2.) In a gearbox such as a differential or a manual transmission, the only type of lubrication that you get is a 'Hydro-Static Boundary Layer', which simply means that there is no mechanical or pressurized mechanism for 'forcing' the lubricant in-between the moving parts. (Other than the rotating action of the components themselves, which is not anywhere near adequate).

If there were insufficient boundary layers of lubrication between the gears in a diff or a manual tranny, then the internals of the gearbox would 'weld' themselves together relatively quickly. That's no good.

So there is a complex group of additives to address just this predicament, and it is called 'E.P'. The additives that make up 'E.P.'(which stands for 'extreme pressure', natch!) are developed from zinc, copper, brass, and other chlorinated solvents. These are commonly referred to as the 'yellow metals', and they possess some very desirable properties. They have a very low coefficient of friction, and they tend to 'stay-put', which makes them very resistant to the gearbox's attempts to remove them from contact surfaces through the mechanical shearing action of the component in question.

Basically, no matter how much pressure is applied to these additives, they cannot be 'squeezed' out from between the contact surfaces. This is what allows gear oils to lubricate so effectively without any type of 'Hydro-Dynamic' protection.

This may bring up a couple of questions amongst the more curious: First, if 'E.P.' is that good, how come it isn't put in motor oil to provide even better protection when the engine is first started, or if you were suddenly to lose oil pressure? Great idea, but it can't work for a couple of reasons;

Mostly because it is not legal for the additive to be put in motor oil, because chlorine and any chlorinated solvent or derivative is considered to be a carcinogen, so it can't be in there. The thinking is that a portion will escape to the atmosphere through normal combustion and exhaust, and the government says no!

Transmissions and gearboxes are considered to be 'sealed', so the same rules do not apply.

Also, when a chlorinated compound is combined with the normal by-products of combustion, it creates an acid that is almost chemically identical to battery acid! This wreaks havoc with bearings and such. In fact, before this was illegal, there were chlorine-based additives in motor oil, and they had a terrible effect on engines. That is why most engines in the 50's and 60's would give good service for about 60-75,000 miles, and at that point they would be 'smokers' and 'knockers'. Basically, land fill material.

By the way, it is not legal for the manufacturers to put EP in the oil, but there is no law that says YOU can't put it in your own oil, if you would ever want to.

EP is the active ingredient (hidden through clever chemical 'copyrights' on the labels) in many 'engine treatments' available out there.

Specifically, 'Dura-Lube' is loaded with it. Stay away from that stuff. Or, if you use it, just make sure you change your oil at least every 3 months regardless of the miles! At least that will keep the harmful acids from forming so quickly.

Did you ever wonder why 'Slick 50' or one of the other 'engine treatment' companies didn't market their own brand of motor oil with their product built right in? Well, because they are not legally allowed to.

Slick 50 tried to get away with selling oil filters with the product already installed, but they had to pull those from the market pretty quickly.

So, as long as the gear oil you are using is of the correct viscosity range, has the correct EP and LS (limited slip) additives in it, then synthetic is in all respects a better choice than any dino lubricant.

ORIGINAL: Twister

my 86's orrigional engine burnt a quart every 1500 miles...I used to put ATF into it about once a year for 200 miles....

ORIGINAL: 86 5.0L

why exactly?

ORIGINAL: Twister

my 86's orrigional engine burnt a quart every 1500 miles...I used to put ATF into it about once a year for 200 miles....