Location of Oil Return Fitting on MSP MBSP

[CrispToast]

Thank you for reading. Just like the title says.

I am rebuilding and attempting to improve upon the durability of a N/A FS-DE for my P5. I'd like to install a Doc B pump and regulator etc. and I'd like to put the oil return line in the exact spot the factory put the turbocharger oil return line. Reasoning: The Mazda engineers probably studied the various locations, and for one good reason or another they chose that one.

My understanding is the oil returns to the sump via the MBSP. Where exactly is that point?

Also, searcing around, I've seen reference to the fitting being placed in an NPT threaded hole and I've also seen reference to it being welded in place. Which is it?

Again, thanks for taking the time to read this question!

P.S. The reason for all of this is I inflicted what later turned out to be a fatal injury upon my motor at a track day and I'd like to avoid any more broken motors in the future. Thanks!

 

[dmention7]

Here is the location of the factory oil return:

The fitting is basically a flange molded into the MBSP. If you're adding your own return, you can do it however you want. The cheapest way would be to drill a hole, tap some threads, and screw in the fitting of your choice. The proper way would be to have a threaded bung welded in. Either option will work, but if you tap your own threaded hole, consider the location carefully. The walls of the MBSP are fairly thin in some areas, and you probably want to make sure that the return dumps straight down into the oil pan instead of landing on one of the flat surfaces of the MBSP.

 

[dmention7]

Also, in case you care, here are reference pics of how I routed the oil return lines when I installed my DocB oil system:

Line routing 1

Line routing 2

Top down on oil return line

Oil return location

 

[CrispToast]

Thank you for your reply with great photos and helpful comments!

Just so I'm clear about this, the hole with the two-bolt flange boss on the front-facing side of the MBSP is the factory return point for the MSP turbo, correct?

I will need to check mine to see if it's been machined and plugged or if it has been left as-cast and unmachined.

I'll also need to see if there is clearance with the exhaust on my non-turbo car.

It does seem like a long way to plumb an oil return from the top rear, (where I'm likely to mount my regulator,) to the lower front where it was certainly convenient for the turbo, but maybe not for my situation.

Your regulator return point seems like a nice out-of-the-way place with plenty of room to work. Is there plenty of metal to work with in the MBSP at that point if I should tap it for pipe threads or machine it for a threaded o-ring fitting?

Does the factory use any kind of baffling on the inside of the MBSP where they placed the oil return?

Sorry for all the questions, but I'd like to get all this right the first time.

Thanks again!

 

[dmention7]

Thank you for your reply with great photos and helpful comments!

Just so I'm clear about this, the hole with the two-bolt flange boss on the front-facing side of the MBSP is the factory return point for the MSP turbo, correct?

Correct.

Your regulator return point seems like a nice out-of-the-way place with plenty of room to work. Is there plenty of metal to work with in the MBSP at that point if I should tap it for pipe threads or machine it for a threaded o-ring fitting?

I didn't take any measurements unfortunately, but in the location I used I felt plenty comfortable drilling and tapping--I believe it was a 5/8" NPT, possibly 3/4" NPT. It was a little thin on the top and bottom but being snugly between two of the oil pan bolt locations, there was plenty of material to the left and right of the hole. I believe I've seen a few other members use the same location.

Does the factory use any kind of baffling on the inside of the MBSP where they placed the oil return?

I'm 95% sure there was no baffling, though it would be a good idea for a turbo oil return where any kind of backpressure is hard on the seals. For this kind of oil return, I would not really be concerned honestly.

 

[CrispToast]

Thanks for taking the time help! I will need to do more recon work on this end, but you've given me some good stuff to work with!

Thanks again!

 

[dmention7]

Anytime.