Nubo

[QUOTE]Originally posted by rotarygod
The seals don't get stuck from normal fuel flooding. They merely have just enough pressure exerted on them from the buildup of fuel that they will allow pressure to bleed into the other chambers. When the engine is severely fuel flooded and seems to freespin, this doesn't mean that the seals are stuck. It merely means that there is quite a bit of fuel present inside the chambers that is still allowing some pressure to get by. If you keep cranking the engine, as it dries out you will hear the compression start to return.[/QUOTE

RotaryGod, thanks for sharing your experience in this and other posts. It helps to hear from someone who's been through it for years with rotaries since this will be my first.

One thing I'm not clear on in your post is how residual fuel exerts "pressure" on the apex seals. Are you suggesting the volume of liquid fuel is in excess of the combustion chamber volume at TDC (or whatever it's called on a rotary?) It seems more likely to me that this is a film problem - the raw fuel washing the chamber walls clean of oil. The effect would be the same though - it won't get better until most of that fuel is gone.

The other thing I wonder about is the effect that centripetal force has on the apex seal. Is it easier for it to effect a seal when the engine is spinning, due to outward force exerted on the seal? Or is the spring stronger than that to begin with?

I was interested in your report that the seal has rounded shoulders from use. Sounds obvious once it's explained, but until now I'd just imagined it as flat. It does help to understand why the compression seal on the rotary is so tenuous at startup.

liveforphysics

Rotorygod-

I am just curious, since pressures of cumbustion are very great, why would they not lift the seal and let the pressure into the next rotor? Gases, compressable and non-compressible(liquid) exert the same forces on there suroundings for the same pressure level.

rotarygod

The most simple explanation is due to inertia of the engine rotating at such a fast speed as opposed to a measly couple hundred rpm's with the starter cranking it over. During startup the term "fuel atomization" is also a joke. It is closer to a fluid deposit on the combustion chamber surfaces that gets pushed around until enough of it combusts to get the engine going. When the fuel mixes in with the air, most of it is not concentrated under the rounded tips of the apex seals but rather throughout the combustion chamber where the pressure against the springs is against them from the side rather than from underneath. Obviously you'd never have any compression if it just pushed the seals back.


Here's a neat little experiment for those who have lots of time on their hands and some spare engine parts lying around. This is easiest if you have just taken an old engine out of a car and disassembled it. As long as you have one good rotor this will work. Basically you need to fabricate one end housing out of plexiglass so that everything is a spinning engine but looks like a display. Make a plate that covers the intake port and has a fitting for an air hose. Squirt some sort of fluid into the intake port so you can see it lightly puddle in the engine. Now spin the engine over by hand and let the engine rotate one complete revolution. You'll notice that the rotor housing surface behind the following apex seal is not dry. It is much drier but not dry. If you could spin it fast enough this wouldn't happen. The second part of the experiment involves filling a chanber completely full of water and then using the air hose fitting to pressurize it. If your handiwork with the plexiglass is good and you have water o-rings in the housings then hopefully your engine isn't leaking. Now add pressure. Suddenly each chamber around it starts to get seapage. If you try to spin the eninge by hand you probably can't do it unless you have a long enough cheater bar. Cool little experiment. Sometimes I have too much time on my hands.

rx8daniel

markpmm- I think that's a good illustration of the amount of smoke!

Silver7

A "normal" rotary spark plug is usually a little black with a little carbon deposit residue on the tip. There is nothing normal about a black oily soot covering the entire tip of the spark plug. If this is normal then your car has some serious issues.

The Rx8 should not need a turbo timer. The issue isn't with cooling the car down. I see the cold shut down happening when someone wants to simply pull their car into the garage. I don't want to run my car for 8 minutes while it's sitting in the garage. Some people have experienced their cars stalling while backing up and the car simply won't restart. I have owned an FD for over 5 years now and have never had the flooding problems that these rx8s are experiencing. I have shut the car down cold numerous times while trying to tune the hot and cold startup settings with my haltech.

As far as I've seen not one person has come forward to say that they have experienced flooding once their plugs have been replaced with a new set after the motor has been fully broken in. This backs up my theory that engine lube could be aiding in the flooding issues with the rx8s.

Smoker

rotarygod, just like your many other articles, very informative. Thank you.

WHealy

Today I did lots of little trips to stores all in the same area. I watched the temp guage, but had no issues as it was normal running temp before my first start and held there for a few hours with the quick trips.

My question is, what is warm? Does the temp gauge need to be at normal running temp to be warm? Or is it somewhere between the needle registering at least something and near half way. My original thoughts were if it’s a quarter to normal running temp, that should cover it. Can somebody let me know if that’s a poor assumption?

Nubo

Here are a bunch more

http://www.rotaryengineillustrated.com/animations.html

wakeech

i have no idea what tempurature the coolant has to reach to end the "cold start" sequence, but whatever it is when your engine idle drops from 1000 to ~800 and stops running so godawful rich, that's it.

mngpao

As I recall, the manual says to warm it up for about 5 minutes.

I noticed that after 3 minutes my guage reaches "normal" (about 2 clicks left of center) and does not go any higher - even after driving all day.

Your guage may maintain a different "normal" from mine and take less or more time to reach that point. When I have to move my AT out of the garage (to get at my pickup) I usually do a round trip to the post office (3 minutes away) and by the time I return, my guage is at "nomal". That's how I avoid the potential flooding problem.

jtimbck2

My "normal" is the same as yours (2 marks left of center). It never seems to go above that. For a while I suspected that the temperature gauge was an idiot light in disguise like the oil pressure "gauge".

paradigm

If it's anything like the temp gauge on the FD, then it is nothing more than an idiot light, and may cost you an engine much further down the road. The gauge on the 3rd gen rx7 was so bad that by the time it started moving above "normal" it was most likely too late, as your coolant temps were approaching 250 and higher.

wakeech

wow... and the engine MADE it to the point where the gauge moved?? yipes.

JeRKy 8 Owner

How does the fuel flooding problem build up?

If the Rx8 is shutdown a bunch of times the wrongway when the car is still cold but doesnt get fuel flooded any of the times it is shut down does that mean it is reaching an "almost" fuel flooded level and will flood if it is shut down improperly a few more times?

If it is at an almost fuel flooded level is there a way to clean and get the car back down to a "nowhere close" to fuel flooded level?

If the Rx8 is in an almost flooded level does it have worse performance or does being close to flooded have no effect on the engine?

Or is there no such thing as "close to flooded" and fuel flooding can occur at any time the car is shut down the wrong way regardless of how many times it was improperly shut down and it happens by chance not by build up of bad shut downs?

I am confused and want to know.

rotarygod

I would classify a car as "almost flooded" when it gets really hard to start but still does. That was close. Almost isn't really an accurate term though. Either it is or it isn't. It's kind of like saying the train almost missed me. You get the picture. If the engine were sitting for a long time or it were fully warmed up, it would be much less likely to flood. Any fuel left sitting in the engine when it wasn't running will eventually evaporate somehow. After all at least 4 of the total 6 chambers are always going to be exposed to some sort of port. A cold engine will make it take longer for any fuel to evaporate whereas a warm engine will make it easier. Time basically will dry out the engine better than anything else. Unforunately depending on how bad the engine was flooded to begin with, it may only take a few hours to several days to just self unflood.

If the car is running than it would be very hard to get it flooded. That would probably be water ingestion or a stuck open fuel injector at that point. Basically a running engine can either not have any negative effects from flooding since it isn't flooding while running or it will ingest enough to combustion lock it and this flooding would be serious. If your engine floods and gets hard to start, don't worry about it when it does again. It will run fine.

FWIW: On several flooded engines I have just replaced the spark plugs with no positive results. While a fouled spark plug may have issues getting the engine started, it will still run. As I've said before, if we can get the engine initially turning fast enough they will always start. The flooding situation does only help to gum up the plugs though.

Greg

I say whenever the needle moves into the first hash marks its pretty safe to turn off as long as you do the 3k rev first. But thats just my opinion. It should mean the engine itself is warmed up but the thermostat just hasn't fully opened.

Silver7

I agree with wakeech. The engine runs very rich at startup. Once the engine reaches it's "warm" state, the idle will kick down a few hundred rpms. This is the point where the fuel map changes to a more "stoich" setting. This is the point where it would be safe to shut down your engine.

paradigm

oh yes. It would definitely get to the point where it was that hot, and it would keep on running, but once you got to a certain point the aluminum rotor housings would warp, leading to coolant seal failure. How soon the failure would occur depended on just how hot it got and how long it was there. It could've been 5000 miles down the road, or when you went to start the car the next day it would be flooded with coolant.

mgalata1

I believe that I've just had my first "flooding" experience...My car has been in the garage for 6 days due to the snow we had in MD. It did not start on the first crank, which it has since August when we bought it, on the second crank it just free spun--No compression. It's dead now. I called Mazda roadside and it will be towed in to the dealer in the morning.

Has anyone figured out a definitive way to get a flooded Renesis started without a tow and dealer intervention?

rotarygod

Push start it and pop the clutch. If that doesn't work then pull start it behind another car. Works every time.

Rx-Appreci-8

Rotarygod

Warrantee, leaky injector and cold stalling issues aside, would we be better off shutting rotary engines down (on a day to day basis) with a kill switch (or PCM software mod) that 'opens' the injector circuit slightly before disabling the ignition circuit to 'fuel starve' the engine. Seems like you could do that when the engine is hot or cold. Thoughts?

rotarygod

The best thing to do would be to delay the fuel delivery to the engine for a couple of seconds when the engine is trying to be started. The ecu should wait for the starter to get the engine fully spinning before any fuel is injected into the engine. It doesn't take much just a very slight delay will do it. The ecu should also have a function that shuts off the fuel after a certain amount of cranking time has passed. Then the slight delay from the next attempt would clear the chamber back out. That would make the most sense to me since the ecu controls the fuel pump anyways.

Patrick

Hello everybody,

No problem whatsoever, even started the car to shop 2 km away, so the engine was not warm, reved up to 3K and shut down. After 10 min started again whithout any trouble.
Even cold, windy and wet weather does'nt make a difference.
I was a little afraid reading all the posts about flooding, but now there seem to be no problem, at least with my RX8.

regards
Patrick
Belgium

perhaps it is a good idea to mention if your problem concerns a LP or a HP, tax regulations and gas prices are favourising the LP in many European country as Belgium, the Neteherlands, ...

8_wannabe

just remember there is no LP or HP choice in America. You get HP with stick; LP with auto.