Increments of Oil Pressure Gauge

Hi Guys,

I was driving the other day in very hot weather here and noticed that my oil pressure gauge was reading right at the end of the red zone (although the idiot lights were not on). :open_mouth: I checked my oil level at the next stop, though, and it was at normal max. level on the dipstick. :relieved: I’m curious as to how the increments shown on the oil pressure gauge (face lift 4.0s) relate to actual PSI. I have heard that standard “acceptable” for oil pressure in all cars is 10 PSI per 1,000 RPMs of engine speed.

Later that night, when temps had dropped outside considerably, my gauge read in the usual range once again. All I can think is that perhaps it’s getting time to change my pressure sender unit (?) With very hot weather (and hot/thinned oil - I’ve been running 10-30 generic synthetic) it inaccurately reads low, perhaps (btw, this is the “true”, OEM type of sender)? Superblue has almost 90K miles on her now, so maybe that’s due … (?) The only other possibility I can think of is that maybe the PO had disconnected/bypassed the oil cooler system for some reason. :confused:

Jaguar issued a number of TSBs when I worked at the dealer. We always had customer concerns regarding oil pressure and engine temperature.

Jaguar’s answer was to ‘virtually’ eliminate the gauges and make them read mid-scale if the input to them was within parameters.

We always used Mobil 15W40 for the inline 6 and V12 engines. We still used that in 1997 when the XK8 was introduced but Jaguar wanted 5W30 in the V8s.

Here are some TSBs related to oil pressure on the 1990s era cars.

12-58 Engine Oil – Viscosity_Temperature.pdf (36.1 KB) 15-13 Oil Pressure Gauge – Fluctuation.pdf (33.8 KB) 88-20 Engine Oil Pressure.pdf (35.7 KB)


My barrel oil gauge on my 88 almost always reads around 50.

I have installed my own oil gauge, with electric sender. When cold, I get 70 at idle. When warm, I get 25-40 at idle. While driving, with some rpm, usually around 40-60.

Sounds like too light of oil…I use 15-50. Mobil-1. Synthetic. … Spring thru fall…don’t drive in winter…

I use 20/50. I’ve never driven a car that recommends such a heavy weight.

Thanks guys, I’ll try that then. btw, back to my original question, so if the oil gauge is, e.g., reading “1” then how many PSI is that (unless the gauge is blinky)? 10 PSI? :confused:

No idea. What’s important, though, is that it’s reading nonzero. And it’s reading pretty much what it’s always read, no dramatic changes.

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Good point, Kirby.

btw, in light of my new 5.3 finally on its way here from PA, I decided to go to the old JLers website earlier tonight and look around for your XJS book. Found it. :smile: Funny thing is I started to print the whole thing off for the second time - all 730+ pages (double-sided THIS time, though, to save paper) - when I noticed, fortunately in time, that you mention in the preface that the Book is also on the Nine Lives CD. I guess I had forgotten about that inclusion. Phew! :relieved: That saved me a chitload of copy paper and toner! That Book is really a major labor of love, btw … How did you ever find the time to write it? :confused: You are to be applauded heartily for putting it together, dude … :handshake:

btw, it is now a little over 10 years since you last updated the Book. Do you see any reason to do so again anytime soon, e.g. anything new, changed, discovered, etc. about the 5.3s since 2009? :thinking:

My 94 4.0 coupes oil pressure gage was all over the place. When I did the coolant system I replaced the op can with a sender which was part of the TSB.

Now the gage is dead center under all conditions using 20/50 Dino oil.


I have literally thousands of notes and emails saved, intending to make additional edits to the Book. Just don’t seem to get around to it any more. I started doing some perhaps a year ago, but didn’t keep at it long enough to justify a new release.

If and when I do issue a new release, it’ll be in LibreOffice document format. I’d like to convert the whole pickin’ thing into HTML as a web site with a few hundred pages (and far more photos!), but it’s just too much work. I also plan to purge quite a bit of stuff from it that’s either not particularly helpful or just plain wrong. Simply editing the outdated information – including dead links – would be a serious undertaking.

you should try crowdfunding it, I’m sure a lot of forum people would contribute. Although it sounds more like a time problem, not a money problem.

Too bad you can’t crowdtime…

So I run Mobil-1 20-50 and have put in some instruments to check temps. Cold the oil pressure is past the 4 (40psi?) and at 80mph on Cruise Control the pressure slowly drops just over the 2 hash mark, this is with the RPM at 2800, it takes about 30 miles at this speed in 90F weather for the oil temps to stabilize. The hot oil is about 230 and the pressure is just above the 2 mark. When I get off the interstate the pressure drops to just above the red at idle. Hot around town it stays below the 2 mark. This is with 230k on it the last 100k by me.

I’m retired, have plenty of money and time. It’s inclination I lack. How do you crowdfund that?

Farm out the work to us! :wink:

Thanks for the data. Is your cat a 5.3 or 4.0, btw?

A 94 6.0L with VDO gauges for oil temps and H2O temps.