Soot on transom after fuel filter change
 

I just changed oil, fuel(low and high psi)filters on twin 500 efi's. I ran boat all summer with no soot on transom. Last couple trips out it has soot on transom. Boat runs same. Anyone have this issue or is it just a coincidence? Haven't scanned, just curious.

Cold block temps telling ECM to richen or incomplete combustion due to colder temps?

With a fully warmed up engine that should take place - You need to check - what is your water temps reading at the gauge and with a hand held temp gun shooting it at the t stat area and then across the housing and then at the coolant temp sensor ?

I would scan the engine next to look at running parameters and fault codes thru out all rpms

next I would check fuel pressure readings across rpm ranges

Possibles of rich running conditions

stuck open t stat or lower temp rated t-stat installed than OEM specific
removed t stat
Map Sensor
Ignition components and or related
spark plugs
fuel pressure regulator
injectors
coolant temp sensor
bad fuel or old or RVP related

I don't think temps, it is happening at Lake Havasu, engine temps look normal. I will have to scan it. Just weird that I didn't have any issues till I changed filters, I even used all mercruiser stuff.

Did you get different gas than you normally do ? If not, is it a different seasonal blend by any chance ?

SB That is EXACTLY what I thought.

I know that the first couple of times we had our boat out I used premium-- only to see some soot on the transom - I switched to the mid grade and nothing-- I don't have anything special 7.4 mpi Bravo 3- captains call. That is all I've been using.

3pointstar

It's possible I guess. Same gas station, different time of year.

Like I said last words - RVP related = Reid vapor pressure = different seasonal blends of the fuel.

Google it to learn more about and or search up here as I have talked about a bunch.

Very common problem for people who work on boats thru out the year that have vast seasonal changes.

The only place in the USA that fuel RVP ratings stay the exact same all year round is Hawaii - it never changes there because it has almost the same constant weather & same temps 365 days of the year.

Ok everyone on the bus -- headed to Hawaii!!!

Aloha