Chad!

Ok, here goes. I have read a lot of threads about which oil to use etc etc. The majority of what I have read is saying to use a semi synthetic 10-40 oil. Can anyone give me an expert answer of why? The two answers I want are to questions of, 1, Why use 10-40 instead of 5-40 (I thought this would be better when cold). 2, Why semi-synthetic and not fully synthetic? I understand that this is a bit of a talking point and always will be. I would just like to know why people recommend what they do.

Thanks,

Chad.

thedeester1

I always use fully synthetic. The viscosity doesnt bother me that much since my engine is old and it wont make any difference anymore. All ive found is that the cheaper fully synthetics seem to fail before the expensive ones. I go on how the oil from the stick feels on my fingers. Its just a long time in industry i guess? I preffer the fully synthetics because they dont carbonise which is better for the turbo.

silent running

The silent majority use fully synthetic between 10w40 and 15w50, on classics at least. A vocal minority use semi synthetic 10w40 because that's what it says in the handbook. It's your choice, but the semi 10w40 that's recommended, like with all manufacturers' recommendations, is a good minimum standard rather than the 11th Commandment. No-one ever had engine problems by using the same weight of mulltigrade oil in a fully synth rather than semi. There is also the cost issue, with semi being half the cost of fully synth. With a car that likes oil changes as much as a Subaru, it does become a significant expense if you're spending £40-£50 on even a DIY fully synthetic home oil change every 3000-4000 miles. But then on the other hand, you don't buy a Subaru for cheap running costs...

jaytc2003

iTrader: (1)

Without sounding like PSlewis or Mreeee

1:- This is what Subaru recommend after research that they have carried out (for the older classics anyway, not sure about bugs and blobs)
2:- Again what Subaru recommend at the time. On older classics if you switch to fully synthetic after using semi for most of the engines life, there have been alleged problems with seals failing. How true this is I do not know as I just use semi 10w40 with regular oil changes.

If you have a modded car then obviously it no longer meets standard specs, so the standard spec oil may not be suitable. In that case speak with the person who has done the mods and see what they recommend.
At the end of the day, you can use whatever oil you feel comfortable using, its your choice. Make a decision on what you feel is right.

Chad!

I've been using 5-40 fully synthetic. To me, that would seem to be the best oil for this kind of engine (unless it's a bit tired maybe). I just wanted to see what other people thought. I've done around 10K miles since I bought the car and oil changes have been done by me since the day I bought it, no problems so far with any seals going on me. So hopefully this won't happen.

Chad.