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MG ZR ZS ZT Technical - Oil (Again)

time for a second main service soon, and so to decide which oil to use this time (1.4ZR). For smooth running, fuel economy, and engine longevity, I think the expense is worthwhile. I had an extra mid service oil change and engine flush, filling up with Mobil One. Been very pleased with that. I noted too, from other contributors that you are supposed to let your engine bed in (for 20,000 miles?) before the switch to Mobil One. Then I saw in another car manual, that you can change to 5w 30 oil and expect to see a significant improvement to fuel economy.

Mobile One comes as 0w 40, and maybe one other - I can't remember. Who makes 5w 30? And just what do these mysterious figures mean?(again)

GARY - Extract from the CASTROL Classic Oil WEB SITE:

The Importance of Using the Correct Viscosity Lubricant

Using oil of the viscosity that is recommended for a particular vehicle is important, as it is the oils' viscosity that determines its ability to flow. A quick flowing oil (one of low viscosity) deposits a thin film on the engines' internals, whereas a slow flowing oil (one of higher viscosity) deposits a thicker film. Furthermore, temperature will affect oil viscosity and thin the oil at higher temperatures and provide less protection than required. To compound matters even further, some oil viscosities are more affected by temperature than others and therefore using the correct viscosity oil is important:

Too high a viscosity and excessive oil drag will cause the oil to heat up, additionally when starting an engine using an oil of too high a viscosity the lubricant will be unable to reach areas requiring lubrication quickly enough and rapid wear will result.

Too low a viscosity and the oil will provide inadequate lubrication and protection at high temperatures, when under pressure - in fact at all times.

The viscosity classification developed by the Society of Automotive Engineers of America (SAE) is universally adopted by both oil companies and motor manufacturers and recognises the following grades:


SAE 5w, 10w, 15w, 20w, SAE30, 40, 50, 60


SAE 5w/20, 5w/50, 10w/30, 10w/40, 15w/40, 15w/50, 20w/50, 10w/60

(The "W" following the number denotes Winter and indicates these grades being suitable in cold climatic conditions)

The secret of good oil is its formulation - the blend of base oil and the chemical additives which provide it with its particular character and safety margins
John McFeely

been doing some reading around myself -

The W number denotes Winter. The lower the number, the thinner the oil on start up. So lower is better. Thin oil gets pumped around the engine much quicker. Most engine wear occurs from cold start.

The second number is oil thickness at operating temperature, older engines need thicker oil.

My 1.4ZR is on a 51 plate. The manual states 10W/40, but I read the manual on a 1.8 non VVC TF on a 52 plate and it states that 5W/30 can be used instead, and the driver can expect to see improvements in fuel economy.



Try these for oily reading


as long as I'm not going to damage the engine, I'd like to use 0W/30

I can't tell from the Shell Helix site what grades the oil are.

That just leaves film strength to think about.

well, had the service done.

Went here -

printed these vouchers -

and/or use your Tesco Club card -

(I think you might need the vouchers from Tesco first)

asked for an engine flush prior to filling up with Castrol SLX at 0W/30 -

and finally, thinking about HGF, added 3 caps of this to the coolant -

the front wheels were checked for alignment, and yes I could feel the difference afterwards.

Very pleased with the car. Better than brand new - that is, apart from the scratches, scuffs, and stone chips. Drives nearly as good as a Metro now ;)

What none of the information on oils will tell you that if you use an unsuitable oil viscosity you may suffer from some oddities in respect of hydraulic followers. The KV6 uses the same as used in K4 VVC engines, which are different to those in the K4 non VVC engines. The characteristics are often diagnosed as worn or faulty tappets as you can hear ticking noises come from them, often coming and going, hot or cold. I have heard that changing from a synthetic with a low viscosity range, even though beating mimimum requirements, to a standard mineral oil with narrower and lower viscosity range provided a cure to the noise.

Food for thought!

Roger Parker


Tend to use Redline Water Wetter but must be worth a try with Royal Purple. Certainly with the V8 it delayed the overheating problem in extreme circumstances.


Brain faded a little so where I wrote 'to a standard mineral oil with narrower and lower viscosity' please read correctly as 'to a standard mineral oil with narrower and HIGHER viscosity'.

Roger Parker

Oh for gods sake - it's only a 'shopping trolley' 1.4 litre 105PS engine and not a fire breathing turbocharged V8! Jeeeeez.

Any 10W/40 semi-synthetic will be fine......unless you have money to burn!

the name says it all - "Eric"

Ignoring Eric, as ever, as you state, you are investing in the long term reliability on the car. I have used the Mobil 1 0W40 in my KV6 160 ZT and found the engine very willing to rev with reasonable fuel economy (I also use Shell Optimax) BUT... the tappet noise was there as Roger explains. Why, I do not know, since logic tells me that the thinner oil at cold start should pump up the hydraulic tappets faster than a 10W. However, I switched to 15W40 Royal Purple and that certainly quietened the tappets at the 36k service. I plan to do the same on wife's 98 214
The Royal Purple agent also mentioned he found that the 15W40 quietened the tappets on his wife's MG F and their Discovery.

The Shell comes in three grades, you need the SHell Ultra Helix. Also, be aware that the 10W40 mineral and semi-synthetic oils use an additive to achieve the multi-grade performance but fully synthetic oils generally have a better viscosity index and do not require additives to achieve the 0W or 5W40. The additives are susceptible to shear damage so a fully synthetic is likely to last better and maintain its original multi-grade status. In addition, apart from being very strong in detergency and keeping the engine clean, synthetics also have a stronger, more slippery, oil film and therefore can operate as effectively in 0W30 format thus offering better economy as you read.
Lastly, if you do a lot of extended driving, or short journeys, or even track days, the Mobil 1, Royal Purple or Shell Ultra Helix are all capable of going the distance, based on their excellent base stock and quality additive package. Yes, they're more expensive than the supermarket type packages, but you pays yer money!
HTH Martin
Martin ZT

(Where's the best place to get Royal Purple?)

It is easy to say - Just buy bigger and better, and spend more money to get more power. Apart from the expense, maybe Big and Powerful loses it's excitement just because you get used to it, and then you need even bigger and better once again. Public roads are clearly limited too, you can't drive as fast as you like whenever you want.

I'm interested in the subtle differences. If a few small improvements add a percentage point each, then together they become something greater.

I'm very pleased with Castrol SLX over Mobil One. Quieter, smoother, better pick up. The only downside is a quieter engine draws your attention to other noises of the car. I don't mind the sound of wind slipping over the car, it adds to it, but road noise isn't so good.

The weakest part of the 1.4 has to be the 1-2000 RPM engine range. This is where the engine spends the most time, so any improvement here is good.

Next part I want to explore is cold air induction. Also, comparing the differences between the standard 1.8 (120 Ps), and the 1.8 in the TF (135 Ps) may give some suggestions.


If the oil pours better then will it not also be better at drain back. Wheras a sticky oil (Magnatec)will already be in place, on basis of sales hype.

Is there a problem with Castrol base stock and additive package as never gets much of a mention.

The alternatives to Royal Purple would probably be Motul, Red Line and Amsoil.


I think that is part of the problem in that the tappet noise is more prevalent since the thinner oil drains back more readily. As far as Castrol goes, I don't have a lot of experience, but I guess one should look at a quality synthetic base with a quality additive package supported by an API/ACEA rating. Magnatec would help, but a quality oil has a balance of surface active additives, and I wonder whether too much stickiness would affect the anti-wear properties. Also, it's a semi-synth. base as far as I am aware. Amsoil - If I see another web site of theirs I shall scream!
Martin ZT


I am wondering whether Magnatec properties only work as a semi, as if as good as claimed, it would be used with a more pure thinner synthetic perhaps to prevent drain back.

Amsoil and Red line can keep you amused for hours!


This thread was discussed between 27/03/2004 and 16/04/2004

MG ZR ZS ZT Technical index

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