Technical What gearbox oil to use? Gl4? Gl5?
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Technical What gearbox oil to use? Gl4? Gl5?
Whilst I would not presume to know "everything" about the vast subject which is lubricants, I have taken a great interest in this subject and I hope I can contribute a wee bit here. Your manual is recommending Tutela ZC75 synth which it defines as an API GL5 with a viscosity (loosely meaning "thickness") of 75w 90. The EP stands for extreme pressure and means there are additives in the oil to combat high pressure contact - ie between gear teeth etc, where shearing forces can be very high.
API is the American Petroleum Institute a very highly regarded organisation who test the quality and performance of lubricants and give then an API rating. In Europe we have the ACEA who do a similar thing and some think, for us, the ACEA rating is actually better? You pays your money and takes your chances I suppose?
So, in an attempt to break down the info from your manual's recommended Tutela ZC75 synth:
1) Tutela? An oil brand made now by Petronas. you could choose anything, Shell, Mobil, Castrol, Fuchs, etc, etc, which had the same specification (ie API GL5 75w-90 which is the important bit).
2)API GL5? if that's what your book says then that's what you want to look for. API GL5 was the subject of a very big "scare" a few years ago when it was discovered that some of the anti-friction additives in it (which hadn't been in the older GL4 spec) were damaging the softer "yellow metal" - so stuff like brass and phosphor bronze. Some people would say it was dissolving it, it was actually more complicated than that but the effect was similar and cause abnormally fast degredation of important parts like synchro rings and thrust washers. The problem was that many people, including those who should have known better like retailers, thought that the "newer spec oil would be better in protecting older boxes from wear due to the "stronger" anti friction additives so were recommending their use. It would seem that the manufacturers quite quickly caught up with the problem and modified their formulations to stop these problems. So, as far as I've been able to find out, in theory, you are now OK to use a GL5 in a box where GL4 is specified? I wouldn't though. If my manual specified a GL4 I'd use a GL4! The oil for my Panda has a particularly interesting spec of GL4 plus! API don't actually specify a GL plus - just GL4. So what's that all about? I've seen someone who was speculating that it's actually basically a GL5 with the anti friction advantages that implies but Petronus have elected to brand it a GL4 plus so as not to frigten us "oldies" who remember the scare around GL5! who knows?
3) 75w-90. This is the viscosity, roughly interpreted as "thickness/ resistance to flow". The higher the number the greater the resistance to flow. So 75w-90, what does it mean? The "w", as far as I know, stands for "winter" but is better thought of as meaning "cold". So this particular oil has a viscosity index of 75 when cold (quite thin so flows easily - a desirable thing as the oil will quickly get to where it's needed) and the same viscosity as a hot 90 weight oil when hot. (This would seem to say that the box actually needs a 90 weight oil when it's up to running temperature and the oil has thinned with heat, but a 90 weight oil would be relatively treacle like when cold so bearings and bushings would not be lubricated properly and changing gear would be like stirring a pot of thick porridge! By using polymers to construct a 75w-90 the oil will have the characteristics of a 75 weight oil when cold but of a 90 weight oil when hot, then you can mix up a variety of additives to reduce wear and oxidation and lots of other "stuff" which further improves the performance.
The more viscous the oil the slower it will be to circulate to all the bits it needs to protect and the greater the drag on the gears and bearings so, of late, and because the quality of both synthetic oils and their additive packages are improving all the time, oils have been getting "thinner". Thinking about engine oils for instance, Honda I noticed the other day are specifying a 0w-20 engine oil for some of their newer cars now - back in the '50's it would typically have been a straight 30 weight in the summer and a change to a 40 weight in the winter. The in the '60's multigrades became common so we didn't need to change oil twice a year, and you would have been pouring a 20w-50 into your Cortina/Anglia/Mini. Our wee FIRE 8 valves to day run very happily on 5w-40 so nice and thin to get circulating when cold but with the "thickness" of a hot 40 weight when hot for added protection. The same seems to be applying to transmission oils. My old SEAT Cordoba ran on a relatively thick 80w-90 gear oil. I change gear oil roughly every 5 years/50,000 miles, whichever comes first (don't believe in "for life" fills) and last time I changed it I bought the genuine VAG recommended oil from TPS (so genuine VAG supplier) and it worried me a lot because it was like water compared to the older oil. I double checked and the recommendation was now to use the newer oil. So, with great trepidation, I did. It greatly improved the gear change which was now "super slick" compared to before. I fancy there was just a "tad" more gear whine, but I'm splitting hairs and she went on to cover many thousands more miles without a problem. I'm mentioning this because your Tutela ZC75 was quoted in your manual as a 75w-90 but looking at the Petronas spec: https://extranetpli-eu.pli-petronas.com/dsp/pdf/eng/scat/1475_scat_eng.pdf it now seems to be a 75w-80? This might well be because the improvement in the oil itself has permitted the same protection but with a slightly thinner viscosity with the associated gains in fuel consumption and gearbox operation.
So what is the conclusion? I think the old saying that "Mother knows best" was never truer. Buy the exact oil the manufacturer recommends if you want to be absolutely "bullet proof" It's what I tend to do. My number one supplier is Shop4parts: https://www.shop4parts.co.uk/?name=store&op=Product&ProdID=72 who have never failed me. The manufactureres themselves have excellent "look up" lists where all you need to do is feed in your reg no or vehicle details to get their recommendation and there are independants, like Opie oils, who also have the same service and where you can often buy at a discounted price. I'm a bit more "liberal" with engine oils - running most of the "family fleet" on Fuchs oils just now but always to the exact manufacturer's spec.
At the end of the day it's the API (or ACEA) spec and the viscosity which should rule your choice and because there are so many oils now which are almost "vehicle specific" I like to go, especially with transmission oils, for the actual manufacturer's recommended product. After all, how often do you change a gearbox's oil? not often eh? so a pound or so extra on the bill for the peace of mind it gives is, I think, an extra pound well spent!
Hope that was helpful? stay safe everyone
regards
Jock
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I've just looked into this.
If it was my car I would use gl4
Just to be on the safe side.
Straight 80
75w80
Or
75w90
Will all be fine.
I'm saying this because the punto was fitted with different engines and different gearboxes.
I looked up oil for gearbox specific for engine in your car.
If it was my car I would use gl4
Just to be on the safe side.
Straight 80
75w80
Or
75w90
Will all be fine.
I'm saying this because the punto was fitted with different engines and different gearboxes.
I looked up oil for gearbox specific for engine in your car.
Auld Jock's bible above is the full story for those with time on their hands. I have just 2 points to add to it. Gear oil seems to lose viscosity over time. Last time I filled my Punto 55 gearbox with fresh 90-140EP the gearchange definitely firmed up - for a while only, then it seemed to return to an easier normal change as the viscosity came down. Thicker oil is often specified for trucks which tend to leak or weep a little, such as 240 rather than 140. Secondly as in everything it's horses for courses. Here in Almeria with 105-110 in the shade as last week, 90EP is fine. In my Ducato caravan 6-berth in the same conditions working hard, 140EP is better. In Siberia both Punto and Ducato would probably prefer something around 20-50 if available. I once read of a round the world trip in a 2CV which had squashed bananas in the gearbox for many thousands of miles!
Your post about viscosity being lost over time has made me think of the rather pathetic way I used to try to explain multigrade oils to my student beginners. So, just in case my lengthy post above failed to be sufficiently boring, here's a simplistic way to think about it.
Firstly lets think about a mono grade oil, for instance an SAE 30 which you might well be using in the likes of your Briggs and Stratton engined lawn mower. You would notice that when cold and fresh from it's container it will pour not unlike washing up liquid. Then, perhaps half way through the summer, you decide to give it an oil change so, after mowing and with the engine hot, you drain the oil. You will immediately notice it's now very thin compared to when it was new and cold. This is because a mono grade oil will thin as it heats up. In days gone bye because only mono grade oils were available you would use a thin oil, maybe an SAE30, in the winter and a thicker, maybe SAE40, in the summer. This was in an attempt to maintain the same viscosity all year round - The thinner winter oil being used in colder conditions would not thin out so much and the thicker summer oil would thin more being in the hotter weather - or that was the theory anyway.
Then Polymers came on the scene and the oil producers learned how to incorporate them into their products. How do they work? Well lets think about one of the earlier multigrades - 20w 50. The "w" stands for winter by the way. This oil will have the viscosity (resistance to flowing, or "thickness" in other words) of an SAE 20 grade oil when cold (there is a specified temperature this is measured at, look it up yourself if you want more) and the viscosity of an SAE 50 grade oil WHEN HOT because the hot 50 weight is similar in thickness to the cold 20 weight. The end result is that you have an oil which doesn't substantially thin out, or will thin by a very carefully specified amount, as it heats up. How does it do this? It's all down to the behaviour of the polymers.
If you want the whole story you'll need to go to college and study chemistry then work for an oil blender. But, in very simple language, you can think of the polymers as behaving like tiny little octopi (plural of octopus). Imagine millions of them swimming around in the oil. When the oil is cold they have their tentacles wrapped tightly round themselves so they are like little smooth balls. In this configuration they will have no measurable effect on the oil's viscosity (ability to flow). However as the oil heats up so will the octopi and now they start to unwind their tentacles. The hotter the oil gets the more they will extend their tentacles until finally they are all linking their tentacle tips together so forming a sort of mesh.
So lets think about this for a minute. If we have an engine that needs an oil with an SAE 20 viscosity and we put a mono SAE 20 into it then that's fine when the engine and oil are cold but when the engine gets really hot the oil might well reduce it's viscosity to the state where it would be considered to be zero! Not good at all for the engine. But with the polymers in it, although the actual base oil itself will thin out as temperature increases, because the little octopi are extending their tentacles, the "mesh" they are creating is now making it much more difficult for the oil to flow. So, depending on what the chemists have done with their polymers, you might well find that the SAE20 grade base oil used still has a viscosity of SAE20 when it's hot. Clever eh?
Of course as it ages the polymer becomes less effective - think of it like some of the octopi arms being weakened or even chopped off - and they don't like getting too extremely hot either, so be very "picky" about your oil if your engine has a turbo (for this reason I prefer to use a straight oil in an aircooled engine where localized hot spots are likely to be generated when it's working hard - a whole different area for discussion). Gear boxes, and especially final drives, subject their oil to very high shearing forces which you don't find much in engines so, although most are now multigrade, they are formulated differently with additional anti friction additives to combat this.
When you start to really look into all this - and what I've said above is ridiculously simplistic - it shouts out one really simple message though, which is, NO OIL PERFORMS AT IT'S BEST INDEFINITELY! Hence the advice to change engine oil regularly (I recon, on your average daily driver that's once a year or 10 to 12,000 miles and gearbox oil I do at around 50,000 miles. But I would be guided by the manufacturer's recommendation if it was less.) For instance I think VW now recommend 40,000 miles on their DSG boxes.
So, anyone still awake and "with" me? Of course there is so much more to oils than their viscosity with sophisticated additive packages also playing their part (I'm not talking about that bottle of stuff on the shelf in the petrol station here but the very carefully formulated additives the manufacturers introduce into the oil during blending) and these additives get worn out and used up with age and use which again is why you must change your oil regularly.
So, as Fred Dibnah was famous for saying, "Did you like that"?
https://www.youtube.com/watch?v=4CV2GuK6CmY
And I can't think of a better way to end folks!
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