Originally Posted By: BuickGN
Originally Posted By: Doug Hillary
Hi,
vxcalais - Your question is broad and therefore the answer must be broad too!
Firstly, multi-grade lubricants were introduced in the 1950s for a number of reasons - one was to provide an all year round product. 10w-30 was really the firste and it suited US engines of the time very well indeed. Another reason for multigrade development was to "cover" the emerging technologies, hench the 20W-50 lubricant that was expressly developed in 1958-9 for the BMC Mini!
20W-50 quickly became a "cover all" viscosity that masked a lot of the technical defects in design prevalent at the time! The expansion of viscosities (ranges) over the last 20 years or so is quite amazing. Many have been introduced to satisfy a variety of "reasons" again - many if not most may have very little to do with the engine manufacturer's wishes or needs
Heavy Diesel Engines
In Australia the most common viscosity used is 15W-40 - across the trucking, mining and earthmoving Industries. Some Euro engines now use lower cold start viscosities and 5W-40 is but one and a number of 10W-40 HDEOs are now available too
Cars
The obvious answer is surely "the lowest viscosity recommended by the engine's manufacturer for the expected ambient temperature range" according to the application
In Australia and New Zealand we still have a large following for the 20W-50 "fits all" theory - surely this is a hangup from the English vehicles that dominated our markets here for so very long?
1 - Practicality
The most popular car service point here in Airlie Beach uses Castrol's RX Super 15W-40 HDEO across the board! This is in Rollers, Benzes, Maseratis, Porsches, Corvettes, Mustangs, Ferraris, Buicks and Volkswagens - and everything in between, both old and new! The ambient range is from -10 to near 50C!
The service point's owner is a well trained ex. BMW Service Engineer and a good friend
This type of servcing approach is very common in OZ and comes from Oil Company Reps. selling a "multi-fit" lubricant to limit inventory requirements, price and etc
Bad example: One independent Porsche service point in Sydney filled most engines with a 25W-50 mineral lubricant - a viscosity NEVER recommended by Porsche - primarily "to get good hot idle oil pressure". Some Porsche engines have 32 hydraulically controlled valves and lubricant intercoolers. In temperatures around 5C and below there is a definte "hydraulic" feel to these engine when using this lubricant.The manufacturer recommends a 5W-40 synthetic lubricant.
There is NO concrete evidence of excessive wear in these engines when using the 25W-50 lubricant (instead of a synthetic 5W-40) but the engines were never operating optimally!
2) - Reality
a - Use what is recommended by the engine's manufacturer! They know what is required for the wide application of their engines
b - Here (generally) Audi use a synthetic 5W-40, MB and Porsche use 0W-40. Many BMW Dealers use 0W-40 too. I understand that most Deealerships follow the manufacturer's Warranty line on viscosities very well here in OZ
3) - Unreality
Most parts and accessory shops such as Autobarn and Supercheap sell lubricants that are made popular via all media advertising! Their "Technical" staff are mostly unskilled sales people that give people what they want - the advice given is unlikely to be based on what is best for a specific application
Personally
For many years - from 1980 until around 1995 and in Sydney (lower end of the Blue Mountains) - and in many different engine families, I used Castrol's excellent synthetic 10W-60 - a lubricant that I helped to develop. I bought a VL Commodore new and it had a diet of that lubricant until 160kkms. The beautiful Nissan engine was still operating as new when sold! It had 10kkms OCIs
Today in my cars and light trucks I only use synthetic lubricants, a 0W-40 lubricant in many engines and 5W-40 in many others. One Toyota engine is on a 10W-40 semi-synthetic
I use of a lubricant with a HTHS viscosity of around 4cP in my Porsche engines (3.5cP is the minimum needed) due to the fact that I live in the Tropics and at times drive fast for hours on end at temperatures from 33-40C. Spirited driving is the descrition I think! These engines (M28 M96 etc) may be "sensitive" to lubricants with a low HTHS viscosity in certain operating environments
Summary
Use what the engine manufacturer recommends.
Synthetics have worked for me for years and perhaps outside of what the manufacturer recommends, and to answer your broad question, either a 0W-40 or a 5W-40 viscoity for Melbourne/Sydney is a broad answer and maybe a wise choice too
As always your posts make a lot of sense.
My only question is when a manufacturer recommends a 5-20 in a car that used to spec a grade higher like 10-30 with no changes to the engine most likely to comply to CAFE standards, don't you think optimal protection would be with the recommended viscosity before the CAFE push?
^^That`s what I`ve always thought. Car manufactures are looking to sell the most cars by advertising the absolute best gas mileage,especially with the uncertain and fluctuating fuel prices.
