A3/B3 5W-30 ? who does one of them then
As you it's say personal preference regarding oil change intervals - will pay dividends for you in the long run hopefully - some people like to change them early, some people let them go to the manufacturers periods - keeping the oil clean is the key.
Interesting comment about minerals - I think you mean some synthetic oils being formulated from Group III basestocks ( very highly refined and hydrotreated mineral oils ) instead of PAO ( very very highly refined mineral oils ) - mineral, semi synthetic and fully synthetic all come from the same crude oil - just that the waxes and inpurities which restrict the performance are taken out during the refining process - interestingly, a very good quality Group III can outperform a poor quality POA ( Polyalphaolefin ) Both Group III and PAO are classed as "synthetic "
Semi synthetics are a blend of basic mineral and fully synthetic base stocks - you get better performance characteristics, but with a cost benefit.
The performance characteristics are defined by the specifications - this is the minimum criteria the oil must meet - so if it says A1/B1 and that needs a semi synthetic formulation to provide the performance, then you won't see that spec on a mineral oil. Then again - you can see A3/B3 on a 15W-40 mineral oil - and also a Fully synthetic - so you could argue it's an easier test? - however, what you won't see on the lesser oils are the OEM specifications as these are a lot more subjective and need specific oils, mostly PAO synthetic nowadays to pass the required engine test criteria ...
Out of curiosity, and off the subject - what mileage should you change the cam belt on a black top ?
forgot to say - oil samples - not really that useful unless you are using them for trend analysis ( which means taking a sample every 2K or something ) - you can use them just before you change the oil I suppose, but all that will normally tell you is if the oil is still fit for service - good company to use - about £15 a sample -
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