Oil advice and recommendations

clearout

Active Member
Messages
50
I've a degree in Chemistry but I find oils quite confusing not because of most peoples issues but more the word play around 'synthetic' and subtle marketing that seems to be used.

One thing though I see that a lot of people use 5w-40 but I was using 5W-30 and have just used 0W-30. The local Honda garage mentions they would use 5W-30 on the engine.

I'm interested to know what we think the main differences are with these oils. I'm assuming that as you guys vary a lot on the oil you use there are perhaps oils better suited to different situations?

Excuse any ignorance on my part :D
 

oilman

Authorised Advertiser
Messages
719
5w-30 is the same as 5w-40 when cold, they are both rated as 5w.

When hot they are different.

The 30 (sae 30) is in fact 11cst at 100degC and the 40 (sae 40) is 14cst at 100degC i.e. slightly for viscous and will handle high oil temps better.

To explain in simplistic terms, they fall into two viscosities.

If you see an expression such as 10W-40, the oil is a multigrade.

This simply means that the oil falls into 2 viscosity grades, in this case 10W & 40.

This is made possible by the inclusion of a polymer, a component which slows down the rate of thinning as the oil warms up and slows down the rate of thickening as the oil cools down.

It was first developed some 50 years ago to avoid the routine of using a thinner oil in winter and a thicker oil in summer.

For a 10w-40 to attain the specification target a 10W ( W = winter) the oil must have a certain maximum viscosity at low temperature. The actual viscosity and the temperature vary with the viscosity grade but in all cases the lower the number, the thinner the oil, e.g. a 5W oil is thinner than a 10W oil at temperatures encountered in UK winter conditions.

This is important because a thinner oil will circulate faster on cold start, affording better engine protection.

For a 10w-40 to attain the other specification target a 40 oil must fall within certain limits at 100 degC. In this case the temperature target does not vary with the viscosity grade, if there is no "W", the measuring temperature is always 100degC. Again the lower the number the thinner the oil, a 30 oil is thinner than a 40 oil at 100 degC., which is typical of maximum bulk oil temperatures in an operating engine.

The engine makers are, of course, very well aware of this and specify oils according to engine design features, oil pump capacities, manufacturing tolerances, ambient temperature conditions etc. It is important to follow these guidelines, they are important and are an are stipulated for good reasons.

If the engine has been modified, the operating conditions may well be outside the original design envelope. The stress on the oil caused by increased maximum revs, power output and temperature may indicate that oil of a different type and viscosity grade would be beneficial.

Cheers
Simon
 

oilman

Authorised Advertiser
Messages
719
Just found this old thread.

If you have any oily questions please post em up here.

Cheers

Guy.
 

logik

Advanced Member
Messages
1,630
Maybe you can go over gearbox oils? You have given super info on engine oils and i have taken your advice and just serviced with Motul 300V 5W-40.

But as for Gearbox oils, can you maybe give us some of your info?
 

tron2k3

Advanced Member
Messages
1,400
more info on Brake fluid please, which is the best for track use, wet and dry boiling points.

I used to use Motul RBF 600 but switch to Castrol SRF because the Motul stuff didn't seem upto the job. or have I made a bad decision?
 

oilman

Authorised Advertiser
Messages
719
logik said:
Maybe you can go over gearbox oils? You have given super info on engine oils and i have taken your advice and just serviced with Motul 300V 5W-40.

But as for Gearbox oils, can you maybe give us some of your info?
Your wish is our command ;)

What does API GL mean?

API stands for American Petroleum Industry and GL stands for Gear Lubricant, see below for their definitions:

API GL-1 Straight mineral oil
API GL-2 Mild EP for worm gears
API GL-3 Mild EP for spur and spiral bevel gears in axles and transmissions
API GL-4 Medium EP, MIL-L-2105 quality, moderate severity hypoid gears, manual transmissions
API GL-5 High EP, MIL-L-2105D quality, all hypoid axles, some manual transmissions
API GL-6 Extra high EP, now obsolete

Is it important to select the right API GL rating?

Yes. Selecting the correct gear oil performance level will provide the best protection to the components of the transmission.

What do the SAE grades mean?

SAE stands for the Society of Automotive Engineers. The SAE classification system is a way of defining how thin or how thick an oil is. This is known as an oil’s viscosity. The classifications are listed here in order of increasing thickness: SAE 75W, SAE 80W, SAE 85W, SAE 90, SAE 140, SAE 250.

What does EP mean?

EP means extreme pressure and refers to the additive used in gear oils. This additive is designed to stop metal-to-metal contact taking place between transmission components. The EP additives are usually based on sulphur and phosphorous. These elements bond to the metal surfaces where there are points of extreme pressure and temperature, forming a sacrificial chemical layer. The sulphur gives gear oils their characteristic smell.

Will synthetic gear oils and mineral gear oils mix together?

Yes, but beware that there two kinds of synthetic gear available: polyalphaolefin (PAO) based and polyalkylene glycol (PAG) based. PAOs are basically a man made version of mineral oils (although with greatly improved properties) and can therefore be mixed with mineral oils. In fact, semi-synthetic products have mineral and synthetic base fluids in them, so obviously, they must be able to mix. PAGs, on the other hand, will not mix with PAOs or mineral oil. Utmost care must be taken when using this kind of product.

What is a hypoid axle?

Hypoid is an abbreviation for hypocycloidal and relates to the geometry of the crown wheel and pinion arrangement usually on rear wheel drive cars. The pinion is usually highly offset to reduce propshaft intrusion into the passenger compartment.

Do I need a special oil for limited slip differentials?

Yes. When the power distribution between two drive shafts is no longer equal (usually due to the surface condition that the drive wheels are turning on, i.e. ice, mud), limited slip differentials are able to effectively lock the two half shafts, ensuring equal power distribution once again. When this limited slip differential mechanism ‘kicks in’ there is a high shock loading on the clutch mechanism that requires protection from wear and slippage. Use of the incorrect oil can lead to clutch degradation and vibration.

Why should I choose non-EP straight oils for my classic car?

Depending on the age, make and model non-EP gear oils may be required for use in gearboxes and final drives. Certain designs contained a lot of phosphor-bronze (copper containing) components that are sensitive particularly to the sulphur extreme pressure (EP) additive. The sulphur attacks the copper and destroys the integrity of the meshing gear surfaces.

Is it alright to use ATF in a manual gearbox?

Certain designs do specify the use of an ATF in manual gearboxes, but they should only be used where it is clearly stated by the manufacturer.

Is there one gear oil that will meet all my requirements?

This will depend on makes and models, but very often the answer is no. Gearboxes, final drives, transfer boxes, etc., all have their own specific lubrication requirements. The specification of the oil required will be outlined by the design engineers, who will determine which type of oil will provide the maximum protection to the transmission components. It may certainly be possible to rationalise and reduce the number of lubricants used, but the magical
single product may not be achievable.

What is the difference between a gear oil, an atf and an mtf and why are they sometimes interchangeable?

There is a fair amount of common ground, all do a basically similar job, an ATF could be regarded as a low viscosity gear oil with more precisely controlled frictional properties.

What is an MTF and why is it used instead of a gear oil?

MTF ( manual transmission fluid ) is a term preferred by some OEMs, perhaps they think it's more descriptive than "gear oil". It doesn't call up any particular performance or viscosity. For example a Volvo MTF will not be the same as a Honda MTF.

How do gear oil, atf and mtf viscosities relate to engine oil viscosities?

Gear oils and engine oils are classified by 2 different viscosity grading systems. A 75W-90 gear oil, for example, is about the same viscosity as a 10W-40 engine oil. In theory ATFs and MTFs can be any viscosity as required by the OEM. In practice ATFs are approx. the same viscosity as a SAE 10 engine oil or a ISO 32 hydraulic oil. MTFs are about the same, possibly slightly thicker.

What is a 75w gear oil as this is only a cold crank rating isn’t it?
The target here is 4.1 cSt minimum @ 100 deg. C + the low temp target. If the gear oil in question is, for example, a 75W-80 it must meet both specs which is effectively the 75W low temp + the high temp targets of both specs.; 4.1 cSt minimum for the SAE 75W and 7.0 - 11.0 cSt for the SAE 80. You can see that the SAE 80 target " overlays" the SAE 75W target so expect the KV 100 of a 75W-80 to be about 9 cSt.

Can one gear oil cover a number of viscosities like 75w-90, 80w-90 and 90 and why?

Yes it can, the viscosity grades are not mutually exclusive, it is possible to blend a gear oil with multigrade characteristics such that it falls within, for example, the SAE 75W and the SAE 90 viscosity bands. A mulitgrade oil ( gear or otherwise ) is simply an oil which falls into more than one viscosity grade.

Why do some synthetic gear oils cause poor shifting in older or high mileage boxes?

If this really happens it can be that the generally lower viscosity of a synthetic gear oil may not suit an older or worn box.

Can engine oils be used in gearboxes if they are the right viscosity and are there advantages to using them?

Engine oils can be used in certain gearboxes, in the past it was the norm to do just that. Modern engine oils can be expected to attain the baseline API GL4 performance required for gear protection. Viscosity is not likely to be an issue, the viscosity of a 10W-40 engine oil, for instance, approximates to a 75W-90 in gear oil terms. The gear oil viscosity grade system uses bigger numbers than the engine oil system but that doesn't mean the oils are thicker.

The advantages? The detergency and antiwear systems in engine oils may cope with excessive "competition" temperatures better. Engine oils are intended for a shorter service life than gear oils so one point to be aware of is the viscosity modifiers used in multigrade engine oils may not be as shear stable as true gear oil VM’s so a bigger viscosity drop in service is possible. If you are considering this, use a top quality shear stable engine oil, or talk to us first.

Are filled for life gear oils a gimmick and are they in the long term bad for your gearbox?

I wouldn't say they are a gimmick but they do assume "normal" service conditions. Having a modified engine putting more power through the box & competition conditions don't lend themselves to gentle gear changes so you may see higher wear rates and more wear debris in circulation. It's logical to change the oil periodically if only to flush out the wear debris.

Of course the discerning owner may wish to change the oil occcasionally even if the service conditions are considered to be less severe.

This may raise more questions than it answers but hopefully it is of use to some of you.

Regards
 

oilman

Authorised Advertiser
Messages
719
tron2k3 said:
more info on Brake fluid please, which is the best for track use, wet and dry boiling points.

I used to use Motul RBF 600 but switch to Castrol SRF because the Motul stuff didn't seem upto the job. or have I made a bad decision?
In pecking order

Castrol SRF (used by F1 teams not compatible with any others, for life)

http://www.opieoils.co.uk/p-740-castrol ... fluid.aspx

Motul RBF 660

http://www.opieoils.co.uk/p-1078-motul- ... stems.aspx

Motul RBF 600

http://www.opieoils.co.uk/p-894-motul-r ... stems.aspx

Silkolene Pro Race 2000

http://www.opieoils.co.uk/p-862-silkole ... fluid.aspx

All superb!

Cheers
 

logik

Advanced Member
Messages
1,630
I have just ordered the Amsoil MTF from Opieoils.co.uk. 3 litres of it so thats why i am asking mate :)
 

barrymcgrath

Member
Messages
21
Just read entire thread... Excellant info....

The oil debate continues to be a sticky one.... I was always using 10w 40 semi synthetic... My local Honda dealer told me to use nothing else... I might add as I'm at it that he is a complete nob!!! Most unhelpful guy ever...

So then spoke to a local tuning guy, and he gave me 5w 70 millers ( i think thats the grade, as it was a weird one).. Well this oil was crap... It used to heat up too much, and it smelled bad.. So I got that out and put back in my faithful Mobil one 10w 40 semi... All was fine.. I then decided to try Mobil 0w 40 fully synthetic... This oil was amazing... Stayed about 10 degrees colder than the semi... More of a surge through the vtec range. I found that the engine liked a lot of this oil though!! Was well happy with my decision, until a friends Dad, who is a mechanic told me that this oil was too light for my car, and it would damage the rings under long term use... So low and behold, I'm back to my Semi Syn again...

Who in the above message is talking waffle, and who is nearer to the truth???

Cheers....
 

barrymcgrath

Member
Messages
21
Also as we are talking about gear oil in this thread, I may ask your opinion....

At high revs, my gears sometimes were reluctant to do as I wanted....

I read on the net that this was a common problem, when gear oils werent changed regularly... I changed the gear oil, which was in it since I bought it last year... I was recommended Silkolene 75w 90... Put in the gear oil, and the changes are so much more effortless.... Going forward anyway.... There is one problem tho... When I want to drop from 3rd to 2nd, it just doesnt want to oblige... Now when the car was started before from cold, it never liked gear changes until it heated up... But 3rd to 2nd was never a problem... Have I got wear suddenly high-lighted by this new gear oil???

Cheers, Barry.
 

oilman

Authorised Advertiser
Messages
719
Barry,

Both are talking tosh, you can use semi or full synthetic with synthetic being the better quality choice as you have discovered, the Mobil 1 0w-40 is not too thin. Its a missunderstanding of how oil works.

For the gearbox the Syn 5 75w-90 is a bit on the thick side hence you are getting an issue down changing.

Try a proper synthetic MTF and it should all be good.

http://www.opieoils.co.uk/c-638-mtfs.aspx

Cheers

Guy.
 

barrymcgrath

Member
Messages
21
Thanks for the info... Good to hear the facts from someone that knows what they are talking about.... I will go back to 0w 40 next service so, and will change the gear oil asap.....

Cheers mate, appreciate it....

Barry....
 

Shanetyper

Advanced Member
Messages
276
castrol fully syn

i got castrol 10w-60 edge sport for mine for road use, was it a wise decision?? :?:
 

George K

Advanced Member
Messages
274
Oilman. at work for racing gearboxes we use Neo Oil - is this suitable for road use if of the correct viscosity?
Thanks
 
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