Chrysler 2009 PT Cruiser Owner's Manual page 315

The best time to check the engine oil level is about five
minutes after a fully warmed engine is shut off. Do not
check oil level before starting the engine after it has sat
overnight. Checking engine oil level when the engine is
cold will give you an incorrect reading.
Checking the oil while the vehicle is on level ground, will
improve the accuracy of the oil level readings. Maintain
the oil level between the MIN and MAX markings on the
dipstick. Adding one quart of oil when the reading is at
the MIN mark will result in a MAX reading on these
engines.
CAUTION!
Overfilling the crankcase as indicated by an oil level
above the "MAX" mark on the engine oil dipstick
will cause oil aeration, which can lead to loss of oil
pressure and an increase in oil temperature. This
could damage your engine.
MAINTAINING YOUR VEHICLE 313
Change Engine Oil
Road conditions and your kind of driving affects the
interval at which your oil should be changed. Check the
following list to decide if any apply to you.
• Day and night temperatures are below 32°F (0°C).
• Stop and go driving.
• Extensive engine idling.
• Driving in dusty conditions.
• Short trips of less than 10 miles (16 km).
• More than 50% of your driving is at sustained high
speeds during hot weather, above 90°F (32°C).
• Trailer towing.
• Taxi, Police, or delivery service (commercial service).
• Off-road or desert operation.
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