I have had a slight chronic oil “loss” to date, which I put as mostly due to Superblue’s “puff of blue smoke” sometimes on first start of the day, or after sitting a long time (leaking exhaust valve stem seals). She has been in that condition since almost day 1 when I bought her many years ago. However, the last few weeks or so she seems to have developed a true leak somewhere, but no telling where. I did take her to NTB last month (I posted about this) and the tech tried to tell me she was leaking at like 5 different places. Since then I have checked some of those supposed places (e.g. oil dipstick tube, fill cap, etc.) out and found no evidence of an actual leak. However, something major is definitely amiss now, as she has not been showing oil on the dipstick despite my putting in quarts here and there. Thinking somehow there was something wrong with the dipstick check (if that is even possible?) I tried running the white plastic “string” part of a spare power antenna assembly I have for her down the dipstick hole, and it’s not showing anything. Not sure how that can be, when I drove her to the store last night and back w/o any problems or troubling noises whatsoever. Unfortunately, both of my oil pressure sensors are not working, so I can’t rely on them to tell me if she is going dry.
I have had someone get under Superblue to check the obvious signs of a major oil leak, inc. a loose oil filter, loose oil drain plug, and the oil gauge pressure sender which was recently replaced with the upgraded version (but is still not working - go figure). Anyone suggest what areas would be the most likely candidates to check next (BEFORE disaster strikes)? btw, was going to check the oil pressure relief valve to see if it might be stuck open for some reason, but don’t know where it is located (or if the 4.0 even has one) …
As long as the dip stick is still in its hole, there should be oil.on the dip stick.
Atty Dallas, the first thing I would do is jack it up (don’t start it to drive it up on ramps) and drain the oil.
How many quarts come out? If you don’t have an easy way to measure what comes out, buy 3 gallons of water, mark where the water level is, then empty them out (using the water as you see fit), then start pouring the oil that drained out into those gallon jugs, filling to the ‘gallon-ish’ mark.
Like proposed, drain the existing oil. Put in proper fill. Then you know you have a “good” oil level. Return Car to be on level ground. Remove oil pressure gauge transducer (which you say isn’t working anyway) and place a folded shop towel or something similar over the opening where the transducer was (and weight it with something). Start car and let it run about 8 seconds. Shut it off. Check the shop towel for evidence of fresh oil. If wet you know your oil pump is getting oil into oil pipes.
With a correct oil fill your dipstick should show oil when car is level.
The best indication of leak would be your driveway (unless sooo messed up already that it won’t make any difference).
Your oil dip stick is right, there is not much things to go wrong with it (unless rats ate it off, from inside)
Your “superblue” (truly super - by condition ) has v12 I assume (assumption made by location from your profile and condition). V12 will eat oil by lunch time, too many pots I’m afraid. Especially with present leaks, stems gone and blue smoke coming out from super-shiny bits on the back of your car.
Your oil pressure gauge is indicating differently than you think. If it drops low - it’s usually - already too late (“supercorpse”) even if working - you would use it incorrectly…
Pour the fresh oil first - until it will appear on the dipstick. Note the indication (f.eg. with Polaroid photo). Then check if your shoes are not wet. If all dry and comfy - do the test ride with (short, 3 miles max) and check the dipstick again (30minutes after engine off) and note the difference in indicarion. That’s your oil superchum-chumm rate.
O.K., by way of update … Tech checked the spots that the NTB tech had claimed were sources of leak. One that he did not mention ( ) was the valve cover. I checked this myself and didn’t think I saw any sign of a leak around there, but tech says there is some at the back and at one of the front corners. I replaced the valve cover gasket, half moon seals and spark plug well seals about 3-4 years ago, due to what was obviously a leak at the back end (probably the half moons). I think though where I may have goofed was to not go back and make sure all the bolts were retightened after 500 miles, or whatever the specified mileage for that check is. So retightening those should take care of that leak.
The two sources though the tech did confirm were the dipstick tube and the oil pressure sender (for idiot light - the NTB tech also missed the latter source). The dipstick tube is a minor leak, and I would assume that small piece called the “dipstick sleeve” by Jag is responsible. ? There doesn’t appear from the parts diagram to be any gaskets, o-rings, etc. associated with the dipstick tube.
The main leak turned out to be from the oil pressure sender, and you could actually see it coming out from around the circumference of it when the engine is running. In fact, the sharp-eyed tech noted a dripping trail of oil on the pavement from behind Superblue where she was driven into her parking slot to park at the time. Makes sense that this would be a major potential leak source b/c of the fact that that area (port) has high pressure to ensure the sensor is operating accurately. Same for the port behind the oil pressure transducer for the oil pressure gauge. What is strange is the tech did not find the old sensor to be loose, but rather a bear to get out. No idea then how a leak developed around it. The past few months I have had problems with the idiot light being “on” all the time, and this may have been related to the leak. Now with a new sensor put in by the tech the lights is off, as it should be, and no more leak.
btw, as to the transducer sender, the tech did put in the “upgraded” version earlier this year, but that thing has never worked right. At most, it goes up to 1/4 pressure (not mid-pressure) on the gauge on first start, and then goes right back down into the red zone (or even left of it). While in there replacing the indiot light sensor, the tech tried tinkering around a bit with the transducer, but apparently it is still not working correctly. He wonders now if maybe reversing the black wire and white wire connections to it may resolve it. ? Has anyone had any similar issues with the upgraded version?
btw, does anyone know off the top of their head which color wires go to the idiot light sender and to the pressure gauge transducer on a 4.0? One is black and one is white, IIRC, but I can’t remember which one goes to which one. My tech is thinking maybe the reason the upgraded transducer is still not working properly is that he might have gotten the two wires turned around when he put the two units in. The wires both connect to the units identically (i.e. via slide-on spade connectors) so that sounds like it could be possible.
for an XJS 94 4lt there’s alternative wiring > oil press/sender orange/slate … oil press/ switch black/brown…odd to have a plain black (normally earth) and plain white (normally ignition switch feed)
…is the white wire just a short one connecting to another in the system? if so white usually oil pressure
However, the last few weeks or so she seems to have developed a true leak somewhere, but no telling where. I did take her to NTB last month (I posted about this) and the tech tried to tell me she was leaking at like 5 different places. 
Since then I have checked some of those supposed places (e.g. oil dipstick tube, fill cap, etc.) out and found no evidence of an actual leak. 
However, something major is definitely amiss now, as she has not been showing oil on the dipstick despite my putting in quarts here and there. Thinking somehow there was something wrong with the dipstick check (if that is even possible?) I tried running the white plastic “string” part of a spare power antenna assembly I have for her down the dipstick hole, and it’s not showing anything. 
btw, was going to check the oil pressure relief valve to see if it might be stuck open for some reason, but don’t know where it is located (or if the 4.0 even has one) …
) has v12 I assume (assumption made by location from your profile and condition). V12 will eat oil by lunch time, too many pots I’m afraid. Especially with present leaks, stems gone and blue smoke coming out from super-shiny bits on the back of your car.
So retightening those should take care of that leak. 
Same for the port behind the oil pressure transducer for the oil pressure gauge. What is strange is the tech did not find the old sensor to be loose, but rather a bear to get out. No idea then how a leak developed around it. 
