Low oil pressure warning- Detriot 671-T

[Genevatexan]

Over the last 6 months, the minimum idle to avoid setting off the low oil pressure alarm has gone up for my starboard 671 turbo. It was originally about 680, but is now up to almost 800. This engine shows about 40 lbs at cruise and right under 20 on electronic guages (no mechanicals installed) at idle. Oil volume is within tolerance. The engine probably has just under 3K hours.

After reading back forums on this, my questions are: 1) Where is the oil pump and oil pressure regulator mounted? It would be cheaper to test that possibility than to assume a bearing problem. 2) Is the R & R on those parts complex? 3) Any other theories for cause, other than bearing weakness, weak pump, or weak regulator spring? Side fact: these are "layover" 671's.

Thanks
GT

 

[Avenger]

Before getting too involved in anything put a good mechanical gauge on it and check the actual pressures. It may be just a faulty alarm sensor on the engine.

 

[jetpowered]

Absolutely! You will always get that low press warning on a warm Detroit coming back to idle. And it will bounce on low when it's warmed up. Just a thing that is typical to Detroits.

 

[captddis]

Bertram had a very complicated alarm system and sometimes the pressure switch had to be readjusted. First check when the alarm goes off with a manual gauge.

 

[Roger]

You may want to consider installing a set of high quality mechanical gauges in engine room, for engine oil pressure, gear pressure and engine temp

 

[Genesis]

The correct switch for the low oil pressure alarm is 7psi. It sounds to me like you have a switch with a materially-higher setting in the engine; you need to attach a mechanical gauge and see what's really there, and if the switch is incorrect replace it with the correct one.

Note that minimum oil pressure under load is specified as 30psi, so if the alarm goes off while under load and you're not "fast" it's basically a "replace engine now" alarm.

 

[Genevatexan]

super feedback guys. I have mechanical temp and gear pressure guages down there now. Clearly time for mechanical oil pressure guages as well. Once I have good readings then we see where we stand. The alarm goes off in neutral, usually after engine good and hot, and my memory is that once it is in gear, even at low speed it stops. I will check the behavior again when I have the gauges.
One more question, where is a good oil connection to use for the gauges? THe only open connection I remember is on the flat side of the engine near the air doors on the cylinders. (I run Delo 100 40wt in both motors.)

 

[Genesis]

There should be a block on the side of the engine that has a short hose going to the port on the side of the block itself (which is the "end" of the oil gallery.) That will have the sender for the oil pressure gauge and the alarm switch both screwed into it. If there is no additional port there with a plug in it either replace the block with one that has an additional port or "tee" off one of the existing ones. If you choose to "tee" make sure you do it in a way that doesn't put stress on the fitting(s) and sender(s) involved as a failure there dumps your oil under pressure -- very bad.

 

[Genevatexan]

Thanks for the direction on the pressure block, Genesis. I have attached picture. I was thinking that end plug could come out and go in with a NPT hose and guage there?
Please see attached picture.

 

[Genesis]

Yep; you have an open plug.

BTW when you do hoses on the engine make sure you remember that one. On my 6V92s it was up under the manifold and very easy to miss and the previous owner did indeed miss it; it had an original build tag on it with a 1985 date!

 

[Genevatexan]

Great point. FO used the braided blue lines you see in the foreground and did a nice job on R & R there. The feedline for that block is blue, but not braided. I can't tell if upgraded or not. I will have to dig in a bit. Thanks for the heads up.

 

[Genevatexan]

with picture.

 

[Glory]

You may want to consider installing a set of high quality mechanical gauges in engine room, for engine oil pressure, gear pressure and engine temp

Or at the helm!

JM

 

[Genesis]

That LOOKS original. It may not be, but it looks like it is. Note that the ends are typically reusable (that one definitely looks like it is; the non-reusable ones are crimped on and it's obvious); the inside part unscrews and then the collar unscrews off the hose. Re-installation on new hose is the reverse. If so making up a new hose is simply a matter of having a length of the proper hose you can cut to length, remove the ends from the old hose and then reinstall them on the new hose, lubricating the inside the hose bore with oil for reassembly. Some of the ends (typically the larger ones) require mandrels for proper assembly; the smaller ones typically do not.

When those hoses get (really) old their internal braid deteriorates and while they look fine on the outside they have ZERO flex remaining in them. If put under stress they can fracture and leak like crazy.

 

[Genevatexan]

I'll work that while building the new pressure guage and hose assembly. Good callout on that hose, because it's really hidden.

 

[Genevatexan]

I added the mechanical oil pressure gauge on the starboard engine and found that the engine runs 39 lbs at 1200 RPM and up to 42 lbs at 1600 rpm, and then drops to 9.5 lbs when engine slowed quickly to neutral after hot. How is that in comparison to expected? Normal idle oil pressure after hot is 10 lbs. Feedback on how that compares to others? I will do the Port engine next weekend. This gives me mechanical temp guages, transmission pressure gauges, and engine oil pressure guages, all in the engine room. Which, by the way, saw a refresh this winter. See attached pic.

 

[Genesis]

Reasonable. What's your idle RPM?

With the proper alarm switch at 7psi it won't ring at hot idle.

Minimum spec is 30psi under load; you're well within that. As these engines age it's not uncommon for them to run 10-15psi at hot idle.

Mechanically you appear to be ok; make sure the alarm sender is the correct one and now you've got mechanical gauges to know what's going on.

 

[Genevatexan]

Starboard Idle RPM was set at 725 by FO, port engine was 625. Bugged me ever since purchase 3 years ago so I brought it down to 625 and started having the alarm issue. At 725 it generally did not go off. I need to go back in to the set screw on the governor and set it back up a bit based on what the mech gauge shows, but that means the carpet and furniture move, and it was just as easy to set with the throttle...I'll read the guage at various low RPMs next trip, and install the port engine mechanical oil pressure guage also.