Does Castrol pay Volvo to recommend their oil? Have they really done studies to see what oil works best in these engines? I have a '05 S40 2.4i (no turbo) should I use Castrol or some other brand? Is Castrol GTX the right kind of Castrol or should I use synthetic?

 

Absolutely they pay volvo for the recommendation. Synthetic isn't necessary on that engine for a NA (naturally aspirated) Non turbo.
Use a 5/30 oil like Havoline, Castrol GTX, or Trop artic Semi Synthetic. All are had at Walmart for a good price.

Just change out between 3 to 5000 miles. You will be fine.

If you wanted to use Synthetic use Mobil 1 5/30 or German Castrol (available only at Autozone it's a 0/30, look for "made in Germany" on the bottle back).

 

I use exclusively Syntex by Castrol. Not only in the Volvo but in two of my Japanese autos and one German. 25 years ago I started using synthetic when Mobil 1 came on the market and have never looked back from using synthetic. Lastly, I have a 1965 Austin Healy that I purchased new in London and used petroleum based oil. When Mobil 1 came on the market I began using it and never experienced an oil leak as you will, I am sure, hear the old wives tales about. I change filter and oil at 5,000 mile intervals. While on the subject of maintenance, don't forget to change brake fluid, trans fluid, and coolant every two years...........you should change the brake fluid every year.
REG

 

Reg, since you are a synthetic guy then get the Castrol syntec 0/30 from Autozone with the bottle saying "made in Germany" it's called German Castrol and has a cult following. Go look at bobistheoilguy.com and you can see it has it's own forum home. I use it and it really does seem to run smoother. I just changed some out after 3 months and it almost looked new, after 4000 miles or so. Only available at Autozone.

 

I use Mobil 1, and wont use anything else. Castrol isn't good I say.

 

Fred, you said change the conventional oil every 3K-5K miles. Why does Volvo only recommend oil changes every 7500 miles even with convetional oil? Also I live in Northern California where the temperature is consistently over 100 degrees right now. Don't I want to be using a 10W-30 in that heat, not a 5W-30 or a German 0W-30?

 

Yes over 100F then no harm going to 10/30 at all. Or German Castrol 0/30 is almost a 40 weight oil and is more robust than 10/30.
Believe me, using a Mobil 1 and saying it's better than German Castrol is hogwash. They are both PAO (poly alpha olifins with esters) best oil one can buy. The regular Castrol syntec made in the US is just grade III base oil. And nothing special. Synthetics like Castrol US, Valvoline, Quaker state and others are only calling themselves synthetic because Mobil sued them and lost. Courts ruled in facor of Castrol saying it can call itself synthetic even though it is using hydrocracked oils.

Choose wisely, choose with knowledge. But saying Castrol (German Castrol syntec ) is inferior to Mobil 1 is simply wrong and without basis. It's actually acknowledged as superior to Mobil by the vast majority of users. See Bobistheoilguy.com for proof.

 

I'm intrigued with this discussion.. I've been thinking about going synthetic, but have been told that with the miles on my car, as long as I change the oil every 3k miles, dino oil would actually be the best choice (225k miles) as the synthetic may actually cause a leak. Is this true, or would Mobil 1 or the german Castrol be a better choice?

 

Regarding oil leaks. That occurs supposedly when gaskets sealing surfaces are gunked up a little, and the synthetic will clean out the gunk. Then the surfaces need time to get relubed and swell properly. In the meantime you may get a leak. I have done this with three high milage cars after 40 K (Volvo S60, Dodge Intrepid, and a Ford Escape) and none have ever leaked.

Now regarding 225K miles...
I would do the following, I would purchase a product called Auto RX www.auto-rx.com, and slowly clean the engine. Once done with that, I would continue only to use conventional oils. It got you this far, stick with it. And continue to change it every 3K like you are doing. Your doing something right. If you wanted to go semi synthetic, using TropArtic 5/30 or Motorcraft 5/30 are very reasonable at Walmart if you do your own oil changes. Get the filter at a NAPA is it's the filter element and not the can. NAPA gold ($8).