Power, economy, oil...

[johnl]

It is not the first few minutes of driving or how gently you rev the engine it is the first few seconds when the engine oil drains back after resting say overnight the initial start the next day is where the most damage is done.

I'm a bit surprised that you think that the difference in cold thickness between a 10w-60 and a 20w-60 oil is so critical. I do agree that all else being equal it is a 'good thing' if the oil can be pumped reasonably quickly at cold start. Penrite also make a 40w-70 engine oil, which could pose a problem on a cold morning (!).

Rpm should still be kept reasonably low with cold oil (even an oil that is relatively quite thin when cold), but that is a somewhat different issue to the initial wear at start up. I still don't buy the notion that the reason to specify a multigrade oil with a low 'cold' rating is that this specifically minimises cam lobe wear, I'm far from convinced that it especially does (more likely the motivating factor might be that it influences average fuel economy downward, assuming an engine with excellent ring seal...).

Oil that is thinner when cold will pump through reasonably quickly, so a 10w-60 fits that bill, and I have no issues with using such an oil in these often oil consuming engines (60 is a bit thick if the engine doesn't consume oil...). However it's my understanding that a 20w-60 isn't hugely thicker when cold than a 10w-60 (if you don't live somewhere like Canada...). Just because 10 is arithmetically only half of 20 doesn't mean that a 20w oil is twice as thick as a 10w, it doesn't work that way (or a 0w rated oil would be infinitely thin...).

At the risk of repeating myself; regardless of the oil used, at cold start the working surfaces are not completely unprotected. There is a residual oil film clinging to them that lubricates 'well enough' until pumped oil arrives at the cam lobes and tappet faces, at best some seconds after start up (possibly significantly longer considering that the oil at the cam lobes isn't pumped there directly). Even an oil that is quite thin when cold takes some time to actually arrive at the cam lobes, significantly longer than the time it takes for the engine to quiet down, but a somewhat thicker oil (within reason) takes only a little bit longer. It's during this time that the residual oil film is important (if it weren't for the residual film then cam lobe wear would be much worse, regardless of the cold oil thickness).

This is mostly to do with the 'hot' thickness. The thicker the 'hot' thickness of a given oil, the more residual oil is likely to be coating the working surfaces at cold start, and to be sitting in 'pools' around the contact points between the lobes and tappet faces due to the surface tension of the oil (less having drained away after hot shut down when the oil is at its' thinnest, thicker equating to less runny). It's this 'pooled' oil that gets wiped onto the lobes as they initially rotate at start up.

You can see these 'pools' of oil if you take a close look at the contact points between the lobes and tappets, most clearly at the moment a camshaft is removed, leaving the oil pool exposed on the tappet faces. It doesn't take much oil to protect the lobes and tappets, but the more residual oil the better, and thicker oil leaves more of it.

This would be more or less the same for say a 10w-60 as for a 20w-60, i.e. it's the '60' that is more important for the residual film. I suspect this might possibly be why thicker oil (when hot) may be more protective of cam lobes etc, i.e. less cam wear during cold starts because the residual film (and associated oil 'pools' between the lobes and tappets) will be somewhat greater, less having drained away. This would be beneficial in an engine prone to cam lobe wear...

So where was I; when I changed the oil I was wanting to use one with a thicker hot rating (more or less as Alfa now recommends). If a 'synthetic' 10w-60 had been available at a reasonable price, then I would likely have purchased it. On the day that I was in town looking to buy a thicker grade oil, the nearest reasonably priced oil that I could find was a 20w-60 mineral oil by Penrite (on a day I was close to being broke...).

IMO a 20w-60 oil will still be fine, it won't cold pump quite as fast as the 10w-60, but it will be quick enough, and there is a residual oil film. Just don't thrash the engine when the oil is still cold (good advice regardless of the oil used), it may not pump easily enough to keep rate of oil flow up to the bearings.

FWIW, I have trouble thinking that an engine that can pump a hot 60w oil (effectively very thick) up to red-line rpm with no problems, would be unable to adequately pump a cold 20w at restricted rpm...

Also FWIW, the SAE cold temperature ratings for oil weights are as follows:
20w from 0°C
15w from -10°C
10w from -20°C
5W from -30°C
0w from below -30°C

My engine is almost never started at sub zero temperatures.

Regards,
John

[johnl]

 

I cannot comprehend the disparity in comments by the original poster; in one instance a change of oil (old for new) results in claims of appreciably better performance - yet in another instance - the actual grade of oil used as replacement, the dismissal is effectively "near enough is good enough" with respect to its departure from OEM recommendation. 

The OEM recommendations are at best erratic. The manual says; "5w-30", "5w-40", "10w-40", and "10w-60". There is a massive difference in the 'hot' ratings, far greater than the difference between a cold 10w and 20w. For "decidedly sportive use" it says to use "10w-60". For "particularly harsh weather conditions" it says to use both "5w-30" (assumed "particularly" cold weather), or, "5w-40" (assumed "particularly" hot weather). I would have assumed that use in very hot ambient conditions and use in a "sportive" manner would both result in quite hot oil, so why the different recommendations?

In the field it also seems that the 30 and 40 recommended hot ratings have been found to be not nearly thick enough to prevent quite excessive oil consumption with many examples of this engine. In response it seems that Alfa retro specified an oil with a particularly high 'hot' thickness rating for all usage (i.e. 10w-60), mostly I assume to reduce oil consumption, but I do wonder if the higher 'hot' thickness rating might have been an attempt to address instances of cam lobe wear as well? 

The OE recommendations are all over the place. Treat them as Gospel if you wish, but I've yet to have any issues using oil with a slightly thicker 'cold weight' (i.e. 20w rather than 10w). Were the car used in sub zero temperatures I might well reconsider this...

While I accept that there are indisputably "black arts" (said tongue-in-cheek, the point being some things are such a convergence of miniscule differences that it's effectively impossible to scientifically reduce it all to measures and procedure) the avoidance of hard data in cases such as the above makes them at best entertainment.

I lack quotable "hard data", but, changing from a substantially knackered thinned out old oil to a new thicker oil has resulted in:
1) Significantly improved the engine performance (suggests less than perfect rings)
2) Substantially improved fuel economy (also suggests less than great ring seal)
3) Elimination of variator rattle
4) A generally quieter engine
5) A substantially reduced rate of oil consumption (oil level has not significantly lowered since changing the oil a few weeks ago, maybe 5mm lower now).

I myself find some of this surprising, since I would have expected the thicker oil to allow the variator to rattle for little bit longer considering a somewhat thicker oil will pump somewhat more slowly. But the variator rattle has completely disappeared altogether...

I understand that these are merely "claims", I cannot prove what I'm saying. To me they are as near to 'hard data' as I can expect, as each is a very obvious effect, before oil change and after. If the engine now suffers from accelerated cam lobe wear due to the thicker cold rated oil, feel free to say 'I told you so"...

Regards,
John.

[Vne165]

Hi all,
Just following up from post #13, with some details of what I eventually did regards drilling of oil relief holes on my CF3 pistons. Decided to do 6 x 2mm diameter holes in each piston. Worked out well so I hope someone finds it useful and I hope I don't have any oil consumption issues.
This engine sure has surprised me in more ways than one - I may make some other posts just for info - someone else might be mad enough to rebuild one one day too...

Cheers Vne
Pic 1 - Marking out hole locations (6 x piston)
Pic 2 - Drilling in the milling machine
Pic 3 - View of ring lands
Pic 4 - De-burring,,