Mixing oil, bad idea?

[TimLambert7]

Please forgive, I'm hugely incompetent.

My MX-5 NC 2.0 is currently using 5W-30 Mobil Oil that's about 5k old.

Need to get some top up and have noticed a fully synthetic 'upgrade' oil for £5 more. Still Mobil but is 0W-40

Car will be spending a bit more time on track over the summer, it'll likely make bugger all difference but will it be OK to use?

Before I get slated, my guess is that it won't be OK and mixing oil is actually hugely stupid.

Thanks

[ohtari]

Firstly, you won't cause any harm by mixing the oils. There's little difference between them.

Secondly, if you're going to be hitting the track this summer, you should probably change it out before that point anyway. Trackdays are seriously hard on the engine oil.

[TimLambert7]

ohtari said:

Firstly, you won't cause any harm by mixing the oils. There's little difference between them.

Secondly, if you're going to be hitting the track this summer, you should probably change it out before that point anyway. Trackdays are seriously hard on the engine oil.

Thanks for your reply.

I'm not going to be doing anything too mental but I'll certainly consider changing the oil soon.

I was quite surprised how much oil it used in my 25 minute Silverstone session recently...

[littleredrooster]

No problem mixing those oils.

The only oil that cannot be mixed is a castor-based oil, like the competition 'R' stuff from Castrol. These castor oils tend to be difficult to find anyway, usually only from specialist outlets; anything you can buy from a local garage or motor factor can be safely mixed.

The only other thing which would make it unwise would be the age - and therefore the spec. - of the oil; yours probably needs something like SF or better and a really old oil which has been stored, for example, may only be SD or SE. ('S' stands for spark ignition - i.e. petrol engined as opposed to 'C' which is for compression ignition, or diesel; the second letter is the spec. and advances alphabetically with each spec. change)

{Memory dump now complete}

[Robert Elise]

noticably using oil in one 25 min session? wow.
The NC engine can fail with low oil, so be careful. It's not good to be low on oil with any engine of course, but the Duratecs are getting a bad name in comparison to the robust NA & NBs. Definitely worth using a full synth and move to a 5/40 for track use.

[skinny]

part synthetic oils are a mix of full synthetic and mineral. i.e. you'll be fine to mix.

i'd suggest you aren't fine on a 5W-30 especially on track tho - this is a pretty thin oil at high temps, probably explains your high oil consumption. change it out to a 5W-40 etc.

[ShaunTheSheep]

I wouldn't change that good quality, newish oil until after the track day

[anonymous-user]

ShaunTheSheep said:

I wouldn't change that good quality, newish oil until after the track day.

Agreed, and I wouldn't fret about mixing two grades of Mobil 1 either.

[cars1993]

Its generally OK if you plan to change the oil in the next few hundred miles but don't mix things like Magnitec with normal oils....

[littleredrooster]

cars1993 said:

Its generally OK if you plan to change the oil in the next few hundred miles but don't mix things like Magnitec with normal oils....

Really? What is so special about Magnatec?