DD 6V92TA Low Oil Pressure

[joesig]

My Mech & I performed an in frame overhaul 50hrs ago to both of my 6V92 TA engines in my 1985 42' Chris Craft Commander. The engines run great but the oil pressure seems very low at idle (~550 Rpm) after cruising for a while and reaching temperature. The pressure is over 40psi while at ~1200-1700 Rpm but when I slow down in the harbor the pressure is ~ 5psi on the gauge. I installed new senders and Teleflex heavy duty gauges to rule out bad senders or gauges. The other day while in the harbor heading for my slip I pulled back to neutral then back to forward and the Stbd low oil alarm bell barely rang for a split second. I have straight 40W Rotella T1 oil in the engines. My main and rod bearings were replaced during the recent rebuild 9 months ago. My Mech did not recommend replacing the oil pumps or regulators during the rebuild. Is this low oil pressure normal for these engines? Is replacing the oil pumps a hard job?
Thanks, Joe

[captddis]

I doubt you have a problem. Check the oil press with MECHANICAL gauges. The electric gauges almost always read low at idle. How low does the RPM drop when shifting? Might just need a 50 rpm change and maybe a touch on the buffer screw.

The regulator and relief valve should be replaced at overhaul time.....

[Tim Powell]

My Mech & I performed an in frame overhaul 50hrs ago to both of my 6V92 TA engines in my 1985 42' Chris Craft Commander. The engines run great but the oil pressure seems very low at idle (~550 Rpm) after cruising for a while and reaching temperature. The pressure is over 40psi while at ~1200-1700 Rpm but when I slow down in the harbor the pressure is ~ 5psi on the gauge. I installed new senders and Teleflex heavy duty gauges to rule out bad senders or gauges. The other day while in the harbor heading for my slip I pulled back to neutral then back to forward and the Stbd low oil alarm bell barely rang for a split second. I have straight 40W Rotella T1 oil in the engines. My main and rod bearings were replaced during the recent rebuild 9 months ago. My Mech did not recommend replacing the oil pumps or regulators during the rebuild. Is this low oil pressure normal for these engines? Is replacing the oil pumps a hard job?
Thanks, Joe

Joe you have a real bad problem ! Those 692 are in the wrong kind of boat.... Sorry i have to inform you of this but the boat makes a heck of a diffrence....just funning I did the same you did i rebuilt my 692 and the oil pressure on both of them at iddle is holding steady at 20 to 25 on the electric gages at iddle and about a steady 20 on the mechanical however i replaced the both iol pumps. I also had the crank checked it showed no whare or all were in tollerance. Hower i did reckonize that when i come to a iddle after turnng it about 1950 rpm for a while the oil pressure will go to about 10 for a sec good luck i am sure some others will chime in tim

[MikeP]

Are the "heavy duty" gauges electrical or mechanical? If not mechanical then I wouldn't rely on their reading as accurate. My mechanical gauges on our 8V71TIs typically read around 12-15 PSI at idle after a day of running. Occasionally they will set off the low pressure alarm though I would never worry about it - 10 PSI of oil pressure is plenty at 550 RPM.

DDs are known for some extremely low idle pressure readings. I know of a 53ED in NY that has the low pressure warning alarms sounding at idle all the time...and, according to the owner, has been doing that for 25 years with no issues at all. I once read about DDs that showed NO oil pressure when hot at idle, had no problems with the engines over 30 years!

Of course, that's not to say that there is no problem but it seems that if there is ANY oil pressure at idle, it's enough for a DD. Certainly it's worth checking but there is a good bit of evidence that DDs show very low pressure at idle. I've been told that it is due to the placement of the sensor at the "end" of the oiling system.

[yachtsmanbill]

Somewhere the book says 1lb of oil pressure per 100 rpm minimum. 1000 rpm is 10 lbs min. Mine are way tired and run 5-10lbs at idle hot but gain up to 40 when underway. Thats on mechanical gages on the lower helm BTW with a 25 foot long hose, which is slow in changing pressures. ws

[joesig]

Thanks to all the Hatteras owners for the information. My new gauges are electric but I plan to install mech ones soon in the engine room.
Thanks,
Joe

[SKYCHENEY]

I agree with Captddis. You may need to bump up the idle a little. One of my 6v92s acts just like yours. At 550 it will show 5psi on the electric gauge and about 10psi on the mechanical. The other shows about 10psi higher at all rpms. Both have 3900hrs on them.

[Genesis]

Pop the idle up a little.

Don't ignore this, incidentally. You can starve the upper end oil passages if you idle for a long time (think trolling in particular) and I've seen severely-galled rocker shafts from that, including one broken one. The guy with that engine got lucky it broke fully inside the tower and stayed there or he would have swallowed a valve.

The usual low oil alarm warning for a Detroit is set to 5psi. If it chirps a bit when coming down from hard running it's not a huge deal but if it's sounding continually it's not a good thing. The low oil pressure switches sometimes leak and owners replace them with 10psi ones that have a habit of ringing on a hot idle. If that's the case rather than risk a real problem you're unaware of put the right switch in there.

Only way to know for sure what you've really got is a mechanical gauge. If you can't keep the alarm silent with a proper 5 or 7psi switch at 550rpm pop it up 25 or 50 rpm and the problem should go away.

My engines would run 10-15psi hot at idle and 40-50psi at cruise. Regulator pop-off in the pump is supposed to be 60psi. If you get 60psi indicated on a mechanical gauge on a cold start the regulator is probably - but not guaranteed - ok.

[krush]

Just to toss in some fun facts, low pressure doesn't necessarily mean no or not enough flow...conversely, high pressure doesn't always mean sufficient flow.

[rsmith]

"My Mech & I performed an in frame overhaul 50hrs ago"

Could be a problem from the OH.Is the oil press the same as before the OH? Did you check the crank was to spec? A worn crank and or improperly installed bearings could cause lo oil press. At 50 hours its still breaking in. You gota take it out and run it hard.