The OILEY Mix-Up

Posted by Michael 30/07/2020 0 Comment(s) TECH TALK,

Seeing so many Diesels through our shop with problems caused by the wrong choice of oil viscosity is at "Plague Proportion".

OIL GUIDE- The good old SAE guide should be used as a guide only. It shows oil viscosity recommendations based on the ambient outside temperature the engine will work in.

AUSTRALIA'S 'MEAN' TEMPERATURE- With such a BIG country comes varying temperature. One thing to consider when choosing the right oil for your Diesel would include where the majority of your driving is done. Average minimum temperatures across the country range from 3'C in Tassie right up to 21'C in the Northern Tropics like Darwin.

REAL TEMPERATURE CONDITIONS- The 'Real' temperature though is far higher than this. Add direct sunlight, radiated heat from road, heavy towing conditions, and high humidity and the SAE temperature guide suddenly becomes a little inaccurate. In fact you should probably add 5'C or more to your calculations when using the SAE oil viscosity guide in Northern Australia.

OPERATING TEMPERATURE- Take a look at where you spend most of your driving time. or choose a wider operating range oil. If you live in Tasmania but travel to North Australia a bit you could look for a wider range oil such as a 10W40 or 10W50.

CHOOSING THE RIGHT VISCOSITY- Based on the scenario created above and using the SAE viscosity guide we see the following. With a 10'C start up temp and an outside operating temperature of about 35'C we could safely say a 10W40 oil would be ok for start up and just ok for the ambient temp at the high end. If you were predominant in hot conditions you could even range that up to a 50 weight oil.

FOOD FOR THOUGHT- The '10' part of the oil (10W40) is good for start up temperature of as low as -25'C!! That's about a 40'C 'safety gap' for the 10'C cold start condition. Certainly we would all be in great trouble if the temperature in Australia dropped to -25'C! On the other hand though, the '40' part of the oil viscosity (10W40) is good for about 40'C. Compared to the cold start up end, that''s a 'safety gap' of only about 5'C if driving on a 40'C day.

OIL STEAM EFFECT- Using thin oils such as 0W30 or 10W30 in our Australian temperatures drastically increases the amount of engine oil steam/fumes being created by your engine. Couple this with the demand we place on our engines from travelling and heavy towing and its a recipe for disaster. These fumes lead to excessive inlet manifold oil build up which greatly increases carbon build up and blockages from the EGR (Exhaust Gas Re-circulation System).

-"I need a thin 0W oil to help with cold start up". We know this argument is wrong as the lowest temperatures that the majority of Aussies live in is no where near -25'C (using a 10W40).
-"A thick oil wont lubricate". Multi-grade oils are thin at start up based on the low index number, and resist thinning based the high index number. Synthetic blends are even thinner.
-"I need an 'oil catch can' to catch engine oil fumes". If you use the right oil viscosity for our Aussie climate such as a 10W40 or 15W40 or 20W50 (mainly up North), you will greatly reduce the oil steaming effect of hot engine oil reducing the need for an oil catch can.
-"The manufacturer recommends a 0W or 10W30 oil, I must use it". While the manufacturer might say this, the reality is that its the wrong oil for Australia. Car makers in Japan. Europe and North America live in a climate far cooler to us here. Whilst the factory choice of oil may be ok for use in the initial engine fill, it does not suit our hot climate for continued use.

OIL COST- No doubt there are dozens of oil choices on the shelves at your local auto parts shop. It actually makes things more confusing when you add the marketing hype to the equation. An example of one popular brand oil:-
15W40 Mineral Engine oil - 5 litres for $22
15W40 Semi-Synthetic Engine oil - 5 litres for $38
15W40 Full Synthetic Engine oil - 5 litres for $67
Bang for buck Semi-Synthetic is a good oil for modern CRD Diesels while there is a proven history that a simple mineral oil will be in your older Nissan TD42 for more than 1/2 million km.

SUMMARY- When its 'all said and done' oil choice is heavily driven by smart marketing, company profits and of course the 'know alls' trolling online forums. In our varying Ausssie climate you need to use an appropriate engine oil. The SAE Viscosity index was formulated based on Northern Hemisphere cooler climates and conditions. We will never see these cool conditions and so you need to be using an engine oil that is appropriate for Australia. A good example would be a 10W40 or higher.

THE SYNTHETIC 'WILD CARD'- Synthetic oil predominantly helps out in colder climates by being able to start thinner whilst maintaining a safe viscosity when hot. Unless you race your vehicle, and we mean race not play, Synthetic engine oils are expensive and unnecessary. A more balanced choice for engine oil would be a Semi-Synthetic.

FINAL WORD- With a Pedrigree of Diesel Engine Knowledge going back to 1956, Berrima Diesel has formed these views from decades of first hand experience. Be smart and question general opinion. Get to know more about your Diesel by talking to The Diesel Experts at Berrima.

To get a first hand experience of the skilled knowledge and services we offer at BERRIMA, CALL NOW on 02 48771256 or drop by our shop. You'll find us 500 meters South of Berrima.