Oil Return Fitting Location - Too Low?
 

I picked up a used engine as a replacement in my '95. Luckily it already has a fitting for the oil return in the pan. Unluckily it looks a bit low on the pan:

https://www.miataturbo.net/attachmen...ine=1358789297

FM says to tap the pan 2" below the upper lip, then adds "no lower!" in parenthesis afterwards. BEGI however suggests 2.3", which appears to be in line with where this hole has been drilled.

Any guidance?

You're fine. Look how low the dip stick goes, it's in the lower part of the pan, below that fitting. And it'll be even lower when the engine is on and there's oil coming out of the drain. It appears to be at 2" anyways. I'm assuming that 2" location from FM is the center of the hole. It looks like it lines right up.

Looks about perfect for a fitting that was installed when the motor was in the car.

If that's bad then I'll need to redo my pan too ;)

It actually looks pretty spot on. I did mine with the pan off during rebuild and it's pretty damn close to the same.

Is it tilting downward or does it just look that way in the photo?

I havent tapped mine yet so I'm just curious.

It looks a little low compared to mine (drilled/tapped on the car, pictures 4-7 on this thread): https://www.miataturbo.net/build-thr...70/#post969041

But I agree with everyone so far, it should be fine.
At the location I drilled mine the oil pan was 100% full to the top of the dipstick, and no oil leaked out with the front of the car raised up slightly. With the motor running there's probably 1/3 to 1/2 of the oil running throughout the engine anyways, so the amount in the pan is almost certainly lower than that bung.

Perfect - thanks guys. I guess I drilled my last one a bit on the high side then. I don't run AC or PS so there is plenty of real estate down there.

if a/c equipped, I agree:

https://www.miataturbo.net/attachmen...ine=1359052356

Why all oil return fittings are located to the front of the engine? Mine has been there in couple of builds as well. To miss the downpipe?

The reason I am wondering is making sure the sump where oil gets picked up has most oil in all times. Spec miatas have oiling issues with high G:s and in that light one might bring the oil return from turbo in the sump area if the car will see track use.

On the other hand the oil from turbo is hot and may be aerated as well, is the front return location thought to allow the oil to cool and settle a bit before returning to pick-up sump.

Any thoughts theory where ideal location should be?

It's the easiest place to put it, both from an install standpoint, and hose routing. You are way overthinking this.

Because most of us drill the hole while the engine is still in the car. That's pretty much the only spot that's easily accessible. Fortunately, apart from having the pickup tube right behind it, it's a perfectly serviceable location.

It you've got the engine out of the car, put it where I did:

https://www.miataturbo.net/attachmen...ine=1359157320

Makes for a straighter drop for the oil, requires less hose, and it's not competing for space with the AC, power steering pump & hoses, compressor outlet piping, coolant hose, etc.

If the engine is still in the car, the front location works fine.

The stuff about oil level in the sump is unnecessary -- the turbo doesn't have that much oil flow through it anyway (remember the feed line is usually -4 and often has a pressure restrictor in it).

--Ian

It's got less to do with flow and more to do with pressure. If you plug up a drain line by submersing the end in the oil, the CHRA ends up pressurized and the seals will leak. That's why it's important to keep the oil drain fitting at least partially above the oil level in the pan.

When I first read hrk's message, I thought was talking about wanting to optimize flow out of the turbo for the purposes of preventing the level dropping below the pickup and starving the engine. On re-reading the thread, I have no idea why I thought he was saying that. I blame friday-afternoon-itis. :)

I agree re: submerging the end of the drain in oil.

--Ian