High oil pressure on gauge

They’re all made in Spain so doesn’t matter which one, you will still need a resistor in series or it will pin the dial.

RockAuto have them also.


I found this…

guys … I have a big confusion! then the code for my 1987 Daimler 3.6 seems to be ca46272 and from the photos you can see that it does not have the resistance we are talking about … then there is this jlm20791 that has the resistance but I don’t understand if it is compatible … but someone with a good heart could not give me a link to buy … and maybe even give me the link for a sensor for the water temperature :crazy_face::crazy_face::crazy_face:

What is in your picture which looks like a simple on/off switch so I do not understand how it can send a variable signal to the dash gauge even with the black resistor shown. Maybe I am missing something. I do recall that Jaguar, circa the 1990s, had warranty issues with the senders that provided a variable signal and that prompted them to go with what Ford used on their cars, such as the Crown Victoria, that did have a dash gauge, to go with the sender that put the gauge continuously in the center position. GM vehicles that had a gauge (pickup trucks as I recall) had real operating gauges. They must have found a supplier that made a more robust sending unit. I even remember a post somewhere that someone found a GM unit that worked properly in a Jaguar. Cannot recall the part number. Jaguar had been using operating gauges since the early 1960s. Why did the unreliability issue surface in the 1990s? Or was it really just a cost saving change?

So … let’s assume that I prefer to see 40 fixed instead of 80 … what do I buy ca46272 or jlm20791? Why I don’t know which one screws on my jag … and for this blessed water temperature sensor do we have any code? Because I went to the jaguarclassicparts section, but finding these 2 sensors is not easy at all.

If you want the gauge to read in the centre, your “40 - fixed”, then just buy the switch, JLM20791. Either that one or the pressure gauge will fit, threads are the same and both need the resistor. The original CA46272 is no longer available. Aftermarket replacements work but are calibrated differently so need the resistor in series to agree with the dash gauge.

The coolant temperature sensor is widely available and fitted to many other cars not just Jags. The Jag part number is DBC3728

see here:

part 9 in the pic

… grande! :crazy_face:

Due to the placement/orientation of the original transducer in the XJ40, there was a tendency for the small orifice to become plugged with a bit of carbon or gunk/whatever. This blockage prevented the oil from pressurizing the diaphragm so the gauge read low or zero. The units themselves didn’t fail, the blockage was the problem. They can be cleaned out too, so I’ve heard.
At one time I considered repositioning the transducer unit higher in the engine compartment and installing it vertically but just said to hell with it and bought an aftermarket one from RockAuto and added a 75ohm resistor.

BTW, If you don’t add a resistor and can put up with a high reading for a while, by the time the next oil change comes around the orifice will have already started to plug up and the gauge will start to read lower on it’s own! :smile: :smile:

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Interesting, Thanks for your insight. I was always told it was the internal wiping contact that tended to burn out due to movement across the coil as oil pressure changed.

John - are you perhaps thinking of the throttle position sensor (TPS)? On the XJ40s they tend to become contaminated with the oil and gunk (is that a technical term BTW? ) that can collect in the throttle body because of the design of the crankcase ventilation system. But they also wear especially in the ‘sweet spot’ that is the normal operating range.
Side note: do you still have your Austin (#3 in the owners registry IIRC)?

Austin 1300 (America) yes, still in my possession and in regular use.

My 1990 XJ6 suffered from the sticky throttle off idle syndrome back circa 1992 a few years after I bought it. Jaguar launched a bulletin and a retrofit kit to address this but only for somewhat later cars, I was able to modify the kit and use part of it on my 1990 car and I have never had the issue since. It comprises a re-piping of the breather hose, introducing a T fitting and a drain line to a new dipstick tube which has a branch to accept the drain tube.