'94 turbo Miata UOA

[jwagner]

First UOA on this car. It's a new (to me) '94 Miata with a FM II turbo. The car has 140K miles on it, but the motor has been apart at least once, and supposedly not that long ago. The oil is Red Line 10w40 with 7,500 miles which is a lot longer than I'd normally run it.

Talked to Blackstone and they were concerned about wear metals, specifically copper which seems high to me but not way out of line for 7500 mile oil. Iron, lead, and aluminum are high too.

Quoth Blackstone: "Lead and copper show bearing wear and iron is from steel parts, probably a rotating shaft, but could be cylinders walls too since aluminum from pistons and chrome from rings are high too. This engine does have a turbo installed, so that might leave a little more metal behind than stock, but probably not this much. Fuel at a trace level isn't harmful. The TBN is 5.0 showing active additive, but drop to 2,000-3,000 miles on the oil since wear is high."

I'm debating whether to tear into the motor this winter since I'll have it out anyway, or to drop it as-is into the Exocet we're building. Before we pull it we'll take compression and put a mechanical oil pressure gauge on it to get accurate oil pressure.

Opinions, analysis, wild speculation, and free beer are always appreciated.

Code:


ALUMINUM 6 Univ Avg 3

CHROMIUM 5 1

IRON 54 10

COPPER 10 4

LEAD 53 3

TIN 2 1

MOLYBDENUM 208 91

NICKEL 1 0

MANGANESE 1 1

SILVER 0 0

TITANIUM 0 0

POTASSIUM 6 1

BORON 66 61

SILICON 15 11

SODIUM 12 37

CALCIUM 2491 2218

MAGNESIUM 139 192

PHOSPHORUS 1010 790

ZINC 1153 918

BARIUM 0 0



SUS Viscosity @ 210°F 67.3

cSt Viscosity @ 100°C 12.24

Flashpoint in °F 370

Fuel % TR

Antifreeze % 0

Water % 0

Insolubles % .4

TBN 5

 

[29662]

How much boost are you running?

I would guess from the UOA that the bearings are taking a beating. If you're going to have the engine out I would certainly MIC the bottom end and maybe do a refresh if needed.

 

[jrustles]

Bearings should be alright with the Redline 40 grade, my questions: who did the machining and rebuild and is it still breaking in? Oil cooler etc etc

 

[jwagner]

Don't know much about the history of the car. I do have a pile of receipts but no machine shop receipts. Just found an old e-mail and the previous owner says the bottom end was rebuilt at around 133K, and doing the math, since the car has 140K on it now, the oil I just changed out was probably the oil put in after the engine work. (didn't realize that until now)

I think the oil cooler is Mazda OEM, doesn't look aftermarket to me.

Running 8lbs boost. The car hasn't been driven particularly hard since I bought it, but it will be...

 

[abycat]

8 psi isn't much. Unless the fuel management system is totally off I would say its still shedding break in material from the rebuild. lets hope.

 

[29662]

Yeah that thing is still breaking in. Does it have an oil pressure gauge?

 

[jwagner]

It's got the standard oil gauge in the dash. Reads a bit low for my liking - probably 15lbs idle hot, and just under 30lbs hot on the highway at ~3000rpm, but Miata gauges aren't known for being real accurate. I've got a mechanical gauge for the Exocet and will try to sort out the thread adapter needed to get it hooked up in the Miata. It's something odd like a tapered english pipe thread.

 

[The_Eric]

It is my opinion that a fresh engine- one that didn't come from an OE, will shed a pile of wear metal. I know mine did. Run a few 3k changes and then move out to 5-6k, taking a sample for UOA at the end.

 

[abycat]

british standard pipe thread is almost the same as regular tapered pipe thread so you may over thinking what thread it is. I'm pretty sure it's 1/8" npt.

 

[29662]

Originally Posted By: jwagner
It's got the standard oil gauge in the dash. Reads a bit low for my liking - probably 15lbs idle hot, and just under 30lbs hot on the highway at ~3000rpm, but Miata gauges aren't known for being real accurate. I've got a mechanical gauge for the Exocet and will try to sort out the thread adapter needed to get it hooked up in the Miata. It's something odd like a tapered english pipe thread.



30 lbs at 3000rpm is right on the edge for a turbo motor. I would definitely try and hook up a real gauge just to make sure. You can probably get an adapter from edelmann.