That is rather interesting OB. You have the full flow system, so I can only guess that it must be to do with the pressure differential in the oil feed system. With the cooler in place, it is pretty likely that there is a pressure drop over the cooler, as the oil has to be forced through the cooler passage ways. A bit like a hosepipe: given a decent mains pressure, if the water goes first into a small diameter hose, then into a larger one, there will be a pressure drop from the one to the other.

In your system, after the cooler, the oil goes directly to the main oil gallery feed system, and the pressure sensor is plumbed into this, via the cam feed arrangement. As your cooler is bypassed, any normal pressure drop is absent, and I guess (repeat guess) this is why you are seeing the higher pressure, as the sensor is seeing pump pressure without any drop across the cooler.


I think that there are two ways excess pressure can be vented in the full flow system:

1. the pressure relief valve that vents into the sump via the question mark pipe, and
2. there is an internal one-way spring-loaded valve within the filter head. This is fitted (I guess) so that if the cooler gets blocked, oil can short-circuit the system and go straight to the main gallery to fed the engine.

I am guessing that these have come into play, and that the pressure you are seeing on the gauge is being limited by one of these. Whereas with the cooler, they are probably still doing the limiting, but additionally the cooler pressure drop reduces the gauge reading. Interestingly, a pressure drop does NOT mean lower flow volume, any more than the wider hose flows less actual volume than the narrower one. So there is no need to worry about the bearings having insufficient oil when you reinstall the cooler!


All the bearings need is a sufficient volume of oil, so they can "wind the oil" through the bearing like clothes through a mangle. The importance of oil pressure is NOT to "force" oil though the bearing; rather only to make sure there is always enough oil at the "entrance" to the bearing to ensure the mangle never runs out of clothes!


Excellent spot though!
Greg

 

That certainly is a big difference!

Two things I see that affect my oil pressure readings may have some influence here.

Your engine temp is lower in the high pressure shot. Oil pressure here is much higher when warming up than when hot. But there's not a whole lot of difference in your two shots.

Also, you're outputting well over 14V in the high pressure shot while the other is below the charging line. the engine wasn't revving in shot two was it? I assume both are at idle, just asking.

 

It can also be the temperature.

Is that picture with the oil at temperature as well as the engine or just upon cold start?

 

Hi Greg

That is interesting!

But now I am starting to wonder if an Oil Cooler 'is all that' in a Temperate Climate like in the UK.

Even driving around the Garden on a really Hot day, the Oil Temp has 'SO FAR' never gone over 110o/c which 'I believe is the ideal Oil Temp'

 

Hi Jig Jag

Those two Photos were never taken in order to make a Comparison, I've just got into the habit of taking Photos of Various parts of my Cars.

Also there was lots of Battery Swapping, as when the battery on my Merc was starting to run low, I'd put it on to my XJS when I went for a run to charge it up.

But the Change in Oil Pressure on 'Cherry Blossom' since I fitted the by-pass pipe, was a real sight to behold, as it straight away went up to 60

and never dropped below 40.

Even when the Engine was nearly up to Full Temp.

This was only driving her round the Garden and things could be very different when I get her back on the road.

So 'if and when that happens' a Full Road Test will follow.

As an aside, I am very impressed with your 'e' Fan and the way that you fitted it into the Fan Cowl, which when you think about it is a 'Tripple Threat'

Two Speeds on the 'e' Fan, plus the AUX Fan as an extra back up.

Mechanical Fans for pre-facelift Cars are now very hard to obtain but what you have come up with seems an ideal solution.

The Main Reason that I ditched my 'e' fans, was that they made my XJS sound like a Sewing Machine but if your 'e' fan is Silent and will fit the Shroud.

Then that would be something, I'd definitely consider.

 

Pressure and flow are intrinsically linked. I like the garden/fire hose analogy.

Turn on your garden hose (without a nozzle) and water flows out the end, put your finger slightly over the end and you raise the pressure inside the hose, the result is that water spurts further, the volume of water won't be much different.

Now connect a fire hose to your garden tap and watch the water dribble out the end same volume of water as the garden hose but much less pressure in the pipe to push the water out.

 

@OB

Why are the mechanical fans hrd to get for prefacelifts? Jaguar still sells them... Okay, now black, which is better due to a longer lifespan (black will nlt fail as quickly) but tomcall it hard just because the shabby old white ones aren't about?

Heck, iirc they are the same as the Volvo ones from the RWD models. Ifmyou really insist onnhaving a white one, then one of them will most likely fit. Most just have 7 blades instead... Some habe more...

 

The black "OEM" fans now supplied by Jaguar are the shoddiest rubbish I have ever seen. I also have a feeling OB found they do not have the correctly dished centre?
I have recently fitted the still-available original quality white fan as used in the XJ40 (I think) to an XJS, ditching the shroud and using a 20mm spacer to get it closer to the rad. This cools the engine fantastically well.
Greg

 

In which way are they shoddy Greg? I mean, they can't be worse than the plastic fan blades fitted to most electrical fans...

 

How do I adjust the Handbrake?

I should know how to do this but I don't and although its never been a problem and has always worked and can even pull the Car to a Stop at low speed.

After doing some research on how they test the Handbrake for the MOT opinions seem divided as to how this is done.

From how many Clicks on the Ratchet, to holding the Car on an incline, or to Test it on the Rolling Road.

The tiny little brake shoes (comparatively speaking) on the XJS Handbrake do seem very vulnerable to being Torn Off in a Rolling Road Test.

But how is it that some Shops are happy to Test the Handbrake on the Rolling Road and yet they insist on using a Tapley Meter in order to Test the Rear Brakes.

It would seem a lot depends on which Shop you go to, as in my own experience this procedure can vary quite a bit.

So I would like to know how to adjust the Hand Brake, as with the 'Wind in the right direction' some Shops may let you give it a 'Tweak' while you're there.

 

On the rear of the handbrake lever. Remove the cover andnyou'll see a nut...

 

Please forgive me for
A Lovely Dumb Question: Full Flow or By Pass Flow?

 

Hi Jonathan

Not a dumb question but I have no idea!

 

Full flow: all oil is pumped to and from the engine to the oil cooler and back in the same area (doesn't enter through the front of the oil pan)
Bypass: exces oil is pumped through the filter and lands in the sump again to cool down.

I'm not sure if the oil on the full flow is then pumped into the engine oil circulation or not...

 

Hi Daim

Greg is right about those Fans, as for starters there is no deep dish.

But I managed to find an Original and so I've put that on.

 

Full flow oil cooler became standard issue in later pre-facelift cars, hard to determine exact date but around 88.

 

OB's car is FF. This can be deduced from OB's oil cooler head photo, which I am sure I have seen somewhere on this or another thread. Bypass cooling just has one pipe exiting the filter head to the cooler, FF has two (flow and return). Interestingly, when the great day comes and I bravely rebuild the engine (so as to pass on a damn-near new car to the boys) I intended to fit FF to my currently BP car. Then last summer in hot weather during a hot run, I measured the oil temp drop across the cooler in real time with my probes, readout in the cabin. 20 C drop, never wavered, in at about 85 out at 65/70. Max oil temp at the oil filter, sump and cam flow 85. So I decided the bypass works fine and no need to change it!
Greg

 

As I'm starting to get 'Paranoid' that She might fail the MOT on the Handbrake, which could mean a simple adjustment or dropping the IRS!

In order to Fix something that I personally never use, I decided to adjust it to try and give the Car a better chance.

Which turned out to be easier than I could have imagined (thanks to Greg for his advice) as its done by screwing a nut up on a threaded rod.

Which is under the rear Carpet by the sill just behind the seat.



Tightening the Nut to adjust the Hand Brake which is under the rear Carpet by the Sill behind the Seat

 

Nice work mate. So what date is the MOT?

 

Hi Bro

She is now already for her MOT, so its just a question of lifting the phone to Insure her before I go.

So today I went to a local garage, with the intention of booking her in

(although I obviously didn't take the Car with me)

Where without even seeing the Car, they said it would probably need a lot of Welding, which of course they would be happy to do.

Conversation over: I'm not taking my Car there or to any other Garage that seems to have an eye on doing repairs.

All I want is an MOT, if anythings wrong then I will fix it myself.