Temperature guage!

[carl4u44]

Ok well the temp gauge gradually got worse on and off now its totally dead. I have replaced both temp sensor and sender with no luck.

Upon testing, I have ground the single temp wire and my gauge fully lights up and gauge rise to the max. When I plug it back in it only works intermitt.

My next thought is the ground cable off the gear box, as moving my air filter housing seems to trigger something now and again near to the gearbox earth lead, but surley other gauges would be affected? Can I create a temporary ground wire near the water temp house to test this for the mean time and would that make a difference?

Many thanks for any input...I shall keep this one posted.. 440 td

[carl4u44]

OK seemed to have solved it. The earth lead coming from the gearbox (below the battery tray) seemed a bit 'ropey' to say the least, giving intermit problems with my sender. I tested the whole engine for its earth and it showed that this earth cable is the only earthing point for the engine block. As the single wired temperature sender relies on the earthing of the engine block it seemed the only possible clause. Hope this may be of help in future!

[carl4u44]

Well folks unfortunately that hasn't solved my problem as it continued to play up again.

Having thought this through I was now convinced it had something to do with the gauge itself. So I took the dash clock out and stripped out the temp and fuel gauge (all one unit). Having found nothing suspicious I tested the resistance from the sender wire to the dash clocks itself and found that the wire was complete and that the correct resistance was given when the engine was warm. This could only have meant that the gauge itself was faulty.

On the back of the fuel and temp gauge(s) there are six pins going into the whole blue circuit board across the back of the dash clock as shown in the last picture. The black/grey wire from the sender went into one of these pins via the short fattest connecting block. I found the pin (pointed with a pen) had come loose!!!! All is now fixed..

Below are some pictures I took of the process........









Ohh and yea I tested both my sender's resistance values (when removed from the engine) the night before thinking they were the culprit. When cold the have 1300 (give or take 100) and when added to boiling water should read as low as 100 ohm's.

[jeff t]

Hi, if you look back at some old threads you will see lots of information on temp problems with gauges.
Had the same problem twice with my 460 over the last 18years, and it proved to be the little brass spacers between the pcb and gauge,as these carry the earth through, slight white powder between the brass and solder of the pcb the cause.
Volvo used to say it was the pcb on the back of the gauge failing and first time I changed the pcb it fixed problem, but failed again after 10 years.
I bought a pcb from a scrap car that I new worked but found cleaning the spacers got the gauge working again.
Not saying this is your problem but it might help checking.

[carl4u44]

I think were on to something here! Yep I know those brass spacers. I have had them clocks out ten times this week. I will double check them again as the problem is back to haunt me.

[carl4u44]

The brass connectors are a bit tarred on one side. Will give all four a clean a keep you all posted!

[Baffler]

Although your PCB is slightly different, every 480 instrument panel I've seen had the pins soldered to the PCB.

There maybe additional info over on the 480 Club Europe site.

[carl4u44]

Big thanks to Jeff for helping sort this one. Yes indeed it was those brass connectors between the PCB board and the gauge instruments. The brass (or gold?) connectors were in a bad state. They cleaned up well with vinegar and a sharp blade. Even on the new clocks I got from the scrap yard had nasty connectors.

In total I spent £45 on two sensors (sender and sensor) for the temperature, terminals, spare clock dash, cleaning products and a week of my time with cut fingers. In the end it virtually cost nothing to solve the issue.

I have had the clocks out at least ten times, and without knowing, swapping those brass connectors between gauges. This explains why at a time my fuel gauge played up too!

Below are some pics of the strip down procedure which is a simple job. All those out there who have issues with either gauges should try this. Sorry for the bad quality pics as my phone camera is touch and go indoors.

Also goes to show the simplicity of the 400 series in terms of its technology (except for those with digital gauges lol). I do remember my old 480 had soldered pins to the instrument, which caused issues, but again that was with the digital gauge.

Thanks again Jeff.

8x torx screws around the dash. 4 nuts holding the gauges, all pulls out. ^ pins on the PCB behind the gauges need put back in with caution and connected with the blue circuit board across the back of the whole dash.

[Baffler]

Good write up Carl Glad you found the root cause of the problem.

[jeff t]

I was 99% sure that was causing the problem ,but always open to new ideas
from anybody.
Glad it sorted it for you.
Jeff.