Erratic Gauges - Any ideas?

[Andrew]

My pressure and temperature gauges seem to have started misbehaving. The symptoms are;

 

- work ok initially. Temp gauge rises to "80" as the engine warms up and the pressure gauge moves with engine revs

- when the car is moving the temp will drop to just above "60" and stay there. The oil pressure gauge stays just past vertical. Both gauges refuse to move irrespective of revs or speed.

- turning the ignition on/off whilst moving temporarily gets them reading correctly again, but this only lasts approx 1 min

- the gauges start working ok as soon as the car is stationary with the engine running

- rev counter / speedo / all other instruments are ok

 

I'm guessing there must be a sensor or connection (earth?) that is common to both instruments that could cause this. Can anyone suggest what & where it could be?

 

Thanks in advance,

Andy

 

[CHRIS CLARK]

Andy,

It does sound like an earth fault. Can't say where the earth point for those gauges are though. Hope someone else does!

Good Luck!!!

[John Whyman]

Earth is common across all instruments so check all instrument earth terminals are clean and in place.(It is on my Xf ss anyway).Also give a tweek on both earth straps on the back of the bell housing to ensure tight.

 

Temp and pressure sender connections get very claggy,(being where they are).Had a similar problem which i cured with some emery cloth rubbed gently over sender terminal and connection and a good squirt of WD 40.

 

Just a thought.

[Asklepios]

Andy,suggest earth on nearside under inst panel.Will look ok but abrasion will cure problem.Mine had an aluminium washer which should be junked for a more ferrous device.

[John Whyman]

Just had a look at my wiring diags this morning, and see that temp and oil pressure guages are earthed through the fan heater switch via red/white to ground. Also live feed comes from ignition switch via the ignition amplifier. (Ford XF cars). Which model is yours?

[Rod]

I also have had gauge probs(1.6ss) over winter. All dials get condensation after 10 mins running. Speedo still misreads (low)& sometimes stays on zero. Problems seem to be improving with the weather! Any ideas?

[Steve W]

I've had a similar problem in the past. Strange readings on the gauges (flick the heated screen switch a couple of times and the readings fall ?). Turned out to be the earth point under the dash on the wiper motor. Make sure you remove some of the powder coating on the motor bracket to get a good earth.

[Andrew]

Thanks for all the help. I've checked the wiper motor earth & the bell housing earth but had no joy.

To display my ignorance (!) can someone point me in the direction of the oil & water senders. I've disconnected and reconnected everything I can see that look like candidates in the engine bay I just want to make sure! It's a 1.6kss.

[elie boone]

On all earth conections use No Corrode battery grease. wink.gif

 

 

[CHRIS CLARK]

Rod.

My gauges too suffered the 'misting up' problem. This was cured by following the advice of a chap with an article in L F some time back (Capt. Mockett ?). The answer is to remove the gauges and saw a slot or two in the outer casing (being very careful to not go too deep). I actually removed a 5mm wide strip from the underside of mine. It allows the warm air from the heater/engine soak to remove the condensation and voila! Clear, legible gauges!!!!!!!

[JampJ]

You can easily check if you have a poor earth

connection by taking a wire directly from the battery earth and connecting it to each gauge earth connection in turn and see if the fault clears.All the earth wires on the car

are black,not red/white as earlier stated,

this wire is for the gauge internal lights!

CHEERS C7 POW.

[Rod]

Chris - thanks for that. Sounds real good sense!

thanks again

Rod

[Nigel Riches]

Andrew, all the previous replies talk of the earth side, don't forget that the gauges are not fed with direct 12vdc, as this isn't very stable in car systems, have a look under the dash towards the nearside, and try to find the voltage regulator, this may look like a version of the indicator flasher box, but a bit smaller, this is supplied with voltage from the car system, and then drops and regulates that to either 7 or 10 volts, and that possibly wont be very stable either, depending on which gauges you have, do you have a meter? check this voltage, the older type use a coil of resistance wire wound around a bi-metalic strip to to regulate the output, but a better solution is to get a solid state device, much more reliable, if your car is fairly new this info may not be relevant as more supplies would be sourced from the ecu.

Hope this is of some help, and may get other readers looking at the fault from the other end, so to speak.

Regards Nigel.

[John Whyman]

OOOOOOOps! sorry, black is earth not r/white, thanks John and Julie. Can't read wiring diags without binoculars!!

[JampJ]

Sorry to keep contradicting people,but VDO

gauges don't use a voltage regulator,they are

directly fed.The needles are damped using

silicone.It's SMITHS gauges that use a regulator to maintain a constant voltage.I'm

in the process of changing all mine to SMITHS chrome and magnolia to give the dash a bit of character.Expensive but very nice!

Good Look.

CHEERS C7 POW.

[JampJ]

Hi Andrew,just had another thought,both gauges are fed from the same fuse,and are operated via the engine earth for the temp gauge,and the petrol tank earth for the fuel gauge through their senders,therefore it seems to point to the live feed as this is the only common connection for both gauges.you could

try taking a live feed from the battery via a spare fuse directly onto the green wire feeding the gauges,this would proove if the live feed is ok!

CHEERS C7 POW

[Andrew]

Thanks for the help but after getting sparks flashing from under the dash I've decided to leave this alone! Luckily I only blew some fuses. Oddly enough a good session at Donington Park seems to have temporarily cured the problem but it'll be in the garage if it reoccurs.

Thanks, Andy