Fully Synthetic Oils

[Cotswold Pete]

Been doing a bit or reading, and I see some folks talk about using fully synthetic on the LS400.

My question is based on my understanding that fully synthetic good for new high performance engines, as the cylinder to head gap is tight and you want oil film to bond ready for cold starts and minimise wear.

But once over 100K miles the gap will be wider so no real benefit with fully synthetic as cold start friction will be less than with a new engine, so a hybrid oil would be fine.

Any thoughts or comments appreciated.

I know the price differential is not huge, but interested in making sure that with 137K on clock the old lady is treated well.

Also if hybrids used in past, then to make best use of fully synthetic a full flush clean is best before a refill

[Malc]

I've been using Wilko semi synthetic 10/40 for years , it's less expensive and the car runs as sweet as a nut and doesn't use any oil, well hardly any, between annual 10,000'ish mile services

car's now done 146000 miles

Malc

[Newbie1]

Viscosity is one thing (and just like semi-or mineral oils, synthetic come in varying viscosities) but if you face temperature extremes (like extreme cold starts or high speed race driving) and perhaps want to get away with not changing oil as often, go for synthetic. For a climate like the UK and for non-race driving I think a semi 10w40 is fine. Pocket the difference.

[Rupert Dubreaux]

In my Mk3's I use Toyota 5w/30w synthetic ,£22.99 for 5 Litres delivered I change it every six months ,do a lot of stop start short journeys .

In the old Mk2 I use Castrol GTX 5w/30w often available at Asda for £12 for 4 litres .The old lady who owned it before told me that's what it liked so who am I to argue ,she had it ten years and I have had it over three and it is still going strong.

If you are changing it regularly then premium priced oils are a waste of money especially if you are on a tight budget .

[ambermarine]

I used Magnatec 15/40 in mk 1 for 16 years or should I say 14 years and 2 months because Castrol obsoleted 15/40s and I continued with the 10/40s I use that in my mark 4 but change every two years because I take that long to do 8k The filter I get in Flo every year its a fram 15k filter and they are highly regarded there.

[Cotswold Pete]

Just found some old notes, as in my Mk2 I used NNL 690 (3%) oil additive. Only tried it because it was free, and I was dabbling with Kleenoil filters about 5 years ago.

Found it made no difference to fuel consumption on the LS, but I was not doing any by-pass filtering with the engine.

Though we fitted a by-pass filter from Kleenoil with some 690 and the owner reckons he got 15% improvement in MPG with a 2.5 litre diesel pick-up with 125,000 on clock - but diesels do all sorts of horrible stuff to the sump oil.

I have seen NSX300's fitted with dual by-pass Kleenoil filters to help preserve turbos by keeping oil super clean, and only replacing the oil every 5th service.

As to what I'll do, probably see what my local mechanic says.

By the way anyone using Magnatec might find NNL 690 just as good, and means you can use less expensive oil as your starter

[bigjap]

i put mobil1 fully synthetic 0w/40w in mine its been okay,it cost about £30,it does'nt use any oil,i only do about 5000 miles a year.i was going to use 5/30,but the oil specialist i use locally put it all info into computer came out with this,as he said oils have improved considerately since 1997

[Malc]

The Wilko 10/40 is about half that price last time I looked !

Malc

[munday]

I will echo whats already been said really, the semi-synthetic oils will do the job. They will need changing more regularly as they break down quicker and are less resistant to temerature and shear loading.

I use Fully synth 5w-30 in mine because I can often get nice cheap deals.

[messi]

I was just last week by Lexus Birmingham that I should be using 5w 30 fully synth oil as its and 13 years old

[Cotswold Pete]

I will echo whats already been said really, the semi-synthetic oils will do the job. They will need changing more regularly as they break down quicker and are less resistant to temerature and shear loading.

I use Fully synth 5w-30 in mine because I can often get nice cheap deals.

This is what confuses me.

Oils do not break down. Lotus did research about 15 years ago (as well as Honda) and showed that oil breaks down when cranks run above 15000 rpm, then it destroys the long chain molecules and they do not re-heal when dropped back to the sump.

So the oil in a Lexus should be totally fine as the shear forces will never be high enough.

But the oil will pick up water, metal and other cr*p in daily usage.

Synthetic oil has a higher shear resistance than mineral oils, but I believe mineral oils break down above 10000rpm - much more than I would attempt in my motor.

Better lubrication at cold start helps the cylinders from re-boring each morning, and the additives in things like Magnatec do help with reducing stiction.

So if I took any oil out of any normal car and filtered it for above 3 micron particles it would be as good if not better than new oil - as it would have next to zero moisture in it (and no Magantec either).

The sulphur in the petrol or diesel will mix (eventually) with the sump oil and create suplhuric acid which is the main reason for having frequent oil change with diesels (more sulphur in diesel).

But all the recommendations are good, I will be checking out prices of the names mentioned.

If I can find the info on my computer on the Lotus V8 trials and oil analysis I will maybe post them - but not sure where i put them amongst all the stuff I have collected on the PC

[Titch LS]

I am using a fully synthetic 5w-30 at the moment but I've had a little bit of start-up rattle since I put it in, which I wasn't expecting. I might go back to a 10W-40 to see if it disappears. It only does it very occasionally and then only from stone cold. Oil consumption is negligible at 120K miles.