Volvo Penta MD7a Severe Engine Blowby Path Forward

[SV_Shadowfax]

Originally Posted by SY Harmony

This just started out of nowhere?
How dirty is the bottom and prop?
Is the exhaust elbow carboned up?

Well, I'm pretty sure this was it! Thank you!

Barnacles! Uses my phone to take a photo underwater and the propeller looked weird. Swam in with goggles and yup the whole propeller is covered with 1/2" thick of barnacles on every surface. Almost looks like a blob. And our prop isn't even that big to begin with. Did some googling and the symptoms match. Propeller just weighs too much and has too much drag so we have inject too much diesel to try and get same RPMs. Engine can't keep up and we don't burn all the diesel. Also explains why it runs great in neutral. Got a diver coming up in about a week to clean the prop and the rest of the boat. Changed oil and fuel filters today as well as the engine oil just as a part of annual maintence. Fingers crossed this solves the problem!!

It is interesting that they were able to grow so fast. Move the boat into salt water 10/1/22 so its been less than a year. Before that was kept in fresh water. Used the boat ~15 days since October. The last time I used it before I noticed it was truly power limited it only sat for ~1 month inactive. I'm guessing they were slowly growing for a while and I didn't notice the slowly reducing efficiency. Looking back I do remember the throttle reducing RPM after a bit and having to keep re-adjust to maintain a certain RPM - that may have been a symptom...