Air bubble in the oil lines

[hytron]

I have a 2004 GTI LE RFI (787 RFI) and recently I discovered air bubbles in both of the oil lines that supply the oil to each cylinder. Filter has been changed about 5 hours ago, and the main oil supply line between the oil tank and oil pump is full of oil - no bubbles of air can be seen at all. What comes out of the oil pump are random air bubbles...very small about 1/8" (2mm) but apparently significant that can cause problems when idling. Bleeding screw on the pump has been checked and it is tight.

Is the pump failing? Shaft seal on the pump? I don't see what else could cause it... Any ideas?

 

[68ragtop]

very small bubbles will pass through the small injection lines with no ill effect. But, if you get a large one at the pump, it can loose its prime & stop working. Also, a lot of small bubbles means less oil in the engine. There is a bleed screw on the bottom of the pump to help purge the air pockets from the feed line. Sometimes you have to manipulate the oil filter to get all the trapped air out. I like to install a new filter by holding my finger over the outlet of the filter, turn it upside-down after connecting the inlet, let it fill, then let oil pour out of the filter into the pump supply line & push them together as the line is full & air escapes. With practice, the filter can be changed without an air bubble & not all that much mess. Keeping a few rags under the area is usually all you need. Sticking an empty filter in line isn't always easy to get trapped air out.

 

[hytron]

Thank you for your reply! That is pretty much how I change the filter. Once I connect the line from the tank to the oil filter, I place the oil filter in the vertical position and since air is lighter than oil it will stay on the top and get purged out of the oil filter, and as the oil starts to flow out, I connect the other end with making the final connection on the top. So usually I don't have any air in the supply lines. Would a failed seal (or O-ring) on the oil pump shaft cause air bubbles to be present in the small lines feeding cylinders with oil? The machine has 190 hrs on it and I had it since new.

 

[Dr Honda]

You may see little bubbles in the injection lines (after the pump) because the engine will pulse the oil in those hoses. It basically will suck a little out, and push a little air back in.


So... as long as the pump is bled, and there are no signs of air in the supply hose, to the pump... you are fine.

***EDIT***


With that said... if you have the old, original hoses... it could be a sign that there are cracks in them. If you suspect cracks... give them a pinch, and twist. Sometimes they just rip, because they are full of small fractures. Better to find the issue on the trailer, than to have a hose fall off while riding.

 

[glsmohio]

you may see little bubbles in the injection lines (after the pump) because the engine will pulse the oil in those hoses. It basically will suck a little out, and push a little air back in.


So... As long as the pump is bled, and there are no signs of air in the supply hose, to the pump... You are fine.

***edit***


with that said... If you have the old, original hoses... It could be a sign that there are cracks in them. If you suspect cracks... Give them a pinch, and twist. Sometimes they just rip, because they are full of small fractures. Better to find the issue on the trailer, than to have a hose fall off while riding.

very interesting, i to am having the same problem and i have bled the pump 3 times. Im still running pre mix to be safe...i have 10hrs on it since i did the lines.

 

[hytron]

Well, each hose is about a foot long, so where I am seeing bubbles is about 3-5 inches after the pump discharge port - That is the part I am able to see...6-7 inches toward the cylinder, the hoses are covered with black shielding insulation so I cannot see any further past that point. Appears to be random as well. So I started the machine, held the pump wide open and watched the little bubbles move toward the engine; there was another set of bubbles that appeared, so I repeated the procedure. As of now I don't have any bubbles, but my concern is when I am out on the lake idling, and these pumps are tuned down to 1:100 oil to gas ratio, so they don't consume much oil, and air bubble in the oil line could cause a serious damage if idling for a long time.

I also loosened the bleed screw and there was oil coming out of it, tightened it up and appears to be ok for NOW. Not sure what will happen when I go riding next time.

I agree that cracked supply hose could definitely cause air to be sucked in. I will double check all the oil hoses tonight and post the updates as well...

What about the O-rings/seals on the pump itself? Has anyone heard of them going ever bad? I am not sure if these pumps have shaft o-ring or a small seal...I would assume o-ring...can they go bad? Any experience?

 

[Dr Honda]

In all my years with seadoo... I've only seen one pump truly "Fail". AND... Mikuni makes the pump on a lot of other older 2-strokes. (including Fuji, Polaris, Mercury, Johnson, etc)

Generally, what happens is...

1) The filter plugs (starves the oil)
2) The hoses rot, and fall off. (pumping oil everywhere other than in the engine)
3) Back-fires will cook the oil in the injector nozzles. (mechanical issue, that would be cleaned if serviced)
4) Some other mechanical drive fails. (it's a known issue with some of the merc engines. A plastic drive gear fails.)

Because of that, when someone says... "I lost an engine because that dump oil injection pump failed !""


What they really mean to say is.. "I have a 15 year old toy, and the oil system was never serviced. And because of that, I need to blame the system instead of my own dumb self." LOL !!

So, if the hoses are old... REPLACE THEM !! (Tygon is a very good, safe replacement. it's clear and yellow. see below)

But seriously... I bet I can go to my own toys, and find air in the small injector hoses.