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Lube for the Lower Unit


Mid-Lake Rock

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I'm going to winterize a Yamaha four stroke in the next few days. Not sure what is in the lower unit for lube. Had it done by a marina free of charge last year. Anyone see a problem with using synthetic if a conventional product in in there now?

Thanks in advance.

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Amsoil lower unit lube is good stuff. What ever you use, make sure it's specifically for lower units and not just 75-90 gear lube.

Regular automotive gear lube is not formulated to handle the high speeds the drive shaft is spinning, and will foam. Foam in your lower unit is very very bad. Lower unit gear lube is forumlated to take the high speeds of the crank drive.

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Best bet would be to pick up a quart of Yamaha gear lube at the local marine dealer.

You'll also need the special adapter for the pump to screw into the Yamaha fill hole, as the pump you need to buy will probably have a different size adapter for other engines. This should also be available at the marine dealer.

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A magazine that writes about bass and walleye boats has an artice in their latest issue about lower unit lube. They did a number of tests and some of their finding were pretty interesting. Basically each lube has a specific application. The average fisherman is better off staying with standard lubes. If you run hard and at full throttle the high performance lubes are better. In the end they recommend using what the manufacturers suggest. Overall Evinrude HPF-XR lube tested the best, but not necessarily the highest in each test.

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Here is an update with some questions. I finally finished fishing open water and put the boat away for the winter. When I changed the gear lube this past weekend, I found a few surprises and wanted some thoughts.

Background: Two winters ago, I had the lower unit pressure tested and there was a leak. Yamaha paid for the seals to be replaced at a Yamaha dealer. They replaced the lube after the fix. Last winter I drained the lube and had a small amount of clear water exit. Lube was not cloudy. Took boat back to dealer that did seals, they did another pressure test and said everything was good. They filled lower unit.

This past weekend, I went to drain and didn't have flow. Looked at the bottom fill hole with a halogen and could see frozen water. No lube, but clear liquid. I put a heat source at the hole, and melted in a few minutes. A very small amount of clear water drained (I'd quess less than 1/4 oz. Following the water was a steady stream of oil. The lube did not look cloudy, however the lube that was in there was golden in color. Looked similar to fresh engine oil.

Here are my questions:

1. What type of lube is this? Every lube I've seen for lower units is dark (green/blue in color), including the lube from the dealer after changing the seals two years ago.

2. Any thoughts on the small amount of water at the bottom? As I said, the lube did not appear to be cloudy and was almost translucent. The seals are only two seasons old.

I put heat on the lower unit and completely drained before filling with the proper lube. My thought is to run the boat a few times in the spring and check for water.

Any input is greatly appreciated.

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If you are getting a small amount of water but the lower unit pressure/ vacuum test ok it is probably coming from the gasket around the drain plug. It isn't a bad idea to replace these every year.

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Not sure what kind of lube it is, but I don't think I'd be too concerned about it.

Replacing the gasket around the drain plug and top vent plug is a good idea, especially if this has happened twice now... and checking it in spring after running it a couple of times isn't a bad idea at all.

marine_man

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You said they did a pressure test. Did they do a vacuum test? A pressure test will not always show a water leak. A vacuum test will not always show an oil leak. You could have an outer shaft seal (drive or prop) that is shot and allowing water to get in and a perssure test will never show that. As Rob and wakeguy also said, it is very possible to have the drain or vent screw leaking as well.

What kind of oil is golden? Regular lower unit lube (dead dinosaurs). The synthetics or synthetic blends are usually the ones that have a green or blue color to them.

Why was the water clear and so was the lube? Oil and water do not mix. Over time they will separate and the water will go to the lowest possible point ans settle there.

I hope this was helpful

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