Synthetic Gearbox Oil - rg

Would list members replace mineral gear oil with synthetic?

Any noise suppresion/leakage issues?

The XM at 76K is probably due a change. The wheel bearing noise I mentioned some time back sounds more like a very slight gear box noise. So slight that my local Citroen indie dismissed it as \"not something to worry about\". He has recommended Slick 50, but I would prefer a drain and decent oil.

Any feedback welcome.

Terry B, Andy Bairsto, any feedback on permissable XM transmission noise?


Synthetic Gearbox Oil - Aprilia
Yes. Synthetic gear oils generally more stable and more benign to synchro components. Noise/leakage unlikely to be any different.

Try Elf 'Synthese' 75W-90S fully synthetic to GL-5 spec.
Synthetic Gearbox Oil - Dizzy {P}

This is what I said in an earlier posting:

"I have used synthetic oil in my Triumph 2500 gearbox and overdrive for the past five or six years. It does leak a bit (slight seepage rather than drips) but it gives a superb gearchange right from cold, rather than the traditional heavy change, and I am pleased I used it."

No doubt the oil that Aprilia has recommended is the right one for your gearbox. Others thinking of changing to synthetic oil on different vehicles should make sure that they use the correct grade of course. Also perhaps worth a look in the owner's manual to make sure that the use of synthetic oil isn't exluded for technical reasons.

I absolutely agree that additives should be avoided.
Synthetic Gearbox Oil - Ben {P}
Avoid slick 50- its snake oil.
Synthetic Gearbox Oil - lezebre
I'm very pleased with the Amsoil I bought, from Demon Tweeks, a bit pricey though. It is one of the few which is compatible with both GL-4 and Gl-5. At least I presume that's what their spec 'GL-2 thru GL-5' means.

Otherwise it's important not to use a GL-4 when GL-5 is the requirement of your car (may not be "shockproof" enough)
nor to use GL-5 in a gearbox designed for GL-4 (the heavier duty compounds which are not required in this case could have a corrosive effect on the non ferrous moving parts).

I don't know which the big Cit is, but one of the most respected synthetics for a GL-4 gearbox is Redline MTL or MT90, depending on the required weight or grade.
Synthetic Gearbox Oil - lezebre
Although having just noticed Aprilia's recommendation, it would seem that the Redline MT wouldn't suit your gearbox, rg.
Synthetic Gearbox Oil - Aprilia
Ref. the 'corrosive' issue with GL-5 oils mentioned above - this is not so much of a problem with synthetics. Most synthetics use zinc-based EP additive (zinc dithiophosphate) - this is relatively benign and is the same EP additive used in ATF's (it doesn't damage the non-ferrous and fibre-based components and linings).
In contrast, most GL-5 mineral gear oils use sulphur-based EP additives - these are acidic and can attack non-ferrous components (gives trouble with the synchro assemblies!). This stuff has that characteristic 'EP smell'.

GL-4 is for 'lightly loaded' final drives and GL-5 is for 'moderate to severely loaded' final drives. You will find that most modern synthetic gear oils can meet GL-5 anyway.
Officially GL-1 - 5 ratings have been replaced by the MT-1 rating since 1995.
Synthetic Gearbox Oil - RichardW

Don't put synthetic oil in a Citroen gear box. For some reason they don't like it, and most people I have heard who have done it have drained after just a few miles and refilled with the recommended mineral oil and found it much better.


Is it illogical? It must be Citroen....
Synthetic Gearbox Oil - M.M

I'd agree with Richard in that the normal 75/80 is fine, it's the change that's important. Make sure it is drained into a clean container and look for any signs of "evidence" if you suspect a problem.

Stay away from additives.

As a matter of interest I put either semi-syn or fully syn into my Xantia last change and it didn't alter the gearchange at all...neither better of worse.

Synthetic Gearbox Oil - Aprilia
Either a synthetic or a mineral will do the job, but synthetics are a little more stable than mineral oils and have a higher film stregth (typically by a factor of four). This important under conditions of high shear (eg hypoid drive).

A synthetic is unlikely to make the 'box feel any different to a mineral oil, assuming the viscosity is the same. If you put the correct grade in, then you will not end up draining it out a few days later.

BTW, the 'EP additive' I was refering to above is the EP additive pack that the oil manufacturer adds to the oil to give it its EP properties. I was not referring to 'aftermarket additives'. Most of these EP additives are made by Lubrizol and then blended into the base oil by the oil company.
Synthetic Gearbox Oil - Dizzy {P}
The comments from M.M and Aprilia have made me rethink my support for changing to synthetic oil in gearboxes.

The Triumph that I mentioned earlier was an automatic and I converted it to manual+overdrive mainly to keep the engine speed down so that I could use unleaded petrol without fear of valve seat recession (that was 6 years and 11,000 miles ago and all is still well). It was at this point that I decided to try a synthetic oil.

What I *didn't* do was 'before and after' tests with mineral and synthetic oil. Having filled with synthetic oil, I found the gearchange to be easier and smoother than in any of the many manual-gearbox Triumphs that I have owned and/or driven in the past. I made the immediate assumption that this was a result of using synthetic oil ... but perhaps it was nothing to do with that at all!

I'm now going along with what I think both M.M and Aprilia are suggesting. That is, if the gearbox is working OK with mineral oil there is no point in changing to synthetic, especially since there is a slight risk of damage to non-ferrous components with some synthetics in some gearboxes.
Synthetic Gearbox Oil - Sooty Tailpipes

For anyone interested, I used to drive a Mazda which had brass/bronze synchros which would be damaged by the Sulphurus additives in some GL5s.

I emailed Comma (ESSO/Mobil) about this, and they confirmed that theirs was safe, and gave a good technical and chemical explanation, which unfortunatly I have lost over the years or would paste here.
Synthetic Gearbox Oil - Aprilia

It comes down to the type of EP additive used in the gear oil. Sulphur-based additives will damage non-ferrous components; zinc dithiophosphate additives are relatively benign and will not damage gearbox components.
Synthetic Gearbox Oil - Sooty Tailpipes
Yes, but what they said was that it does contain suphurous additives in the form of (I can't remember some alkali aliphatic something or others) and not Sulphur whats it which is what will corrode brass etc... It's a shame I lost the email. If someone is really interested, they could email them the same question.
Synthetic Gearbox Oil - mark999
I've just changed the Yaris gearbox oil with castrol synthetic,
even though it meets the required spec (75w-90 API GL-4 or 5)
The gear change when cold is appalling. Any Suggestions?
Synthetic Gearbox Oil - Sooty Tailpipes
Was it not appaulling before? or has your change coincided with these recent cold mornings? Is it just the cold shift that is bad?

Some people on www.c********.org , complain about Yaris (what is the plural of Yaris?) being reluctant to engage gears.
Synthetic Gearbox Oil - mark999
Definitely much worse than before the change and worse than the depths of winter last year. I'm going to change it again for some genuine Toyota gearbox oil at the weekend.
Synthetic Gearbox Oil - Cyd
I changed from Rovers own oil to Torco fully synthetic MTF about 2 years (30k) ago in my Rover 820 Vitesse Sport (the 200bhp version with the close ratio, torson equiped box). Noise is reduced and gearchange at all temperatures is much improved, especially when driving hard. No leakage at all.

These boxes are weak on the end of this engine and I know of people who've required rebuilds after 20k or so. The evidence is anecdotal, but the improved oil quality seems to be helping 'box longevity. My box was rebuilt at 94k, 6k before changing to the Torco.
Synthetic Gearbox Oil - mark999
Had the Yaris gearbox oil changed with Toyota own 75W-90, still very poor cold gearchange. Toyota had a look under warranty - initially they fitted a modified gear linkage. This improved the gearchangs markedly.
The final fix, however, was to change the gear oil for ATF fluid.
they used Shell DONAX TA.

Since the problems started when the gear oil was changed for the 75W-90 specified in the owners manual, I can only assume they use ATF as the factory fill.
Synthetic Gearbox Oil - Aprilia
ATF is a much lighter oil, so gearchange will improve. Obviously it is very different to a gear oil and you need to be sure that the warranty still applies. I would get a statement from the garage (or toytota UK technical dept.) that substitution of ATF for gear oil will not be detrimental to the durability of the gearbox.
Synthetic Gearbox Oil - KevDGill
Just out of interest - how often should gearbox oil be replaced? My Astra 1.7 TD has done 109k and I don't know whether it will ever have been done, and I don't recall seeing anything in the owner's manual about it (though I could easily be wrong)

What sort of oil would I be looking at and is it a big job to drain and replace it? Also is gearbox oil significantly more pricy than regular engine oil?


-- Kev (trying to look after this car after the last one died)
Synthetic Gearbox Oil - Aprilia
In *theory* the oil can last the 'life' of the 'box. However the oil does degrade (the long-chain molecules are sheared over time) and so in my view an oil change every couple of years is in order. It also flushes out suspended debris etc.
Many cars don't have a drain plug (inc. the Astra) so you need to remove the 'box oil pan and replace the gasket.

Gear oil varies greatly in price - there are some very expensive syths out there. £15-25 should get you a 5 litre can of a branded 75W-90. 5l of Elf fully-synth 75W-90S is about £22 to me at my local oil supplier.
Synthetic Gearbox Oil - Sooty Tailpipes

Bought this to change diff oil on my Omega, and also have used to change the oil on the mower by sucking it ou the fill hole rather than removing a hidden drain plug.

It holds 3rd of a litre.
Synthetic Gearbox Oil - Sooty Tailpipes
OK half a litre!


Value my car