Oil pressure light (again) grrrrrrr

Yes its annoying and the last one lasted ~8yrs or so and as I remember a bitch of a job to change — so getting ready to order another LMD5640AB, almost caved and went for the idiot switch this time but to heck with it, I LIKE a real gauge so off we go again.
Seems to me that I remember Bob made up a wrench to do this job …If you’re reading this @motorcarman , wouldn’t mind a pic so I can make one up myself …
Oh and BTW has anyone had any luck cleaning one of these units? I think most of the time they just get plugged up with crap and if they can be cleaned, well, $50 saved eh? I imagine a good soak and shake in diesel might do the job - what say you?

Looking at this unit, any opinions on whether or not this would work? I can’t see why not but …

Larry …

First we can all agree that the original equipment oil pressure transmitter is; A. Overly expensive, B. Very difficult to get to and, C. Usually very unreliably.

The AJ6 engines used in our Jaguars are very robust and I believe the last time one of these engines actually lost oil pressure was three and a half decades ago when a wayward bullet from an English Duke’s bludderbuss punctured a royal’s crankcase while out on a fox hunt … :yum:

Being a more or less “purest” as far as my Jaguar is concerned after replaced my “original” oil pressure transmitter 3 or 4 time over the past 30 years I decided that I could indeed live with the new “idiot” oil pressure switch that the Jaguar company itself actually started retro fitting their cars with.

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Fair enough. I’m toughing it out and sticking with the oil can type though as you can see I’m going the el cheapo route.

They’ll probably take my driving licence away before I need another one anyway, so what the hay. :grin:

Hi Larry, just in case you change your mind and decide on the ‘upgraded’ pressure switch bear in mind you will need to make two different sized tools, the original canister type is 19mm A/F but the replacement ‘upgrade’ fixed type is 21mm A/F.

I think I remember reading on some forum years back that there was a GM transmitter that fit and worked. Maybe these are more reliable than the “Jaguar” ones?

Larry …

I seemed to recall that years-s-s ago when I had trouble with my original transmitter I sprayed brake cleaner in the small intake hole and let it sit overnight. I then sprayed it again in the morning and after letting it sit for about an hour blew it out with compressed air holding the nozzle about an inch from the hole.

It worked fine again for a few years and then slowly I had the same problem. The trouble with this is of course that because the transmitter is so hard to get to that if it doesn’t work it’s a lot of wasted time.

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Thanks for the info Casso, however I’m pretty sure (not definitely) that the original part is just a plain ol’ 3/4" (which is of course roughly 19mm LOL) with 1/4 NPT thread? Part goes back to the 1970’s AFAIK

Well John, sacrilegious as it is, I ended up getting one from Walmart! the single pole one gloss finish …


Well that’ll be my strategy too, a good swill-out and clean. I don’t think these units actually fail electrically - my bet is they just get plugged up, or at least partially plugged up with crap.

Gonna fit the new C$17 Walmart special though … they’re all probably made in China now, regardless of branding so who cares.

Larry …

Well maybe China, but since Jaguar Cars is owned by Tara motors maybe you can pick one up in India.

Larry, Very interesting. So this one is the type that allows the gauge to show varying oil pressure? What are what appear to be two electrical connections? I thought the OE type had only one male spade connector. I do not think they get clogged up. From my Jaguar warranty days the word was the rubbing coil inside would wear out from constant variation in oil pressure but I have never had one apart to see the innards.

Yes these are transducers so indeed they do show varying pressure.

If you look at the options on the linked page, you’ll see there are three types available. Select the single connector one and the illustration will change. The single spade type is what I purchased. The types with 2 connectors would also work, but the second terminal is the low pressure “alarm alert” for vehicles or gauges that have that function.

I don’t think anyone today working at Jaguar cars or their parts dept. have any clue what an XJ40 is let alone anyone skilled enough to work on them or order parts. Different world now Dennis!

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Well John this same unit has been fitted to Jag engines from way before the XJ40 and it seems that the main failure rate was (is) attributable to the XJ40 fitment. It seems to be fine on earlier cars. Some say it is the temperature (I don’t think so as all engines would get hot) and others say location or position/orientation …possible, as horizontal fitment could be more prone to leaving residue inside the unit which over time could build up. The unit would always be 1/2 full where a vertical fitment would allow the unit to drain.
I believe that is the issue, which could possibly be remedied by fitting and L shaped adapter or piping the unit out of it’s home down next to the filter and relocating it vertically in another spot. Just my 2cents.

You could be right, the one on my 1965 3.8S has been working OK for decades. It is a vertical mount but I thought the one on the XJ40 was also a vertical mount but I could be wrong, haven’t looked at it being so inaccessible. .

I found pictures of the tool used for the replacement: https://www.jaguarforums.com/forum/xj40-xj81-25/oil-pressure-sender-133621/

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John it is a horizontal fitment on the 40. On the 94MY it’s even less accessible from above because of the placement of the air pump. I intend to remove the air pump and try to do the job from the front. I suppose I could remove the throttle body and associated plumbing and go in that way too but I think I’ll try going in from the front first. Last time I went from under the car and had to remove the oil cooler bypass before I could get onto the 3/4" fitting and even then it was a nightmare.

A ground down 3/4" crowfoot. Good work - thanks!

Larry, the one time I did this job I did as you suppose and used a crowfoot wrench (didn’t have to do any grinding) and I don’t recall it being a difficult job.

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Thanks Mike, always good to know a fellow 94’er says it’s possible to go from the air pump side and not be a total PIA as I’ve been led to believe!

I go forward with renewed optimism …just have to wait for the part to arrive from China now!