Detroit 671N - Safe to cruise at 1000rpms?

[Alaska93]

I've done some searching, doesn't look like anyone's asked this question directly here to anywhere online.

I have a 42ft Uniflite Yacht Fisherman with a Pair of J&T 671Ns - 310hp I believe.

Been cruising these engines at 1000rpms for the past 3 seasons and very happy with the fuel consumption, also hardly leaks oil. You'll call me a liar but experienced no oil loss for a 8hr cruise. Almost Zero wake and engines are quiet seem to be working very easy.

1000rpms gives us a 6-7 knot cruise depending on the tides/current. Oil Pressure for both engines normally sits at 22psi, starboard engine appears to dip down to about 15 psi every now and then during 6-10hr cruise but comes right back up to normal after a few minutes. Both Engine Temps stay right at 185F. Engines start up if you even look at the switch even when cold, no smoke after 5 seconds even when cold, we're talking all the way down to 10F

Does anyone see any ramifications of operating engines at 1000rpms if engines are up to temp with 15-20psi oil pressure? Please chip in

 

[Ken E.]

I've done some searching, doesn't look like anyone's asked this question directly here to anywhere online.

I have a 42ft Uniflite Yacht Fisherman with a Pair of J&T 671Ns - 310hp I believe.

Been cruising these engines at 1000rpms for the past 3 seasons and very happy with the fuel consumption, also hardly leaks oil. You'll call me a liar but experienced no oil loss for a 8hr cruise. Almost Zero wake and engines are quiet seem to be working very easy.

1000rpms gives us a 6-7 knot cruise depending on the tides/current. Oil Pressure for both engines normally sits at 22psi for both engines, starboard engine looks like it dips down to about 15 psi here and there during a 6-10hr cruise but comes back up to normal. Both Engine Temps stay right at 185F.

Are there any ramifications of operating engines at 1000rpms if engines are up to temp with 15-20psi oil pressure?

I had Detroit 8v71n's, operated them similarly for many years and never had any problems. There are thousands of these engines in work boats around the world used like this.

If you're interested in more information on 2-cycle Detroit operation, go to boatdiesel.com and read up on the posts from Ron Sparks, a contributor there and very knowledgeable.

 

[READY]

Could be just an urban myth but seems many say ok to run at lower RPM but periodically run them up for 30 minutes +/- to prevent glazing of the cylinders or pistons or ring build up? Unless anyone has any scientific evidence that running 100% low RPM is OK I think I would follow the common thought that best to run them up maybe for 30 minutes out of any 3-4 hour run. I dont see how that would do any harm other than slight increase in fuel cost.one other benefit would be knowing if you need the higher RPM engines are able to reach it. Possibly make it easier to detect and possible engine/fuel issue that might not show up at low RPM.

May turn into an interesting thread.

 

[Comodave]

I agree on running them up occasionally. They should be fine though.

 

[Alaska93]

We do like to run them up and hear them sing at 1600rpms every now and then!