Jaguar Repair: oil warning light, oil pressure gauge, hydraulic gauge

Question
Hi,
On my XJ6 S3 - the dash oil warning light started to come on the other day. Checked the levels, topped up the oil but it remains on. The oil pressure gauge shows good. I've noticed that when the engine's cold the warning light disappears when the engine's speed is above 2000 rpm. When warmed up it remains on at all revs. Could it be a clogged oil filter or anything else? Thanks. Jérôme

Answer
Hi Jerome,
The oil warning light and the oil pressure gauge sending units are on the engine block plugged directly into a main oil galley so both are receiving the same pressure what ever that is. If your oil pressure gauge says good and the light says bad, one of the two is wrong. It is rare for a gauge sending unit to fail in a mode that it reads good when you have very low pressure, so it is most likely either a light sending unit failure or a wiring problem.
"Most Likely" is not sufficient when you are talking about something as important as oil pressure. Electronic oil lights and pressure gauges are less reliable than direct hydraulic pressure gauges.

So You "MUST" get a direct hydraulic gauge and fittings to check the actual pressure to be sure. Most auto parts stores have these gauges as accessory gauges. They are not expensive and then can be used as one of your diagnostic tools from now on.

To confirm that the light and the wiring are ok, remove the wire off of the sending unit. (the small unit screwed directly into the side of the engine block on the right side) Turn on the ignition and note that the light is "Out" then ground the wire to a clean metal part of the engine and confirm that the light is "On". If the light works as I indicated and the hydraulic gauge reading is good, You just need to purchase a new "Light Sending" unit.

The Larger unit screwed into a small aluminum block that is bolted to the right side of the engine block also, is the oil pressure sending unit.
Howard