NEWBIE:How to drain oil from lower unit 150 Black Max?

[peiserma]

I'm going to look at a boat tomorrow. It has a Mercury 150 Black Max. Owner has stated it has sat for about a year. This would be my first own boat (my family always had a sailboat when I was growing up, so I am not completely clueless on boats)

But I am new to outboards. I'd like to drain a little oil out of it to see if its got water. Even though I do most of my own car maintenance, I am not sure I can find the drain plug on an outboard's lower unit. The boat is an 85, so I assume the motor is 85 or later. I'm guessing they are all similar enough for my question. Where is it on this type of outboard, and what tools should I bring to remove it?

I assume the spark plugs are basically like on a car, so those should be no problem. Is there any special trick I need to know to remove the cowl (or whatever the equivalent to a 'hood' an outboard has)

Normally one would start the motor, but the batteries are dead and since it has sat for a year, I guess asking to start the motor would a "bad idea" without draining the gas, putting new fluids in, and other preventative maintenance. Is there anything else i can/should check? Would there happen to be a manual on-line?

any advice appreciated.

 

[swimmin' for shore]

Re: NEWBIE:How to drain oil from lower unit 150 Black Max?

Hi. The lower unit oil check is pretty simple. On the bottom of the lower unit, you'll find a screw. You'll need a pretty stout flathead for it. Take that screw out and if it spits water, you've got a seal problem at the very least. That screw may be magnetic, which means there's a little magnet on the inside of it. Take a second and look for metal shavings. It tells you if the gears are grinding and that you may need a new lower unit or at least a rebuild at some point in the near future.

There's more to buying an outboard than just checking the lower unit oil. A year of sitting won't usually freeze up an engine and if it has, you don't want it anyway. I'd really advise either taking a battery or jumping or charging his. Go by auto zone and buy a compression gauge for 30 dollars if you don't already have one and test the compression on that motor in each and every cylinder. It's usually around 140-150 on a motor that size and age but the bottom line is over...some people say 100, I'd say 125...and within 10 psi of each other. I like them even closer but I'm particular about that. You seem to be mechanical enough to know how to check compression, so I'll leave it at that. Test them all. I have no estimate of times I've gone down the first 5 and had the 6th cylinder be the bad one.

From there, I'd give the motor a thorough going over. A lot of those have wiring problems, so check for cracked, broken, corrroded wires throughout. Check the stator (under flywheel), for what you can see of it. Same goes for connections at the switchbox. Faulty wiring will give you nightmares in times to come if it's your motor. Bad compression means you're out a motor that will cost a lot to replace. Just some extra thoughts. Good luck tomorrow.

 

[peiserma]

Re: NEWBIE:How to drain oil from lower unit 150 Black Max?

I appreciate the thorough answer. I would not have brought a screwdriver otherwise!

I do know in theory how check compression (had a mechanic walk me through it two years ago when he was diagnosing an engine code). But was hesitant to try it on an engine that sat for a year for fear of damaging something that I wasn't sure i'd buy. But your feedback caused me to bring along a compression tester, so thank you. And I will again the next time.

Just for everyone's information, Autozone has a tool loan program. You put down a deposit equal to the cost of the tool. Then you use it as long as you need. As long as you bring it back undamaged, you get your entire deposit back. So there is really little reason not to do a compression test. Since there is no time limit on the tool loan program, pay the $40 for the compression tester, practice on your own car if you need to, check the prospective engine, and then bring back the tester for a full refund.

In the end, water poured out instead of oil, the trailer's axles were almost solid rust, one of the leaf springs was so rusted the U-bolt holding it to the frame split in half, and the other looked like it was not far behind. So I did not make it to the compression test Too bad, because the hull was otherwise in good condition with the exception of the hatch over the gas tank needing to be replaced.

 

[swimmin' for shore]

Re: NEWBIE:How to drain oil from lower unit 150 Black Max?

Water in the lower unit, for future reference, won't be the end of the world. Reseal kits are reasonably priced. I'd be much more concerned if the water came out looking rusty or if it came out with metal shavings. I know that if I intended to buy the boat no matter what i was seeing, I'd use it to talk down the price by at least 400 or 500 dollars. I can replace a lower unit on ebay for that price ( I sell them, so I'm pretty clear on the pricing). Compression, in your case, would be a huge issue. As for the trailer, this forum is full of people who fix those, too. For the average boater who just wants to get it together and go boating, though, I think you made an overall sound decision! Sometimes the money we don't spend is a much wiser decision than the money we do spend, so congrats on your good decision making and keep plugging at it. There are a lot of used boats out there for sale, so don't rush perfection.