21 replies to this topic

[Miki Leyland]

viscosity aside, the other factor that needs to be taken into account with 

 

There is no issue with 20w50 and catalytic converters. Any oil related concerns with catalytic converters deal with the oil specification ratings - specifically, the amount of zinc or zinc-based compounds in the oil.

 

More modern (mid 2000's on) oil ratings specify lower levels of zinc to avoid poisoning the catalytic material. Any 20w50 oil with a modern rating will be perfectly safe with a catalytic converter.

 

 

on this point, it's my understanding that the manual gearbox needs an oil with decent amounts of zinc etc compounds to avoid excessive wear on the synchro assemblies, so this as well as viscosity should be taken into account when choosing an oil

As far as I know, the zinc/phosphorus additives are for lubrication of the tappets (without rollers in A-series engines) against the camshaft.

 

The issue with synthetic oils in Minis is that they lubricate so well that the synchros, which need a point of friction, cannot work properly.

[super6al]

Would semi synthetic (with high zinc/phosphorus) be any better than mineral?

[ThermalEvent]

Would semi synthetic (with high zinc/phosphorus) be any better than mineral?

I am currently using Millers CTV 20w50 Semi so I would also be interested to hear people thoughts on this?

[bluedragon]

The zinc issue is somewhat overblown IMHO, because the manufacturers can and do use other compounds to combat wear. Also more is not better - there is a point where you can have too much zinc compound.

 

The frictional issue with synthetics being excessively slick is a potential one, but if I read the technical explanations correctly, it applies to any modern-certification oil not just synthetics. Improved friction reduction is part of the latest specs for motor oil.

 

In the case of synchronizer operation, I would think any negative effects from "too slick" oil would show up very quickly after switching. Shifting characteristics would change very quickly. So IMHO if the oil you are using is giving "normal" shifting action, then there's nothing to worry about from the friction aspect.

 

I've used Redline full synthetic for years, including a 5,000 mile round trip in summer heat going up grades from sea level to a mile and a half above. No issues or failures. But Redline doesn't maintain an official certification. They say they meet those standards but are not certified, presumably so they can adjust their formulation as they think necessary. There are other such manufacturers.

 

I've considered motorcycle oils as an option as well, since those oils also lubricate transmissions (not to mention clutches) and have friction modifiers for that purpose.

 

Zinc poisoning of cat converters might be overblown anyway from my viewpoint. Those devices have been around since the 70's but the low-zinc oil standards came out 25 years later. My guess is that some governing body was looking at long-term emissions control compliance and thought "well, all those aging engines with worn out rings and valve guides are burning oil and killing catalytic converters as a result, so we need to fix that."

 

A healthy engine that's not burning oil poses little danger to the catalytic converter, high zinc levels or not, IMHO. And someone who's OK with an oil-burning gasoline motor is probably little concerned with emissions control performance anyway.

 

 

 

 

Dave

Edited by bluedragon, 28 January 2022 - 09:14 PM.

[OzOAP]

Valvoline VR1 20W-50.
I supply it with every engine I build.

[Cooperman]

Valvoline VR1 20W-50.
I supply it with every engine I build.

+1. It does seem the best oil for the old transverse A-Series. There is an arguably better oil called Kendall 20w50, but it is hard to find in the UK.

The only advice when using a 20w50 oil is to not start the engine from cold with the clutch pushed down. If you do, the clutch load is resolved through the thrust bearings and they can be a bit starved of oil until the pressure comes up. That causes higher crank thrust bearing wear and leads to crankshaft end float. Always start in neutral with the clutch engaged. Don't push the clutch down until you have a good indicated oil pressure.

[Miki Leyland]

I am using Valvoline VR1 20W50 for the first time in my Mini after years of reading how good it is, but It seems to loose oil pressure sooner than the Millers Classic Mini I always used, once the engine is at running temperature.