I have had this happening since I bought the car, it has done about 15000 miles since then
When the engine is cold there is about 20 psi on the gauge around town(up to 30-40 at highway speed when temp is not up to normal),and drops to zero at idle, once the engine is at normal operating temp the pressure will run between 10 and 20 psi at highway speeds(some times as low as 5 psi),0-10 psi around town,often 0 psi at 40-60 km/h.
I have never had the oil light come on except on starting the engine as usual.
I am running 15w40 oil as the book recommends. My initial thought is the oil is getting thin with engine heat and giving a low reading ,I'm about 2000 km from next oil change so I thought I would try an additive to see if a heavier grade oil will help, if it doe's what oil grade would you recommend.
If it makes no difference I will try the oil pressure sender next,$75. after that the oil pump $140.
I do have a spare set of gauges but thought if the gauge was faulty it wouldn't be so predictable as it is.

It is not a pressing issue, but do want to sort it eventually. I drove it 500 km at 70-80 mph 2 weeks ago(gauge between 0-20 psi the whole time), and did 250km yesterday at near 40c temps and same thing.

I have owned plenty of cars with no oil pressure gauge and just relied on the oil light for a warning, will the oil light give me warning if the pressure is too low?

 

Faulty pressure sender is my first thought. Not uncommon for these to fail. I agree with you, that because the issue occurs predictably the gauge isn't most likely. Oil indeed gets thin when warm.

You should be fine a long as the oil lamp doesn't come on.

If the pressure level indeed is low, it could be your pump or the overall engine condition. Old, worn engines usually have lower oil pressure as well.

I am running 20w50 oil, which will give higher pressure. Unless you live in cold areas this is fine.

 

15/40 is very thin for an old engine in our warm climate[i can understand that grade in the UK], i would run 20/50 or even 20/60[penrite extra 10] and see what the pressure difference is or install new main and big end shells

 

That was my line of thinking, try the 20w50 or penrite first to see what happens before throwing parts at it.
Don't know the mileage or history of the engine, it has good compression(can't recall the figures right now and car is away with my books having suspension parts fitted), and blows no smoke,uses no oil and makes no unwanted noises.

 

Yeah, I had my adventures with the Jaguar sensor. Erratic numbers. but, my car is fitted with an LT1. Hydraulic lifters sound off when the pressure is low. they were quiet, so I wasn't alarmed. The idiot light light didn't come on either.


I went shopping for a mechanical guage to verify. found none,. but, I did get a Sun Pro accessory set. Plumbed and wired and it showed good numbers. All is well!!


I got a NOS sender from David Boger of everydayxj's. All is well.


I've a bias as to the low viscosity oils, from a misadventure way back in my early 20's. It cost the engine in my net 47 Ford V8!!!


My present cars do just fine on 20/50. But, tis a mild clime. If t were reallycold, I'd have to rethink that !!!


As to the idiot light, if it comes on, it's usually bye bye baby!!


Although, I bought a nice 71 Mustang with a really tired engine. it's less than ethical PO had removed the bulb. It clunked on firing up at times, and smoked a bit more than a tad. But ran really well. A great sounding set of pipes on it.


I got it looking decent and fixed some anomalies, but tired of it and sold it .


Carl

 

Clarke,

Dont buy the snake oils, waste of drinking money.

I run 15W/40 in the V12's and the XK 6 cylinders, and 10W/40 in the X300. SWEET as, even in our 45+ summers. The XJ12 in my "garage" has topped 500K kms and still runs 15W/40 Nulon.

Jag oil pumps and for that matter, bottom ends of engines, rarely give grief, they are sooooo big and strong.

Wait till you strip an engine, you will 2 STRONG guys just to lift the crankshaft.

Flow is more important that pressure in MY opinion.

 

1. By snake oil's I guess mean additives?

2.I have 6 x 5 ltr packs of 15w/40 Nulon from a sale a few months back($14.99 for 5 ltr), stocked up for the Jeep & Jag then sold the Jeep.

3.The lighter grade oil would give better flow?

If it doe's turn out to be the pump, is a second hand one worth touching?
Jaguar Oil Pump 4.2L - C21765

Pressure sender is $115 from Jagdaim or $90 delivered from ebay.
Jaguar E Type V12 XJ6 12 S1 OIL Pressure Sender Twin Terminal C31177 | eBay

Not sure where this is going yet, just gathering info and opinions for now.
Front end has to be finished before I do anything else.

 

What is considered normal oil pressure in these engines?

The bar scale on my Series 3 makes it next to useless for me (about 30psi cruising), I'm assuming the real engines run very high oil pressure.

FWIW I run 10W40 in the modern cars and all the assorted small machinery engines, and the Penrite 20W50 in the older engines. The only real difference I notice is that the BMW's top end sounds very rattly when cold if I use the lighter oil.

For those that havent already discovered this site is a good one to get to the reality of oil grades/usage/additives etc Used Oil Analysis - Bob is the Oil Guy - Bob is the Oil Guy

and sorry Clarke for the thread drift

 

40 psi at 3000 RPM

Steve, it only takes one post to get back on topic.

 

Clarke,

I have seen some seriously sad XK engines over the years, and near NO oil pump failures. I would be surprised if the pump is at fault, they simply are a tough sucker.

The Smiths sender unit on the other hand, SAD. We have some in stock during my time with the dealer that leaked at first start up once fitted, and others that read all over the shop.

I use a VDO 360006 with an adaptor on the V12 engines, and it is sooooo accurate and being VDO is reliable. No reason it wont work on the 6cyl.

I have had a Ryco Oil Pressure Tester for 40+ years and has served me well. Probably not made anymore, but any mechanical style gauge with a flex hose attached (proper hydraulic hose please) and some simple adaptors and you are done.

The XK engine has a 1/8BSP thread on the oil filter housing that has the idiot light is screwed into it, and that is one place to tap into for the test.

I forget the specs, but 20PSI +/- at idle HOT and 40ish at 3000rpm rings a bell.

Once you confirm the actual pressure, peace of mind sinks in, and the dash behaviour becomes less of a panic.

 

Grant,
1. spot on from what I read in my small but growing XJ library, ordered more books today to add to it.

2.Not a lot of panic going on, I have been driving it like that for 10 months. Including a few trips to Armidale, Ballina and Sunshine Coast.
Also did that 80-90 mph 340km run from Coonabarabran to Goondawindi with it reading around 20 psi at 4000rpm on the same weekend we covered 1200km when the temp was running too cold.
Put it this way, I would drive it to Melbourne tomorrow without batting an eyelid. Actually I am loaning it my brother next week while he is in Brisbane for a week.

Do you reckon this gauge will do the job? I have a local hydraulic guy who could make up the connector.
13pcs Engine OIL Pressure Test Tester Tool KIT SET Diesel Petrol Gauge CAR Truck | eBay

 

Perfect.

 

"Also did that 80-90 mph 340km run from Coonabarabran to Goondawindi with it......"

naughty corner for you!! :-)

 

Loong straight road passing road trains, flat ,smooth and fast. The wife didn't even notice we were cruising 30-40 kph above the limit because we were being overtaken constantly....and not that long after I got my licence back

Will be bidding on the gauge tonight.

 

No room, I'm still here.

Last round OZ trip in the XJ-S and coming out of Mt Isa, heading for Darwin, and gaining on a road train, as you do in a V12, and pulled out to overtake at about 140kph, and "oh bugga" there are 3 of them.

Too late now, pedal to the metal, and hang on for the ride.

Topping well north of 200 at the other end and the damn thing was still climbing, damn I miss the V12's, A LOT.

Ya need a V12 Clarke, trust me.

 

Well Kirsty(her indoors) did fall for Paul's Goose, I think that leaves the door wide open. Just the budget that is lacking.

Got the gauge for less than $17

 

Well, an old rule of thumb fore oil pressure is 10 pounds per 1000 rpm.


The sender that came with my Sun Pro after market set worked well. More robust than he Jaguar unit. it had two options, one made my guage read just about like the jaguar unit did, when it was working correctly.


Wow, 17 bucks for that neat tool, what a score.


Well, the GM starter in my car is biting the dust. It refused to crank yesterday. Luckily, in my drive. A couple of bangs with one of my sheleaghles and it complied.
Rebuilt unit on the way from Rock auto.


Carl

 

I hooked up the mechanical pressure gauge today,took out the oil light sender and screwed it straight in with one of the many adapters it came with.

Running at idle I had 35 psi, nothing showing on dash gauge

at 3500 rpm it was showing 50 psi, the dash gauge was showing just shy of 20 psi.

Have ordered an oil pressure sender today.



$17 is cheap for peace of mind, not sure how accurate the Chinese tool is but even if it is reading high I'm running way more oil pressure than the dash gauge is showing.



Thank you all for your input.

 

Back around 1970 I saw a guy put another engine in his E Type because the oil gauge read low. Once he got the new/used engine in, it read the same. Until he finally replaced the sending unit.

 

That is an interesting diagnostic approach. All good, as long as he is spending his own money I guess.