XJ6 & XJ12 Series I, II & III 1968-1992

Series 3 temp guage high, when lights on!

Old 09-18-2014, 08:03 AM
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Default Series 3 temp guage high, when lights on!

Hello all.

Once again I thought it best to turn to the owner-experts on a query, and once again I will be extremely grateful for the help.

My 1985 xj6 series 3 was sitting beautifully just below 90 degrees on a long run of about 90 miles. However, for the last 20 miles the engine temp gauge starting going right up, and I mean right up to 130, but then dropping back down again.

I pulled over when it first crept up, let the engine cool a bit, and checked the fluid levels, all of which were fine, no steam, nothing.

The only variation that had occurred from when the gauge was sat just below 90 was that I'd had to put the headlights on as it was getting dark. I'm therefore thinking it could be an earth issue somewhere? Do forumers think the gauge itself should be replaced, or would it be an issue further back in the electrics, if indeed that is what caused it?

Many thanks. I realise that text is boring and pictures are exciting, so here is a pic of the newly-acquired dream car
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Old 09-18-2014, 08:34 AM
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Almost certainly an earthing/grounding issue.

There's no telling where the search will end but the best place to begin is behind the panel itself.

The wood dash has a metal backing plate with two earthing tabs where the earth wires attach. You'll find these near the tach and speedo, down towards the bottom of the metal panel. Make sure the wires are firmly attached, no corrosion, etc. While fussing about in that area it can't hurt to run a new, redundant earth wire to the metal backing plate.

If none of that pans out, shout back

Old 09-18-2014, 09:31 AM
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Fantastic, thank you for the guidance Doug. Indeed, it's a great help to know where to START looking at the very least! I shall report back once the car is back from the mechanic.

I had the plugs changed, oil and filter, air filter, and fuel filter, and after that she's been running as if on only 1 cylinder! He's having another look to see if something could have been knocked during the service, but that's a whole other story in the wonderful world of the car....!

Best wishes.
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