Faulty temp gauge.

[vlasnia]

Hi, I wonder if anyone could offer any clues as to why my temp gauge is playing up. Sometimes it doesn't move at all, sometimes its moves halfway across the dial then drops back to zero and remains there but usually it doesn't move at all. I tried fitting a new temp sender which briefly seemed to improve things but now its back to how it was.
The van was a 1.6 diesel now upgraded to a 1.9td.
Any ideas appreciated.
Will.

[MattBW]

I believe there is a voltage regulator in the dash which i am told could be the cause of my problem which sounds similar (no fuel gauge and temp gauge is lower than it should be).

Have a search for fuel gauge regulator and lots of threads will come up.

https://club8090.co.uk/forum/viewtopic.p ... r#p7821262" onclick="window.open(this.href);return false;

[vlasnia]

Thanks for that I'll check out those treads.
Since I was last on I tried making a new earth for the temp sender because I'd read somewhere that if a sealant has been used around the pipe joint, the earth could be lost. This had the effect of making the gauge work but it now goes way up into the red and causes the light to flash once the engines been running for a few mins.
Anyhow I'll check the treads you mention and see where they take me.
Thanks again,
Will.

[vlasnia]

So 2 weeks later and I've tried replacing the transistor on the pcb on the dash with no effect, the temp gauge is still going way up into the red and the fuel gauge is a bit erratic. I tried testing the voltage on the back of the temp gauge and it seems to be reading about 11.5 volts (should be 10 according to the other thread)
Any further ideas gratefully taken.

[Oldiebut goodie]

Have you put the new voltage regulator in the correct way round?

[vlasnia]

Well I think so but as there was no info on the new regulator regarding which of the pins were pos or neg I just put it in as suggested on the other thread which is back to front. Do you think I should try it the other way round or will it be damaged now?

[Oldiebut goodie]

Metal tab outwards/writing to pcb. Heatsink required as they get hot.
Are you getting 10v on the output from the regulator or is it 11.5 the same. (trying to visualize what is happening there)

[vlasnia]

I'm going to have to check this again tomorrow, I've been taking a reading off the back of the temp gauge and I need to double check which way round the voltage regulator's facing. Thanks for the help so far, I'll be back on tomorrow pm.
Cheers,
Will.

[vlasnia]

The voltage regulator was fitted the way suggested, tab facing out writing to pcb, i tested the voltage come off the voltage regulator and its reading 11.7 volts. I tried putting the voltage reg in the the other way round and still no change. I also took it out completely to see what happened and both fuel and temp gauge still worked and read the same as before. Electrics are not something I pretend to understand much about and I'm at a loss at what to try next.

[Oldiebut goodie]

It is sounding like you have put a LM78 12 instead of a LM78 10!
Are you sure that it was a 10v one that you put in? Did you put a heat sink on it?

[vlasnia]

Its an L7810 1.5 amp. its screwed onto the back of the temp gauge through a small rectangular metal plate approx 3cm by 2. I haven't removed or lost anything so whether that's the heat sink or not I don't know.

[Oldiebut goodie]

L7810 is a TO-3 package not a TO-220, are you sure that it is a L7810?






Are you following the Wiki article and diagram when you are removing and replacing it? HERE

[vlasnia]

definitely an L7810. Should I be going for the L7810C. I have to say I've not been following the wiki article but it looks like mine has gone in the same way.

[Oldiebut goodie]

You didn't overheat it when you soldered it to the pcb did you? That is all that I can envisage if you have mounted it correctly and are testing it correctly. What voltage was your original one giving you?
Nothing to gain by using a L7810C.

[vlasnia]

Maybe this is where I'm going wrong. I have simply pushed it into the little receptor that's attached to the pcb. Should I be soldering it into that. The old one just pulled out once the tab was unscrewed and I assumed it was a push fit. Didn't ever test the old one just assumed it was faulty as everything else seemed ok.