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Fully synthetic oils


Swindon, Wiltshire
Anyone experienced any issues using 15-w40 synthetic oil in a 845cc R4?
Just making sure before running brand new engine bearings on it. I can only imagine it’s far better than the old mineral oils.
But nothing like experience from others?!


Personally from running various marque older engines and trying both fully synthetic and full mineral I would stick to good quality original spec oils, have run myself into problems using modern spec oils in old mineral design engines in the past( admittedly not Renault, but air cooled VWs and 60s Fords ), one in particular used 250ml of. synthetic every 1000 miles use from using zero mineral, back to zero when switched back to mineral, just think the lubrication properties of modern oils are different to straight mineral and also the detergents in the synthetics sludge up more in an older mineral designed lump whereas they don't in a more modern design.
If its designed 20/50 running it with 15/40 being slightly thinner wouldn't that increase the chance of early bearing wear on start up due to the 15 instead of 20 not giving the bearings the correct lubrication until oils up to pressure?
laxeian- must say I'm with you on this one.Synthetic oils are no doubt very good -for moderm engines with tighter tolarances and fancy alloys made of unobtainium and moon-dust, but simply not suitable or needed for ours. -R.

David M

French car tragic!
I have read that oils with a high zinc content are the most suitable for older engines. From my understanding, these oils protect the internal movements with a softer metal than the components of the original metals made by the manufacturers. I’m not going further because I can’t explain the science beyond equating it with galvanising.
We have a few local oil manufacturers in Australia producing these oils. Most appear to be mineral based. I think that one is a synthetic but that could be a potential issue with seals. I can’t say with certainty.

I’ve done a quick search for to UK and Castrol appears to have a mineral oil for “classic” engines. As do others. High zinc content does not seem a featured item so you would have to do some research. Because you have so many suppliers it should not be hard to make your engine well protected. Look for zinc (often with phosphorus addled- zddp). It’s an old oil technology developed in the 1930’s for racing engines- probably ok in ours!


Grumpy ol man
Hawkhurst, Kent
I have had a number of older cars inc my current ones Triumph TR6 engined and the GTL, I would never use synthetic unless it was Millers designed for Classics but bloody expensive. I use 20/50 mineral Classic oil, these were designed around our engines. I buy a classic oil from Rye Oils who make it for a number of suppliers it is very good, change it at less the manufacturers suggest to keep it clean. Never had a problem in the last 30 plus years in Rover V8, Chevy V8, Riley, Toyota and current engines.

Most synthetic will sludge up. they work best under tighter tolerances.



Laarbeek The Netherlands
I've always used (Elf/Total) 20w50 mineral based multigrade engine oil on my R4 GTL. Other good oild brands are Millers, Penrite or Gulf.
Never use modern synthetic that's for modern stuff,


Athens, Greece
Millions of R4s over its almost 60 years of existence have done hundreds of millions of kilometers, most of them on single grade mineral oil, and having changed a lot of oil formulation along this time span. I doubt there was a single engine failure caused by inferior oil quality. The lubrication system of this engine is designed around '50s oil technology, and should not need any more than a good mineral oil. There is a good point of argument here, mineral oils of the past were primary products of crude oil, not recycled like today's, but even so, today's low detergent and additive stuff is fine.
There are no weak links in our lubrication system, and points that do not receive hydrostatic lubrication like camshaft/followers or rocker gear are very well conceived and need no further attention, lubricant-wise. Talk about this with a Simca or Ford Pinto Escort owner for example, and you are going to hear horror stories!
Synthetic or synthetic blend oils are a definite no for using in engines without an oil filter, as is the case on pre-70s R4s. The detergent additives in these continuously flush the lubrication system, which is good, but debris, sludge etc. is meant to end in the - efficient - oil filter of the modern engine. Without this, they float around in the oil and usually end up on a main or big end bearing.