Oil
Purpose of oil
• Lubricate
• Cool
What is oil?
• Petroleum product
• Up to 25% artificial additives
– Detergents
– Anti- foaming agents
– Sulphur containing compounds
– Viscosity
• Degrades
• Diesel oil has a hard life
Oil grading
• API - quality
• SAE – viscosity
API
• American Petroleum Institute
• 2 letter designation eg. CD
• First letter
– S for petrol/spark ignition engines
– C (or D) for compression ignition diesel engines
• Second letter denotes quality
• Higher the second letter, the better the quality
• Always use quality specified in your manual or
higher eg if CD specified can use CG
SAE
• Society of Automotive Enineers
• Measure of viscosity (how thick/runny is
it?)
• Lower the number, the more runny (less
viscous)
• Followed by W for winter eg 10W
• Modern technology allows multigrade oils
Multi-viscosity oils
• Eg 20W-50
• First no. still relates to cold viscosity
• Second no. relates to viscosity at 100
centigrade
• The higher the second no. the les the oil
thins as it warms up
• Due to polymers which uncoil and tangle
up as oil heats up, making it more viscous
Why is viscosity important?
• Low oil viscosity
– means easier starting and running –don’t have to stir
the oil so much
– Oil is easily pumped to all parts of engine – less wear,
especially on starting
• High oil viscosity
– Oil clings to surfaces better
– Seals piston rings better – compression
– Harder to pump to all areas of engine
• Compromise required
Clean oil
• Change oil regularly
• Renew filters
• Use correct oil
http://www.btinternet.com/~bmservices/bms/engines/index.htm
• Avoid load-free/cold running
• Monitor oil pressure
– Gauge
– Warning light
Changing oil
• Wear gloves – used engine oil is highly
carcinogenic
• Run engine – warm oil is easier to get out
• Ideally pump out oil
• Replace oil filter
– Remove old filter
– Remove any old o-rings
– Fit new o-rings correctly
• Seating
• Wipe with clean oil
• Dispose of old oil correctly