Lies, damned lies and X300 idiot oil gauges

(PeterCrespin) #1

I seem to recall the idiot oil gauge and the oil warning light are linked but different, with the light signifying pressure below 5 psi and the gauge signifying a pretty mid-scale needle and not much else.

Either way, when I noticed the gauge at zero and the warning lamp on, it was quite a jolt. My first thought was how long had it been like that? Being about five miles from home and in bad weather, I eased the car carefully home, wondering when the clonking sound would start.

Next day it seemed OK and I suspected a temporarily stuck pressure relief valve. Over the ensuing weeks, the 97 XJ6L performed dependably as usual in its roles mi, apart from every so often throwing wild zero pressure signals. I began to notice faint knocking noises - or did I? after a total of about fifty miles of ‘zero pressure’ errand driving I finally got it on the ramp and plugged in a wet OP master gauge where I removed the oil . Result said 80 psi for a cold engine.

My CD ROM is currently not usable, so can anyone figure out which location to find the gauge sender and how to check the gauge wiring?

(j limongelli) #2

Very early 1995 xj6 oil gages were a gage…they were changed to a preset dummy gage and sensor about 2 months into production.
People did not like the fluxuating needle by 1995.
If yours is crapping its the sending unit itself on the block as you said it was a 1997.
The gage is fine, the sending unit need to be replaced.
Good luck

(Andy) #3

Look at purchasing a sensor. The picture will help you locate it. Look under the car.

Check the wires aren’t rubbing on metal as this will cause the light and zero reading iirc

(PeterCrespin) #4

Bad typing. I meant to write that I attached the wet gauge where I removed the oil pressure switch up near the filter on the left side of the engine. I don’t regard that as a sender, just an on-off switch.

Such single-wire switches connect a simple warning light in series and are normally closed to earth until oil pressure forces them open at a few psi and the light goes out. A dud switch could either stick open or the wire come off and the light never comes on (it does come on) or stick closed or the wire shorts somewhere and the light never goes out (which is the case).

This is the opposite logic to a gauge (fake in this case but it would apply just as much to a variable electric meter). Unlike the OP switch, a gauge has no signal with the ignition on but engine not running, and whereas a warning light switches off at start-up, this is precisely when a fake or real gauge comes on.

In my case I have a permanently energized warning light and a dead gauge, which presumably means they are independently actuated and is why I was a bit worried.

I know I have good pressure and find it hard to believe two independent systems would fail simultaneously. I can try a different switch, no problem, but do I have to dig into the instrument cluster to fix the dummy gauge? I saw the usual cannister type sender on an AJ6 engine but can’t find one on my AJ16. I thought the gauge was supplied by a fixed resistor independently when they dropped the variable sender?

The car owes me nothing and I know the oil pressure is fine but I’d prefer a living, if useless, gauge.

(Neil Bennett. Patron) #5

Hi Peter,
It is indeed an idiot gauge just like the temperature one. Jim Butterworth played about retrofitting a linear one and did a write upon his website which has a lot of day to day service and maintenance information on the X300, see:

(Andy) #6

When gauges are fitted as real gauges, the sensor and oil light are fitted into the same package and only use one hole in the engine.

It has 2 terminals. one for light, one for the gauge

This link may work:

For gauge wiring:
short to earth = zero oil pressure
open wire = gauge on maximum (and off scale)

It sounds like yours is the later car without a real oil pressure sensor, and the gauge wire is connected to the oil pressure light through a resistor.

(Andy) #7

anyway, just replace the oil light sendor with the same, and your problems should go

(gary breyer, 09 X358 LWB Sovereign, Liquid Silver/Warm Charcoal. Ex Ministerial car.) #8

They’re no longer called idiot gauges. They are now known as ‘The Crespin Gauge’!!

(PeterCrespin) #9

Long time no see Gazzer!

Still, I’m not bitter - it was bound to end.

(gary breyer, 09 X358 LWB Sovereign, Liquid Silver/Warm Charcoal. Ex Ministerial car.) #10

All good things must end Pete. Given time you’ll get over me but, in the meantime, I could send you some pics that may ease the pain:-)

(Neil Bennett. Patron) #11

Not with Iggy in place I imagine!

(j limongelli) #12

Guys remember the x300 was the first jag to run a 1 wire system through map programs, so one wire would do many jobs.
This did many things.
It eliminated the 300 miles of wire in the xj40 and reduced the costs and cut down the guess time for issues.
Today its the same but 10 times more modern.
Your xf/xj and f type had a dash with basically 3 or 4 wires which go to a map pad circuit that does EVERYTHING.
Th e xj6 was just an early version.