SAE 90 Hypoid Gear Oil Options

[Pot Hole]

Need to change the lower unit gear oil on my 2002 DF40 and I've finally exhausted my stash of the SAE 90 Hypoid gear oil that my owners manual calls for. I would like to put back something that meets or exceeds manufacturers specifications and it is my understanding that the term: "Hypoid Gear oil" has been replaced with the term GL-5. When I replaced my engine oil, I went with a synthetic 10W-40 Lucas Outboard Oil and I see that they also make a synthetic gear oil for outboards with a viscosity listed as 75W-90. Will this 75W-90 specification meet the SAE 90 spec that my manual calls for? I am assuming the 75W-90 spec is the oils viscosity over hot and cold temperature ranges, but I would like to know for sure if this is a good option before I put it in my engine. Thoughts?

[briscoe]

It has been my experience that most GL5 gear oils are not 75W-90. They are usually specific to wt of oil, such as 90 gear oil. Or it will say hypoid on the bottle. If it doesn't say GL 5, it's not.

[Pot Hole]

It has been my experience that most GL5 gear oils are not 75W-90. They are usually specific to wt of oil, such as 90 gear oil. Or it will say hypoid on the bottle. If it doesn't say GL 5, it's not.

Looking at the spec sheet for this oil, it says it meets or exceeds all API and GL classifications including GL-5, so I think we are good there, I just wanted to make sure that the 75W-90 weight would be OK given that my old specs called for SAE 90

https://lucasoil.com/pdf/TDS_M8_GearOil.pdf

[Harper]

I'm sure it's fine. The one thing about marine gear oils though, is that they are formulated to help mitigate any problems due to water intrusion. Some people use automotive oils and gear lubes. Automotive gear lubes do not have the additives to combat water intrusion. The 75W-90 is not a problem at all. I have used Amsoil 75W-90 since the motor was new (10 years). And it is a full synthetic marine formulation. Since you say your Lucas is formulated for outboards, I see no reason to worry.

[Greg Moore]

Like Harper said, your biggest objective is to find one that remains a premium lubricant even with a very small amount of water in it. Some basic auto gear oils will turn into an almost non pourable slime with just a teaspoon of water in a quart. It isn't hard to get very small amounts of water in a marine lower unit and they're under huge gear face pressures, you don't want peanut butter as a lube

[Hoosmatroos]

Widely available and good gear oil is the quicksilver high performance gear oil (dark green color). I use it in all the outboards, big or small.

[Kartergreg]

While I agree Quicksilver gear oil is very good, the last time I checked what I had it did not meet the Suzuki requirements. It was a GL-4 and not GL-5. I just used Star brite hypoid 90 weight which is a GL-5 marine gear lube.

[Pot Hole]

I'm sure it's fine. The one thing about marine gear oils though, is that they are formulated to help mitigate any problems due to water intrusion. Some people use automotive oils and gear lubes. Automotive gear lubes do not have the additives to combat water intrusion. The 75W-90 is not a problem at all. I have used Amsoil 75W-90 since the motor was new (10 years). And it is a full synthetic marine formulation. Since you say your Lucas is formulated for outboards, I see no reason to worry.

I hear what you are saying about automotive oils and gear lubes and I would never put those in my outboard. Lucas makes some high quality products and I have used their engine oil for some time with no issues at all. I figured the gear oil would be an excellent product as well, I was just worried about the SAE 90 to 75W-90 differences.