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Detroit Oil Pressure Dave G 9-5-02  
How much oil pressure should a 1975 Detroit 6N71 (245,000 miles) have and how much should it vary? Just got back from a trip to Ronthebusnut in Ia. ( boy has he got the bus stuff !) and my bus indicates 35lbs at highway speed and drops to 5 lbs at stop lights. When I come to a stop and depress the clutch while using the brakes the engine drops to an idle and the low oil pressure buzzer ( I think ) sounds for a second or two. The braking has some effect. If I depress clutch and coast to a stop the pressure drops to 5 but the warning buzzer does not sound. Crankcase is full.
Re: Detroit Oil Pressure Joe 9-5-02  
Dave, 5lbs at idle is normal for a Detroit Diesel. 35lbs at high idle is still ok, but I like to see them run at least 45lbs. The high pressure on your engine is regulated by a relief valve in the crankcase. Shims are added or removed to change the oil pressure. The idle oil pressure will range from 5-7lbs and won't change with regulating the high oil pressure. If the oil pressure has dropped, then I'd worry, but if it has been the same, I wouldn't worry. The reason it drops to 5lbs when you coast to a stop is that when you have the clutch in, the engine has dropped to an idle.
Re: Detroit Oil Pressure Mark O. 9-21-02  
I would agree that 35 PSI at highway speed is a bit on the low side.

What you might consider doing is spinning a new set of main bearings into your engine.

For years LAUSD would bring their Crowns in during the summer and spin a new set of bearing in. Their buses ran virtually forever without any major engine problems.

As for the low oil pressure buzzer going off, my '79 Crown with a 5-speed does the same thing sometimes. I have noticed it does it whenever I push in the clutch late while coming to a stop. It tends to pull the engine RPM's below idle speed momentarily which does reduce the oil pressure low enough to make the buzzer go off.

Good luck and happy trails.

Mark O.
Re: Detroit Oil Pressure tony Craig 2-8-03  
JOE DOES THE LOW OIL PRESSURE QUIRK GO FOR THE 8.2 ALSO ??
BEST OIL FOR 8V92...1991/92 YEAR BRUCE 4-7-03  
HI..WHAT OIL IS BEST FOR 8V92..91/92 YEAR..WEST COAST DRIVING....COOL AT NIGHT 25-35 DEGREES DAYTIME....60-70 DEGREES
I lend out all kinds of loan reliablelender 8-29-06  
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