Condition of Gear Lube upon changing..kinda dark

[crazy charlie]

Changing out my lower gear oil and i remember pitting in dark blue gear lube.Came out very dark charcoal gray/blackish..Had the typicall amount of shavings on the magnet plug.Possibly slightly more which didn't surprise me since I was having an issue engaging into reverse for a while last season.Replaced the shift cable and solved the issue but i did have a few ratcheting events before i had the cable replaced.Any way to test the lube?? I ran the boat frequently last season so it wasn't lightly used last year.

 

[James R]

A few shavings is not unusual bearing in mind your shifting problems. The oil has no water in it so it is safe to say that the seals are still good. Just replace the oil with a quality 80/90 Hypoid gear oil. Grease the drive shaft splines and remove the prop and grease the shaft splines. Don't forget to replace the plug seals. Replace the water pump impeller, the shaft seal on top of the pump housing, the seal around the shift shaft. I always use OMC gasket sealer on all the bolts, the full length of the bolts that is, pump and lower mount bolts. Helps eliminate corrosion.

 

[emdsapmgr]

Black oil can be a couple of things-none of them good. 1. the oil level in the gearcase is low, and the oil ran hot because it is abnormally low. Heat is the enemy of any gear oil. 2. If the gear oil is full, and is still black, it likely still got hot. This can happen with a high perf gearcase which is running high out of the water with a jackplace and low water pickup. This can generate enough heat to cook the oil on really long runs (The Mercruiser guys put a transom shower on to spray cool water on the case.) 3. The wrong oil is inside the case. Needs to be a marine-quality Hypoid type oil.

 

[emdsapmgr]

Also, oil will get black if not changed according to factory intervals/time frames.

 

[crazy charlie]

None of the above.No hi performance ,just a 150 on a Mako.Correct amount came out so level was fine.Correct lube though it was dark blue going in.I usually use the honey colored but I may have used synthetic,can't remember.

 

[racerone]

But your lower unit could be considered " high performance " in my opinion.-------Just look at the size of it and compare it to the rear end of your favourite pick-up truck.----Only takes about 40 hp for the truck to roll on the highway.----Not so for a boat.---Use the best oil and change once a season !

 

[Stumpalump]

I never stay on plane for more than 25 or 30 minutes. Slowing down sinks the lower and mid unit deep in the water to cool it. That's especially important on sterndrives and is why some run a drive shower. The tint in colored oils are designed to loose their color when they get hot. That's why they tint it.

 

[Vic.S]

Changing out my lower gear oil...........................................................................Any way to test the lube?? I ran the boat frequently last season so it wasn't lightly used last year.

I'd not be unduly worried about some darkening of the color although I've not seen blue gear oil.

Becoming charcoal grey or black would trouble me. However the most important thing is that the oil should remain "clear and bright" If there is any turbidity it indicates ingress of water.

If the oil is too dark to see any turbidity then Google for "crackle test". It is a standard lab test which I have done many times but it can be quite sensitive.

I fear you may have some water ingress ( salt water I assume from your location) which has caused some corrosion which in turn has caused the very dark color you see

 

[emdsapmgr]

The Merc high perf gear oil is a sort of blue/green in color.

 

[oldboat1]

If shifting issues are resolved, think I would drain the oil and pressure test the unit. With satisfactory results, would probably fill it up and go again -- drain some out for a look at midseason, and change it on regular schedule. Given history, I would break up periods of high speed running. Additionally, older Makos get very heavy with water down under the flooring (as all hulls do, I guess). The Mako is a heavy hull to begin with, and it might be helpful to dry it out and lighten the weight.