300 promax empty oil line?

[Bunger]

Just got back from 4 days at the river. Pulled the cowl off to give it a once over and noticed the line from the oil pump to the vst was empty.... drained the vst and the fuel appeared to have a normal amount of oil. I had ran it wide open for a few miles before putting on the trailer On Monday. Checked compression: 123-125 across the board on a cold motor with plugs pulled and throttle wide open. Cranked it with bleeder screw out of oil pump and oil came out. Pulled check valve going into vst and it seemed to be in working order. Cranked it with throttle(and oil pump lever) wide open and couldn’t get it to pump oil into the line. Pretty sure I didn’t hurt the motor according to the comp readings. Did notice it idled super low the whole trip more towards the end almost wanting to stall which was weird because I put a lower pitch prop on for this trip. Any ideas on what to check?

[Chaz]

I take it we are talking about an early model ... :confused:

Is the oil bag on the side of the motor full ?
If not , check valve on lower starboard side of the block or cracked filler cap on the oil tank in the boat.

If that is good, pull the oil pump out, it has a metal gear. The drive gear on the crank is Bakelite and strips fairly easy . If its bad you'll see grey plastic bits on the oil pump gear , or see debris down inside if you look with a light or borescope.
The good thing is that it lives in it's own little compartment , so the junk will be contained.
Those motors are easy to convert to premix ... unless ya wanna pull the crank .. :eek: :nonod:

[Bunger]

Yup the resivoir on the motor is full. I ran for a few days and the remote tank in the boat went down considerably so it’s working/was working. I normally don’t have the kind of luck to where I’d catch a bad pump BEFORE it took out my motor haha that’s why I’m kind of confused. Is there anyway the line could lose its prime?

[Chaz]

You said , you pulled the bleeder screw and there was oil.

My luck usually runs like that too .. or I get the needle in the haystack type issues that only happen on a full moon, at low tide in months that have 31 days .. :eek: :)

I'm still going with the drive gear ... :thumbsup:

[Bunger]

You said , you pulled the bleeder screw and there was oil.

My luck usually runs like that too .. or I get the needle in the haystack type issues that only happen on a full moon, at low tide in months that have 31 days .. :eek: :)

I'm still going with the drive gear ... :thumbsup:

yup pulled the bleeder and cranked it and oil cane out as soon as I cranked it.

im going to try to and run it on premix on the hose and see if I can get it to pump oil.

if that does t do it I’ll pull the pump and look at the gear.

[KIRCHNER]

iF i remember correctly, you can pull a wire, triggering the alarm, to check pump operation, and alarm. just a thought...

[Chaz]

iF i remember correctly, you can pull a wire, triggering the alarm, to check pump operation, and alarm. just a thought...

That would the "low level" switch in the engine oil bag.
Nothing between the bag and point of entry into the VST .. except for the pump .. ;)

[Bunger]

Do these motors have the same rotational sensor that the 2.5s have?

[KIRCHNER]

isnt there a magnetic flow detector of sorts?

[Bunger]

So I pulled the pump and the shaft looked clean. Turned the pump with a drill motor and it pumped oil like a oil rig. Put it all back together and cranked the motor with my remote starter and it pumped oil. Ran it for 25 minutes on the hose and it smoked like a chimney. What would cause it to lose its prime?

[KIRCHNER]

did you have your mask on, when you removed the cowl.... LOL

[Bunger]

Nope my merc is immune to the rona

[KIRCHNER]

Maybe a heat soak condition could create your oil line air pocket. pwr head cooling down, oil & hoses cooling, expanding, contracting,oil tank pressure.i regret removing my oil inj. stay safe..

[Bunger]

That’s what I’m thinkin. Where our place is at the river it’ll be 115-120° during the day and 70 at night. Go up and down 3k in elevation on the way home. Figured it had to be the engine mounted tank expanding and contracting that cause it.

[KIRCHNER]

yep, another mystery solved. i had a problem with my tank loosing pressure. checked EVERYTHING, clamps,hoses. hit the cap, accidently with a soapy rag,where the lanyard connects, had a ring of bubbles appear. cap looked perfect..lucked out.

[Bunger]

So the line stayed full for a few days. Checked it yesterday after a 2 weeks of sitting and it’s empty. No leaks anywhere. It must be back flowing through the pump back into the reservoir I would imagine? I guess this is the point where I pull it out and start pre-mixing. Right? I really don’t want to because pre-mixing with my boat is a pain in the ass

[KIRCHNER]

It may be normal. can u make a drip-loop with a little longer hose, and watch the movement of the oil log/air pocket?

[Bunger]

It may be normal. can u make a drip-loop with a little longer hose, and watch the movement of the oil log/air pocket? the 5 other Mercury’s I’ve had that line always stays full.

[KIRCHNER]

maybe the vst fuel level has to drop somewhat, for the oil flow to show? if u cut fuel to the engine, running on vst reserve mix, you should see oil, before engine quits...u think 2-3 min.