Which Oil Grade?

[screwloose]

Hi guys, I've been reading up on what type of oil I should use for a MX5 Mk2 1.8 and haven't really found a definitive answer. Recommendations really seem to vary so what would you guys use?
The car has done just under 100k if that has any baring on it?

Thanks

[Munter]

I'd stick Mobil 1 0w-40 in it if it was me.

[robgee1964]

Owners manual viscosity chart suggests 10W40 for UK temperature range. I ran mine on 10W40 semi.

You don't want to go too thin on a higher mileage engine, or if you intend to drive the car hard.

[MX-5 Lazza]

Ignore the owners manual. Oil has come a long way since that was written. The Mobil 1 0W-40 is ideal for pretty much any MX5 regardless of miles (and is around £29 for 5L at Costco ).

[PlayersNo6]

My car (01X Mk2) has always had 10W-40 semi synth put in by the main dealers. Over the years various stuff has been used - BP Visco 3000, Castrol GTX and Magnatec.

I used my local independent this year and bought s/s 10W-40 Shell Helix HX7. Castrol can sometimes be found half price at Tescos.

I'd be happy to upgrade to fully synth but not sure of the benefits in a relatively old design engine like the MX5 - plus the car only does 4k a year.

[screwloose]

Its happening again....

[attym3]

Not sure if the 1.8 uses the same as the 1.6 but when I changed my oil I used Castrol Magnatec 10w40 part synthetic.

Mark

[Munter]

screwloose said:

Its happening again....

The point is that the last number should be a 40. The first number can be anything from a 10 down. And if you want the engine to do 300,000 miles use a top quality fully synth. If you'd be happy with 200,000 miles, use a good brand semi synth.

The engine is tough. And normally will outlast the body/your ownership, pretty much regardless of the oil used.

[MX-5 Lazza]

Back when Newbury Mazda were an MX5 specialist main dealer they would only ever use Mobil1 0W-40 as they said it was the best oil for these engines. I've always used it and never seen any reason not to believe them.

[screwloose]

This may sound daft but which type of Mobil 1 0W 40 should I be using?
There seem to be a few at that grade.

thanks

[denniswise9]

Autolink - the MX5 specialist near me use 10w 40 semi synthetic.

[MX-5 Lazza]

screwloose said:

This may sound daft but which type of Mobil 1 0W 40 should I be using?
There seem to be a few at that grade.

thanks

There is only 1 Mobil 1 0W-40 assuming you aren't looking at the Turbo-Diesel version (which is actually exactly the same anyway). I think they call it something like "New Life" now

[thecremeegg]

I put 5W-30 in mine, am I a bad person? Over on Nutz most people on there seem to be running 5W30 or 0W30 from what I gathered.

[robgee1964]

MX-5 Lazza said:

Ignore the owners manual.

Don't go changing the recommended grade just because some glossy magazine ad says so. All the durability testing and validation of these engines will have been carried out using the grades shown in the manual. The engine is still 20 year old technology - keep it fed with what it was designed with and you can't go wrong.

Although the second number relates to the hot viscosity, this is only at quite an elevated temperature. At normal and intermediate temperatures, the oil will be thinner. Further more, the viscosity curve is very non linear, which means at intermediate temperatures it will be a *lot* thinner than a 10W40.

One possible advantage of a thinner oil is lower friction, although on a well used engine friction is lower anyway, as the running clearances are all greater than a new engine. At the same time, these greater clearances means a thinner oil will hold less pressure, thus increasing the risk of metal to metal contact on big end or main bearings. Unless some serious validation work has been carried out on that particular engine then its really not worth chancing it. Its worth noting that some of the motorsport boys actually go a grade thicker, on certain cars.

Edited by robgee1964 on Tuesday 16th August 00:14

[skinny]

robgee1964 said:

Although the second number relates to the hot viscosity, this is only at quite an elevated temperature. At normal and intermediate temperatures, the oil will be thinner. Further more, the viscosity curve is very non linear, which means at intermediate temperatures it will be a *lot* thinner than a 10W40.

the second number relates to the hot viscosity, which is based on the kV100 number - i.e. the kinematic viscosity of the oil at 100 deg C, which is pretty much normal operating temperature.

at lower temps, the oil will be thicker, not thinner.

[robgee1964]

skinny said:

at lower temps, the oil will be thicker, not thinner.

Sorry what I meant was, at intermediate and lower temperatures the 0W40 will be thinner than the 10W40. So 0W and 5W oils are good if your doing a lot of sub-zero cold starts, which is shown on a typical owners book viscosity chart.

Edited by robgee1964 on Tuesday 16th August 14:24

[screwloose]

OK....I'm really sorry but I'm still no better off than when I started.

0W 30?
5W 30?
0W 40?
10W 40?

I'm at a loss. All I do know is that I will be using fully synthetic.

[skinny]

yep. a lot of people get scared by 0W oils, saying they will be too thin for their car. however, they are only thinner than a 10W oil at lower temps, where it's a benefit to have thin oil for circulation. if the second number is the same, then the hot viscosity is the same.

[robgee1964]

Right well to get back to the OP's question

The following options have been suggested :-

1) The manufacturer recommends 10W40. Their choice will have been fully validated during development.
2) Some people on the internet have used 0W40, and 5W30, and don't appear to have encountered any problems.
3) If you go on the mobil website, for a 1999 MX5 1.8, they recommend mobil super X1 10W40, or 5W30 if operating below 0degC.
http://www.mobil.co.uk/UK-English-LCW/carengineoil...
They also advise you to double check their recommendation against the manufacturers specification.

So you pays yer money and takes yer choice, but it does seem a 2 out 3 vote for 10W40.

If your going for fully synth, are you confident thats whats its had in before? Some people advise against suddenly switching to fully synth on a high mileage engine.

skinny said:

if the second number is the same, then the hot viscosity is the same.

Based on that reasoning the viscosity charts could be dispensed with, however there has to be a good reason why the manufacturers continue to publish this information. I wonder what happens to the viscosity of a 0W40 once you go above 100degC, compared with a 10W40?

Edited by robgee1964 on Tuesday 16th August 17:59

[rovermorris999]

''Based on that reasoning the viscosity charts could be dispensed with, however there has to be a good reason why the manufacturers continue to publish this information. I wonder what happens to the viscosity of a 0W40 once you go above 100degC, compared with a 10W40?''

Nowt untoward if it's a decent fully synth which it would likely need to be to reach that spec in the first place.