oil transfer won't stay primed

[jsparker]

2004 150TXRC

Is it normal for oil in the engine tank to siphon back to the sub tank in the bilge when the engine is tilted back for storage? Never noticed if this has been happening since purchasing new in '04, but it seems to be tied to my intermittent low oil alarm problem I've been wrestling with that started at the end of last season. This is a long one, so I'll appologize now for the length and thank you for any ideas you might be able to offer.

I've checked out everything in the oil transfer process, replacing CDI, engine tank sensor, oil transfer pump, oil filter, cleared out the lines with compressed air, measured 14v at the pump and 12v across the pump when the CDI turns it on at start up. In short, everything seems to be working but I'll still get a low oil alarm, so now I'm pretty sure I'm not looking at an electrical problem.

I noticed that with the engine tilted back, over night the engine tank oil level will go from the full line to the low level line. If I just use the boat that way, 5 - 10 minutes out my low level alarm sounds and the engine goes into failsafe mode. Once I transfer oil using the emergency switch, I can run all day without a problem. No leaks that I can find in the bilge or engine. Can't see into the stringer area, but no traces of oil if I snake a string into the area. I'm guessing the oil is siphoning back into the low sub tank from the high engine tank. I don't see any kind of check valve in any of the lines to prevent this, and the pump doesn't have any valves internally. If I prime the system, which is a slow priming system to begin with, and start my day with the oil level high in the engine tank, I don't get the alarm.

Any ideas? For now, I'm just making priming the oil system part of my startup when I use the boat, but since I never had to do this before and I bought it new, I just want to be sure I'm not missing something, or if there was a Yamaha modification later on to deal with this.

Thanks

John S.

[jb123]

they are a bit slow pumping but have you replaced the sub filter?
Ive never heard of a main draining back down but sure it could happen.
Any extra smoke at startup?
unhook the sub tank, tilt motor, stick hose in a jar etc and see if indeed the main drains back to sub overnight.
if it were a bad check valve at motor or bad oring at motor pump, you would have smoky starts.

[jsparker]

Yes. Sub filter was replaced. Not much smoke at startup. Replaced pump already. I clamped the oil line off at the sub tank, rechecked level next day and engine tank was still full. Definitely draining back to the sub tank, which I don't think it's supposed to do but can't say for sure. Never observed how the system is working until I started having this problem. I do know that if I start my day at the low level line, I will get an alarm shortly after leaving the dock.

Nothing in the diagrams shows a check valve or anything in the oil line to prevent the flow back.

John S.

[boats.net]

There is no check valve between oil tanks. The oil feed line going to engine tank is located at top of engine oil tank, above oil level and can't siphon oil back into boat oil tank. The oil would have to be leaking through oil pump or out the vent hose into air silencer which would cause engine to smoak excessive at start up or you would see oil puddled in engine cowling. Do you have Yamaha tach with oil level indicators? If so check to see if the middle bar is flashing, signaling low oil in boat oil tank and making oil transfer pump inoperative.

[jsparker]

That is correct with the motor in a vertical position, but this is happening when I tilt the motor up out of the water. With the engine tilted, the fill tube to the engine tank is no longer above the oil level in the tank, and that's when the back flow is occurring.

If I clamp the oil fill line at the sub tank with hemostats, I don't 'lose' oil in the engine tank so it definitely is going back to the sub tank. Also to be sure, I've briefly loosened the sub tank cap to be sure there is no vacuum on that side pulling the oil from the main tank, but still the oil back flows.

I have the digital tach, and all 3 bars are lit and do not flash. Sub tank is full to about 2" from the top.

[boats.net]

You can install a fuel check valve(6R5-24408-00-00) at remote oil tank in place of hose nipple. Test it several times before starting engine by draining engine tank and refilling, should take about 3 minutes or less to refill engine tank.

[jsparker]

Thanks. I'll order it and try it. Sounds like it should do the trick. Just curious though, why this is a problem after 3 years of not needing it. Is this something the folks at Yamaha advise doing because of this problem happening?

But if it fixes it and everything still works as it should, why care?

John