Leak testing on a DF150

[cap10joe2000]

Thinking about buying a boat with a df150 that has 1300 hrs. The dealer performed a compression test all cylinders between 148 to 158. Leak test show most cylinders 20 to 35%. Mechanic says it is likely due to short trips and low rpms (motor is on a skiff) and is a 05 or 06 model. They believe carbon is the culprit and after running some gas with ring free they have seen a small improvment thus far. Former owner has history with this shop and has yrs of data. Last 3 or 4 yrs of leak test hav tested similar 20s to 30+%. Motor runs out well and seems to have been well maintained. Dealer and mechanic have good reputations and seem honest. The price is fine, should I let this one pass or buy the boat with a case of ringfree? Or should I ask for further testing how normal is this

[boats.net]

Were they able to tell if it was leaking past rings or valves?

[cap10joe2000]

I am not sure will have to find out, They ran the motor a little while with an aux tank with the ring free additive and checked this morn the numbers dropped some.
They first noticed the leak down issue started when the motor had 519 hrs. (Several yrs back) Right about the time ethanol hit all the gas stations in the area. The motor has 1320 hrs now and still runs strong. 3 test in the last few weeks and the numbers have not been very consistent some up a lil some down some up and down. But the trend is showing about a 20% improvement across the last 3 checks from the first to the last.

[redlowrey]

leak testing

When you do a percentage leak by test you first put the cylinder on test on compression and lock the engine so the piston cant move and put air on the cylinder and watch the dial on the gauge, but most important you should take the oil filler cap off and listen into the crankcase then listen at the throttle plate for air leaking past the inlet valves and the same for the exhaust valves. Theoretically there should not be any air leaking past the valves and if the ring gaps were good a small amount air leaking into the crank case. You have to this test for each cylinder, IMO an engine with those hours will have big ring gaps but still should be ok.

[cap10joe2000]

Thank you for help, found out the day the boat got sold out from under me...oh well, back to the listings