Electrical? Mechanical? Overheating no fan, no idea

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MoritzTheDoka
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Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Hello once again!

I'm hoping someone can help with this.
Today on the way home from work I noticed that the temp gauge was a little higher than normal, needle past the led, and it doesn't normally get there on my short run home.

Maybe I'd been sat in traffic longer than normal, I've no idea, but on a regular day the needle climbs to half way as the van warms, goes just past half way by a hair or two and I guess as the thermostat opens? and the air over the rad starts to do its job the needle drops back to almost dead centre.

This in itself is a bit concerning, what worries me more is that at no point did the fan come on (and it was a fair bit past the mid way point) in fact, I've never heard the fan come on.

Now, I've Jumped the pins on the radiator/fan switch
(only 2 pin I might add) and the fan whirred into life, so as a precaution I replacedd the fan trigger switch in the rad.

The rad felt hot, but not mega hot, and more importantly felt the same top and bottom.

I've checked the rad bleed point for air and there is nothing, same at the thermostat bleed point.

The main coolant tank is full to the brim (and fully pressurised as I'd been driving and the van was still hot) and the overflow was low but not stupidly low.

What am I missing?
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Stesaw
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Stesaw »

If the light doesn't flash on your temp gauge then you aren't overheating and its OK. If I don't have my heater blowers on my temp gauge sits just above the light, with the heater on it sits right over the it. I checked mine recently and found that a relay was at fault for my fan not coming on as I thought my van was running hotter than normal. But as your fan works when you jump the connections I woulda thought your relay should be OK.
 
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MoritzTheDoka
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Stesaw wrote: 14 Apr 2021, 17:26 If the light doesn't flash on your temp gauge then you aren't overheating and its OK. If I don't have my heater blowers on my temp gauge sits just above the light, with the heater on it sits right over the it. I checked mine recently and found that a relay was at fault for my fan not coming on as I thought my van was running hotter than normal. But as your fan works when you jump the connections I woulda thought your relay should be OK.
 

Hey man, thanks for the input...

The light doesn't flash, it's never flashed, it doesn't flash on start up either though to indicate a "test cycle" to show that it works.

Yup, fan works fine when connections jumped, is there anything else I'm missing that controls the fan, relays? Temp switches?

The only thing different today was that the van stood for a day yesterday, now it's getting hotter than it ever has (it was a pretty cool day today to, so it can't even be that it's just the ambient temperature
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TONYT25T25
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by TONYT25T25 »

You need to get that light sorted so you can narrow down the problem, it should flash on start up then go off if all ok, if the gauge goes past the halfway mark and the light comes on it means the engine is overheating.  There is an example of how the light functions on here somewhere, i think posted by MOCKI several times, explaining its operation but I can't find it at the mo.  In meantime have a read of this from the WIKI.
Coolant and Heating Flashing red light on dash - VW T25(T3)-Tech (club8090.co.uk)
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Stesaw »

As Tony says sort that light out so it works so then you will know if you are overheating or not.
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MoritzTheDoka
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Thanks guys, yup I need to get it working, but I have no clue where to start or how to do that. I took the dash pod off the other day when doing the slave cylinder and bleeding the clutch and had a close look at the back of the cluster, checked connections were sound and in tact and everything looked, to the untrained eye to be in relatively good order so I'm stumped at how to get it on.

I'll have a close read through the wiki and see if that helps but if anyone has any simple instructions on how and what to check, or how to diagnose the issue specifically with the led not turning on that would be really helpful.
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Robsey
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Robsey »

Being an early water-cooled engine, there is less to check.

1 - There is the coolant temperature sensor on the engine / thermostat.

2 - Fluid level switch in the main tank, not the expansion tank.

3 - The sensor loom connectors in the engine bay junction box.

4 - And the coolant level / warning light control unit on the left inner wing / under the dash, close to the earth crowns.
This looks like a relay and is marked 42 or 43.
This may be faulty as there appears to be no self-test function.
- or it's connector pins or earth tag may be dirty / corroded.
Check the connections and ensure that they are all clean and dry.
Last edited by Robsey on 15 Apr 2021, 09:39, edited 2 times in total.
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Mocki »

Morning 
a couple of points......

the rad fan is not dependent on the gauge , it only operates from the switch in the radiator, as you know from your first post .... and it’s normal for it to not come on until the gauge is at least 3/4 of the way over .
Infact it’s unusual for the rad fan to come on at all in the U.K. from October to May under normal driving conditions
The flashing red light in the temp gauge has two functions ....
 1. If the gauge is above 3/4 and it's flashing it means over heating 
 2. If the gauge is below 3/4 and it's flashing , it means low coolant in the header tank. 
  
 If it's says low coolant , and you can see the header tank is full to the brim ( not the number plate flap top up tank) then it's an electrical issue , and simple fault diagnostics will need to be employed ! 
  
 Red flashing coolant light self tests when you switch the ignition on and then goes off ......


There are a couple of very simple  tests you can do to establish the issue 
you say it’s not self testing , so first port of call is the control unit , labelled as either 42 or 43 and looks like a relay , located up above the fuse box near the earth crowns - unplug it and clean it’s connections and the earth connections . 

unplug the level sensor in the top of the header tank , that will make it think you have low coolant , and it should flash 

unplug the temp sender connection at the thermostat housing and if it’s early "ground" it to the engine body , if it’s last ebridge the two connections in the plug you just removed , this will make the gauge think it’s over heating and move completely to the right . 
 
  
 The system is very simple....
 The headertank ( the one in the engine bay ) should always be full to the brim, and the top up tank ( behind the number plate flap) should be full to the max mark when cold. When the engine is up to normal running temp the coolant expands and is pushed into the top up tank, when the engine cools down the coolant is sucked back into the header tank

 
  



 
 
Steve
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MoritzTheDoka
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Mocki wrote: 15 Apr 2021, 07:20 it’s normal for it to not come on until the gauge is at least 3/4 of the way over .
Infact it’s unusual for the rad fan to come on at all in the U.K. from October to May under normal driving conditions

This is solid gold info. Thanks mate 👍

I'll run through the tests you mention and see where it goes
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Robsey wrote: 15 Apr 2021, 07:09 Being an early water-cooled engine, there is less to check.

1 - There is the coolant temperature sensor on the engine / thermostat.

2 - Fluid level switch in the main tank, not the expansion tank.

3 - The sensor loom connectors in the engine bay junction box.

4 - And the coolant level / warning light control unit on the left inner wing / under the dash, close to the earth crowns.
This looks like a relay and is marked 42 or 43.
This may be faulty as there appears to be no self-test function.
- or it's connector pins or earth tag may be dirty / corroded.
Check the connections and ensure that they are all clean and dry.

Sorry, completely missed this ☝️, thanks also for the pointers.


Am I right in thinking that I his is the thermostat temperature sensor?

Image

The thing is, it has two wires? Not 1, which I'm guessing is to do with it having a later dg fitted at some stage?

Interestingly enough I had the opposite of my initial problem occuring just before the weekend; as in I was driving along, fully up to temp and the gauge actually dropped below the led, by a fair margin?

I'd say if the LED is 12 o'clock, it was easily sitting at 11, if not 10:30?

Possible dodgy temperature sensor in the mix?
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Robsey »

There are two wires to the gauge sender.
These wires are -
Yellow / red towards the gauge.
Brown to ground.

So if the wires in the plug match, then yes that is the correct plug.

After taking a closer look, I see
Lilac / black and
Black.
That is the connection for the manifold pre-heater.
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Robsey wrote: 17 Apr 2021, 20:24 I see
Lilac / black and
Black.
That is the connection for the manifold pre-heater.

Thanks again Robsey, I'll have another look tomorrow and I'll run through the tests mentioned by @Mocki 👌
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by MoritzTheDoka »

Update!

So, I started with the easy bits... pulling the plug on the level sensor seems to do nothing, so I pulled the connector off the temp sensor and bridged the connection, sure enough straight round to hot, but still no led.

*As a side note, the sensor was only "thumb" tight? And as I was fiddling trying to get the boot off coolant was leaking out, and I couldn't see a way to get a spanner on it from underneath, how are these tightened?

I managed to find the control unit, but it's tucked a bit out of reach to get a good purchase on, but I checked the earth's as best as I could and all the wires in/out look in place so it might have to wait until the dash comes out (I have a dead blower to fix) unless someone has any led specific pointers?
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Robsey »

If it is a gauge sensor, then it is held in by a clip that pushes in from one side.

Maybe you need a new seal (O ring) to stop the leak.

If you are getting no led on the dash, but you are getting needle deflection, then I would consider that the gauge itself is faulty.
As soon as you apply an ignition live feed, it should flash for about five seconds.
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Re: Electrical? Mechanical? Overheating no fan, no idea

Post by Mocki »

Ok, that pictured is the carb heater switch position , the temp gauge sender is the other one , facing the front of the van .....
it’s not unheard of for the two senders to be in the wrong positions, and the wiring loom switched over as well , or not sometimes ....

to test the red flashing light , unplug the low coolant sender in the header tank , that should set the light flashing no matter what the temp gauge says 

if it’s not flashing on first turn of the key before cranking, check the control unit ( looks like a relay and is marked either 42 or 43 ) up above the fuse box . Clean it’s contacts and the earth crowns while you are there . 
also check the 14pin connector onto the the dash pod is clean and making a good contact . 


 
Steve
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