I have an issue that I am unsure of, hopefully someone in these forums have seen this before & shed a little light on the situation. The engine is a Detroit V8-92 Diesel engine that show very low if any oil pressure @ an idle (15 psi or less). This reading is coming from the mechanical gauge on the dash & the panel (its a fire truck). When the rpm's climb, so does the oil pressure, which doen't bother me. But my question is, do these engines have a tendancy to run low on pressure @ an idle? What can cause this?

 

Thats excellent oil pressure. I thinks the min spec is 1lb per 100/rpm's. Also don't trust 1 guage always test with another and compare.

 

That is common for the old detroits once they get up to temp. Nothing is wrong. Our 6v-71 drops to 10psi at idle(~450rpm).

 

The oil pressure gauge on a Detroit always reminded me of a tach. We have an old 4-71 at work that is hooked to a water pump, when shutting it down I bring it down to idle for a bit and it reads a little less than 5 lbs.
Been that way for years. The thing doesn't get used much, sits for months but always starts right up. It uses lots of oil

 

Uses lots of oil or leaks lots of oil? Just kidding. They have always said that if a detroit ever stops leaking oil, something is wrong.

 

Love the Detroits, they have bought and continue to by me a lot of toys.

 

6cylinder, the reason an 6V-71 or 8V-92 uses a lot of oil is because they both are 2-stroke engines. Two-stroke engines have an exhaust stroke every time the piston is advancing toward top dead center. Two-stroke engines, especially when their oil control rings get worn unevenly by sliding on the contact surfaces of the intake port, leave a lot of engine lubrication oil on the cylinder walls to get forced up out the exhaust port. While the engine is working and turning fast the higher combustion temperature vapourizes the oil that the oil control rings don't scrap off the cylinder walls and it rapidly goes out the exhaust stack along with the combustion fumes. If a two-stroke engine is left to idle for an excessively long period of time the combustion chamber temperature decreases causing the partially vaporized liquid oil that is forced out the exhaust port to cool quicker and mingle with the soot in the exhaust fumes moving at a slower velocity up the exhaust stack. The cooling and condensing oil vapor in the exhaust having more density per volume then the combustion fumes will be slobbered slightly down the inside and much more down outside of the exhaust stacks. The outside of chrome exhaust stacks will become covered with a black tar like thick sticky liquid slowly being pulled down the outsides of the cool stacks by gravity. Down the outside of the exhaust stacks the slobbering heavy black oil tar will be built up with layer upon layer as it slowly advances down the outside of the stack. Engine oil on the cylinder walls in a two-stroke engine can't be controlled as well as in a four-stroke engine. In a 4-stroke engine the exhaust valve is open less of the time then it is in a 2-stroke engine. Idling is not good for any diesel engine or gasoline engine. Turn them off or set the high idle at least at a minimum of 1200 rpm.