GL4 gearbox Oils. Keep using Mineral or try Synthetic?

[mudnut]

G'day, all. I am having trouble finding a GL4 90W mineral gearbox oil.

There are alternatives, such as Penrite 75W 90 Full Synthetic. The Manual states an 80W 90W should be used.

What are the long term problems arising from using a synthetic oil on the softer synchromesh metals?

[garett]

I am running a synthetic GL-4 so far no issues, don't use GL-5 like the parts interpreters say cos that is baaaad.
mine has been in it for maybe 40k km still shifts smooth. I used Nulon can't remember any details it was at least 5 years ago.

[nissannewby]

No problems with using synthetic oil. You should always use the best oil that you can afford or are willing to pay for. Just as long as it lines up with original spec. Patrol gearboxes do prefer GL4.

[Cuppa]

There are alternatives, such as Penrite 75W 90 Full Synthetic. ?

Thats what we use in our gearbox. Not cheap though.

[mudnut]

Thank you for your replies. GL 5 was put in by the mechanic when the gearbox was changed out. The first cold day and the synchromesh was just useless. I ended up using vmx 75 w
as it was all I could get. Now we will use the Trol for towing I was hoping to get 90W GL4, but 75 W 90 will do.

I was told, years ago that some oils or additives are slightly stronger than the brass and cause it to erode as it gets used up.

[Plasnart]

Thank you for your replies. GL 5 was put in by the mechanic when the gearbox was changed out. The first cold day and the synchromesh was just useless. I ended up using vmx 75 w
as it was all I could get. Now we will use the Trol for towing I was hoping to get 90W GL4, but 75 W 90 will do.

I was told, years ago that some oils or additives are slightly stronger than the brass and cause it to erode as it gets used up.

Crikies I'm not a mechanic's back pocket and even I know not to drop GL5 onto a GL4 spec gearbox! Find a new mechanic muddy!

[garett]

the parts interpreters state that gl-5 is the replacement for gl-4....it is in diffs but not old gearboxes, if ur 2nd gear is 'sticky' or stiffer then the rest my guess is u got gl-5 in it, I had this argument with a parts store. apparently the sheer strength of the oil is the problem,

newer cars use the gl-5 in gearboxes without issues, I forget when they changed the composition of the synchros so they could handle the higher sheer point..
I'm guessing a lot don't care cos its an old car and it would take awhile for problems to arise from the wrong oil.

[mudnut]

Sorry, Plassy. It was a few years ago. The gearbox oil is due to be changed out.

[Cuppa]

the parts interpreters state that gl-5 is the replacement for gl-4....it is in diffs but not old gearboxes, if ur 2nd gear is 'sticky' or stiffer then the rest my guess is u got gl-5 in it, I had this argument with a parts store. apparently the sheer strength of the oil is the problem,

newer cars use the gl-5 in gearboxes without issues, I forget when they changed the composition of the synchros so they could handle the higher sheer point..
I'm guessing a lot don't care cos its an old car and it would take awhile for problems to arise from the wrong oil.

All I know is that my gearbox used to be stiff & clunky when it was cold & would gradually improve with smoother changes as it warmed up. When I changed from GL5 to GL4 it had smooth changes from cold.

[nipagu7]

gl4 and gl5 are different blends of oil for different purposes gl5 is not an upgrade for better or higher performance , it's just for a different purpose . gl4 is what the patrol gearbox requires . some have used gl5 and said they have no problems but many more seem to have issues so for my money i'd stick with gl4 . who are these parts interpreters , sales people at supercheap or autobarn or such , in my view they are just sales people just trying to make a sale . the nulon synth 75w-90 is gl5 , don't use that . i had the 75w-85 gl4 in for 5000ks and it seems to be good . don't worry about the 75w number , this helps when cold , and the oil will still be thicker than the 85 warm viscosity . synthetic oil is a lot more stable and has a lot higher shear strength than mineral oil so using 85 instead of 90 weight won't cause any issues but it could help with smoother gear changes . when i bought my oil , i got 2 2.5 liter bottles at 50 percent off , they also were selling the 1 liter squeeze packs but the price was rediculous but they don't seem to sell the 2.5 liter bottles any more only the squeeze packs and 20 litre drums .