Temperature gauge reading high

[shrig1969]

Done an overhaul on my cooling system but the temperature gauge reads higher than before, sitting around three quarters. Before it always sat around half way.
Things changed involved new radiator (32mm, half the size of the old one), thermostat and housing, temp sensor, Dalek cap and all the rubber hoses.
System has been bled and everything gets hot as it should. And fan cuts in.
Tried the wiki test on relay 43 and the needle goes all the way over.
Having read a little on here am I right in saying I could have an earth problem. I have looked closer at 2 things...
The connection to the sensor looks poor but am unable to get the crimps out of the plastic housing to clean up.
Also the earth connections in the junction box in the engine compartment look poor also but am unable to work out how to clean them as well. There are 2 earths that connect under a relay with No. 1 written on it.
Any advise appreciated but go gentle with me when you answer in electrical lingo, I wired a plug for the first time yesterday

[shrig1969]

Still trawling previous posts on here for guidance.
If I manage to somehow clean up the earth connections mentioned above is it possible that the temp needle will not move when testing relay 43? And also give a more accurate temp reading?

[RogerT]

It's late, and I'm a bit confused. So from reading your first post what stands out for me is that after replacing your radiator with a thinner one (i.e. One with less cooling capacity), your engine is running hotter. I'm not sure why you're concerned about the needle position as it's possible that it is accurate. But maybe saying you have a smaller radiator was a typo?

[Mocki]

surely a bad earth would make it a lower reading, as fully earthing a temp sender makes it ready fully to the hot end??

anywhere between the two white boxes is "normal" according to the ownwers book
from experience, where ever it sits when its running normally, is normal, its when it suddenly changes when you havent changed anything you need to take investigative actions

[shrig1969]

It's late, and I'm a bit confused. So from reading your first post what stands out for me is that after replacing your radiator with a thinner one (i.e. One with less cooling capacity), your engine is running hotter. I'm not sure why you're concerned about the needle position as it's possible that it is accurate. But maybe saying you have a smaller radiator was a typo?

No not a typo unfortunately. Is my radiator choice still ok or will it damage the engine?

surely a bad earth would make it a lower reading, as fully earthing a temp sender makes it ready fully to the hot end??

anywhere between the two white boxes is "normal" according to the ownwers book
from experience, where ever it sits when its running normally, is normal, its when it suddenly changes when you havent changed anything you need to take investigative actions

When you say two white boxes I hope you mean the centre box and the one to the right?
I read on here that the temp sender was faulty if the needle went over to the right when testing. Is that statement correct?

[syncroandy]

I agree with Mocki, the temp sender is NTC (decreasing resistance with temp), so any extra resistance in the circuit (eg. due to corroded terminals) would tend to cause a low reading on the gauge. That's not to say ensuring all electrical contacts are in good condition isn't advisable though.

When I was developing my dash product, I did some measurements on the T3 temp sender, and at 87 degrees, its resistance should around 115 ohms. You could try measuring your sender at normal running temp to see is it deviates from this.

As Mocki says, due to component manufacturing tolerances etc, its better not to think of the gauge as giving an absolute measurement of temp, more just an indication of change.

[shrig1969]

Thanks for all your advice. Much appreciated.
Hopefully now I can drive with 2 eyes on the road instead of focusing on the gauge all the time.

[shrig1969]

Firstly apologies for my reply Mocki about temp needle between centre box?? And one to the right. I think I still had the Golf dash in my brain when replying. (Centre box )
Anyway I can't stop thinking about it. I know you all said it is normal but I would still like to get it back to middleish if possible. In my eyes it all points to the sensor/connector. Worked out how to measure the resistance and got around 1500 ohms with a cold engine. Then measured voltage on connector (yellow/red) side and got around 9 volts. All a bit vague I know but am I in the right area of attempting to measure correctly? I am away tomorrow but back next week so will be looking to have more time to investigate further. Any pointers would be very welcome on where to begin and end if I am starting in the wrong area.

[marlinowner]

I think it's most likely the temp sender is different to the original one, do you still have the other one to swop back? My South African van shows a "normal" temp with its original gauges, but if I fit my spare gauges from a dg, the temp reads high, I assume this is due to the Audi derived engine using a different temp sender which was allowed for in the matching gauge.

[shrig1969]

I do still have the old one, which I will look to swap over on my return and go for a test drive to see how much the
Gauge changes.
Just curious in how to test it prior to installation. I presume a similar test to a thermostat using boiling water?
Any idea on resistance values etc

[shrig1969]

I'm back on it as promised....

Bit amateurish I know but it did give an insight into the sensors resistance. As the photo describes I tested 2 sensors in 50/50 coolant, the same as in my van.

As you can see, the newer sensor started off with less resistance, which I presume allowed my temp gauge to start
Climbing earlier than the old one before sitting on the three quarter mark, although they did become more similar, the hotter the temperature. The older one I have re-instated as I find it more reassuring when driving.
Am I correct in my assumptions and if so does anyone know where to find a ohms chart specific to T 25's so I can compare my results.

[Oldiebut goodie]

If your gauge is a vdo one you must use the vdo sensor. I don't know if the factory gauges are vdo in our vans. Good listing of them here: https://www.vdo-gauges.com/sensors/temp ... witch.html

[shrig1969]

No it's not a VDO gauge but thanks for the tip. The sensor has a 2 pin connector, round and black.