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MG MGF Technical - Oil revisited

I've left a query about oil on the saloon thread, but I might get a quicker answer here!

I read in a TF manual (52 plate non VVC) that you can switch engine oil to 5W/30 and see improvements in fuel economy. Can I do the same on a 51 plate 1.4 ZR?

Thanks!!!
Gary

I can't see why not, but you should note that the alterations in the viscosity of the oil may have an impact on long term longevity of the oil and ultimately, the engine too.
Rob Bell

Not sure if its just coincidence but i used Castrol Magnatec and only recently changed to Mobil 1

A week and 300 miles later HGF !!

Like i say probably a coincidence but i suppose the first HGF (only suspected) at 72000miles aint too bad ...

Changing the oil for the sake of a couple of miles more per tank could prove costly...

Stu

Stu Dickens

Stu,

In theory a full synthetic should help cooling, wheras Magnetec may help with start up.

Thicker the oil film on engine the better protection and cooling, but if the oil film is too thick and restricts parts from easy sliding there is an excessive drag and additional loss in power.

F1 for example, on a small and twisty circuits of Monaco where speeds are low, thicker oils are used which provides better protection for engine.

For high speed circuits like Monza they would use an oil which will reduces mechanical waste of energy on friction.

So tends to be a compromise, although better quality oils should have a better additive package whatever viscosity.

Paul
Paul

Mobil 1 comes as 0W/40, but Castrol could be one of several grades. Mobil 1 would be a superior grade to what ever was in there before, and not too thin at operating termperature either. But you say, "suspected" HGF? I think oil would only cause HGF if it were not circulating properly or there was not enough oil, say, caused by a leak. But not, as a cause of the oil itself.
Gary

I ran my F on Mobil 1 for 120,000 miles without problem. I switched to it after the engine had been sufficiently run in (12,000 miles). I switched back to Magnatec at the 132,000 mile service.

Prior to using Mobil 1 and after reverting to Magnatec the oil temperature regularly exceeded 120 degrees. Whilst using Mobil 1 the needle hardly ever went avove 90 degrees.

Ralph
Ralph

that's interesting Ralph, because ( I assume) cooler equals better, and you only know this because of an oil temperature gauge that most cars don't have. I'm going to use 0W/30 because that is thinner than 5W/30 at start up, the same as the 0W/40 in Mobil One. 5W/30 comes as Castrol Magnatec, and 0W/30 comes as Castrol SLX, but unfortuneately I haven't been able to find if these grades come in any other brands.
Gary

I have two full bottles of Mobil 1 (legacy of my old 220 which used to use on average 1/2 litre a week)which I was considering using in my TF but so far 6,600 miles later, the oil level which I check on a weekly basis, hasn't moved which is starting to worry me after being used to 1/2 litre a week.

However, I'm had second thoughts as I've read somewhere that the recommended oil for the K (can't remember if it was VVC only) has been changed from fully synthentic to part synthentic due to oil thinning out when the engine heats up and casing the big end to go!

AHHHHHHHHH!!!!!! Why can't life be straight forward?
J Ip

Since the last service I have not seen the oil temp rise about 90 even after a good motorway dash. Yesterday I spoke to Techspeed to find out what oil they put in as it needs a top up. It turns out to be Mobil 1, so I concure with Ralph's comments about oil temp.
Steve Ratledge

Hi,

<I've read somewhere that the recommended oil for the K (can't remember if it was VVC only) has been changed from fully synthentic to part synthentic due to oil thinning out when the engine heats up and casing the big end to go!>

I would be interested to read this: if there is any change to the VVC oil specs I would think it's to do with the VVC mechanism rather than the big-ends, which are fairly robust proven items.

As for synthetic oil thinning when its hot (thinning more than mineral oil, presumably), this is, like the government's ethical foreign policy, just a myth. A 40 weight multigrade oil, if that's what we're talking about, conforms to the SAE spec in that it will have the same viscocity range at 100 deg C as a straight 40 grade oil. This spec applies to any automotive oil, whether vegetable, mineral or synthetic.

All this is fine, except that the viscosity range for 40 grade oil is quite wide, and an oil can be at the low (thin) end or at the high (thick) end and still be within spec. The viscosity range for 40 weight oils is between 12.5 and 16.3 cSt (just take it as a range please). Info I have is..

Shell Helix Ultra 5W-40 - 13.8
Mobil 1 0W-40 - 14.4

So both of these are towards the middle of the range: of course specs can change, and even each batch can vary. If you bear in mind that a synthetic oil is more likely to remain in spec when in use than a mineral oil, then the accusations of thinning are even more silly.

For the dedicated tribologist there's lots more on this to be found with a few hours surfing.

Regards, Kes.
Kes

Thanks Kes, At least I haven't wasted all that oil. Forgot to say that I noticed that my old car seemed to run at lower temp when I was using Mobil. Also, I switched from Magnetec 10/40 because I found that it made my car sound like diesel at start up whereas the Mobil didn't.
J Ip

Kes,

Comment in relation to hydraulic followers see ZS.

I would agree with you that a full synth in same viscosity range should be better performer to stay in spec, allowing for extended drain.

Paul
Paul

This thread was discussed between 30/03/2004 and 10/04/2004

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