DigDug

Wow, I didn't think that thread would have gone so steeply downhill so quickly - honestly, I posted and forgot about it, and just today remembered to check on it!

Anyways, I guess I wasn't clear enough in my description - what I'm getting is clearly fuel dilution, not metal particles or coolant or anything else. The fuel smell is strong by 100 miles after a change, and when you pour the oil out on a flat surface after draining it (don't ask), you can literally see the oil separate a bit - not sure of the actual quantity, but it's significant. Not only that, but while my engine burns oil like it should (with no cat, it's easy to tell), the oil level never drops, even after 1500 miles with no top-offs. When this engine was newly rebuilt about 6 months ago, the level dropped about a quart over that interval, but that gradually turned into what I see now.

I checked the injectors and found no obvious leaks. My plugs do tend to foul pretty quickly, but it appears to be carbon buildup from running pig rich all the time. No starting issues or wetness of the plugs after engine shutdown whatsoever. I've also tried changing the plugs at the same time as oil changes, and even after more than 1000 miles since the last change, and there is no meaningful difference. Coolant level has been rock solid ever since the rebuild with no measurable loss, and it does not appear to be contaminated.

For me, throttle blips on downshifts (or any quick change in engine speed) are a clear and repeatable indicator - they are either smooth and predictable, or rough and inconsistent. As I mentioned previously, mine start getting rough after only about 700-800 miles. It gets bad enough that I have to compensate with my timing on the throttle (earlier/more throttle) to get accurate rev matching. This last time, after 1250 miles, even full-boost acceleration felt lumpy and inconsistent, and there was a noticeable loss of power. Changed the oil, and it was back to normal. I've been through this cycle quite a few times now.

From the last thread, the suggestion about a drain valve in the cooler line seems like an excellent idea, and I think it's worth a try. Maybe if I can improve oil dilution on every change, I will get longer intervals before fuel dilution becomes a noticeable problem as it has.

Any other ideas?

alexdimen

iTrader: (13)

did you happen to catch the several posts in the old thread where it pointed out that:
*thinner oil actually improves engine performance*

this is because of the reduced drag. however, it would cause increased wear. if the oil were thinned enough it would begin to lose all lubrication properties and you would eat up your bearings/bushings then you would feel something. for this to happen, you would have to dump a huge amount of fuel into your oil. if this were happening even with a functioning OMP, i would think you would see your oil level rise significantly.

as far as your oil seperating... something is wrong there, because the gasoline and oil should mix fully and without saturation or seperation.

it is very strange that the performance problem seems to be remedied by an oil change. maybe it is just coincidence/driving behavior induced.

personally, i find it hard to believe. the oil in my FC smells of gasoline within a few hundred miles of an oil change and it has no performance issues. it will be interesting to see what your problem is.

have you had a sample of your oil analyzed?
btw, where are you in VA?

skotx

If you're getting major fuel dilution and your plugs are fouling quickly, why don't you figure out why your running so rich?

impactwrench

Both of these problems can be directly linked to short or infrequent trips. If you don't have leaking injectors, drive the car for 50 or so miles and the fuel has to evaporate from the oil. This is why highway miles on a car require less frequent oil changes, tires, etc. If you bought a car, ran it without shutting it off, it might never wear out. Sitting causes condensation, allows seepage of condensation into bearings, and excess fuel into the oil pan, amongst a host of other things. Drive it and see if the smell does'nt clear up.

JConn2299

Well, since this thread has revived I might as well take the opportunity to validate some of the points I was making. It just so happens that the Tech Correspondence section of the Sept. 2006 issue of Road & Track contained this item:

"I thought it was only a cheat option in the PlayStation2 games Gran Turismo 3 and 4 that used oil will make an engine less powerful, and that the full horsepower would be back when an oil change would be made. It hit me strongly when I pulled out of the Honda dealership right after an oil service. I felt the car gained power and accelerated faster. Is it normal to have a power loss (because of the carbon deposits and viscosity of the oil, I assume), and is there a rule of thumb concerning how much power is lost prior to an oil change?

A. Killjoys that we are, we have to say there is no noticeable performance degradation associated with used/dirty oil. Oil consumption may rise with dirty oil, but noticeable performance gains or losses stem more from the owner's mind (JConn: Damn, isn't that exactly what I said? LOL!) looking for affirmation for spending the money. Chances are good your dealer did something else to improve response."

Couldn't have said it better myself.

DigDug

Yeah, mine is a daily-driver, so I do make some relatively short trips. I usually end up getting at least one 10+ mile drive in per day, but going to/from work is only about 6 miles (the crazy thing is, it still takes me 30 minutes each way because of the ridiculous traffic light timing around here). I figured this was a big contributor to the plugs fouling so quickly, especially because I'm not running the engine at high loads on these trips. I also try to get a few full-boost runs in each night on my way home to get the plugs cleaned up some before I shut it off for the night.

Overall, I'd say about 95% of my driving lately is low-load and off-boost.

I'll try a long drive this weekend, and I'll post my results...

DigDug

Exactly - the potential loss of lubrication is exactly why this issue concerns me. I'm far less interested in whatever gains can be had from thinner oil, than I am in protecting the engine.

As I mentioned, my oil level doesn't really drop anymore, where it used to drop around a quart per oil change. When I first noticed the drop in consumption, I considered the possibility that oil injection was no longer functioning, and that maybe the roughness I felt was lack of apex seal lubrication. But then it's clearly burning oil just as much as ever. I checked out the coolant as well - no traces of any oil, and I haven't lost a drop of coolant.

If it really is burning just as much oil as it always has, and the level no longer drops, then I should be looking at roughly one quart of fuel in my oil when I change it. I still have a hard time believing that much is accumulating.


Yeah, that's what I figured too. It was sitting there for a good hour before I noticed it, and it was still subtle - not like oil floating on top of water. Moving the puddle around, you could definitely see two distinct densities of fluid. There's a chance it was something else, like something that was present on the garage floor before the oil was "added".


Haha, why are people around here so quick to jump to that conclusion all the time?

No, I don't believe for a second that it's induced by any change in my driving. If you can drive, you really should be able to detect changes in the response of the engine to any particular input. I'm just saying that if I do anything different from one moment to the next, I'm well aware of it, and I've driven this car plenty to know how it reacts to my inputs.


It's more like 700-800 miles for me before the smoothness on downshifts starts to degrade. Last time, it was around 1200-1250 miles that full-boost consistency started falling off. I really have to run the oil well past 1000 miles before "performance" degrades significantly. And the power loss isn't like 30HP, probably more like 10HP or less. Then again, when you reach full boost with these engines, provided you're not having ignition or tuning problems, they run more or less the same regardless of oil quality. As I've said, it's quick changes in engine speed (at low loads) where I notice this the most. Maybe "performance" isn't the most descriptive term.


No, I haven't, but I probably should. I'm in Arlington VA.

DigDug

That's a good question! Actually, I'm running about 12.5 AFR on boost across the board, but off boost, it varies because I haven't taken the time to really tune cruise. Actually, it's more idle and low-load cruise that it's running pig rich. Once you get the speeds up above 2.5K off boost, it leans out to around 16-17 AFR.

wanklin

iTrader: (2)

Joe, have you checked your injectors? I wonder if a leaky injector might cause the symptoms that you are describing as fuel gets poured through the engine instead of being atomized and burned away. You might also watch your fuel consumption and see if you notice a large difference in consumption to support the leak theory.

GoodfellaFD3S

iTrader: (213)

Who rebuilt the engine 6 months ago? If the side seals were clearanced very loosely, or you reused old and out of spec side seals, you will experience fuel dilution due to blowby. Many years ago, i had similar problems as what you speak of, and upon teardown of the motor (after detonating and breaking a seal) found the side seals were very loose. Ever since, I have built my own engines.

Improved FD

more power to Rich, but I don't buy his "side seals" theory

high % fuel dilution (approaching 10% after 2000 miles) is unavoidable with these cars, so I believe the best overall solution is run a higher viscosity synthetic which resists degradation as long as possible (I run the new "extended life" Mobil 1 15w-50) and change the oil every 1500 miles

now, little jconn will say, "don't worry about it, your coolant seals will take a dump long before any oil related failure"...I don't doubt that is usually true, but why not do everything you can to keep the engine tip top?

to the original poster of this thread: I just finished installing the drain valve on the line between the two oil coolers, you will get about another half a quart of nasty oil out!

JConn2299

By that logic why not change your oil every other day? It's called the law of diminishing returns. Again, where's the evidence of all these oil related engine failures? We don't see them. Lots of coolant seal failures however. I don't see any good evidence showing greater engine longevity for those doing 1,500 mile oil changes versus 3,000 mile oil changes. It doesn't appear to make a significant difference. Your engine is much more likely to go out from a coolant seal failure before you see a wear problem due to oil.

As for being able to "feel the difference" between a 1,500 mile oil change and a 3,000 mile one, as stated in the original thread, well, serendipitously (or was it the hand of god? LOL. You mean god is on MY side? Ha, ha, ha....) the editors of Road & Track with the engineering degrees made my case for me.

I'll say it again, the focus of many owners seems misplaced. They often get obsessive about oil changes, but I hear very little bragging about frequent anti-freeze changes. Yet these cars are dying from coolant related failures.

My personal theory is that it's because oil is a sexier topic. The bottles have all sorts of tempting performance related claims and snazzy labeling. It's also easier to do an oil change and dispose of the old stuff. So the focus goes on the oil. Anti-freeze and distilled water is so dull and cumbersome by camparison.

I'd like to see more posts from knowledgeable people examining the reasons for coolant seal failures. Why is it some engines go at 50-60k miles and others make it to 100k and more? I'm going to guess that Mazda doesn't have widely varying
build and materials standards. My guess is that is has to do with the way the cars are used and maintained.

If one engine goes at 60k and another goes at 120k there is some significant and real difference there. I've seen numerous examples on this forum of both, but one has double the engine longevity of the other. That's a big difference. What accounts for it?

I don't think it takes too much insight to theorize there's probably a correlation between the degree of modification and engine life.

Are there other factors?

-Getting on boost before the engine is fully warmed up?
-Letting the engine sit for extended periods, weeks or more, so corrosion from the water in the coolant sets in?
-Not changing the anti-freeze every two years?
-Using hard water in your anti-freeze mix?
-Are radiators and other components of the cooling system not able to handle the heat being put out by modified cars?
-Is a quick engine shutdown after a hard or even a moderate run doing damage to the seals?

Why do some coolant seals blow at 60k and others last well over 100k?

Against all this, and the rash of coolant seal engine failures, whether you change your oil at 1,500 miles or 3,000 miles becomes a footnote in your car's history.

JConn2299

Here's another thought. People often go to a bigger, more efficient radiator when they modify their car. But the water passages in the engine block are set. The coolant has to get to the radiator before heat is exchanged. Are these modified cars exceeding the design limits of those little coolant passages around the hot spots in the engine?

Improved FD

coolant seal failure probably has alot to do with the fact that coolant changes as very often neglected, most people change their collant every three years or so (I change mine every year), if that, so we agree on that aspect of it....I'm just **** about maintenance in general....I believe 1500 miles is a good oil service interval if you are on the boost often

DigDug

Yeah, I checked the o-rings and they looked fine. Maybe an injector is sticking open a bit when I turn it off, but then it doesn't seem to have any problems when it's running. Maybe I should test fuel pressure for some time after shutting the engine off. Never had to do that before, but maybe I can see a pressure drop that would indicate a leak.

As far as consumption goes, it's been consistent since the rebuild - no increase that I can detect.

DigDug

Good point - my apex and corner seals needed replacement, but my builder asked me whether I wanted to reuse the side seals. I asked if he thought they were in good enough shape to be reused, and he said yes. He's a very experienced rotary engine builder, so I took his advice and they were reused.

Actually, that decision has been in the back of my mind ever since, and in retrospect, I wish I'd just spent the extra money to go with all new seals. When I got the car back, it was running great, so I didn't sweat it. It still runs great and makes plenty of power with no compression issues, but the oil quality issue has gotten worse lately.

DigDug

Yeah, I've been thinking about going to a higher viscosity oil too. I'm trying 10W40 on the upcoming change. Maybe that will help.

And I definitely plan to install that drain valve. My setup has an Aeroquip hose running between the two coolers. It would be nice if somebody made a suitable valve with AN fittings which could simply go inline at one end of the hose, where it meets the cooler fitting. Anybody seen something like this?

DigDug

Haha, you put so much faith in these magazine editors. If they're so smart and wise with their engineering degrees, why are they working for a magazine, and not for a car manufacturer designing their engines?

If you can't feel a difference in 1500- vs. 3000-mile oil in your car, then all the better for you. I can with my car, though it's most likely a symptom of a problem, which is the point of this entire thread.

And if you want to put your own sense aside in favor of what some C-student "engineer" writes in a magazine, go for it. I suppose if they wrote that pissing in the gas tank helps fuel efficiency, you'd probably do that too. For me, my own senses have made my point that either these magazine editors you idolize are a bunch of idiots, or else you've taken what they've said completely out of context.

I'm really not trying to be mean here, I'm just getting sick of these posts where somebody says something can't possibly happen, though it is clearly happening to someone else. Just like the assumptions that the driver noticing a noise/vibration/etc must be "psychological", it seems very common around here anymore. Trust me, I have plenty of experience driving to be able to notice a subtle change in how my engine responds to my inputs. Period!


You have some very good points there. Maybe a little out there on the speculation about why oil is "sexier" than other maintenance items, but for the most part, I agree with you. I've always been more concerned about coolant seal failure myself, especially since I've experienced it firsthand.

Honestly, aside from changing it on a somewhat regular schedule, I don't generally think much about oil. That is, until I start to notice a problem, and that's what got me to this point. I would have been more than happy to just keep pouring in the same 10W30 oil every time for the entire life of the engine, and even better if I can go 3000 miles on it. But for whatever reason, my engine exhibits this symptom after some period of time/distance, and changing the oil absolutely cures it. Hence, I'm down to around 1000 miles per oil change, which sucks big time. You think I like changing my oil? I'd much rather drive the goddamn car!

JConn2299

My own sense says you can't tell the difference in a blind test involving a properly running rotary engine which is one of the smoothest running engines around. On the one hand we have the editors of Road & Track, on the other hand we have you, just some guy spouting off online. You just don't measure up.

JConn2299

A completely baseless charge which makes it obvious you don't know what you are talking about and are prone to make unfounded accusations. Anyone can go to page 148 of the September 2006 issue to see that I have reproduced both the question and answer in their entirety.

JConn2299

You are a person of very limited vision. People with engineering degrees can do all sorts of things. To take an extreme example, which would you pick, being stuck in a cubicle at Ford designing a new valve stem, or traveling around the country and world testing the latest exotic cars? Don't answer that. I can tell you're a valve stem guy.

wanklin

iTrader: (2)

Yes a dripping injector is what I was refering to.

If your compression #s are very strong I would assume that your side seals are doing their job. If compression is mediocre....

DigDug

Haha, whatever you say buddy. Justify your thinking to yourself all you want. Resorting to insults shows everyone just what you're made of.

And to answer your question, I'd rather drive my car. Maybe you should have read my post completely before typing three separate responses to it.

DigDug

Clarification - the side seals did get replaced. Looked back at my bill for the rebuild and remembered that we changed some things around. Sorry for the confusion.

I'll check compression again when I get a chance, but it looked good a few months ago. I switched up to 10W40 and things have gotten a little better. Fuel smell's still there, of course, and follows the same general schedule as before. However, it doesn't feel quite as rough as it did nearing 1000 miles, but then again we've had some climate changes lately, so who knows what other variables are involved. All injectors were replaced during the rebuild, but maybe I've got a bad one. Honestly, I'm less worried about the whole thing now - given track use, the engine's probably going to die for some other reason anyways.