Oil system : mystery

[johnsw]

2004 Yamaha 150TXRC 2-stroke

Here's an odd one. What keeps the oil in the engine tank from
flowing back to the sub-tank in the bilge when the engine is
tilted up out of the water? I thought I had an electrical
problem, but after checking everything out and working as
it should, this is where I'm at.

I've got an intermittent low oil alarm problem that I've linked
to the engine tank draining back overnight. If I fill the engine
tank using the emergency switch to the top level line, tilt the
motor up and check it in a few hours, the level is reduced to
just about the low level line. If I clamp the oil line at the sub
tank and do the same thing, it stays full. Definitely back flowing
due to gravity feed, siphoning oil from the engine tank in the
process. No leaks in the bilge or motor.

If I just jump in the boat and go, 5 - 10 minutes out my low
oil alarm sounds and the engine goes into failsafe mode, as it
should. Fill the tank with the emergency switch, and I'm good
for the rest of the day.

My startup routine is now to prime the system with the emergency
switch and fill the tank before starting the engine.

Checking the oil lines and diagrams in the service manual, there
doesn't seem to be a check valve in any part of the system. The
oil transfer pump (which I replaced) doesn't have any internal
valves. I took my old one apart to check it out, so I know that
is the case. Any ideas or suggestions?

John S.

 

[goinsfishin]

I'll take a guess that the main tank isn't vented properly. As you run and use oil it's creating a vacuum, when you stop the vacuum pulls oil back from the engine tank.
Check the vent on the fill cap, you should be able to blow thru it...some resistance is normal.
Next time you are done for the day, loosen the cap b4 you leave the boat and see if the results are different.

 

[johnsw]

A logical guess and a good one, but no cigar. After using the boat today, I took the cap off the sub tank, filled the engine oil tank to the full line using the emergency switch, put the cap back on the sub tank and tilted the motor up. Checked it after a couple hours, and the oil level dropped to 1/2 way between full and low limit lines on the engine tank. Not a vacuum pulling the oil down.

Thanks for trying.

John

 

[Wicho]

Maybe #13 - "pipe joint"?

 

[johnsw]

Nothing visible in the way of cracks in either the connectors or hoses. No signs of oil leakage at any of the joint connectors. They're tight fitting connections, but I doubled up on the cable ties securing the hoses just to be sure. I've clamped the oil fill line at the engine tank and again at the sub tank, and both times I didn't lose oil. But if it back flowed just from the oil line when I clamped off the hose at the engine tank, I really wouldn't know it. I'll give this one a second look next time I'm at the boat.

Update 12:44:

Excuse me while I use this as a sounding board a bit. When I'm checking these connections out, I'm going to take goinsfishin's suggestion a bit further. Maybe it's not a vacuum in the sub tank, but pressure in the main tank pushing the oil out and down to the sub tank? I'll check out the venting on that side to be sure there are no restrictions. Although I'd think it would pop the sensor out if that side was pressurized from the rising oil level when filling the tank with the emergency switch, but you never know.

I've also ordered a new sub tank cap. I took a closer look at it and there is actually a small check valve within the cap. It's a small plastic bead that just butts up against a small hole in the center rubber insert. My first thought was that it's there to prevent oil from escaping through the vent system, but I'm really grasping at straws with this one. There's just not that much to go wrong, unless I'm off base thinking the engine tank should maintain it's oil level even when it's tilted. Can someone verify this?

Thanks

John

 

[Wicho]

I was thinking that one of those connectors are maybe a valve thats letting the oil go back into the tank. So no leak -.. just reverse flow..

Have you asked the guy on thehulltruth - I think his name is andy.. just looked him up: [email protected]

He sells yummy parts and probably can help diagnose..
wp...

 

[johnsw]

Thanks for the lead. I'll shoot him an email and maybe he can provide some insite.

The joint connectors are just pass thru's. No valve. The sub filter is just a strainer. No internal valves in the transfer pump. Looks like a clear path tank-to-tank.

After a couple messages with the folks over at yamahaoutboardparts.com, they suggested I put a fuel check valve in place of the joint connector at the sub tank. That should work and I'll try that if everything else fails. But I'd really like to get to the bottom of what's gone wrong here.

John

 

[goinsfishin]

I can verify that the oil level in my sub tank remains full when tilted, sometimes for a week if I dont get out in the evening.
My engine is older 89 200 EFTX but from what I can see from the parts diagram the oil supply system is basically the same.

Just out of couriosity what happens if you leave the engine down? Does it still drain out?

 

[johnsw]

Thanks for the verification. I didn't think I was going totally crazy, but you never know. I don't think the year matters much with this system. I know the oil transfer control was changed from a seperate controller to a circuit inside the CDI in the newer models, but other than that, the actual system of tanks and hoses hasn't changed much, if at all.

If I leave the engine vertical, the tank stays full. Makes sense since the oil fill fitting of the engine tank is above the fluid level at that point, so there's no way for it to siphon back. That's a last resort option, but I keep my boat in a slip and don't have antifouling on the lower unit.

Thanks for the info. I'll keep hunting.

John