Excessive oil pressure

XJ
1

Dear all,

last Saturday when I took the Jag out for some errands it started and ran flawlessly. Then I noticed the oil pressure needle was pegging out. It stayed at full right for some time, while the engine was already warmed up, then hovered a bit and got back to 40 lbs on the driven car.

I suspected the oil pressure sender to be faulty and ordered a new one which I was about to install today. Before taking more efforts than necessary I pulled both spade connectors and reinstalled them. Upon starting the engine the oil pressure guage again went to the full right position.

Much to my chagrin the hex at the new sender was stamped 19/26 on one flank which I couldnā€™t work on on site - only later I found that a simple 17 mm spanner fits just fine. Moreover the old sender seemed frozen tight on top of that hex tube.

Do you have any ideas what else but a defective guage - or an intermittent short in the pressure guage connection - might cause the oil pressure on a hot engine to rise even above the oil pressure valve (60 lbs, I think)?

And, if itā€™s just the shot sender, are there any tricks to get the old one out?

Thanks and enjoy the sunshine - stay alone with your loved one (!) ā€¦ and your cars - how many you like!

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

2

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An intermittent short in the oil pressure sender itself is the most likely reason for a pegged gauge, Jochen, itā€™s sort of a ā€˜movingā€™ part - or indeed a wiring short. But I doubt if the gauge is faultyā€¦

Did you actually check the resistance over the two prongs on the sender - with and without pressure, cold and hot? The resistance when gauge shows 40 psi is in any case a benchmark referenceā€¦

While unlikely, though not impossible, for the relief valve to stick, giving excessive pressure - but peaking the gauge requires very high pressure indeedā€¦

A sometimes fault with the pressure sender is that the port, or the channel of the sender, gets clogged. But that would rather give a ā€˜no readingā€™ anywayā€¦?

Frank
xj6 85 Sov Europe (UK/NZ)
**

1 Like
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Hi Jochen,

I like Loctiteā€™s Freeze and Release product for getting a differential expansion working in my favour. Also while using only reasonable torque, effectively shocking the threaded connection by ā€œtappingā€ the head of the spanner.

Good luck.

Simon

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Simon beat me to the ā€œshockā€ Technique. Iā€™ve seen proā€™s on You tube do thatā€¦ From gentle to brutal. depending on the size of the offender!!

I have used my impact with successl

And, I have an old tech impact screw driver. Set to LH or RN and then whack it. An internal spiral delivers a turning motion and a vertical twist.

Heat also works. Not to cut, but to incite an expand/contract motion and break a material difference weld or mere corrosion Not a good idea here.

I am impressed with the freeze ideaā€¦

With oil present, it seems odd that it would stick ??

Carl

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Thank you all, Gentlemen!

I can measure resistance across the spades with the engine running, but with a now ongoing indication of +80 lbs I cannot compare to the benchmark resistance for 40 lbs - at least, if I measure the correct resistance for +80 lbs (what would that be?) I know the guage is doing its job correctly and the fault is either in the sender, its circuit or - worst case - the oil system.

Hitting on the sender is kind of hard to do as the sender looks pretty much like a mushroom with two spades.
grafik
So I doubt whether hitting it on the head of the housing even affects the threaded part - Iā€™ll try anyhow with care and a large socket over the spades.

Also, if I heat up the engine I could use some ice spray on the sender - then again, Iā€™d like to avoid any unnecessary engine operation during that state of uncertainty. The impact wrench idea may be working best with an open ended spanner and slight taps with a hammer in both directions.

Frank, a friend of mine just encountered the situation you describe on his Mk II - all of a sudden total loss of oil pressure with good working engine. For fear of consequential damage they started with the oil pressure sending unit and the oil filter head and found that the oil pressure valve was blocked open by some piece of metal. After they had pulled the engine out they found that in the course of an earlier engine overhaul the securing pins used in early XK engines had obviously been reused and subsequently decomposed, causing visible damage to the cylinder wall ā€¦ fortunately one chunk had made itself visible by blocking the oil pressure valv.

My concern would be that the oil passage is blocked in some other critical point causing oil pressure to rise. Before such big tasks I 'm trying to exclude all simple causes. Is there any way to bench test a new sender? ā€¦ just trying to escape the ā€œtwo-faulty-parts-errorā€!

Iā€™ll get to it these days and report back!

Thanks again and stay safe

Jochen

75 XJ6L 4.2 auto (UK spec)

6

The two spades are connected together.,ā€¦resistance across them is zero. The relevant electrical connection is between either spade and ground (the 1/4 BSPP male threads) but the sender isnā€™t the resistive type, so useless to measure resistance in that path either. IMHO.

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Just to be clear here, Iā€™m talking about hitting the head of the spanner while itā€™s on the hex of the sender, not hitting the housing. The diameter of the housing means you my have strike the beam of the spanner somewhat out from the head engaging the sender.

Iā€™m not sure how using a socket is going to help you on thisā€¦

8

Interesting that a piece of securing pin can get through the mesh and pump and then block the relief - but not impossible although more often than not this would give very low pressure; at least that is how I got to know.

Ice spray sounds valid, but one would think that given the location of the sender a few hits on the spanner(!) should do. Also try leverage by all means possible with the confined space. You surely know how to use a ring spanner as extension? Good enough for the crankshaft bearing bolts on leverage.

A fault in the oil system would likely result in dry cams first - so, to see if the engine sees lubrication and for peace of mind, see if the cams are receiving oil (through the oil cap, and a little oil is enough). Damage would have been done, but there should be no way this could ever happen. I think it is safe to say that the sender is faulty. The wiring/gauge would be either intermittent or constant if at fault, but the sender is known to fail and might still change with oil pressure, just not giving the right results. I would simply replace the sender and start her up. Good luck!

David

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One of the benefits of shock tactics is avoiding XS torque and the associated risk of breakageā€¦

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It is indeed a valid concern, Jochen - though it is highly unlikelyā€¦

The relief valve and filter is in series, and the pressure transmitter is after the filter - between the engine and the filter. With the relief valve is stuck ā€˜closedā€™, the pressure gauge reads pump pressure - gauge will then read very high with extreme cold engine. ā€˜Closedā€™ in this context means that the return port to the sump is closed - the passage to the filter is always open. Such excessive oil pressure is sort of harmless - unless prolongedā€¦

A clogged filter will block oil flow - and the oil pressure will read low/zero. A clogged passage, after the pressure transmitter, will indeed read pump pressure - which will now read very, very high, independent of temperature. (The stalled pump pressure is not specified)

Such blockage is not inconceivable, but I have never heard about it - and blockages of the oil delivery pipe will give zero pressure. Blockages may occur in separate pathways, like to/in the crankshaft or the head/camshafts - but will just more or less increase oil pressure, while leaking bearings will lower itā€¦

Oil pressure reading is not a good indicator of such individual problems - which may be just as destructive long term. But valid reading is still important - so a trustworthy gauge is important. So in your case I would simply replace the transmitter - and see what happensā€¦

As an aside; the point raised by Robert is interesting. I always considered the two prongs as the resistance path between the gauge and ground - the higher the pressure the lesser the resistance, and the higher the gauge reading. With two wires at the transmitter; one white/brown from the gauge - and one black to ground. Or with one wire; transmitter body as ground. But it may be more to itā€¦? :slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

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The tension continues

  1. Bobā€™s comment as to the function of the two spades is interesting! I dimly recall that the Op sensor also serves as a fail safe. No oil pressure, no fuel pump operation.
    In an accident or to protect the engine??

  2. Probably risky to bang on the can. .It might bust ands thusly no read at any PSI! And little if any ā€œshockā€ to the threaded portion.

  3. I had a failed unit. It read lower than the real OP. If I still had it, I could cut it open and study the insides.

  4. Shock and torque to the ;lower part. As suggested spanner + ring. wrenches. USA speak, Open and box.
    Twist and tap.

  5. A blast of liquid nitrogen as dermatologists use for warts and moles?

  6. Dropping he sump to access the pump and screen is . not easy, but might be the last resortā€¦

The saga continues.

Weather better. lock down continuesā€¦

Carl

12

Great to hear from you, Carl. Glad youā€™re hanging in there with the lock down.

AFAIK, the second spade wasnā€™t used, and the signal there isnā€™t suitable to figure out whether thereā€™s OP unless you are the matching gauge. But the concept of stopping an electric fuel pump when the engine stops (not a problem with a mechanical pump) has been around a long time. Later Jaguars have inertial switches that switch off the pump in a collision. Requiring OP to operate the fuel pump is easy to wire using an OP switch (rather than a gauge sender) but the problem is starting the engine. Iā€™ve thought about how to work around thatā€¦for example bypass the OP switch if the engine is operating under choke.

This reminds me of a typical Jaguar kludge executed when they were forced to introduce EGR (and the dreaded ā€œgulp valveā€) starting in 1973. For some reason, EGR made engines ā€œrun onā€ after the ignition was switched off, particularly if they were good and hot.

I donā€™t remember the details, but Jaguarā€™s solution was an OP switch whose function was opposite that of an idiot light switchā€“it was closed with OP and open without OP. There was also a power source plumbed into the engine compartment that was on when the ignition was off and off when the ignition was on. Fuel supply was shut down if and only if the ignition switch was off, but there was OP (indicating that the engine was running on despite no ignition). I think the shut off was via some sort of solenoid valve, and not by disconnecting power to the pump.

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Photo and diagram of an oil sender

20170711_115857
20170711_1158572048Ɨ1152 496 KB

2 Likes
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Thanks again to everybody!

Frank, from the looks of the sender Robert is dead right - both spade connectors are obviously connected; in fact - on my new sender like on the picture above - the two spades are pressed from the same piece of metal; they are insulated against the sender housing though, which is nicely illustrated by MGCJAGā€™s picture - thanks mate!

The problem begins where my wiring pattern shows two wire connections to the sender: one white/brown going to the oil pressure guage, one black wire leading to ground. In the wiring pattern they are separated, of course, but remembering the setup in my car there was one white/brown wire on one of the top spades and only one other wire also connected to the top spade. The spare sender on my desk has no other possibility to attach a ground wire, and that would certainly not be necessary with the body firmly bolted into the engine steel.

For the moment, to solve the mystery, Carl, I contempt myself in the assumption that Jaguar got it wrong in the wiring pattern: oil pressure guage sender, the idiot light sender and the water temp sender are all flagged out in the wiring pattern with ā€œearth connection via cableā€ and yet Iā€™d bet there is no ground wire on either of them.

In my naive understanding putting both the white/brown and a ground wire to the top spade connectors would mean you simply ground the oil pressure guage, which would not make any sense to me. Anyway, Iā€™ll check color of that second wire as soon as I get there and try to track it.

In fact, from the wiring pattern my car has an anti-run on device: with the ignition ā€œoffā€ an anti-run on solenoid is powered connecting to an oil pressure switch anti-run on with brown/red wire. However, the latter is not the same part as the oil pressure guage sender.

Iā€™ll give it a go with better spanners - the neck on which the oil pressure sender is mounted seems to have a hex profile as well, so Iā€™ll be able to use a second spanner to take some load from the engine block. Space is an issue with the carbed car, though I did take the air filter housing off.

BTW, the ROM advises not to exert any pressure to the capsule and to use the correct size spanner. My spare sender has stamped on the hex ā€œ19/26ā€ which, if I donā€™t get it wrong, comes out at 18.56 mm. However, the hex measures 16.96 mm, explaining why my 17 mm spanner fits well. A 3/4 is a tad too big. Any ideas about that mysterious indication ā€œ19/26ā€? I couldnā€™t even find such an imperial size. Or is it some kind of torque indication?

Guess Iā€™ll check out tomorrow.

Thanks again and stay safe

Jochen

75 XJ6L 4.2 auto (UK spec)

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The description of the ā€˜anti run onā€™ set-up was indeed with the extra oil pressure switch, Robert. Connected to an extra contact on the ign switch - only powered with ign ā€˜offā€™. With oil pressure, ign ā€˜offā€™ and engine winding down, power is applied, through the (closed) switch to a vacuum valve opening the carb bowls to manifold vacuum. Effectively preventing fuel from being drawn from the carb - no fuel, no run-onā€¦

Another oil pressure switch was used as a ā€˜fuel safety switchā€™ performing the job of the inertia switch on the EFI. Without oil pressure, engine not running switch is ā€˜breakā€™; fuel relay is disabled - pump not running. Function overridden in ā€˜crankā€™ā€¦

Frank
xj6 85 Sov Europe (UK/NZ)
**

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It does not show how pressure data is presented to the gaugeā€¦?

Frank
xj6 85 Sov Europe (UK/NZ)
**

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Indeed, Jochen; the wiring diagram practice is to show a ground connection as a *blackā€™ wire - even when the ground connection is in fact internal, body itself is groundā€¦

Basically; as ā€˜ourā€™ set-ups are analogue variable resistors (usually - but pressure sensitive crystals is possible) are used to give relevant data - varying current/voltage to suit. As such items may fail in various ways; they may give false readings in some positions. Like ā€˜no connectionā€™, no reading or ā€˜shortingā€™, max/excessive readings. seldom repairable; faulty items require replacementā€¦

Intermittent faults are unusual, but no necessarily impossibleā€¦

Frank
xj6 85 Sov Europe (UK/NZ)
**

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Hi Frankā€¦the diagram shows the Cct inside the sender unitā€¦variable resistance is supplied to the guage depending on pressure via the contacts and heater elementā€¦output is at top of diagram

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Most OP senders were variable resistance, but not the Smiths sender used by Jaguar until the Series 3. As described numerous times on both XJ and E-type lists, this sender operates ā€œdigitallyā€ via pulse width modulation (PWM). It is similar to the instrument voltage regulator (IVR) and indeed serves as the voltage regulator for the OP gauge. Itā€™s a very spiffy mechanical design, albeit prone to failure in the harsh conditions of the engine compartment. IMHO.

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YUP! My opinion only sans any support that I know of.
19/26 is slightly less than 17mm. So, it must be to assure a tight fit. Tight fits are desirable between tools and fasteners. Why expressed as a fraction in this format. only the designer knows, whomever that might be.

I cringe when folks use pliers and crescent wrenches, when proper spanners should be employed!!

It will take some effort. working in a confined space. One arm twists or pulls one way and the otherthe opposite wayā€¦

Good luck.

Carl