I noticed today that my OMP lines look about half full. The car has been sitting for about three days. Is it normal for the lines to drain back a bit over time, or could this indicate an issue? I’m running a PFC, so no limp mode would be triggered, but VMOP seemed to be scaling with throttle on the datalogit last I time I casually checked. This is a new Mazda engine that’s been running for < 1000mi, and new OMP lines/injectors/etc. I’ve been premixing but plan to mostly stop if I can confirm the OMP is working correctly.

You can see in this pic where the oil level stops under the alternator.

 

Free bump.
I don’t usually push it, but have been premixing at half-rate with the OMP since adding WI about 50k miles ago. IF this is an issue it might be another reason to stay the course with a little premix.

 

Thanks! I don't really mind premixing the .5 oz/gal or so I've been adding, but I'd like the car to smell less and I figure that's probably part of it. Is that about what you put in? I also want to go back to stock cat and not prematurely kill it by burning a ton of oil through it.

 

I do use .5 oz. @ gal guesstimating at the pump. With a hi-flow cat over the years I haven’t noticed smoke or abnormal smell, but honestly not sure on the stock cat.

 

I've been doing about the same, probably more since I've been "eyeballing" it and would rather have more than less. I'm on the stock cat (no pre cat since I'm JDM) but don't notice any smell or smoke. I don't think I drive it enough to worry about long term damage to the cat.

 

Normal. Mine do the same. I never noticed it before replacing the lines when I put the new engine in. I suspect that's because the interior stains overtime with dirty oil and it makes the lines look yellow and full of dark oil.

 

Thanks. It's actually very difficult to tell looking at even the new lines whether they are full or empty, as well. You can only be sure when you see the fill line.

 

Oil pressure is what keeps the oil moving through the engine. Once there is no oil pressure, the oil drains to the oil pan.

 

But how fast do the OMP lines refill and re-supply the nozzles? If it’s as fast as I see oil pressure rise on cold start I guess it may not be a big deal.

 

If this drain-back was a real issue, we'd be hearing about a lot of early engine failures, and in FB's and FC's also, since I think they use the same setup. FB engines (I had an FB from new in 1979 and sold it still running great at 140K after I got my FD) often lasted up to 200K miles and just gradually got to the point they had so low compression they wouldn't start.

 

The OMP isn't even supplying much/any oil until the motor is under load, so the lines likely fill right back up as soon as you start the car. It makes sense that, through gravity they'd drain back a little through the OMP in absence of some sort of check valve to specifically prevent it.