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2.5td temperature mysterys


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The odd behaviour I've got is an oil pressure gauge that went off the scale suddenly when driving. The gauge is one of three (water temp and oil temp as well). All three are wired with a common Pos and Neg and have been installed and working perfectly for 6 years. The other two were unaffected and giving the appropriate readings. Of course I thought an overpressure in the engine was the problem.

However I could replicate the problem with the engine switched off, cold from an overnight parked up and not run. That made me suspicious. So changed the sender. Same problem. Then renewed the wiring back to the gauge. Same problem. Then unbolted and cleaned and reattached the earth straps from gearbox to chassis. Same problem.

I then thought the gauge might be defective. Replaced the gauge with a new one. Same problem!

I then started poking about in the dash wiring and found that I could replicate the problem on the water temp gauge if I disconnected it from the the common earth it shares with the oil temp gauge.

In fact putting the two oil pressure gauges on the kitchen table (well away from the 110!) and wiring a 9V battery to the Pos and Neg terminals on the gauges replicates the problem, with the needle pinging right off the scale in exactly the same manner. I've used three separate 12V batteries - wiring directly to them - two are connected to the vehicle - starter and aux batteries, both earthed to chassis, but the third battery I pulled out of the shed and connected directly using both the old wiring and new wiring directly to the pressure gauge so bypassing the entire vehicle system (except the connection to sender) and I'm still getting the problem.

So I'm kind of stumped! Curiously the pressure gauge needle responded to the throttle, when I noted the problem and pulled over to the side of the road the needle went down to the normal position on the scale, but flicking the throttle made it go straight over past the 120PSI mark hard to the edge of the scale. So.......its either a massive overpressure - which doesn't seem to be the case (although I've not had a mechanical gauge on it yet - but the problem persisting with the engine cold and switched off leads me away from this) so...thinking as I'm typing here.....might it be an alternator connection problem?

Whatever it is its got me baffled! And I'm on the verge of buying a mechanical gauge and fitting that, but I really need to find out what was causing the issue in case it's going to affect any other aspect of the electrics because I ignored it.

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  • 2 weeks later...

Update...

After changing the thermostat and the guage deciding to just sit inbetween the red and white sections I decided yo remove the thermostat all together yo see if KT was maybe the temp sender at fault and now the guage just sits barely into the bottom of the white which would signal to me a dodge thermostat?

So does anyone have the part number for the correct part as the garage I dealt with is adamant they gave me the right part even though its different from the one I took out originally.

Thanks

Jamie

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Yeah my old stat used to sit roughly vertical when it was working. now it sits just in between the red and white with the 88c thermostat in.

I'll be in the garage this week to try and get this sorted out.

Cheers

Jamie

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