Jaguar XK8 Nikasil Engine Problems
Every XK8 and XKR built before August 2000 has Nikasil-coated bores, and the engine number, not the VIN, tells you which you have. In everyday use the trouble is usually a no-start after a short cold run, not a worn-out engine. I'd read the engine number, look into the intake, then have a blow-by and compression test done.
How bad is it · Safe to drive
Fine to drive if it starts and runs cleanly
Worn Nikasil bores fail gradually, with rising starting trouble and oil use first. Avoid short start-and-stop runs, which cause most no-starts.
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.
Fuel-washed bores after a short cold start
A cold start runs very rich. Shut the engine off within a minute or two and the surplus fuel rinses the oil film off the Nikasil bores, so the rings stop sealing and compression all but disappears.
It was started briefly — moved out of the garage, for example — and now cranks quickly and freely, as if there's no compression, perhaps with a pop but no catch. A slow, laboured crank on a charged battery is part of the same picture; a tank run low just before is a red herring.
Pull a plug: it comes out wet and smelling of petrol. A compression gauge reads low on every cylinder.
Charge the battery and crank with the throttle held to the floor, which cuts the fuel, to clear the cylinders. If that isn't enough, fit fresh plugs, put about a tablespoon of oil in each bore and crank in 60-second bursts; expect smoke once it fires. Endless cranking can backfire and blow the air box apart — for example about £400 in labour on top of parts. Crank in bursts of about 15 seconds on a fully charged battery and ease the pedal back slightly as it catches. Afterwards, never shut it down before the temperature gauge has started to move.
Oil pressure warning from the sender, not the engine
A low oil pressure warning on a Nikasil car looks like the start of the end, but the oil pressure transmitter itself can fail and give a false reading.
After a cold week standing the gauge reads normal for a few seconds, then drops to red with the low oil pressure message, and is fine an hour later. Hot oil at idle in very warm weather also reads lower. Hot oil reads lower, and about 600 rpm at idle is normal.
Screw a mechanical gauge in where the sender lives and compare. A true reading that is low all round points at bearings, not bores. The dash gauge works from a switch that trips at about 6 psi, so it normally sits mid-scale; a needle that wanders points at the sender or its plug first.
Replace the oil pressure transmitter. If a mechanical gauge confirms low pressure, look at the filter for debris and the bearings before anything else. If the true pressure is low, drop the sump and look at the pickup screen for bits of plastic tensioner.
Nikasil bores worn through by sulphur
Before August 2000 the AJ-V8 had no cylinder liners — the aluminium bores carry a nickel-silicon carbide coating. High-sulphur fuel attacks it, and once the coating goes the rings no longer seal. A Nikasil engine that escaped bad fuel often outlasts a steel-liner one, well past 150,000 miles.
Starting trouble that gets worse over months, oil pooling in the intake tube and at the bottom of the throttle body, black soot, and oil use that keeps climbing.
A blow-by test first, then compression on each cylinder. Low compression all round with oil and soot in the intake is the picture of a finished engine.
Get an independent second opinion before paying for an engine. If the bores are gone there is no half measure: a later steel-liner AJ27 engine fits and can go in over a weekend. Thicker oil such as 20W-50 only buys a few thousand miles. Keep a yearly blow-by record — a steady figure, for example about 14 litres a minute, is the best evidence of health. The timing chain tensioners are the bigger risk on the same engines; check them too.
Oil in the intake from a blocked breather
If the part-load breather is plugged, crankcase pressure rises at low revs and pushes oil up into the intake and the combustion chambers — which looks just like worn bores.
Oil in the intake tube or throttle body while compression is still even and the engine starts straight away.
Clear the part-load breather and its hose, then watch whether oil keeps collecting in the intake.
Worth trying before any bore test is taken as a verdict: clear the breather and see if the oil stops. A blown breather pipe, together with tired tensioners, can produce a flooding no-start that gets condemned as a dead engine.
Blue smoke at start-up from valve stem seals, not the bores
Oil seeps past hardened valve stem seals while the car stands and burns off on the next start. A puff of blue smoke after standing, with good compression, is the seals, not Nikasil.
Blue smoke on a cold start after the car has stood, none once it's driven, even under full throttle; compression even on all eight.
A compression test first. Good, even figures and little blow-by take the bores out of it; clean the breathers inside the cam covers while you're there.
Worth doing when the smoke is bad: new valve stem seals in the heads. Sludge and past overheating harden them.
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.
Read the engine number, not the VIN
It is stamped at the back of the block as NC, then the build date as yymmdd, then a serial — a mirror helps. Engines from 0008181043 on (built 18 August 2000) have steel liners; earlier ones are Nikasil. The VIN and model year don't follow the engine number, and some early 2001 model-year cars still have Nikasil. Bulletin S491 gives September 2000 for the change, so treat August–September 2000 builds with care.
freeLook into the intake
Take the intake tube off the throttle body. A film of oil and black soot is the warning sign; dry and clean is good news. A pint between services is normal, going from max to min within a 10,000-mile service is not.
freeHave a blow-by test done
It measures crankcase gas with the engine running. Under about 30 litres a minute the bores are taken as healthy. It averages all eight cylinders, so one or two weak ones can hide — repeated yearly, it shows the trend. It's this test, not a leak-down, that answers the Nikasil question.
about $180 at a dealerCompression, then a leak-down test
A compression test shows each cylinder on its own — for example an even 140–150 psi on all eight is a sound engine. If one is low or oil use is real, a leak-down test says where the pressure goes. Before buying, remember an additive can flatter both tests until the next oil change.
a compression gaugeDon't start it just to move it
On a Nikasil engine every start should end in a proper warm-up. Start-and-stop runs of a few minutes are what wash the bores and leave it refusing to restart.
freeWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XK8 Timing Chain Tensioner ProblemsThe other weakness of the same early engines — the same engine number tells you which tensioners it has.
- Jaguar XK8 Turns Over But Won't StartIf it cranks but won't fire and the bores aren't the answer — fuel pump, battery and chain.
- 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.