Changing Engine & Lower Unit oil

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bartender66

New member
Hi All,
We just hit the 100 hr mark on our 2004 BF90. I want to change both the engine and lower unit oil. The owners manual gives fairly detailed instructions for the engine oil however I couldn't find anything on the lower unit. Has anybody changed their lower unit oil themselves or is this strictly a dealer job? Any advise or tips would be appreciated. Thanks!
 
Hmmmm On the older motors there was simply a drain plug on the lower unit and then a separate fill plug up above it. Take the fill plug out and then pull the drain plug. Once the oil has finished draining replace the drain plug and pump in the specified amount of oil into the fill plug (IE: Until it won't take any more). Replace the plug and you are done!

Before doing this I would check the service manual though.
 
Thanks Gary, i appreciate it. This is the standard method that I've used in the past with my old Johnson motors. I think the BF90 came with a hand pump to pump the new oil in, I'll go over to the boat and try to find it. Thanks again for the advise!

Terry
 
There are two plugs on the lower unit. The very bottom one is the drain plug, and the upper one is the vent plug. Be sure to place a bucket under the unit before you remove any of them to catch the oil.

Now, how I do it is I remove the drain plug first (lower plug). Then I remove the vent plug. This way I don't get oil all over my screwdriver and hands when I remove the drain plug, although oil will start coming out. Once you loosen the vent plug, the oil should come out rather easily (you have now introduced air into the area and gravity will take over). Once it's all drained out, you want to pump oil back into the lower unit from the drain plug (the lower one), not the vent plug. You want to force the oil up to the vent plug. You can either buy the individual tubes (have 3 of them ready) or if you buy it in the gallon, you'll need a pump to do this. I use the individual tubes and just have them all precut and lined up ready to go. You need to wedge the tip of the tubes in the drain plug real tight so the oil doesn't seep out while you're forcing it up into the lower unit. I then squeeze the oil into the unit from the bottom of the tube and roll it up as I go, that way I get all the oil out of the tube. When it's empty, have the next tube ready in the one hand, because when you remove the used one, oil is going to come flowing out freely! Jam that next one in tight and repeat. You'll need to do this until you see oil start to come out the vent plug (top plug). My BF75 takes 2 full tubes and part of the third before I see the oil come out. Once oil starts coming out this plug, quit squeezing oil into the unit and put the vent plug back in the hole. Then, have the drain plug ready to put back in the lower hole once you remove the tube. You need to get it in quick once you remove the tube as oil will start coming out (that darn thing called gravity!). That's about it. My Honda owner's manual recommends you fill it back from the drain hole, not the vent hole, even though it would be easier to put the drain plug back in and fill from the vent hole. I believe doing it the way Honda recommends in the manual ensures the entire cavity gets filled with oil and all air gets out of the lower unit.

I guarantee you'll get some oil on yourself and it's easier if you have somebody there ready to hand you stuff as you need it. Have lots of paper towels on hand just in case. Not hard to do, though.

Jack
 
Always fill through the bottom (drain) hole until the grease comes out the vent hole. That way you know that the unit is full. You don't capture any air to stop the fill process. I have a paint pressure pot that I rigged to do the job. I set the pressure at a couple of psi, and wait till the gear lube comes out the vent. Works great. Trying to roll tubes or squeeze them till the unit fills is one of those thankless jobs that seems to take forever. Ron
 
Also - when just checking the oil level and condition, remove the lower (drain) plug and look at the oil that comes out. If there is any water in it, it will be at the bottom and will be the first out of the hole. If water and/or milky looking oil comes out, then you need to figure out and correct how the water got in there. It is tempting to just remove the top plug and add oil until full, but then you will never know if there is water at the bottom.

After checking it, remove the top (vent) plug and refill. That's what the dorky little squeeze tubes are best for- topping off the resevoir after that. Squeeze it in the bottom until it comes out the top.

It seeems to me that most often when cracking open one plug or the other, there is a little pressure inside the resevoir that gets relieved. That is (I guess) because the gear case is not vented in order to allow it to pressurize and help stop water intrusion.

Yep - you'll make a mess. But as someone on here pointed out to me a while back, if you plug the top hole with your finger until you get the tube nozzle plugging the lower hole, you won't lose too much oil in the process.
 
These things remind me of a pressure cooker for painting. They hold a couple of gallons usually, and once you put the grease it, you put the lid on with a gasket, and usually there are about 4 bolts that tip over the lid that you tighten down. Then you can pressurize it. It has a quick connect for an air hose, a pressure regulator, and an exit hose usually with a ball valve that you open to allow flow. It works absolutely great for doing the lower unit grease. Probably can see them in a Sears Catalogue. Ron

Try this: http://lib1.store.vip.sc5.yahoo.com/lib ... setup1.jpg
 
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