RX8 cold start OMP issue?

Recently I purchased a 2004 Mazda RX8 from John Mills with both of us under the impression that the engine was shot. Signs were typical: hot start issues, bad oil consumption and terrible fuel economy (down about 40% from advertised).

There were a lot of top shelf aftermarket items thrown at this car. K&N Typhoon, Magnecor wires, 3" Greddy exhaust with cat delete, Tokico D Specs and Tein springs. I sold the orange car and bought this FOR LESS... I had enough money left to buy a replacement wheel as well!

I replaced the starter with a $40 eBay 2.0kw 13 tooth unit and started driving it to see what didn't work and what did. What didn't work was the cruise (active CEL) and trying to drive the car without warming it up. If you didn't give it a solid 5-7 minutes it would bellow smoke until it was up to temperature. Once up to temperature in either case it would drive without smoke. Like none noticeable. Yes I know the Oil Metering Pump is supposed to inject a controlled amount while running but I think that it may be bad.

I know that there are Mazda and RX8 people here has anyone seen this before?

Every OMP that I have seen fail, and that would be all of them, failed by no longer injecting oil.

In reply to QuasiMofo:

Are you sure the smoke on startup is from oil and not from an internal coolant leak?

Coolant level has stayed at the same point through 2200 miles. I've consumed a lot of oil and gas in that time.

Throttle valve is clean as well. It's like the car can't hold oil unless it's warm. Of course that doesn't rule anything out and points more to seals but why won't it smoke on cold idle or after warm up?

I'm with knurled on this one, IME the OMPs fail in a way that causes more expensive engine damage.

Are you sure it's oil smoke? If so, it would make me wonder if the oil control O-rings may have failed and let oil seep into the combustion chamber? The oil consumption on these is pretty mild by rotary standards (on mine it's mostly measurable on the track) so if this one uses a lot of oil, some is getting into the combustion chambers that shouldn't be. Have you pulled the spark plugs and checked if they're really oily?

Have you replaced the coils yet? Of all the things I know about RX-8s, the big one is that replacing the ignition coils can often solve a bunch of really bizarre issues.

Yeah, coils and plugs are missing in the list above. Definitely not a bad thing to change, but that usually doesn't help with oil smoke.

If it has horrible oil consumption, the oil control rings are probably shot. With bad oil rings, when you shut the car off, oil drools into the chamber and then pools in the bottom. With a peripheral exhaust engine, th rotors sort of sweep it up into the exhaust system where it gradually burns out. With a side exhaust engine, it can't do that, so the oil goes around and around until it's eventually burned up.

New OE style replacement coils. New Denso plugs. Changing oil this week to a heavier base weight oil just to see if it causes a different reaction.

I would wholeheartedly say seals and oil blow by if it did this AFTER its warmed as well but when driven at temp you get zero smoke and the car makes full power. I mean I can run WOT through fourth and well into triple digit speeds and it still pulls up to the redline.

If it maintains this level of performance I am considering keeping this as is and buying sea neighbors broken Automatic car and swapping it instead!

Knurled wrote: If it has horrible oil consumption, the oil control rings are probably shot. With bad oil rings, when you shut the car off, oil drools into the chamber and then pools in the bottom. With a peripheral exhaust engine, th rotors sort of sweep it up into the exhaust system where it gradually burns out. With a side exhaust engine, it can't do that, so the oil goes around and around until it's eventually burned up.

I think I understand the concept now. So while idling it's likely burning the same oil off but not in the smoke and fury manner as when being driven cold?

Pretty much, yes. Only that you probably don't have quite as much oil dribbling into the chambers when then engine is running, or at least it's not pooling in the same place.

QuasiMofo wrote:

Knurled wrote: If it has horrible oil consumption, the oil control rings are probably shot. With bad oil rings, when you shut the car off, oil drools into the chamber and then pools in the bottom. With a peripheral exhaust engine, th rotors sort of sweep it up into the exhaust system where it gradually burns out. With a side exhaust engine, it can't do that, so the oil goes around and around until it's eventually burned up.

I think I understand the concept now. So while idling it's likely burning the same oil off but not in the smoke and fury manner as when being driven cold?

Pretty much. The ends of the chamber don't see combustion, especially at low loads, so it can take a very long time to clear out. IF this is the failure you're having, driving it hard sooner should cause it to clear out faster yet more emphatically.

Heck, on a peripheral exhaust engine, it can take a long time to clear out. And Mazda went away from peripheral exhaust because the unburned end-gases tended to get swept right out the exhaust port, causing horrific emissions.

So, if the performance isn't terribly affected yet, should I continue driving it or am I asking for major trouble?

It's always cheaper to rebuild sooner than later. I still have yet to get my hands on a dead RX-8 engine to see what, exactly, is failing in them. my gut feeling is that it's a combination of irregular apex seal wear, rotor housing warping near the plug holes since Mazda has progressively moved the spark plug locations and the cooling in the area gets worse every time, with no way to fix without relocating tension bolts, (and warping rotor housing surface also exacerbates apex seal problems), and warping of the side housings near the exhaust ports and/or rapid wear of the side seals since they now pass over a hot exhaust port.

If you wait until it FODs something, you're replacing a lot of parts. If you rebuild early, you may get away with hard seals and maybe some resurfacing. But I don't know what FODs in these motors yet.

I am prepared to replace this engine with a 4.8L LS with a mild cam, F Body manifolds adapted to the 3" Greddy cat back, Chinese intake, light flywheel, and a WC F body T5 trans.

It's not worth rebuilding the Renesis to me.

The common failure on the RX8 OMP is not the pump itself but the position feedback switch. The strip the wiper rides on wears right through and sends it into limp mode when it can't complete the function check. You can't buy the switch separately either... Luckily the fact that you aren't in limp mode means the metering part at least is working. The pump should outlast an engine or two.

Pull the oil cap when it is/isn't burning oil and see if there is a difference in blow by. Maybe an oil control ring is sticking when cold and frees up hot? Kind of grasping for straws there though.