GL5 gear oil in the gearbox?

[KyleR]

I've heard GL5 has twice the sulphur and/or phosphorus levels of GL4 oils, is there any reason it can't be used in the 350 manual box? Apparently it corrodes yellow metals, any of those in there to worry about? I think GL4 is recommended?

 

GL5 is recommended for the diff apparently, so its fine in there

[karlh]

The yellow metals in your gearbox include the synchros. Using GL5 oils will damage them and make shifting difficult and noisy.

[KyleR]

Interesting, traders offer GL5 oils for the gearbox.

[KyleR]

So there's quite a few more choices of GL4 oils at 75w-80 or 75w-90 as apposed to the recommended 75w-85, which is apparently quite rare with Redline being the only one easily available after a quick search (I'm sure more are available if I put the time in).

 

What implications could there be using an oil with a slightly thinner or thicker viscosity? Or does 5w not really matter?

[Willsy1980]

I would think the thicker oil would make what can be a notchy box when cold, remain notchy a little longer than usual. I'd go with the recommended oil and add the molyslip. There are a few traders on here who can supply both.

[KyleR]

I went for the Fuchs Titan Race SYNCHRO 75W-90 in the end. I'm aware the viscosity will be marginally thicker than 75W85 when cold, But I'd like to try something other than the typical OEM stuff and prefer not to use any additives that may or may not actually do anything.

[Ekona]

75w-90 will be permanently thicker than 75w-85, as it's the last number that dictates ultimate viscosity at a set temperature (100c). It'll be identical when cold, that's the 75w bit.

 

Will the difference be noticeable? Possibly, but it'll also prevent against wear better.

Edited January 13, 2017 by Ekona

[KyleR]

75w-90 will be permanently thicker than 75w-85, as it's the last number that dictates ultimate viscosity at a set temperature (100c). It'll be identical when cold, that's the 75w bit.

 

Will the difference be noticeable? Possibly, but it'll also prevent against wear better.

 

Logic would suggest that, since they are both 75w they would be the same, however, from the researching I've been doing regarding the differences between 75W85 and 75W90, I've discovered that if the warm viscosity number changes, so does the cold, despite the number being identical. I'm pretty sure it was Oilman/OpieOils who spoke about this, on another forum I came across.

[Ekona]

He would know better than me, however it shouldn't do: the whole point of the numbers is so you know how oils behave compared with each other at fixed measurements.

 

http://www.upmpg.com/tech_articles/motoroil_viscosity/ is possibly the easiest to understand version of the data I've seen. If you look at the tables, it gives the limits as to where an oil will sit based on how it performs.

 

That said, my knowledge of oils isn't infallible by any means, this is just my understanding of them at a very basic level. It would seem very odd if by altering one rating the other then moved relative to a competing oil, as otherwise what's the point in giving measurements at all?

[KyleR]

He would know better than me, however it shouldn't do: the whole point of the numbers is so you know how oils behave compared with each other at fixed measurements.

 

http://www.upmpg.com...roil_viscosity/ is possibly the easiest to understand version of the data I've seen. If you look at the tables, it gives the limits as to where an oil will sit based on how it performs.

 

That said, my knowledge of oils isn't infallible by any means, this is just my understanding of them at a very basic level. It would seem very odd if by altering one rating the other then moved relative to a competing oil, as otherwise what's the point in giving measurements at all?

 

I completely agree. It was made worse when he or someone else listed the viscosity values of several oils from different manufacturers which are all sold as the same weight. To my understanding its calculated based on the amount of time it takes the oil at a set temperature to drain a set amount from a set sized hole, thats how the experts measure the weight. Well some of the times were almost twice that of other oils at the same weight, which puzzled me to say the least.

[KyleR]

This is one example I seen, I have no idea which manufacturer it is or if they are even from the same manufacturer, but it's taken from 2 data sheets, one 75w80 and the other 75w90.

 

SAE Viscosity Rating 75W-90

Relative Density @ 20º C 0.890

Viscosity @ 40º C, cSt 84.8

Viscosity @ 100º C, cSt 15.2

Viscosity Index 189

Flash Point (closed) º C 133

Pour Point º C -45

 

 

Viscosity Rating 75W/80W

Relative Density @ 20ºC 0.880

Viscosity @ 40ºC, cSt 56.3

Viscosity @ 100ºC, cSt 10.32

Viscosity Index 166

Flash Point,open ºC 159

Pour Point, ºC -39

 

As you can see, the viscosity measurements at both cold (40°C) and warm (100°C) are around 50% lower for the thinner 75w80. However, the thicker 75w90 appears to have a lower pour point, which I assume is the temperature at which the oil stops pouring at all.

[Ekona]

According to the wiki, the pour point is what you say but it's also much more affected by the paraffin content of the oil: High pour point, high paraffin content.

 

So would that make the bottom one 'not as good' in terms of quality as the top? That's how I read it, but I don't know how paraffin content affects the quality of the oil or it's intended purpose overall.

[KyleR]

I think we need an expert to educate us

 

Now if only we could tag people on this forum