89 XJS Running on the Hot Side, No Oil Pressure at Idle

So as I mentioned in my project post a few days ago, I have an 89 Jaguar XJS that was not running when I bought it and I completed an overhaul of most components on the car (short of pulling the engine). I took it out on its first outing to a Jag event last summer and as it goes I was a bit pins and needles driving to the event not knowing how the car would behave. It ran fine for the hour each way it took to get to and from the event, however I was a bit troubled by a few things. In stop and go traffic, temps were hitting 210 on the aftermarket gauges (75 degree outside temps), and as is common, I had zero oil pressure (engine has around 120k on it). What is a bit surprising is it has a brand new radiator and new tested thermostats in it as well as being well bled so I was a bit disturbed being that close to boil over. Those types of readings in stop and go traffic make me nervous. I guess my next plan is to change out the thermostats to 175’s, throw in some water wetter, change the oil to 20/50 and go from there. The engine runs very good so I am not inclined to pull out and rebuild it just yet. As far as fans, the car has the original pully fan as well as one of those new auxiliary fan setups from Moss. Aux fan was on at the higher temps and overall airflow seemed to be good. Temps were lower at freeway speed. Might need a new fan clutch. Thoughts? Thanks.

Oops, looks like I had this in draft from last year and hit the publish button. Well, I haven’t had a chance to mess with the car since last summer so, still some issues. I believe part of my problem is I need to set the timing. Duh, I guarantee it is off. I set it by the sounds good method!

Zero oil pressure showing on the barrel gauge, zero oil pressure shown by the low oil pressure light being on, or zero oil pressure on a separate oil pressure gauge?

Also, what does the barrel oil pressure gauge read when first starting the car, as the car first sets there and idles, and than as the engine warms up?

My 83 starts a ‘no reading’ on the gauge, then slowly raises to 100, after which it slowly drops to 50, then slowly drops to maybe a 5 or so reading while idling, but goes back up (40-50 range typical town driving as I recall).

If the red low oil light is on …, yeppers, you’ve got low oil pressure for sure.

If the barrel oil pressure gauge reads almost nothing continuously, does the reading even move? Could be a bad oil pressure sending unit, or wiring to the gauge?

The car has 60 to 70 PSI cold when started. After an hour or two of driving I am having no oil pressure on the dash gauge and the mechanical oil pressure gauge I installed when sitting at a stop light idling in gear. No low oil idiot light. The car has about 126k on it but otherwise runs very good. I am actually going to swap out to 20 50 oil shortly and complete and oil change. It has 10 40 in it now so that will likely help.

And as a mention, when you hit the gas, the oil pressure comes back up I believe to 45 PSI or so even when hot. Just non existent at idle, but, I have been told it is pretty common, but definately not something that gives you a warm and fuzzy feeling!

I run 20W50 in mine.

Based on what my mechanic told me years ago when I had a similar concern, he said that there is sufficient oil pressure and not to worry about … unless the red low oil pressure warning light comes on … in which case pull over and shut the engine off!

Yes. Took me years to get used to that needle being so low at idle. Used to bounce at bottom of gauge with fully warmed engine. As long as the red light stayed off I learned to just accept it.

20w50 definitely makes a difference for me. Not using synthetic anymore, my mechanic convinced me to go with design spec regular oil. Dino 20w50 and change at 6 months. 65 psi on crank. 20 -25 psi at idle when fully warmed. 6.0 liter v12

Assuming sea level and at 16psi cap, boil over would be something like 260ºF.


If ambient temp was 95 or 100ºF I would not be too surprised at seeing 210ºF on the temp gauge in stop-go traffic. But at a mild 75ºF ambient the system should be able to hold about 190ºF coolant temp. Something isn’t quite right. Did you install the correct thermostats? You have to measure the length.


If the engine is running 210º then it makes no difference if you have a 175º thermo, or 195º.

Good conclusion; I agree.

You’ll get used to it. :slight_smile:


1 Like

I heard, but don’t recall who I heard it from right now (probably will later), that there were so many visits to the dealerships for “low oil pressure”, that Jaguar eventually stopped putting in ‘real’ oil pressure sending units, instead putting in oil pressure switch sending units which would, when oil pressure reach sufficient psi, ‘switch’ to read around 50-80 psi (regardless of actual oil pressure).

And that the “low oil pressure” visits dropped to almost zero. It serms that people then said ‘Jaguar finally found the problem and fixed it, maybe thry redesigned the oil pumps?’ :roll_eyes:

Yes. They issued a TSB. And cane up with new part

Yup, and Jaguar is not alone in this. The so-called “dummy gauges”.

And coolant temp gauges as well.

For example, on my X300/XJR the temp gauge would give the exact same reading (one needle width below N) from 175ºF to about 220ºF. After that, it would rise. Same for the oil gauge, although I can’t remember the pressure window.

I can’t recall if Jaguar used a dummy coolant temp gauge on the XJS.

From my own dealership days I can attest that customers are often anxious about gauge readings, sometimes inconsolably so.


1 Like

Jaguar may have used those coolant sending units in later XJSs, but, in my 83, the coolant gauge rises slowly, will go above N, then back down or up, or up even higher (stuck in traffic), then down again (fresh air on highway), so I’m sure they didn’t do that in 83.

Unless they crafted a varible circuit just to move the gauge around.

I can see <---- (where did that come from?)

If they did it would’ve been on the later cars, maybe 1994-later?

Behavior which has caused considerable anxiety among V12 owners over the decades

Not that I’m aware of.

But on the Series III sedans Jaguar did use some trickery in the 80s. Some cars…nobody has ever established a pattern as far as I know…had an inline resistor added to the temp gauge sending unit. The part is clearly shown is the parts catalogs. The purpose is to lower the gauge reading.

My conclusion is that these resistors were installed as-needed. I envision a guy at the end of the assembly line with a pocket full of resistors. On the cars where the reading was too high he’d slip one into place :slight_smile:


My 95 V12 shows logical reactions in the temp gauge

Regarding oil pressure, when I removed both upper and lower oil pans on my V12, I had the opportunity to remove the oil pump piping and replace all O-rings in there. I replaced the old rubber Orings with Viton Orings, as recommended in The Book by Kirby.

I noticed my oil pressure slightly improved (it was already running well)

so, you are cocerned as to two issues. Iverheat and oil pressure.

  1. Perhaps, the after market guages are running hot. is the OEm guage functioning? What does it show? Get an IFR sensor. check varous sots on the engne.
    Swappong stas does nt cure a overheat condtion. @10 is nt that bad. I prefer 190 to 299. F of course. But, yes, it may be the mechancal fan. Not enouh air flow at low speed. Test the viscus coupling.

  2. If you really had zero oil pressure you would ha ve not made it to the Jaguar event. Stuc k on the side of the road with a ventilated engie block. Oh, I ave bbeen there!!!

But, yes, as temp fges up OP ges down.

My moneyis on faulty after marked guage. or what s quite common, Teh OEM sensor.

I had that issue in my lump. I kew I had OP. No valve rttle.

A new sensor fixed the low OP on he guage.

Teh sensrs are far from robust.


A few years back, on our 1990 XJS, I replaced the white OEM white cooling fan with the updated black version and I replaced the stock thermal viscous fan clutch with a new heavy duty version I believe GM used on 455 station wagons. These changes had a huge positive effect on engine temperatures that also resulted in a improvement in the idle oil pressure because of lower operating temperatures.
Our car only had around 30,000 miles when I did the work and I believe the stock fan clutch was completely free wheeling.

I agree on your thought process, I have thought about the fan clutch and how it might be toast. I just ordered two new clutches for my cars. I already have the black fan in it. So between that, thicker oil and a few other things, I think we will be in good shape. I also replaced the old style auxiliary fan with the revotech model which works really good. My coupe already has a full electric fan setup. Funny, some folks switch back as they are loud, but, it is nice because they don’t shut down immediately when you shut the car off.

1 Like

Having the same problem with low oil pressure on two xjs’ s . One was resolved by using an oil engine cleaner as residue builds up in the oil pressure relief valve. Once functional oil pressure keeps around 20 and 50 on start up. Many forums mention to change the oil pressure sending unit. Done that and new oil change and pressure keeps well for one or two runs then runs low again. The other xjs has same problem but red warning light of low oil pressure . Not quite sure what to do. Some mention repairing the oil pump itself. From my understanding low oil pressure is due to worn bearings but I am not a mechanic. I only have experience from repairs on several motors. Anyone has any suggestions whether it should be an engine rebuild or just an oil pump problem or possibly a completely blocked oil pressure relief valve ?

As an update, I recently finished rebuilding a V12 for one of my projects. After starting the engine up for the first time, I immedately noticed the oil pressure wasn’t where I thought it should be for a new engine (30 psi) and was thinking the worst. I had a thought that maybe it was the oil filter. You can buy oil filters that will spin on, but aren’t very big. They will say they are a fit, but such a large engine, the smaller filter was suspect to me. I bought a full size filter and the change was instantaneous. I have 80 PSI oil pressure at start up that settles to about 60+ when warm. I plan on switching the filer out on my convertible when I get it back in the garage. I don’t recommend using anything but a larger filter for these engines.

1 Like