Oil ain't oil

[Don123]

In my car I'm using the shell Helix AJ 10W30, So I was talking to the local auto shop about changing to the Valvoline engine armour 10W30, and he told me that If i wanted to change oil brand I will need to flush the engine because it's not a good idea to mix with other brands of oil. Well, I say it's a BS, as long as the oil specification is the same according to the car manufacture it shouldn't make any difference, after all when you buy a car you don't know what oil the previous owner used, you just put your own oil in it. What do you people think?

 

[XioiX1983]

I flush as a precaution. But I think the problem stems from changing from mineral oils to synthetic oils, some dont combine to well. IMO

 

[Drewie]

I wouldn't worry about it, I bought my VX SS brand new and on the first service the Holden Dealer popped Mobil 1 synthetic 10w30 in it, after a few years the same Holden Dealer changed to a Valvoline dealer and it then went onto a 10w40 Valvoline semi synthetic brew, when I was finished using the Holden dealerships and started using a local workshop which specialise in LS powered cars it went onto Castrol Magnatec 15w40 semi synthetic which is a workshop only grade a bit different to the Magnatec 10w40 you buy retail, to be honest I have never noticed any diffference in the performance or oil usage between any of them, the car ran fine on all of them, been on the Castrol for around 6 years now and from what I can see looking inside the rocker cover the engine is spotless, looks brand new, I think the big thing is regular oil and filter changes more than the brand, providing the specs are correct for the car.

 

[Don123]

That's what I thought, I always change the oil myself but If I had to take it to a dealer, they will put what ever oil brand they have an agreement with.

I wouldn't worry about it, I bought my VX SS brand new and on the first service the Holden Dealer popped Mobil 1 synthetic 10w30 in it, after a few years the same Holden Dealer changed to a Valvoline dealer and it then went onto a 10w40 Valvoline semi synthetic brew, when I was finished using the Holden dealerships and started using a local workshop which specialise in LS powered cars it went onto Castrol Magnatec 15w40 semi synthetic which is a workshop only grade a bit different to the Magnatec 10w40 you buy retail, to be honest I have never noticed any diffference in the performance or oil usage between any of them, the car ran fine on all of them, been on the Castrol for around 6 years now and from what I can see looking inside the rocker cover the engine is spotless, looks brand new, I think the big thing is regular oil and filter changes more than the brand, providing the specs are correct for the car.

 

[Drewzor]

Different oils have different characteristics other then viscosity, Different degrading and detergent qualities are of main concern.
Your old oil brand would have degraded a particular way, leaving deposits it would never have removed and over time, oils lose their viscosity a particular way.
So imagine this, in some parts of the engine there is carbonized shell Helix AJ 10W30 oil gunk caught up in some hot spots and some bearings and moving parts have worn slightly wider from slow increase in thickness of the old degrading.
Now you change the oil to Valvoline engine armour 10W30
It starts running through your engine and begins to work at the deposits, eventually breaking off a chunk that flows through and plugs a oil gallery or worse your oil pick up?
or
normally your moving parts are use to the performance of your oil after a few 100kms, but with the new oil which may have better preserving properties remains 10w-30,
those moving parts that are use to only rattling around a few 100km before the oil starts to thicken keep rattling.

Engines seem to take on the character the oils they use, the ever so slight friction works at the moving parts but that level of friction is different between oils regardless of similar viscosity at purchase.
I was once advised to either change oil brands every oil change to prevent this or always use the same oil for the life of the engine.

I may have not made myself clear, but I hope you can understand this, regardless, as said above consistent oil changes are of greater concern then brand of oil.

 

[diysv6]

This a bit of an epistle, sorry about that. I have tried to cover some lubricating oil history and maybe where we are at today.

This was how lubricating oil compatibility was explained to me some years back.

In earlier days, the grade of engine oil, not synthetic types, was set by the cars' engineering people. The car manufacturer would require a certain oil quality, or specification, which the lube oil producers were producing and capable of producing at the time.

The oil producer tried to ensure that the new lube oil was backward compatible with earlier spec oils to minimise inventory and production line runs. Hence the back panel on retail packs of oils generally states that the oil meets certain specs for the modern engine, but is compatible or exceeds earlier formulations of engine oil.

The old engine oils grades, straight and multigrade evolved over the years. There was always debate about changing from one brand of SAE30 to another brand's SAE30 and then switching to the "new" multigrade was another debate.

The world's biggest consumer of lubricating oils in the early days was the US Government and their Defence Forces. Since the US government selected the lowest quote year to year, it was specified that the incoming lubricating oil brand was to be seamless and incur no extra costs. Basically, dump old engine oil, refill with the new brand oil. (eg. no flushing was to required between different contracted suppliers' products).

Good old Uncle Sam would buy from the cheapest supplier and that was that. Also it was good business to ensure that competing lube oil producers' products were compatible to take advantage of these oil supply contracts. The cost of flushing out old engine oil would have been prohibitive as each supplier's lube oil came on line in workshops etc. Government Warehousing locations, oil stock inventory levels and wastage, engine and equipment failure etc, would have been a nightmare if there was no brand compatibility.

With the advent of full synthetic and synthetic mixes can I presume brand change-over should be seamless as it was for the old straight mineral oils to multigrade etc.?

Maybe the US Government/Defence Force does not hold as much financial sway over lubrication oil producers as it used to. Maybe vehicle manufacturers now determine the service oils for their "fleet" and expect oil producers to manufacture oils to keep up with their engineering requirements (early turbo oil cooling problems spring to mind);
or, do oil producers disregard lucrative government supply contracts worldwide?

Maybe similar specific branded lines are still compatible.

 

[Grennan]

He is correct. Certain companies do put different additives in their oils and whilst it may be unlikely something happens, something can and if it does they will just wipe their hands.

For example, Castrol and Penrite both have a premium full Synthetic range.

Both are extremely different.

But I think this would more refer to topping up with different oils. You wind up with 6L of lucky dip. When you drain the engine most of its gone and I wouldnt be to concerned about putting a different brand in there.

 

[diysv6]

For example, Castrol and Penrite both have a premium full Synthetic range.

Both are extremely different.

Maybe the key word here is Premium oils.

US Government supply contracts might want a specific premium oil for the space shuttle, but want a good quality synthetic/mix oil for eg. its fleet vehicles.

I'm not up to speed with mixed or full synthetic oils. It appears that premium synthetics are not very compatible by their very nature, as Grennan suggests. Whereas the "day to day" mixed synthetics in their fleet vehicles are not so compatibility sensitive, and that is where the competition is for compatibility, price and access to supply contracts?

 

[Don123]

The VZ alloytec engine takes about 6.4 litres of oil, I have a can of 5 litres Shell helix and I need another 1.4 litres, so I was going to buy a 5 litres Valvoline and add 1.4 litres to the 5 litres Shell, so you think I should not to do it?

 

[Deuce]

The VZ alloytec engine takes about 6.4 litres of oil, I have a can of 5 litres Shell helix and I need another 1.4 litres, so I was going to buy a 5 litres Valvoline and add 1.4 litres to the 5 litres Shell, so you think I should not to do it?

Don't do it