Semi/ Fully Synthetic Oils. New Forum.


Well Iv'e read all the advice/argument/discussion.
And I hope all on here realise what a cracking site this can be even though we can't always agree. Smile
Many on here are the "Ole Timers" (Like Me)
And have done most of my servicing repairs myself for many years. (Although not many repairs on the two Sirions I have owned as they just run and run with just basic replacements as you would expect) Smile
Iv'e enjoyed this debate although I only read it and didn't get involved this time. Smile

So it is clear that we will never come to a full concensus on what oil to use in what vehicle.
Or how the various types are made
So use what you feel is good for your vehicle and be happy with that.

For me that will be a Fully Synthetic 5/40.
It has been for many years in many types of cars including two Turbo Diesels with High Mileage.

Never had a problem.

Good discussion.

Any one out there can get me some rear springs for a Rally 4 ??

Regards, Bob F.

Wot? No blood.

Like you Bob I read the other thread with fascination but was wary to poke my nose in for fear of getting it bloodied.

One aspect of the advances in lubrication is rarely mentioned, that is better fuel consumption. In the 90s I had a Mazda 626. It had a smooth-as-silk 2.5 litre V6 engine. I was doing 28000 miles a year and using 10w40 semi-synthetic on a 6000 mile service interval. As the car was used for business I kept a log of mileage and fuel used. During 1999 Halfords had a two-for-one offer on their own brand fully-synthetic which made it the same price as semi-synthetics so, with an eye to a bargain I bought 4x5 litres of 5w40.

The first thing I noticed was the mpg figure was consistently higher using the new oil. Not by very much as it only increased from 29.5 to 30.3 mpg but this was noticable because it broke the 30 barrier. These figures were not measured over a few tankfuls but over many weeks. At the time petrol was 69.9p per litre, (happy days), and based on the extra 0.8 miles gained every gallon I worked out an approximate saving of £79.00 over a year. When you consider the extra cost of fs over ss it makes the saving a lot less but it was a saving nontheless.

I have used this oil ever since and keep an eye out for Halfords promotions which are usually an annual event.

I'm getting my head back under the parapet now.

A very interesting

A very interesting discussion. I use mineral oil in my 1990 non turbo FourTrak.


One interesting comment is the advancement in lubrication technology, the part which is missing is the advancement in engine manufacturing and technology. This is a crucial aspect of the debate, and a basic understanding of it is required.

Modern advancements in engine technology involve the actual engine manufacturing to ever tighter tolerances, this means more power and thermal efficiency. This also means more heat and smaller mechanical clearances, so a thinner oil film is required, but with a higher shear and compressive strength. This is where synthetics excel.
Modern engines also have such things as catalytic converters fitted, this means the old vapour or misting of mineral oils has to be minimised to acceptable levels, or eliminated. Oil contamination from misting will ruin a cat. Other factors are such things as manufacturer applied anti-friction coatings to engines, usually the pistons, piston rings, and the valvetrain. Mineral oils would simply destroy these quite quickly, synthetics are designed with these in mind.
Modern engines work with lower oil pressures, but higher flow rates for synthetic oils, this means faster heat dispersion, and shorter times lubrication the hottest parts of the engine. This also means contaminants from combustion are removed quicker and held in suspension in the sump until they pass through the filter.

Some engines cannot use full synthetics, these being the Fourtrak engine as it is simply too old, it was an obsolete engine when it was used in the Fourtrak. This can use semis as an alternative to plain minerals, but minerals are the preferred oil to use, unless you run on vegetable oil, or veg/diesel mixes. These mixes leave a larger unburned fuel and the additional detergency of semis makes them the preferred option.

Cost is a factor, as you state it is the increased service intervals which makes the extra expense of these oils viable.
My old vehicles required 3000 mile oil changes, my new company car lasts 18000 miles plus between changes. This makes synthetics economically viable in some cases, but not others as it is subjective; if the vehicle is dealer or garage serviced the additional costs can make mineral oils expensive. Home servicing can make minerals the cheaper option.

Go on, stick your head above the parapet.

Cost is a big factor.

I agree with this, especially the 2nd last paragraph about cost. That is why I service my own cars, and some I use mineral oil, others I mix a bit of fully synthetic in, and there are cars I will never use anything other than fully synthetic. That being said, on my more valuable cars I have the oil sampled and analysed to see exactly what is happening in the engine (wear/contaminants/degradation etc). It's the same method I employed at work when maintaining any mechanical equipment from 6.6kV motor driven pumps to 380V feedwater pumps. The best way to make decisions on what to use is to decide what is most important to you, and then what you need to get to address that. Some people choose cost, others performance, others longevity...

Just call me G... Wink
2004 Yellow YRV Turbo

More Valuable Cars ??

2004 Sirion 1300 4 Track. And I love it.
Don't like the new shape much.

Criky - I can only afford one.

That's why I look after it like a baby. ;);-)


2003 Sirion Rally 4. And I love it.
Don't like the new shape Sirion much.Sorry.

not at the same time

hehehe... I didnt mean all at the same time. I have a rule of never owning more than 2 cars at a time. Sometimes I keep one for many years while changing the other frequently, other times I just feel like a change and get 2 different cars. I just meant that I changed service routines depending on the car. I've lost count on how many I have owned though...

Just call me G... Wink
2004 Yellow YRV Turbo