Jaguar XJ (X350). Manual — part 309

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Ambient temperatures.

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Quality and viscosity of oil.

Operation under varying conditions can frequently be misleading. A vehicle that has been run for

several thousand miles on short trips or in below-freezing ambient temperatures may have

consumed a "normal" amount of oil. However, when checking the engine oil level, it may measure up

to the full mark on the oil level indicator due to dilution (condensation and fuel) in the engine

crankcase. The vehicle then might be driven at high speeds on the highway where the condensation

and fuel boil off. The next time the engine oil is checked it may appear that a liter of oil was used in

about 160 km (100 miles) per liter oil consumption rate is about 2,400 km (1,500 miles) per liter.

Make sure the selected engine oil meets Jaguar specification and the recommended API performance

category "SG" and SAE viscosity grade as shown in the vehicle Owner's Guide. It is also important that

the engine oil is changed at the intervals specified for the typical operating conditions.

Oil Consumption Test

The following diagnostic procedure is used to determine the source of excessive oil consumption.

NOTE:

Oil use is normally greater during the first 16,100 km (10,000 miles) of service. As mileage

increases, oil use decreases. Vehicles in normal service should get a least 16,000 km (10,000

miles) per liter. High speed driving, towing, high ambient temperature and other factors may

result in greater oil use.

1 . Define excessive consumption, such as the number of miles driven per liter of oil used. Also

determine customers's driving habits, such as sustained high speed operation, towing, extended idle

and other considerations.

2 . Verify that the engine has no external oil leaks as described under Engine Oil Leaks.

3 . Verify that the engine has the correct oil level.

4 . Verify that the engine is not being run in an overfilled condition. Check the oil level at least five

minutes after a hot shutdown with the vehicle parked on a level surface. In no case should the level

be above the top of the cross-hatched area and the letter "F" in FULL. If significantly overfilled, carry

out step 5, sub steps 1 through 4.

5 . Carry out an oil consumption test:

Drain engine oil and fill with one liter less than the recommended amount.

Run the engine for three minutes (10 minutes if cold), and allow oil to drain back for at least five

minutes with vehicle parked on level surface.

Remove the oil level indicator and wipe clean. (Do not wipe with anything contaminated with

silicone compounds.) Install the oil level indicator making sure to seat the oil level indicator

firmly in the oil level indicator tube. Remove the oil level indicator and draw a mark on the back

(unmarked) surface at the indicated oil level. (This level should be about the same as the ADD

mark on the face of the oil level indicator.)

Add one liter of oil. Start the engine and allow to idle for at least two minutes. Shut off the

engine and allow the engine oil to drain back for at least five minutes. Mark the oil level dipstick,

using the procedure above. (This level may range from slightly below the top of the cross-

hatched area to slightly below the letter "F" in FULL.

Record the vehicles mileage.

Instruct the customer to drive the vehicle as usual and:

Check the oil level regularly at intervals of 160-240 km (100-150 miles).

Return to the service point when the oil level drops below the lower (ADD) mark on the oil level

indicator.

Add only full liters of the same oil in an emergency. Note the mileage at which the oil is added.

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Check the oil level under the same conditions and at the same location as in steps 3 and 4.

Measure the distance from the oil level to the UPPER mark on the oil level indicator and record.

Measure the distance between the two scribe marks and record.

Divide the first measurement by the second.

Divide the distance driven during the oil test by the result. This quantity is the approximate oil

consumption rate in kilometers per liter or in mile per quart.

If the oil consumption rate is unacceptable go to Step 6.

6 . Check the positive crankcase ventilation (PCV) system. Make sure the system is not plugged.

7 . Check for plugged oil drain-back holes in the cylinder head and cylinder block.

8 . If the condition still exists after carrying out the above tests go to step 9.

9 . Carry out a cylinder compression test. Refer to the procedure in this section : Compression Test.

This can help determine the source of oil consumption such as valves, piston rings or other areas.

10 . Check valve guides for excessive guide clearance. Install new valve stem seals after verifying

valve guide clearance.

11 . Worn or damaged internal engine components can cause excessive oil consumption. Small

deposits of oil on the tips of the spark plugs can be a clue to internal oil consumption.

Intake Manifold Vacuum Test

Bring the engine to normal operating temperature. Connect a vacuum gauge or equivalent to the

intake manifold. Run the engine at the specified idle speed.

The vacuum gauge should read between 51-74 kPa (15-22 in-Hg) depending upon the engine

condition and the altitude at which the test is performed. Subtract 4.0193 kPa (1 in-Hg) from the

specified reading for every 304.8 m (1,000 feet) of elevation above sea level.

The reading should be steady. As necessary, adjust the gauge damper control (where used) if the

needle is fluttering rapidly. Adjust damper until needle moves easily without excessive flutter.

Interpreting Vacuum Gauge Readings

A careful study of the vacuum gauge reading while the engine is idling will help pinpoint trouble

areas. Always conduct other appropriate tests before arriving at a final diagnostic decision. Vacuum

gauge readings, although helpful, must be interpreted carefully.

Most vacuum gauges have a normal band indicated on the gauge face.

The following are potential gauge readings. Some are normal; others should be investigated further.

1 . NORMAL READING: Needle between 51-74 kPa (15-22 in-Hg) and holding steady.

2 . NORMAL READING DURING RAPID ACCELERATION : When the engine is rapidly accelerated

(dotted needle), the needle will drop to a low (not to zero) reading . When the throttle is suddenly

released, the needle will snap back up to a higher than normal figure.

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