XJ40 ( XJ81 ) 1986 - 1994

Oil Pressure Switch JLM 20791

Old 07-26-2018, 07:04 AM
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Default Oil Pressure Switch JLM 20791

In my research, I am seeing that the replacement part to resolve 'LOW OIL PRESSURE' at idle is JLM 20791. Research shows that this replacement part will always read mid range on the gauge as long as the oil pressure is above 7 psi. so in reality you will not be getting a real oil pressure reading on the gauge.
Mid reading on the gauge is 40 psi. So with the dummy replacement oil pressure switch, if my oil pressure is 7 psi or higher, the gauge will read 40 psi. As I understand it, Jaguar made this change after many, many complaints about the OEM switch/sender failure to pacify the customer base.
If I want my oil pressure gauge to display the correct oil pressure (which it should) what should I do?
Is there an oil pressure sender available to replace the OEM sender that would display the correct oil pressure on the gauge?
I am sure that other members on this forum have successfully used JLM 20791 with no issues, but I can't seem to wrap my head around driving a car with (hypothetical) 7 psi oil pressure and a gauge that is displaying a rigged reading of 40 psi. Or is this the only choice I have?
Also, I am about to purchase a head gasket set to resolve the oil leak above the distributor and I also want to purchase the oil sender unit. Not having the opportunity to look under the intake manifold, is there a oil pressure switch for the light and an oil pressure sender for the gauge? or it it one unit that does both light and gauge.

Old 07-26-2018, 01:45 PM
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It's a FORD thing. Ford started using the switch/mid-scale thing in about 1997. Jaguar was forced to follow.



These should work as actual transducers, not switches.

Old 07-27-2018, 12:33 AM
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It seems we're lucky, because as I recall, X300 vehicles were originally equipped with pressure transducers but were modified with pressure switches and, more importantly, a software update to the Instrument Pack which would prevent any kind of retrofit back to the original transducer... My 1996 XJ12 is one of those vehicles.

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