Coolant temp gauge replacement (late petrol)

[itchyfeet]

80 degree stat in today (I'm ignoring yesterdays results the new 87C stat is clearly faulty)

old 87C Stat- 80C Stat (as before first number is the sensor location second number the metal pipe)

22C 22C - 16C 16C Switch on
50C 49C - 45C 44C 3 mins
62C 60C - 60C 57C 5 mins
68C 66C - 65C 63C 6 mins
72C 69C - 69C 66C 7 mins
78C 74C - 74C 71C 8 mins
82C 78C - 78C 74C 9 mins
94C 89C - 85C 78C 12 mins
93C 85C - 86C 79C 15 mins
92C 85C - 85C 77C 20 mins

So looking at the 20 minuite line the 87C stat is at 92C and the 80C stat is at 85C both have the same offset of coolant being about 5 degrees higher than the stat rating.

Then after 20 mins with the 80C stat I revved to 2000rpm for a further 5 mins and the temperature rose to about 92 then cycled between 92 and 88 with the stage 1 fan cutting in and out.

So you can assume your coolant may be as much as 10-15 degrees hotter than the thermostat rating.

But the point of the test is that the old thermostat was not faulty it was behaving as it should.

P1100692 by Paul_Barr, on Flickr

[itchyfeet]

This is a real curious one. I predict whoops of joy and much self kicking when it's finally solved.

Whooooooooooopppppppp Whooooooooooopppppppp

[937carrera]

Don't want to rain on your parade but have you solved the problem ?

I got a bit sidetracked, but I thought the problem was the temp gauge going to the right and the LED illumuminating

[itchyfeet]

Coolant temperture checked and new sensor in, it has 115 written on it and on the box which nicely aligns with the 115C on the gauge so I think we can conclude that full gauge is 115C and I'm getting no where near that.

P1100695 by Paul_Barr, on Flickr

P1100698 by Paul_Barr, on Flickr

Using the thermocouple on the metal water pipe ( because the other one is not removed) this is where the coolant is about 85C

P1100700 by Paul_Barr, on Flickr

and this is where is when fan is kicking in and out so 88-92

P1100703 by Paul_Barr, on Flickr

pull the plug off the level sensor and light flashes, I think it raised a little but definitely not full gauge so it appears the PCB does not affect the gauge just the LED.

P1100702 by Paul_Barr, on Flickr


So in summary I had 4 faults

A broken gauge
A faulty regulator contact which was making my fuel gauge read high ( and would have made the temp gauge high if it worked)
A faulty sender which was creating a much lower resistance path.
A faulty brand new sensor which was creating a much lower resistance path.

The brand new sensor being faulty was the thing that really cost me so much time but it is a good lesson to remember.

Just like the brand new thermostat

DON'T ASSUME A NEW PART CAN'T BE FAULTY

I could well of broken it dunking it in boiling water so

DON'T TEST SENSORS IN BOILING WATER

I think I would be moving from bench test in the van to bench test in the kitchen. Quicker and cheaper to boil the kettle.

It appears I'm not the only one who would have made this mistake.


Big thanks to everybody who helped , particularly AngeloEvs for his excellent knowledge of the circuit and 937Carrera for keeping me going when I got bored of it.

Hopefully some good data here to help others in future , I may just measure voltage and current across the sensor to have that info to hand.

[937carrera]

DON'T ASSUME A NEW PART CAN'T BE FAULTY

Indeed. Been there, done that, got the T-Shirt

Pretty much a full house of issues there, well done for finally getting to the bottom of it. With your new 80 degree thermostat I suspect your temp gauge needle will probably not go past the LED now.

On the LED / gauge interraction I read somewhere, probably Samba that the early ones did go full deflection, a revision to the relay module changed the behaviour

[bigbadbob76]

So do 42 relays send it full scale and 43's not?
I have a 43 that doesn't.

But that's just the level sender.
A faulty temp sender would still send it full scale.


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[937carrera]

Beyond my ken, but these guys seem to know

https://www.thesamba.com/vw/forum/viewt ... &start=123

[itchyfeet]

I found a good use for the broken sensor

P1100711 by Paul_Barr, on Flickr

[itchyfeet]

Not happy with the 80C degree stat, think I will put the 2 year old Whaler 87C back in, oil running no more than 80 yesterday must have done 50 miles.

[937carrera]

It's a fair bit cooler than it has been of late so engine temperature would be lower and less of an issue than recently. I wouldn't be concerned by oil at 80, but I know you think that's too low to evaporate the moisture off, though it's the length of journey rather than temperature that gives the mayo / water in oil issue.

What were the oil pressures like, bet they were good.

[itchyfeet]

What were the oil pressures like, bet they were good.

Same.

Not tried motorway yet.

[bigbadbob76]

I found a good use for the broken sensor

P1100711 by Paul_Barr, on Flickr

Damm... wish i'd not binned mine now. Think i have an old thermoswitch though, that's the same size.
Cheers for the tip.


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[bigbadbob76]

Beyond my ken, but these guys seem to know

https://www.thesamba.com/vw/forum/viewt ... &start=123

Cheers for the link.
All is now clear.


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[Cobra88]

mine works great with the 80 degree.

But mine is auto and has no oil cooler/warmer at all.

Regards
Rick