It's been so long since I've driven the car with the stock engine, I'd like to hear from the few people with an original engine (or new engine from Mazda) concerning how much fuel dilution you are noticing (either based on smell or actual analytical report). I had a debate with this guy who said his turbo FC had absolutely zero fuel dilution. I've never heard of that. Thanks.

 

Well you saw my report and it was 2.5%. The motor has approximately 3k miles now.

 

is that a new engine from Mazda or a reman/rebuild?

 

Rebuilt by me and my pops.

 

Read the first post! I'm not interested in hearing about rebuilds, they almost always have horrible fuel dilution

 

I have an original 93 motor with about 50k miles.based on odor there is obvious fuel contamination.This is the case with every rotary I have owned including 2 FC TIIs,convertible,GXL and my new RX-8.
The guy you talked with was on drugs!

 

^^^^^^^^^

Same here...

 

Same here - on both my FD and FC. FD is original engine and I've had it since 40k miles. The FC is a Mazda reman. Everyone I've talked to who has owned a rotary has fuel dilution. It's why regular oil changes are so necessary and critical.

 

FWIW, from 50k when I bought it, to about 80k miles my original motor on the stock ECU didn't seem to have much dilution. That's based on odor though, I never had it tested. It wasn't until I relocated the IAT that I noticed a significant increase, especially when the weather was cooler...spring and fall.

 

I have a stock engine and i havent had my oil tested for fuel dilution but all i know around 2 months into an oil change, i notice a real fuel smell. Its not strong but any idiot can tell you it does smell like fuel.

So i change my oil every 3 months REGARDLESS of mileage. I remember one 3 month period i only put like 100 miles or something and i changed the oil anyway.

Thats why from doing this, everytime i change my oil, it always comes out like gold, soo clear and clean. I think its because i dont drive the car much for it to get dirty lol.

That or the internals of the engine is really that clean because of me

 

Our '94 has 97066 miles on the original, near-stock engine; 1207 miles on this oil change. Because of this thread, I removed the oil filler cap and sniffed. I think all I smell is hot oil, after a 30 minute drive about an hour ago. How is fuel dilution measured? (We change oil every 3K miles.)

 

Oil dilution is measured by sending in a sample to a lab such as Blackstone (the standard analysis is $22) http://www.blackstone-labs.com/standard_analysis.html Typically these cars range from about 1-3% fuel (or more, I've heard reports as high as 10%), which would be considered super high for any other engine (should be zero, or less than 0.5% max). I noticed RX-8 owners are reporting similar numbers on factory engines, so that pretty much excludes the "sloppy side seal clearances" theory

 

Pull the dipstick and hold that sucker right up to your nose...hopefully you won't pass out

Strike 18 for the rotary, haha...it really is amazing the number of shortcomings rotorheads put up with

 

we really do put up with alot, lots of cons and so few pros, oh well.

 

What's the alternative? Evo?

 

i have a blueprinted, its not rebuilt... If you get a 5 gas analyzer and put the sniffer by the oil filler neck... an average reading would be about 600-800 hc's. Mine was about 580

 

?? But oil is a hydrocarbon, too... What is the mechanism, or path, for fuel to return into the crankcase? I know how it happens in a piston engine... it's dragged from the cylinders past the compression and oil rings down into the pan. But the rotor's trailing sides are inside the intake, combustion, and exhaust chambers. How does the fuel get into the oil? Around the side seals?

 

Sloppy side seal clearance seems to be the prevailing theory (Rich has commented on this several times), which is why I posted this thread...how can you get better side seal clearance than a newer factory engine?

 

My stock motor (original as far as I can tell) had about 45,000 miles when I got it in '04, now it's around 86,000 miles. The oil has always smelled like fuel when I change it; the smell is stronger if I leave the oil in for longer. Sometimes I'll leave the oil in for as few as 1500 miles, other times closer to 3000.


I have zero data to back this up but I suspect that fuel is sometimes sprayed at the side of the rotor at high injector duty cycles, unlike a piston motor there aren't any valves that close to shroud the intake ports.

 

This has been a common issue with every fd I have ever been around. From low mileage 15k-130k on the original engine. The only case where I have noticed any real difference between different cars is when a car is running a pettit ecu or has a chipped apex seal causing less compression/vacuum making the car run rich at idle.

 

10K on a mazda factory built core. I still smell fuel and notice a "thinning" of the oil. I counter that by going to shorter oil change intervals and just using dino oil to keep costs down.

I was always under the impression that this was caused by the higher than average amount of fuel that is put into the rotary combustion chamber.

I'm sure you've followed the threads on bobistheoilguy about direct-injected performance engines having similar troubles (it's been a while since I've checked them). Do you think the problems are similar?

 

Slightly softer, thicker seals for a tighter fit, maybe? But then they would wear faster, I guess.

 

I take it you're implying running a Pettit ECU would make the problem even worse