Jaguar XJ6 (X300) Oil Leak
On the X300 six the usual leaks are cheap seals, not the head gasket: the four O-rings under the oil filter housing, the camshaft sensor O-ring and the cam cover. Clean the engine, run it and find where the oil first appears before paying for anything big.
How bad is it · Safe to drive
Usually fine to drive while you keep the level up
Most of these are weeps. After a sudden puddle, check the dipstick before you start it, and keep oil off the exhaust and the steering rack boots.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
Hard O-rings under the oil filter housing
Below the filter head sits a half-donut block where an oil cooler used to fit. Its four small O-rings bake hard with age and stop sealing.
Oil on the left of the engine around and behind the filter, running down the foot of the dipstick tube onto the sump. It can go from a spot on the floor to a sudden puddle.
Wipe the area dry, run it and look at the joint under the filter head. While you are there, look at the short rubber hose at the bottom of the dipstick tube.
Fit four new 3 x 19 mm O-rings in hot-oil grade, nitrile or Viton (KSH119530), at the next oil change; or take out the adaptor sandwich and use one gasket with four shorter bolts. Taking the road wheel off gives room.
The camshaft sensor O-ring
The cam position sensor sits where the distributor used to be and seals on one O-ring. When it goes hard the leak looks just like the famous head gasket weep.
A fresh oil track starting at the joint between the sensor and the block, front right of the engine, below the top tensioner.
Clean it, drive a few hundred miles and see where the oil starts. Above the tensioner it isn't the head gasket; below it, look at this O-ring first.
New O-ring 513682J. Turn the crank to TDC (33 mm socket), line the round mark up in the middle of the sight glass and mark the flange before undoing the 8 mm bolt. Turn the sensor clockwise as it comes out; refit on the half-moon mark about 20 degrees back so it settles centred.
The upper chain tensioner housing
The housing is held by two screws of different length. The long one in the wrong hole bottoms out before the gasket is clamped, and overtightening bows the oval housing.
Seepage around the top tensioner on the right of the head, often a few months after the tensioner was changed.
See which screw went where. The longer one goes on the left, the shorter one lower on the right.
Swap the screws round, or use the shorter bolt from the service bulletin, or take about 1/8 inch off the long one. Torque quoted for housing to block is 21.5-28.5 Nm.
A sump bolt, the drain plug or a cracked sump
The sump has no gasket, only a bead of sealant, so it rarely leaks unless a bolt weeps or the pan is cracked. One bolt above the crossmember is the usual spot.
Drips onto the front crossmember with the engine running, sides and front of the engine dry. A drain plug with odd-looking repairs round it tells its own story.
Clean the sump and crossmember, run the engine and feel along the bolt heads. Old oil can fool you, so wash it and look again after a short drive.
Take the weeping bolt out and refit it with a thin aluminium washer, or with the bolt shank coated in a Hylomar-type sealant, not threadlocker and not the vinegar-smelling kind. A stripped drain plug hole can be retapped and sealed with epoxy; a sump cracked by debris needs replacing, front crossmember off and the engine supported.
The cam cover gasket and plug-well seals
The six has few hold-down screws, so the cover is very sensitive to torque. Overtightening is what makes a new gasket leak, and the rear half-moons are the hardest part to seal.
Oil on the exhaust heat shield, at the back of the head running down the bell housing, or pooled in the spark plug wells, which can cause a misfire.
Run a finger along the lower edge of the cover and look into the plug wells. If the gasket is fairly new, loosen every screw and re-torque in sequence before buying anything.
Re-torque to the low figure, about 5 Nm, in the bulletin order. If it is old, a genuine gasket with all six plug-well seals and the bolt seals, the half-moons cleaned, dry and given a little black silicone. A light sweat is tolerable on the six, which has few hold-down bolts.
The front crankshaft seal and cover plates
The front seal wears with age, and its runner wears with it. A seal not renewed while the timing cover was off is a common way to get this leak.
Clean oil on the front pulley, puddles under the front and frequent top-ups. Oil from the tensioner or cam cover can also run down to the pulley.
Clean the front plates and see what wets first. The oval plate on the right has a one-use gasket; the triangular one has a seal and a drain notch. Also look at the small two-bolt cover for the steering pump drive on the front cover.
Worth doing the seal with a new runner: 33 mm crank nut, balancer off, the new seal on its sleeve. It can go in with the cover on, but there is no inner stop, so don't drive it in too far.
The head gasket at the front-right oil feed
Oil under pressure goes from the block up to the exhaust camshaft through the head gasket at the front right. The ring round that hole can give way, and Jaguar revised the gasket for it.
A dusty stain or weep at the head-to-block seam in front of the exhaust manifold, behind the tensioner cover, above the crank sensor; no water in the oil.
Rule out the sensor O-ring and the tensioner first. Clean it, run it and find the exact seam the oil comes from.
A slight weep can be lived with; thinner high-mileage oil, for example 10W30, may slow it. The cure is the revised gasket with new bolts. Jaguar time is 11 hours, so a much bigger quote is worth questioning.
The rear oil gallery plug behind the gearbox
The main oil gallery ends in a plug with an O-ring held by the gearbox adapter plate. The O-ring perishes, and the oil appears at the engine-to-gearbox joint only while running.
Oil coming out high at the back of the engine, running down both sides of the bell housing and smoking on the exhaust; a new head or cam cover gasket made no difference.
Degrease and rinse, run it on stands and use a bright light to find the first wet spot. Rule out the rear of the cam cover first. Shine a torch on the top of the bell housing: a thick crust there means a leak at that joint, fresh streaks mean oil running back from higher up.
The O-ring costs very little, but the gearbox has to come out, so do the rear main seal at the same time.
A blocked crankcase breather
If the breather can't vent into the intake, crankcase pressure pushes oil out at the weakest seals.
Leaks that keep coming back after new gaskets, at the cam cover or the rear of the block.
Look at the small hose from the cam cover to the intake elbow; it can collapse inside.
Worth trying a new breather hose before another gasket.
Power steering fluid, not engine oil
The steering pump and its hoses sit right in the path of an engine leak. A pump shaft seal can blow fluid back onto the exhaust.
Red fluid, or a level that drops in the steering reservoir rather than on the dipstick.
Hose the pump area clean, check the reservoir clamp and the hose O-rings, and watch which level falls.
Fix the steering leak: pump seal, hose or clamp.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Clean it and find the first wet spot
Degreaser and water, then run it on stands with a bright light. Oil runs back and down, so the lowest drip is rarely the source. A sheet of paper overnight shows where it lands.
freeCheck it is engine oil
Red fluid is steering or gearbox. Watch which level drops.
freeUnder the oil filter housing
The bypass block O-rings, the filter seal and the dipstick tube hose. Best done with an oil change.
four O-ringsFront right of the head
Camshaft sensor O-ring and the top tensioner housing before anyone mentions a head gasket.
an O-ring or a gasketCam cover and plug wells
Loosen and re-torque to about 5 Nm in sequence; look into the plug wells. Check the breather hose.
free to re-torqueSump bolts
Feel along the bolts above the crossmember with the engine running.
sealantThen the big jobs
Front-right seam: head gasket. Engine-to-gearbox joint: gallery plug O-ring and rear main seal together.
a head gasket or gearbox outWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ6 (X300) Low Oil PressureA leaking pressure sender by the filter gives a zero reading and an oily mess at once.
- Jaguar XJ6 (X300) Misfire, Ignition Coil FailureOil from the cam cover in the plug wells causes misfires.
- Jaguar XJ6 (X300) Power Steering ProblemsIf the fluid is red, the leak is the steering, not the engine.
- Jaguar XJ6 (X300) Timing Chain Rattle, TensionerIf the upper chain tensioner also rattles on a cold start.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.