XR6 Oil Pump Problem?

[Stearman]

My '96 150 XR6 stopped filling the motor oil reservoir Saturday. Alarm worked fine, so I continued the day filling the reservoir manually. What should I look for, other than oil pump failure (high$$$ to repair) that might cause this? Thanks.

 

[j_martin]

Re: XR6 Oil Pump Problem?

My '96 150 XR6 stopped filling the motor oil reservoir Saturday. Alarm worked fine, so I continued the day filling the reservoir manually. What should I look for, other than oil pump failure (high$$$ to repair) that might cause this? Thanks.

Crankcase pressure is delivered to the boat tank by a "check" valve, located low and forward on the starboard side of the engine. It's limited to about 2.5 psi, and bled off when engine is shut down, all by that valve that looks like a hose barb. That could be bad. If there's a hole in that hose, it'll lose pressure. If there's a kink in the hose, or a battery got on top of it, it'll fail. The screen in the boat tank could be plugged. It usually turns out to be one of those $*^&* foil seals off an oil bottle. The T looking fitting just starboard of the engine tank is a check/relief valve. It could be blocking flow, but I've never seen it. Usually the relief valve gets damaged and it pukes oil all over the lower cowl.

So, here's the plan. Make sure the hose is in good shape, the connection at the boat tank is right, not half latched. The pickup screen is clear, then replace the first check valve I mentioned.

When you get delivery working, you fill the engine tank by running the engine, and cracking the cap on that tank till it overflows, then tighten it. Go easy on it, they split out way too easily.

hope it helps
john

 

[Stearman]

Re: XR6 Oil Pump Problem?

Thanks, John. That gives me lots of things to check over while looking for the problem. Hopefully one of those items you mentioned will be the problem and not the pump gear. Given your description of how the system works to get oil from the main tank up into the motor reservoir, it sure seems there could be a more simple system designed to do that - like an electric pump that operates off a simple level control on the motor reservoir. Being an old almost-ready-to-retire instrument engineer, that shoudn't be too hard to design and build. But I am sure much better minds than mine have worked on this system for years, so what we have is likely the best solution to the oil/gas mix requirement of 2-stroke outboards. Thanks for your help, John. Its great for newbies like me to have access to good advice from folks like you who have answers to our questions. I'll let you know what I find out about the boat. I want to go fishing this weekend............

Mike

 

[Chris1956]

Re: XR6 Oil Pump Problem?

Mike, There are different systems to deliver oil to the mixing pump on different outboard brands. The Merc system has advantages and disadvantages, over the BRP system.

BRP uses a pump to pull oil from the remote tank and mix it with the gas. If the system develops an air leak in the oil line, it will not function.

Merc uses crankcase pressure to keep the motor resevoir full, and has gravity feed to the oil pump. The Merc gravity feed mechanism is more robust (IMHO) than the BRP system, however, I dislike the pressure tank concept of the Merc.

 

[j_martin]

Re: XR6 Oil Pump Problem?

Mike, There are different systems to deliver oil to the mixing pump on different outboard brands. The Merc system has advantages and disadvantages, over the BRP system.

BRP uses a pump to pull oil from the remote tank and mix it with the gas. If the system develops an air leak in the oil line, it will not function.

Merc uses crankcase pressure to keep the motor resevoir full, and has gravity feed to the oil pump. The Merc gravity feed mechanism is more robust (IMHO) than the BRP system, however, I dislike the pressure tank concept of the Merc.

It's more than gravity that gets the oil from the engine tank to the pump. That T fitting just before the tank is a 2 lb pressure release so the pump doesn't crush the tank like a pop can if the delivery hose from the boat gets plugged.

Mike, I can have empathy for you being a controls engineer. My wood fired, multi zoned heat exchanger and hot water heater control system looks like the inside of an old pinball machine. It's pretty hard for me to imagine that electric pumps and controls can be simpler than a check/pressure valve pushing the oil out of a tank.

The only weak spot I know of in this system is the plastic crankshaft gear, and I believe that is a reasonable risk tradeoff. If it fails, it probably would do minimal damage to major parts, unlike brass pieces wandering around in the crankcase. The alarm system is adequate if you pay attention to it.

John

 

[Stearman]

Re: XR6 Oil Pump Problem?

You're right, John. I'm an absolute believer in keeping things as simple as possible. I'll be digging into the oil system starting late this afternoon, and am really interested in what I'll find among the tubing, check valves, and other things. I'm really hoping to find an air leak or a kink in a hose rather than a broken pump gear. I'll give the boat tank suction line strainer a good lookover and cleaning too. I'll let you know what I find out. And good luck keeping your heating system online. I heat our home with a wood-fired stove with a good air/air heat exchanger, too. But living on the Texas gulf coast, I only run my heater about 10 weeks out of the year. A/C is another story.................. take care.

Mike

 

[j_martin]

Re: XR6 Oil Pump Problem?

You're right, John. I'm an absolute believer in keeping things as simple as possible. I'll be digging into the oil system starting late this afternoon, and am really interested in what I'll find among the tubing, check valves, and other things. I'm really hoping to find an air leak or a kink in a hose rather than a broken pump gear. I'll give the boat tank suction line strainer a good lookover and cleaning too. I'll let you know what I find out. And good luck keeping your heating system online. I heat our home with a wood-fired stove with a good air/air heat exchanger, too. But living on the Texas gulf coast, I only run my heater about 10 weeks out of the year. A/C is another story.................. take care.

Mike

You could take the oil pump off and throw it in the trash can and it would not have any effect on whether or not the engine tank fills. Quit worrying about the pump gear.

Most of the parts in the control system are computer surplus stuff, like gold plated cradle relays with million operation mtbf's. It's pretty reliable.

John

 

[Stearman]

Re: XR6 Oil Pump Problem?

John, my Black Max oil problem seems to be ok now. Based on your system description and the motor manual, I drew a diagram of the oil system and proceeded to pull it apart and clean and check things as I went. Put it all back together with new tie-wraps and substituted some air pressure at the inlet from the starter side of the motor, and sure enough, oil flowed out of the hose up on the motor tank! Connected the hose back to the motor fitting (what is the real name for that crankcase pressure supply fitting?), left the cap loose on the motor tank and fired it off. Before I could get back to the motor, the tank was running over. Killed it and put the lid back on the motor tank. Cleaned up the puked over oil, and put it all back together. Fishing trip Saturday afternoon was great!! No alarms and the tank stayed full. I'm not sure what I fixed - maybe the suction screen was dirty enough to be the problem - but the boat ran great. Now I have a good understanding of how the system works. Only question I have now is this: Does gravity alone feed enough oil from the motor tank to the pump, like when I had the tank lid loose to check oil flow from the boat tank? I know while running, the motor tank sees pressure from the motor and that helps push oil to the pump. What about when the motor tank lid is loose for maintenance purposes? My guess was it would be ok for that short period of time, and just let the motor idle. Thanks again, John. You've been a great help.
Mike

 

[j_martin]

Re: XR6 Oil Pump Problem?

The oil pump will pull a lot of suction. The valve just before the engine tank is a 2 psi relief valve that will let air in if the suction pressure gets over 2 lbs. That's so the oil pump will get adequate oil. Theory is, if the oil delivery line from the boat gets kinked, pinched, or damaged, the check valve will admit air, the engine tank will pump down, the alarm goes off, and at that time you have about 1/2 hour at WOT before the engine fails to oil.

Oil delivery problems is usually a bad check valve, (that part on the engine) a pinched (battery) or kinked oil delivery line, or a plugged pickup screen.

Enjoy yer boat. It'll do well.

John