How does the MOP / injectors handle air bubbles?
 

So tomorrow I'm going to be adding a Sohn adapter to my metering oil pump.

Obviously I'm going to prime my oil reservoir line with premix before I attach it to the Sohn nipple, but there will still be air in the system from the internals in the Sohn.

In addition, I plan on replacing all the seals including the 5 hole and individual crush washers on each of the 4 oil line nuts. I suspect disconnecting the lines on the MOP side will drain some oil from the line.

Will the injector lines automatically bleed the system on startup, or is there a procedure I need to do to prime the whole system before startup? In other words, do I need to worry about air in the system?

This makes a new question occur to me... say I'm on an oval (Oz style), or a very long off ramp - basically any long, right hand turn - with summer tires at full tilt with 1+G of side force. Is oil being starved away from the MOP? Is that detrimental as far as oil injection goes? And say the MOP is pumping air during this period... does it run into the same trouble of air bubbles/pockets in the injector lines?

Thanks.

I'm mid project on this and would like to see a answer too.

I used a syringe to prime the adapter as much as possible before attaching the oil feed, but it does seem to pass air out of the system on its own. You have to drive it hard though, run it up to top of 2nd or 3rd a few times, to get the high OMP rates.

As far as lateral force: if there is no air in the line, there is no air for the OMP to pump, so I wouldn't worry about it. The oil in the line has to go somewhere, so even if the lateral force is pulling it to the side, it can only really go into the OMP or back up into the reservoir, which is pretty unlikely as it still has the pressure of all the oil above it keeping it down. I'd worry more about the reservoir being of the right shape so the oil sloshing to the side under cornering doesn't let air into the line from there. Still unlikely, but you never know. You should burn about a litre an hour under race conditions, so plan for that.

you guys are thinking too much ...

If it concerns you, run some premix or disconnect the OMP lines from the higher end and fill them carefully with a syringe. Bubbles in the line will pass quickly enough without any cause for concern.

What about if you replace the MOP lines? You would have a large amount of air at that point, so what does the system do to correct that, if anything? From the vids I've seen the MOP doesn't pump at high pressure really, so that air would be going to the injectors for a while.

Basically I'm more curious about how it works.



Sorry I didn't clarify, I was asking about the stock setup on this one. As far as I know the sump is below/beside the MOP as stock, so wouldn't cornering to the right cause the engine oil to slosh left, away from the MOP/MOP pickup?

There's one offramp near me that is almost 360 degrees around, and if I take that hard my oil warning light comes on for about 3-5 minutes. During this cornering, is the MOP just sucking air?

Correct, it isn't high pressure, the stepper just inches the oil along.

I was going to add an additional point, but I'm not so sure about it any more. Do the oil injectors actually open/close? I don't think they do, I've never seen a reference to that, but I don't know for sure. If they are basically just nozzles that are always open, then engine vacuum should be pulling on any oil in the line. However, even if this is true, I don't know if that is enough to pull a bit of oil from against the OMP all the way through to the engine. Try sucking liquid through a straw with the other end blocked... it generally doesn't move much liquid.

I guess that I can't really answer your question for how long you would be driving without injected oil. Someone that knows the OMP system more thoroughly would probably provide a better answer.

In a stock system the omp is supplied with pressurized engine oil. It will not get starved unless you starve your engine. The rotor bearings would suffer a lot more than apex seals from lack of oil.

The injectors are just free flowing and engine vac will pull in extra oil. That is why there is a relief line. Some people use a restrictor in that line to increase oil flow.

With a sohn you could potently starve your OMP, but it would have to be high g load and a low oil supply for a long time to drain the hose from supply tank to the adaptor.

High engine load gets more oil to it would reduce the time. Maybe use a larger supply line if you are really concerned.

And bubbles will remove themselves naturally and are of no concern. Consistent bubbles would be.

Cool stuff, thanks guys.

Back to the drawing board......the OMP is a positve displacement pump that isn't supplied pressurized oil from the engine.....if it was the Sohn Adapter wouldn't work ;)
You could use a -10 line and the pump will still put out the same amount of oil :)

From my experience, just disconnect the vacuum line that goes to the oil metering pump injectors at the intake side and keep it plugged up, let the car idle.

I could be wrong, but the vacuum line there helps keep a neutral pressure atmosphere in the metering pump lines. If you didnt have that vacuum line, it would become a negative pressure environment and engine vacuum would suck the oil through the lines/nozzles. (Again correct me if I am wrong)

I had to get a line replaced once before after having my reman installed and i had air through the entire line.. I fixed it by doing exactly what I just mentioned.

Only on RX8Club would anyone think it makes sense to run the engine under high load to remove air bubbles from the critical oil lube system that protects the engine under that operating condition

1. Start off with a tank of premix.
2. Block the air supply tubing between the oil injectors and the intake air supply elbow/tube.
3. Operate engine normally until the air bubbles are gone, then unplug the oil injector air supply tube and resume gasoline only use at next fill up.

So the air tubes are delivering air TO the injector or FROM the injector?

For the record I have not done the adapter yet, waiting for more info from this thread. Also waiting for a torque wrench which I thought I had but didn't...

Yes it is a positive displacement pump, but in the stock form it gets oil that is pressurizes. In a SI at least.

I was just describing that to starve a stock pump you would starve your engine.

In a sohn setup it is not being supplied with pressurized oil. So If you turn so hard to starve the hose you have more chance of getting a air bubble in the system. If you're turning hard enough to drain the supply hose then I don't ever want to drive with you, but a larger hose would give more supply time for a long tight high speed curve. At high loads and rpm.

Every time you double the ID of a hose you quadrouple the capacity.

thinking too much man ... way too much ...

The pump will determine the flow in this scenario......so inlet and outlet sizes are immaterial. Only issue is loss due to leakage of larger lines...thats why the small lines are there...big enough for the flow...and small enough they dont drain out

Have a look at the inlet and outlet area on the oil feed for the pump...and you will see it cant be pressure fed :)