Oil viscosity

[arcturus]

Hi, at the moment I am using a 20-50 oil and I was wondering if this was necessary. The reason is that this oil protects from below 0.c which temperatures never reach here. A 20 grade would cover me from 0c to 30c + which is my average temperature range. Is there any reason why I shouldn't do this?

[Zebster]

20 seems like a very high cold viscosity to me. Surely getting the oil flowing quickly around the engine on a 'cold' start (even if that isn't ever sub-zero) is a key benefit and so a lower cold viscosity would be desirable? Even using a 5w would surely not break the bank?

I don't know what engine you have, but isn't the 50 operating viscosity a bit on the high side? The load on the oil pump would be far less with, say, a 30 viscosity oil.

While I recall exclusively using 20w-50 back in the 1970's, things have moved on a lot with semi and fully synthetic oils.

[BorderVolvo]

My understanding is that due to the engine tolerances being greater in an older car due to manufacturing processes, a higher viscosity is required ?

Unless the engine's been rebuilt/blue printed?

At a push why not try a 10/40 oil?

[DORETTI]

Some old car engines require a zinc content of over 1000 ppm to protect the cam and followers, which is not found in modern oils as it may poison the catalyst.
Cheers Richard

[AndyV7o]

It is important to consider what oil the engine is built around, what additives and properties the engine requires, and why multigrade oils exist.
Old engines were designed around different oils to today, thus are often slacker by design to use thicker oils. Using too thin an oil can result in low oil pressure, metal-metal contact, noise, etc.
Multigrades exist because monograde oils were very narrow in their ideal temp range, being too thick when cold, too thin when hot, etc.
Older engines require much more anti-wear additives (such as the infamous zddp) but arent always happy with some modern detergents, etc

Thus, yes you are better using a multigrade oil, a straight 20 will be too thin when hot (youd probably want sae 30) whereas a 20w50 thins out far less, maintaining sufficient oil cushion in the bearings and appropriate pressure. Bear in mind a 20w50 is still much thicker cold than it is hot. A modern contemporary oil might cause issues with wear/seals/etc. Thus, use a classic 20w50/15w50/10w50 and you will do the best for your car. Use s monograde you may accelerate wear, require more frequent changes, spend more money. There is no point on cars built after ww2 (or thereabouts), with the exception of some such as some air cooled engines, using monograde oils. They were superceded for good reason.

I think though, that the amazon/p1800 were designed around thinner oils though, do check this out, as if they were 20w50 won't be the best.
A 5w40/10w40 classic oil would be better in this instance.

[arcturus]

Thanks for all replies. Sticking with Millers Pistoneze 20/50 classic with z. I was concerned about oil leaks but that' all sorted now.

[AndyV7o]

Originally Posted by arcturus

Thanks for all replies. Sticking with Millers Pistoneze 20/50 classic with z. I was concerned about oil leaks but that' all sorted now.

When you say 'with z' do you mean zddp? and if so do you mean it contains zddp or do you mean adding zddp? A classic oil contains enough zddp and adding more can be counter-productive, there is a definite sweet spot for the amount, so please dont add any more to a classic oil if you are! If not, 👍👍

[arcturus]

This contains zddp,not adding.

[AndyV7o]

👍👍👍
Yeah, its good stuff.