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Oil Change - 10w40 Semi Synthetic or 0w40 Fully Synthetic?

28K views 30 replies 15 participants last post by  IanMc 
#1 ·
Hi all,

I'm looking for a bit of advice from you all on what oil to use on my 53 plate TF 160.

I understand oils and chemicals well, as I've worked for an automotive oil company for some time now, but as much as I understand about the different oils, flow rates, additive packages, manufacturer approvals, etc, I need a bit guidance about the mechanics of the VVC engine.

I plan to change the oil in my TF every 6 months and having read the owners manual, I understand that any 10w40 (Fully or Semi Synthetic) oil is ok to use. It states that 5w30 can be used on all TF engines, except for the VVC. Anyone know why?

Halfords recommend 10w40, but state that if you want 'extra protection', to use a 5w40 Fully Synthetic. Castrol also recommend a 5w40 as their first choice oil for the VVC.

I was planning to use Mobil 1 0w40 Fully Synthetic, as I trust the brand and it's quality. This oil is basically thinner when cold than 10w40 and 5w30 oils, but it's flow rate when at full operating temp, is the same as 10w40 and a little bit thicker than 5w30.

So, does anyone think that 0w40 is going to be too thin when cold? Will it not be sufficiently protcting the engine at start up? I don't think it will be a bad thing to use this grade, as the oil pump will be able to pump it round the engine faster at start up and hopefully limit wear at the top of the engine.

Sorry for the long post, but I wanted some opinions on this from you guys and also to find out if I'm talking rubbish or not!

Many thanks,

Nick
 
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#4 ·
The lubrication scheme for the VVC mechs is frankly barely adequate. I understand your theory and can't really fault it except that experience on here has shown that problems do arise with the lower viscocity synthetics.
I used a 5W40 synth for a period but started getting some tapping from the VVC. Changing back to 10W40 semi hasn't totally cured it but its better and at least not getting any worse.

Not sure I agree with your statement about the oil pump delivering more flow with a thinner oil ; its a positive displacement gear pump so delivery will be related to engine speed (until the downstream resistance causes the relief valve to open) If anything a thinner oil will result in less delivery due to leakage through the pump clearances.

We all seek extra performance through less viscous drag but for the VVC its just not worth it imo.
 
#5 ·
Thanks for your replies guys.

Tim, some goods points made there, ones which I hadn't thought about! Great info about the oil pump too, I wasn't aware it functioned in the way you described! (You've tought me something new for the day!) I see your points with regards to oil viscosity hindering the oil pump, so on this basis I think I'll skip the Fully Synthetic options and stay with a good quality 10w40 Semi Synthetic.

I would normally use Mobil Super S, if I need a 10w40 Semi, but to be honest, I think I'll go with the Castrol Magnatec, as it seems most of you guys use it with no issues.

Thanks again Tim and others who have read/replied to this thread.

Kind regards,

Nick
 
#6 ·
For 6 monthly changes I would consider using a manufacturer reccomended oil - i'm using GM's 10w40 at the moment and change that every six months. I think the xpart stuff is as good quality and about the same price.

Trade off between quality, tiem it will be in the engine and how much you are prepared to spend.
 
#7 ·
I've used Mobil 1 and Castrol RS 0w/40 with no problems whatsoever. If you are planning on changing the oil every six months then a semi would probably do but depending on mileage and usage you could use a synthetic and change it once a year.
The viscosity range is dependant on the ambient temperature of where you live. Here in the UK a 10w/40 is suitable from -20 C to 50 C, however in Scandinavia where the temperature is lower in winter a 0w or 5w/40 would be more suitable. In a hotter climate where the temperature doesn't drop below freezing then a 15w/40 or 15w/50 would be suitable there. So does that mean we have to use 10w/40 in the UK - no. A 0w or 5w will work fine and provide quicker circulation and protection on a cold start.
 
#8 ·
So many opinions and experiences. It would be very interesting to nail this business.

Anthracite - do you have access to any viscocity/temperature graphs, I've never seen any published. Its probably not just about viscocity at the two end points but what happens in the middle.
 
#9 ·
So many opinions and experiences. It would be very interesting to nail this business.

Anthracite - do you have access to any viscocity/temperature graphs, I've never seen any published. Its probably not just about viscocity at the two end points but what happens in the middle.

I've used 0w 40 fully synthetic for the whole life of my last engine, ok it went bang last weekend but I'd done 175,000 miles on that one, I tried semi but it seemed to smoke a little
 
#15 ·
I'll see if I can get hold hold of any graphs/technical data.

This debate is very interesting. I have never known an engine spark such discussion! The dedication of all of you guys, in wanting to assist other mebers of the forum with any issues they have, is second to none!

What I am shocked with, is that an engine that seems to so complicated and advanced, requires an oil that is, by today's standards, a pretty basic blend and that is mainly relying on mineral oil technology, with very erratic and inconsistent molectular structures.

10w40 Semi replaced 15w40 Mineral about 5-6 years ago, as the generic choice of bulk oil for most decent independent workshops, and although I still see workshops today that use 20w50 and 15w40 in every car they service (becuase they genuinely believe that 'oil is oil'!), 10w40 is really the minimum standrard for most 'mondern' engines.

I know the VVC engine has been around for some time now, but so have VTEC engines and most of them now require 5w30 Fully Synthetic oils.

My concern with 0w40 Mobil 1, is that it would not offer the right level of protection at start up. With it being so thin when cold, compared to 10w40, I thought it might cause some wear. But then I thought it might not be a bad thing as the oil pump might not have to work as hard to get the oil to the top of the engine, thus getting it there quicker and preventing wear! Tim's concise response ended that theory, so I am now willing to stick with 10w40 Semi and Magnatec is leader the way with Mobil Super S a close second!

Nick
 
#18 · (Edited)
BPR 160,

Thanks for your response too. I can see this oil topic is the subject of contrasting opinions!

I was all set to use a Mobil 1 0w40, but for the time being I'm going to use Magnatec 10w40. I'll flush the engine with some cheap 10w40 tonight and fill back up with Magnatec, as well as change the filter.

A service is due in October, at which point my car will be 5 years old, so it's cambelt replacement time too! At this service I'll do it in accordance with MGR guidance and by then I should be clearer about what oil I'm going to use in the future! I'm going to speak with some of the industrial chemists at work later today and see what they think.

I felt that using Fully Synthetic 0w40 or 5w40 wouldn't do any harm compared to a 10w40 Semi Sunthetic and the fact that Castrol, Comma, Mobil and even Halfords recomend a Fully Synthetic as 1st chioce oil for the VVC, seems to confirm some consistency in this theory. However, I take the opinions and experiences of other VVC users seriously and I've got be honest, the negative experiences they have had, has put me off Fully Synthetic slightly! The ACEA specs across all of the aforementioned oils are pretty much the same (A3/B3).

Slightly off topic, but looking at your signature, it suggests you have a Milltek exhaust fitted? If so, is it any good?

Nick
 
#19 ·
You're right there on the contrasting opinions! But I think you will find that the postives outweigh the negatives! Both Lotus and Caterham by the way recommend synthetic oil for their K engined cars.

If you haven't bought the filter yet then I suggest Unipart GFE404/Halfords HOF231 - its a higher capacity filter. You will need to prime it with oil at least twice before fitting it.

I do indeed have the Milltek SP exhaust and it is excellently made. However it's distinctive sound is not everyone's cup of tea so you will need to listen to some at Silverstone or MGFest to see which one you prefer.
 

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#20 · (Edited)
in an older non-rover application, well an old lancia all alloy injection flat4 actually,I found that mobil1 could give knock on start up when hot. That engine design was prone to oil drain even given a non drain bowl in the oil filter a slightly thicker oil provided much quicker lubrication to the important parts maybe not just due to drain but because the oil pump could push it more effectively. I've found that thin synthetics are fine on brand new/nearly new engines or older engines that have always been run on them but in general older engines seem happier on a bit thicker oil but this can be synthetic they aren't all thin!! only my opinion by the way based on my experiences i can also say that many old engines run conspicously smoother at the red line on synthetic. If i remember right Fiat lubricants used to, and probably still do, make a synthetic specially for higher mileage engines it was 20w60 and rather good HPX I think it was called?? and also a 'racing' synthetic of similar grade (10w60 I think)
 
#21 ·
I once searched the net for info on the semi v fully synthetic oil subject albeit aimed at motorcycles, I found an interesting article by a former oil company chemist & his opinion was that unless you are racing a bike you are wasting money buying fully synthetic oil, so maybe thats the same for cars?
 
#22 ·
Castrol lost me as a customer when the changed the 4.5 litre bottles to 4 for 10w40.

I now use Mobil 1 Super S and have no issues. The engine runs well enough on 10w40 so I see no reasons to change it to fully synth as I doubt it would make any beneficial difference. All you are left with is risk from what people have said.
 
#24 ·
Howard retired Lubricant specialist >30 years

Re the SAE viscosity grade for MGF VVC.

The K series engine was designed in the 1990s like many other engine manufactures at that time, did not produce the fine piston and ring clearances of the engines built in the last 10 -15 years where ring and piston clearance are tight to meet the tailpipe emission requirements.

So the previous generation would use some engine oil small amount depending on engine condition which the engine manufactures had to factor engine oil viscosity into the equation.

At that time SAE 10W-40 gave the best conditions for oil control with the viscosity at 10W (W= winter) to protect the engine at cold morning starts and as a multigrade oil the SAE 40 viscosity gave good engine lubrication in the high temperature and high shear stress at higher rpm engine speeds. The synthetic oils gave better protection at start up and SAE 40 'stay-in-grade' gave better protection at the normal operating engine conditions which is due the oil's very high viscosity index (HVI) of 140 to 150 vs standard mineral VI around 95. What this means is at the when the synthetic oil is at running temperature the oil will lose less viscosity than a SAE 40 mineral oil so it will give better lubrication.

These 5W-30, 0W-20 etc are only suitable for the modern engines that have to meet the more severe EURO 5 and 6 tailpipe emissions and where turbo charges are becoming standard issue.
 
#31 ·
More like boring....
 
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