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Discussion Starter #1
I have a 2002 volvo-penta DPX package in my boat, that uses a 502, similar to a mercruiser 502mag motor. It runs great, but seems to be using way to much oil. 130 hours on it, original motor never been apart. Runs 25-40 mercruiser oil. I put 2 hours of extended rpm run time on it (4200+rpm) across havasu, up river, then back down again later in the day, and maybee 40 minutes of idling in and out of no wake zones / coves......and it used almost a full quart of oil. There were maybe a total of 15 minutes total of 5000rpm operation here and there @ redline. Is this excessive oil use for a 502? I've heard these motors use a poorly designed oil ring, similar to the GM factory 502 crate motors, and they will "use" oil. Opinions?
 

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I have had customers with that kind of oil consumption yes. Only way to fix it is for it to come down.
 

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Discussion Starter #3
I have had customers with that kind of oil consumption yes. Only way to fix it is for it to come down.
Factory ring / piston issue?
 

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yep, In a hopes to reduce emissions they moved the ring pack. By doing so if the tolerances were on the big side these engines would have oil consumption problems.
 

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Pulled plugs today after work, they are burning clean and AFR looks good, no deposits of any kind, but cylinders 1, 2, and 5 do show signs of oil on the threads that protrude into the chamber. Ran out of time for compression and leak down test, will do tomorrow. I examined the oil, and it is looking much worse than i thought. It has only 18-20 hours on the oil, but its pretty black and smells fuel-diluted, and appears thin. Now that I think about it, this boat has been to a small local lake alot this summer, and often makes very short runs from the dock to coves with the oil probably never getting anywhere near operating temperature, sometimes it runs for only 10 minutes @ a time, and that lake has a speed limit of 40mph so its not being run hard at all to get hot enough to burn off the crap from cold starts and short run times. Im gonna change it with some good quality oil and test it out this weekend, thinking Mobile 15w50 or 20w50 Vtwin. Was running Merc 25w40, but when @ WOT at full operating temps, the oil pressure drops to 47-50lbs @ 5000rpm, I think a little extra viscosity would put the pressure when oils @ full temp closer to 55lbs @ 5000 when run hard.
 

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Oils cheap if she is still making good power run her!! They will use some oil man!!! I have seen many new builds use oil too. These boat motors are built lose, lots of temp swings on a open cooling set up. I had a LS1 with about 30,000 miles on her use about 1 Qt every 1,500 miles Gm says normal. (i think that is high for a car motor where the RPM is not so high all the time. I had a RX1 sled (1 liter yamaha 4 stroke) Where the RPM stays 6-9000 RPM that would use 1 qt and 500miles! Both still made good power and still run good to this day. Well Ls1 needed a Cat from the oil but other than that all good!! :) RUN HER!!! :) :)

GOOD LUCK Skydog P.S. Try alittle lighter oil easier for the rings to wipe the oil off the CYL walls over the thick oil.
 

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Pulled plugs today after work, they are burning clean and AFR looks good, no deposits of any kind, but cylinders 1, 2, and 5 do show signs of oil on the threads that protrude into the chamber. Ran out of time for compression and leak down test, will do tomorrow. I examined the oil, and it is looking much worse than i thought. It has only 18-20 hours on the oil, but its pretty black and smells fuel-diluted, and appears thin. Now that I think about it, this boat has been to a small local lake alot this summer, and often makes very short runs from the dock to coves with the oil probably never getting anywhere near operating temperature, sometimes it runs for only 10 minutes @ a time, and that lake has a speed limit of 40mph so its not being run hard at all to get hot enough to burn off the crap from cold starts and short run times. Im gonna change it with some good quality oil and test it out this weekend, thinking Mobile 15w50 or 20w50 Vtwin. Was running Merc 25w40, but when @ WOT at full operating temps, the oil pressure drops to 47-50lbs @ 5000rpm, I think a little extra viscosity would put the pressure when oils @ full temp closer to 55lbs @ 5000 when run hard.
FWIW from the sounds of what you are saying about hours, oil consumtion and oil condition. You are Making oil and blowing oil(to the bottom end) at the same time. Ring stack maybe a problem as well as induction. (feul wash) Leak down will tell the tale! Just do a warm-up prior to the test. M
 

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Discussion Starter #8
Thanks for the info. Was raining and didn't feel like doing the leakdown today. Might postpone till the weekend when I change the oil.
 
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