So my second UOA came back since I have had my 8. Everything looks good except the oil is showing high fuel content.

2.0% with a 340* flashpoint. OCI at 3500miles.

The only other negative symptoms I have are low mpg (16) and high LTFT (+10.5 at idle).

The engine runs great with no other issues or codes. Has about 7k miles on reman. Compression is good, ignition has about 4k miles on it. The cat is a new BHR pipe, but the old cat was/is fine.

I noticed the oil gets dirty quickly after a change. That and the fuel point to blow-by. How much is to be expected? Should I be pursuing fueling or vacuum issues? I do premix .5-1oz per gal and it typically gets a full 8-9k pull every day. Full power pulls show A/F as rich as 11:1. Its all stock tuning.

Thoughts?

 

What were the conditions when you pulled the sample? Car just shut off after a long drive where everything got good and hot? Whenever I've had elevated fuel levels it's because I started the car up to get it in the maintenance position and then shut it back off.

 

I drove the car to bring it up to temp. However I am sure it idled for a bit while I set up the lift. This was the second oil sample that came in at 2%. However the first oil sample was the previous owner so I don't know the history.

 

Most likely sloppy/loose sideseal to corner seal clearances from the reman facility. Mazda allowable tolerance is unfortunately pretty wide, I'll bet yours are on the big end. What weight oil are you running?

 

+10 LTFT is not normal, nor is low fuel mileage. 11:1 is way too rich as well ... You're letting unmetered air in somewhere, which under some conditions could cause it to run rich and overtime build up fuel. Especially at cold idle when it's already enriched. Based on that it might have learned to enrich more than normal in open loop full throttle as well.

What intake is on there? Cheap aftermarket intakes have this effect, as can a small loose hose, like the VFAD

 

Running 10w40 weight and the viscosity is at the bottom of spec with the fuel dilution. Oil gets dirty fast, which makes me think blow by is an issue.

 

Stock, the VFAD is gone though and I have it capped at the T-Body. Driving around there are no +LTFT and actually very little STFT, assuming closed loop of course.

 

consider 20w50, it's all I run in my FD RX-7s here in the NJ summer months. Just let her warm up fully before beating on the car

 

Hmm. So under what conditions does LTFT and AFR spike?
What's the history of the engine, has it been removed/replaced? How long has this been happening?

 

If you have a big +ve fuel trim at idle and nothing higher up that usually indicates a vac leak.

Rotaries get fuel dilution driving around on the street. Especially short trips where they don't get warm enough to evaporate the fuel out of the oil.

Remember that you only change about 80% of the oil when you change it in an RX-8... so looking dirty is kinda normal. Not like a piston engine where you change out 95+ and get that clean oil look for weeks after an oil change.

 

Ltft is highest at idle. +10.5, maf is around 4.6
just off idle ltft is now +.8
The 11.2:1 afr was the richest I recorded on a log. Conditions were wot at redline.
I just found out about the 2% fuel in the oil recently. No other uoa issues.
There are no drivability issues. Power pulls to redline feel good. Only thing I would say is I can occasionally feel step ups in power maybe around 7k. Nothing like a vtec hit, but a power pull is not seamlessly smooth. Steady with small ramp ups.

My question is how are these issues related? How does the vac leak create excess fuel in the oil. Or multiple issues?

 

luckily the fuel did not drop viscosity too much, there is no significant wear metals in the oil. However I see shorter oci in my future. That and I will be chasing vacuum leaks.

thank you,

 

The fuel trim issue is basically not directly related to the fuel dilution in the oil.
The fuel in oil thing is a rotary issue and one of the reasons that oil changes are important.

Like I said... lots of shorter trips and it makes it worse. After a track day it's usually less of a concern 😏

 

it’s a rotary engine issue in general, but more so on the typical low compression Renesis blowing-by the seals into the oil/sump.
.

 

My 2006 rx8 is averaging at about 200 miles per tank (around a little over 14mpg I believe), and quite a lot of fuel in the oil.

I drive almost exclusively rural country roads and highway with little to no stops. I always let the car warm up before I drive(about 6-8 minutes or until stock temp gauge just about reaches the middle)

I use Valvoline fully synthetic 10w-30 and my car does have a SOHN oil adapter so my oil level shouldn’t normally rise or drop much.

after about 1000 miles I have about a quart overfull on my dipstick checking warm after about 5 minutes after shut off. And it smells a lot like gas.

my car has no cat, A BennetBuilt ignition coil system with wires installed last December around 12,000 miles ago, very recently changed plugs, and an AEM cold air intake. I’ll pick up a coil tester tomorrow and check them to be safe.

I don’t think my car is getting normal rx8 gas mileage and the fuel dilution in my oil seems above average to me.
Other than that the car runs great and always starts quick hot or cold

anything you could think of to help me figure out what’s going on would be a great help thanks.

 

All that idling warming up might be one reason. It's not really necessary, just don't beat on it while it's cold.

Your mileage is low though, so good though to check coils and make sure it's able to burn the fuel it's given at least.

Check the fuel trims to see if it's having to compensate for vacuum leaks, which might give you more clues. I assume since you have no cat you have a check engine light on, but see if there are other codes in there.

 

Agree with Loki ...stop spending so long warming it up . One min. max. then drive sedately till fully warm.
Also , you don't mention if you premix or what fuel you use ?
It's common for oil level to rise if you stop drawing oil from the sump but add premix into the fuel .

 

yes I premix the fuel with 220 milliliters of idemitsu premix and then around 13.5-14 gallons of 93 shell premium fuel

I just flushed my oil today and checked my spark via an inline spark tester and it seemed healthy.

I also found that my vacuum cap for the VFAD line that I had was missing so I put another on, hopefully that helps and I have no more vacuum leaks.

I’ll keep from letting it idle too long and document my situation. Thanks for the info guys, I’ll update in another 1000 miles or so