Earthing 300tdi and temp readings

Hi all, I've got a 1987 90, converted to 300tdi. I recently had the 300tdi replaced with a newer 300tdi. All is well, except for one small annoying thing... temperature readings.

I'm pretty certain the actual engine temperature is fine, and I've swapped out the sender, then tried replacing my guage, and finally tried replacing the cable to the sender. No joy.

I'm now certain it's an earthing issue. The readings on one sender are very low (50 to 60 when warmed up) and high on another (110 to 120) but here's the big giveaway, if I turn on my electric radiator fan, the temp readings instantly fluctuate. Suggesting it's an electrical resistance issue to me, as I know that's how the sender works (something to do with measuring resistance).

So I'm wondering, did my garage forget to earth the engine when they fitted it? If so, where can I check for this... The internet isn't helping me much so far on this. If it's missing, is it something I can do myself as a moderately capable home tinkerer?

Cheers.

Hi ,

If you think they have forgotten a big black earth lead, should be fairly obvious, have a look at the rear of the engine for a black lead going to the chassis.

Or you can always try a jump lead connected to the engine and the chassis to act as an earth lead to see if it solves your problem.

Cheers

Yeah I'm struggling to find anything like that, which suggests to me it's missing. But where would I attach one of I'm doing it myself, is there somewhere specific/recommended? Or just any old bit of engine metal to any old bit of bodywork?

iirc, mine bolts onto the back of the engine and goes to the chassis rail on the passenger side below the heater box.

My 300tdi had bad earthing when I got it, the temp gauge would jump to the red when the lights were turned on, I found the earth strap at the rear of t the engine was missing , got one from halfords, plus I went and checked the others to make sure they were lean and tight.

Cheers

HeywoodFloyd said:

Yeah I'm struggling to find anything like that, which suggests to me it's missing. But where would I attach one of I'm doing it myself, is there somewhere specific/recommended? Or just any old bit of engine metal to any old bit of bodywork?

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back of head to bulkhead

jamesmartin said:

back of head to bulkhead

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I can't even find the right point to fit it to on the back of the head. God I'm useless lol.

HeywoodFloyd said:

I can't even find the right point to fit it to on the back of the head. God I'm useless lol.

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either of the lifting eye bracket bolts would do

jamesmartin said:

either of the lifting eye bracket bolts would do

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Ah ok, that's easy enough. Cheers!