C5 2.0i engine oil

[Paul-R]

Can I just say that I think that people are getting too wound up about the W specification. Really it is more important to get the "correct" summer grade.

I remember when the first multigrade oils appeared. Duckhams was the name to go for and it was 20W/50. As time went on the W specification went lower and, more importantly, the summer specification went down. The first oils were 50 in order to keep lubrication going with the quality of oils and viscosity modifiers available at the time. As synthetic and semi-synthetic oils appeared we saw 15W/40 and then 10W/40 for sale. IIRC 10W/40 was what I used in my Montego TD (synthetic if I could afford it, semi if I couldn't) and that had 12,500 miles oil change intervals.

This thinner oil has a beneficial effect on power loss and the engine becomes fuel efficient and this is what has driven use of 30 grade oils. These can provide the lubrication needed due to better machining accuracy and materials in modern engines. In addition the oil itself is more stable.

Finally, I still say that 0W could be used in place of 5W. The first scan of Marc's above clearly shows that the only difference between the 0W30 and 5W30 is the low temperature capability. But I did qualify this by saying "If it's cheaper than 5W why not?". This did assume that 5W30 was the more normal specification. But if it's 5W40 then that doesn't apply. But it wouldn't vastly wrong and if the 0W30 is still cheaper then I might be tempted to give it a go as it's a quality oil.

One final twist. Some 25 years ago the firm I worked for stocked 20W60 oil for use in lumbering old B-series engines. I think it was just psychology as it immediately raised the indicated oil pressure (MGBs had a proper oil pressure gauge) making the engine look better. It wouldn't have helped fuel consumption though.

[GiveMeABreak]

But surely engine technology has moved on significantly since the Montego days Newer oils were needed to cope with the advances in technology and the constant requirements for leaner and greener engines, components have been lightened and designs now call for these newer fully synthetic oils. If 0W-30 was suitable, why would they bother making all the other grades at all?

[Paul-R]

I thought I was making the point that technology has moved on. Just saying that my Montego was the first of my cars to use a multigrade that wasn't 20W50.

Why do they make different grades if 0W30 is suitable? Probably cost I would think. 5W30 has got to be cheaper under normal circumstances than 0W30 and 5W40 covers a different temperature range.