6-71 help

[dunn6253]

I need a little help guys. Tomorrow I have a friend I need to help out with a oil leak on his detroit 6-71. He explained to me that he changed out the oil, bilge was nice and dry. Took it out on a four hour charter, came back to check the oil, and was down about two gallons. Bilge was full of oil. He cleaned it, added oil, and let it run in the slip for a while, not being able to find a leak. Im going to check it out tomorrow in the mourning, just wondering if you guys know of any common problems with these and oil leaks. Thanks for the help guys.

I checked out boatdiesel, but I had to join to see archived post, so I couldn't really get any info from there.

[budddavid]

It may not leak, or at least leak alot less at lower rpm's. I think most 6-71 owners find that they start to leak oil about ~1900 rpm but will be significantly less at lower speeds. Most will tell you that this engine is only running correctly if it is leaking oil. You never have to worry about taking a detroit apart thanks to their self lubricating design

[Questsportfishing]

if the old oil filter o-ring gasket stuck on the engine or someone didn't oil the new one before you tightened it it will leak pretty bad when your running. pass your hand over the engine and see where it is coming from. check to make sure the oil fill is closed also they tend to blow oil out also. the 6-71 is a great engine but they do like to blow oil out of everywhere. look where it is coming from

[JD5652]

671's are like a Harley ....no matter what they are going to have a small oil leak here and there......BUT 2 GALLONS is not an oil leak..... that's a gusher. I have 1989 vintage 671's and they do NOT blow oil out everywhere. If there are more than a few drops here and there on a engine room diaper, then there's definitely a larger lack of maintenance issue.

Quest pointed out a few obvious things to look at.....one not so obvious potential source is the air sep drain. Typically a DD 671 has an air sep that incorporates an oil drain line from the air sep routed back to the crankcase. The purpose of this drain line is to return oil that is "pulled over" from the turbo back to the oil pan. Where the hose attaches to the engine, there is a very small check valve. This check valve can clog and stick open. If it does, then the crank case becomes pressurized and can force oil out of the crankcase vents and/or oil fill port. The crankcase vents are located on the outboard side of the engine and may not have been readily seen as a potential source of the leak.

They are easy to remove and check/clean. It's a $10 part if you decide to replace it.

It would also help the diagnosis if we knew the vintage of the engine, whether it has turbo's (wet/dry), blower and if it's marinized by Detroit Diesel, J&T, S&S or Covington.

Pic #1 is the oil drain connection at the air sep
Pic #2 and #3 is the check valve and is connected to the oil pan
Pic #4 is the crankcase vents located on the outboard side

[dunn6253]

Thanks for the input guys, I was able to find where it was coming out of. Added dye to the oil, took it out for a blast. Found oil coming out of some canister looking thing on the starboard motor, left side of the motor in the middle, kind of by the dipstick tube. Owner of the boat said it is coming out of the blow by canister??? It only happens when it is under a load. Doesn't happen at the dock. The boat was just purchased, and it seems the previous owner didn't take very good care of the boat/motors. So im thinking that the rings are shot. Any other ideas of why that would be filling up? Thanks for the help guys, it is appreciated.

I believe the motors are 1984, turbocharged. Not sure of the hours on them.

[JD5652]

Dunn-

The "blow by cannister" accumulates oil pullover from the turbo as I described above. Instead of returning it to the crankcase, it returns it to the cannister.

Check the "check valve" as I described above. The check valve is the device just below and to the left of the numbers "223" stamped on the block in Pic #2.

The check valve opens on shutdown and is suppose to close when the engine airbox comes up to pressure. If the check valve is stuck in the "open" position, then the oil has a path to outside of the crankcase.

Remove the check valve and immerse it in diesel fuel. This will clean out the "gunk" that it has accumulated and allow the check valve to function normally. Check to make sure it's functioning properly by blowing through the valve on each end. It should seal in one direction and then open in the other.

If you had bad rings, then compression would be low and you would see LOTS of white smoke at start up.

If you're not comfortable with performing the above, I would strongly suggest calling a good local DD mechanic.

[dunn6253]

Thanks for the help JD, im going to check it out in a couple mins. Will let you know how I make out.

[JD5652]

Thanks for the help JD, im going to check it out in a couple mins. Will let you know how I make out.

Dunn-

If you have a cell phone with a camera, take some pics of the setup and where the oil is coming from and send them to this e-mail address ....... aes@idsi.net

I find that a Pic or two goes a LONG way in troubleshooting.