warning light

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hippy chick
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warning light

Post by hippy chick »

Hi i have a problem that i just cant get to the bottom of on.my 1983 1915 water cooled t25. i changed the temp guage sender, since then the needle moves just to outside the white on gauge, i get no flashing red light on start up, so i ran the 6mm spade to earth but the needle didnt move. the low water warning light works with just ignition , but with the plug pulled on header tank with engine running the light dont come on. i have read and done what wiki says but im now at a stand still with it. can anyone please give me any advice as to what to try next.thanks jen

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marlinowner
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Re: warning light

Post by marlinowner »

My possibly incorrect understanding of this circuit is that the low coolant warning works by putting a voltage pulse on the temp sender input to the gauge which causes the light to flash but the pulses are too short to have much effect on the gauge itself which is damped. So maybe if the temp sensor is shorted to ground it would ground the pulses from the level sensor and cause your problem?
Standby for someone to correct me though!
1993 SA VW T25/T3 2.5i Microbus/homebrew camper
1981/1968 Marlin Kitcar TR6 Engine

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

Can we assume it all worked fine before you changed the temp sender - or was it doing odd stuff before (and is that why you changed the sender).

1) "i get no flashing red light on start up" - this can only happen if the gauge isn't getting a good 10V supply and/or a good ground connection (assuming that the gauge is working ok). Is the fuel gauge working correctly - the fuel gauge uses the same 10V power supply so it's a good indication of the health of the 10V.

2) "then the needle moves just to outside the white on gauge" - does the needle move a little then i.e. it comes off it's lowest stop position and moves to show a slightly warm indication (not sure from what you've said here) or is it always at it's 'lowest' position? If it does move, does it do this immediately when you turn the ignition on or only after the engine is warm?

3) "low water warning light works with just ignition , but ... engine running the light dont come on" - this is the oddest part of it all - so to clarify; the 'low coolant warning' flashes the light on the temp gauge when you have pulled the low water sensor plug out of the header tank, and the ignition is on (engine not running) BUT the 'low coolant warning' does NOT flash the light when you have pulled the low water sensor plug out of the header tank, and the engine is running? (Is this correct?) Odd behaviour like that usually points to a bad ground connection (have you cleaned the usual suspects of the ground crown behind the fuses in the glovebox?)

However none of these point to anything that would be caused by changing out the temp sender - have you recently messed with anything else??
1987 Westfalia Van, Petrol 2.0 AGG

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

marlinowner wrote:My possibly incorrect understanding of this circuit is that the low coolant warning works by putting a voltage pulse on the temp sender input to the gauge which causes the light to flash but the pulses are too short to have much effect on the gauge itself which is damped. So maybe if the temp sensor is shorted to ground it would ground the pulses from the level sensor and cause your problem?
Standby for someone to correct me though!
Almost - The low coolant warning works by putting a 'ground' pulse on the temp sender input ....
So grounding the temp sender input should send the needle to the fully 'hot' position and flash the light.
1987 Westfalia Van, Petrol 2.0 AGG

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marlinowner
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Re: warning light

Post by marlinowner »

Oh well I was only 180° out.
1993 SA VW T25/T3 2.5i Microbus/homebrew camper
1981/1968 Marlin Kitcar TR6 Engine

hippy chick
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Re: warning light

Post by hippy chick »

Thank you for your replys. i changed the temp sender as the gauge stopped working so did the fuel gauge . the fuel gauge works now but the temp needle takes ages to move , then only just out the white, i get no red flashing light on start up and the red light dont come on at any time. i did ground the 6mm conector to ground with ignition on but the needle didnt move. i also have taken the water sensor out header tank with engine running no red light to warn low water , but the low level will light up with oil light on ignition ( the one near the little watering can ) sorry if i confused you . i havent messed with anything That i know off. jen

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

hippy chick wrote:i changed the temp sender as the gauge stopped working so did the fuel gauge . the fuel gauge works now but the temp needle takes ages to move
Any idea what you did to fix the fuel gauge?
Are you sure that the fuel gauge is working correctly - i.e. is it reading the right value (I know that they are pretty rubbish generally but is it vaguely showing the right value)?

hippy chick wrote:but the low level will light up with oil light on ignition ( the one near the little watering can )
Not sure that I quite understand what you are saying here - the light next to the 'watering can' (it's actually meant to be an oil can! :D) shows when you have low 'oil' pressure - so it's nothing to do with the coolant system. The oil warning light should come on when you turn the ignition and then go out when you start the engine.

Anyway - back to the coolant gauge - it does sound like you have a problem with the 10volt supply to the coolant temp gauge and the fuel gauge (these are the only two gauges that use the 10volt supply) - and as they both failed at the same time it would strongly suggest that the 10volt supply might be the culprit (hence why I ask how the fuel gauge managed to start working again?)

Do you have a voltmeter/multimeter and are you happy to go poking around with it in the back of your gauges?
If so there are a few more tests that we could try to see if the 10volt is the problem?
1987 Westfalia Van, Petrol 2.0 AGG

hippy chick
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Re: warning light

Post by hippy chick »

thank you midlfecrisis
The fuel gauge is a bit up and down , it can read half full then drop to almost none , but goes back up. I did do anything to fuel gauge it just came back on its own. Sorry about the oil can :oops: thats all working fine then. lol. i will have to go and borrow a meter but i dont mind poking around with it. thank you for your help jen

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

That does sound like you may have a problem with the voltage regulator which is a little doo-hickey that is fitted to the plastic PCB sheet that makes up the circuit on the back of the gauges - it's job is to convert the battery voltage (which can vary from 12-14volts) to a nice stable 10 volt signal that the gauges use.
If this is playing up then you would get 'weird' behaviour with both the fuel gauge and temp gauge;
Have a look at this Wiki entry which explains it a bit;

http://wiki.club8090.co.uk/index.php/VW ... uel_gauges

I have a few spare voltage regulators (I think) - so I could post one to you if you fancy having a go at changing it?
But as I said before - if you can get hold of a voltmeter we can test out a few things and confirm that the voltage regulator is the problem .....
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hippy chick
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Re: warning light

Post by hippy chick »

THank you so much . i will get hold of one tonight . Then if you dont mind i will get back to you. jen

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

Good stuff!
1987 Westfalia Van, Petrol 2.0 AGG

hippy chick
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Re: warning light

Post by hippy chick »

Right i have my volts meter at the ready. lol :ok

MidLifeCrisis
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Re: warning light

Post by MidLifeCrisis »

OK - you'll need to pull the cover off the gauge cluster (there are a couple of indentations in the back to get your fingers into then just yank it forward).
Now you need a double-jointed neck to look at the rear of the gauges!!
What you should see is something like this;
Image
(This view is of the back of the temp gauge section viewed from the windscreen side (if that makes sense?))

So - if you can see the three nuts that are the terminals of the temp gauge (the ones ringed in the picture).
You need to use your multimeter to test that you are getting 10.0 volts at the '10Volts' terminal (ringed in orange in the pic) - this would be with the ignition on.
So you'll need to touch the negative probe of the multimeter to a piece of bare metal on the van (to get a good ground connection), then touch the positive probe of the multimeter to the '10Volts' terminal terminal (of the three terminals, it's the one closest to the middle of the gauge cluster when viewed from the drivers seat - if that helps)

Have a go at that and report back what you see?
For extra points - try it with the ignition on (engine off), then with the engine running - it should be 10.0 volts in both cases.
1987 Westfalia Van, Petrol 2.0 AGG

hippy chick
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Re: warning light

Post by hippy chick »

Thank you midlifecrisis. i will go and have a go. will let you know thank you for pic to jen

hippy chick
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Re: warning light

Post by hippy chick »

Oh dear this is what i have found. :cry:

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