Optimax 200 engine oil tank leaking down

[wtlee3]

I have a 2001 Mercury Optimax 200 DFi and the engine mounted oil tank leaks down and sends an alarm when I run it 3500+ rpms for an extended period of time. The cap rubber gasket is cracked and it looks like some oil may be leaking at the sensor insert. I was going to replace the cap gasket but worried there may be more than just that issue. I replaced the brass t on the other engine at the bottom of the tank but wasn't really sure what that did. Do you think I should replace the whole tank assembly or could the torn gasket be causing all of the problems? Also when I haul it up and down the road, some of the oil will drain back to the main holding tank.

[XstreamVking]

Sounds like the proper air pressure is not being maintained in the boat mounted tank. Check the caps on the main tank,and the hoses/connections going from the motor to the tank. Anything that leaks air or oil should be addressed and repaired. There are connections in the rigging hose on most optis that can also leak, check them also..... With the motor running spray some soapy water on them and look for bubbles....

[KIRCHNER]

Good advise, i did the soapy water trick and found a leak on new looking cap. where the lanyard attaches, invisible no cracks but leaking..

[Jim Speros]

I few things come to mind. First like Xstream mentioned it sounds like the main tank isn't holding the pressure to fill the engines tank. It could be a leak in a number of places hose or caps on big tank. Could also be bad check valve on block where pressure hose connects.
Second if the alarm is sounding for low oil it will beep a pattern every 2 minutes and has nothing to do with RPM. Once the tank runs low it starts a clock and ultimately will reduce power once enough run time has elapsed.
Third point regards gasket on engine tank. That tank is under pressure when everything is operating correctly. If it is in fact leaking it may be allowing oil to back flow into main tank while trailering. Never actually witnessed that though.
Finally if you do replace the tank on engine it will include a short piece of hose and the t brass fitting, cap and sensor. However, There is nothing I have read to confirm that is actually your problem. Typically the tank get changed because the sensor goes bad and indicates its low when it is not.