- My model of MX-5 is: NB 1.6 California__
- I’m based near: __
- I’m looking for technical help or recommendations on: __
Can I use 5W30 semi-synthetic instead of 10W40?
I have 5L in my garage and wondered if i could use it for an oil change?
For what it costs I’d stick with using the 10w 40.
3 Likes
Never skimp on oil
I have a list of things not to do but most are nsfw 
1 Like
my comment was more about using semi-synthetic. For the UK mainland 5W30 or 10W40 but the 5W30 would be better if you had to choose from those two.
However I use Mobil 1 Fully Synthetic 0W40 in mine, change oil and filter every 10k or two trackdays whichever comes first.
2 Likes
I always prefer to rely on the actual manufacturer’s own manual for the type, rather than ask for online opinion. 
1 Like
yes quite agree with that. using 0W40 Fully Synthetic in my car is my own decision.
2 Likes
Oil technology moves on.
Why not take advantage?
1 Like
Certainly, why not?
But the the world-wide SAE standards for measurement of viscosity haven’t changed since they were first laid down and my preference is to stick by the manufacturer’s recommendations.
Yea but as i said its a personal choice however 0W40 Fully Synthetic has better cold and hot flow characteristics compared to the oils recommended in the manual.
Its not like engine manufacturers never got things wrong with anything… 
2 Likes
Oil technology does move on and I’m sure the current 5w30 will be better than the 5w30 from 21 years ago…
2 Likes
If mine was a more highly tuned track day car I might be persuaded that its engine would possibly benefit from a more expensive, “high tech” oil. But we’re not talking F1 here; it’s an under-stressed, 1998 1.8, used on the road and it gets a good quality part synth, 10W/30 oil as per the owners’ manual.
Although the car is now 24 years old the engine is in very good condition and the latest MOT test emissions figures (from 4 weeks ago) indicate that it’s probably still just about as good as new…i.e. 5 ppm HC (limit 200 ppm) and 0% CO (limit 0.3%).
As the saying goes, you can pay your money and take your choice. TBH, I’m not sure that the older engines are actually too particular!
1 Like
I’m sad enough to have read a couple of oil studies and what came out of both if them was the leap in performance between fully synth and the rest
1 Like
I doubt it would provide a leap in performance in my NB though so there’s no point in me paying the extra to buy it, but if you think your car will benefit, that’s OK by me.
On the other hand, I recently bought a can of fully synthetic turbine oil for my other “fun” car because it does need it.
This guy usually makes sense but at the end of the day it would be hard to say anything is wrong as it’s impossible to run them side by side. Do what you are comfortable with.
1 Like
Not engine performance, oil performance.
Ie how long it lasts before needing to be changed, how high temperatures it will remain stable at and how well it protects the engine etc
1 Like
I fully understood what you meant. I meant that it will provide no tangible benefit in my car. 
To put it in perspective it’s over 24 years old and it has done an average of just 1890 road miles per year. The oil gets changed every year because of the low mileage. The factory recommendation is 100% fine; filling it with a higher quality oil would be a waste of money. As i said, the engine remains in very good condition despite its age.
My other car (not an MX-5) has a more highly stressed engine because it’s supercharged and I do use a fully synthetic oil in that plus a jet turbine oil in the blower gearbox.
Horses for courses.