the replies,
I have had another look today.
as the battery was disconnected due to other works I re connected first before checking the thermostat wiring,
turning on the ignition the temp flashing light stopped after a few seconds, the gauge remained cold, then within a few seconds more the gauge climbed to max and the light continued to flash.(still without the engine running)
I disconnected the spade connector on the thermostat housing and the gauge remained max, looks like a battle of elimination back to the gauge,
also the wiring on the second sender to the auto choke looks like its been bodged with crimps and tape,
I have a capillary gauge I would like to fit as a back up ,
as its going on the dash somewhere is there a 'best place' to put in a hose fitting, ie top radiator hose or the bottom one, the pipes have been changed to plastic at some point so need fastening properly, also I plan to do a full coolant flush ( thanks wiki)
regards Malminor

[Mocki]

The wiring to the carb and manifold and choke has nothing to do with the temp gauge at all
It maybe a bodge but it's not contributing to the temp gauge issue

The temp gauge wire goes into the large cylinder connection in the black box in the engine bay , you can disconnect there to narrow down further .
It's likely to have damaged insulation and be shorting back to earth somewhere , as that is how it works being a single connection sender , the neg connection is though the thermostat housing to earth

[Malminor]

thanks Mocki, I will track the wire back, to the box, at least I know it's yellow with a brownish / red stripe it joins the harness pretty close to the thermostat, I guess it the appears in the black box,
the haynes wiring diagram is a bit difficult for me to figure out
regardless of the extra gauge I would like to get this solved, I guess that's part of the fun of owning a 33 year old bus,
It's great to have some advice, when I did my first restoration ( Triumph stag) 20 odd years ago we didn't have the internet, I remember writing in to the club technical section,(that makes me feel old)
I am really enjoying working on the bus, it would have been broken for parts had I not jumped in for it,

[Mocki]

The Haynes wiring diagram is crap , but it's not any worse than any other !

Simplest test is to find the correct wire at the fuse box end of the loom and disconnect it there and see if it stops the gauge rising
If it does, it's prob esker to run a new single wire from the front back to the engine if you can't find where it is damaged ......

[Malminor]

Hello, just a note to say thanks for all the advice, problem turned out to be a broken wire, new section soldered and shrink wrapped in, gauge working great,