Engine/Transmission (1994 - 1998) Oil Pressure/human error/turbo failure.

[James M]

98 Ram 2500 12 valve 5.9 47RE in need of admonishment and advice. The oil pressure gauge hasn't worked in my vehicle for quite some time. I threw a new sending unit at it a while back, which improved matters for a while, but it went back to intermittently reading zero psi and dinging at me every 5 seconds or so. I may have talked myself into believing the gauge is faulty and therefore disconnected the sending unit wire. I assumed if there was indeed no oil pressure the motor would've destroyed itself several thousand miles ago.

The turbo failed recently. It was old, I assumed time had just gotten the better of it. So I bought a new one and slapped that in. I primed the new turbo, even held the impeller in place with a socket and extension and cranked until oil was coming out the bottom.

To my chagrin, the new turbo has started to make the tell tale scraping noise. I took intake filter off and sure enough, the impeller is loose and scraping against the housing after only a couple hundred miles. So I was forced to dealing with the matter head on and bought a pressure gauge and threaded that into the top of my oil filter housing to try and get a sense of what exactly I'm dealing with. The gauge shows pressure immediately after starting, but by the time I get out of the drivers seat and walk around to look at the pressure gauge, it's dropping to zero in a matter of a few seconds. Revving the motor does not increase the reading on the gauge (I hope you cringed when you read that?).

My first inclination was that the bypass valve in the filter housing is opening. Here are the questions I'm hoping to find answers to.

When the bypass valve opens, does that circumvent the line that runs to the turbocharger?
Could my problem be the flexible line to the turbo getting clogged and generating excess pressure to activate the bypass valve?
Is it worth changing the oil and filter to see if the problem resolves, or should I divert my attentions to the oil pump and hardware within the oil filter housing?
Is there value in installing a second gauge on the oil port where the sending unit threads into the block? Will this give me new information I don't already get with the gauge on the filter housing?


Anyway, I'm clearly a moron and should've endeavored to get to the bottom of the oil pressure issue long ago, so feel free to roast me for that.

 

[Grumpy8811]

maybe the pickup tube is loose or otherwise obstructed..
oil is literally the first thing that goes to the turbo before it goes anywhere else in the engine.

 

[James M]

I guess it's possible the pickup tube is obstructed, but I don't know why that would cause an initial spike in oil pressure followed by a precipituous drop.

Also, I can't imagine that the engine is not being lubricated, because I've probably put close to a thousand miles on it with these symptoms and it hasn't had any obvious issues besides the turbo failure. I feel like the motor would be blown by now if the pickup tube was at fault.

 

[Grumpy8811]

I guess it's possible the pickup tube is obstructed, but I don't know why that would cause an initial spike in oil pressure followed by a precipituous drop.

Also, I can't imagine that the engine is not being lubricated, because I've probably put close to a thousand miles on it with these symptoms and it hasn't had any obvious issues besides the turbo failure. I feel like the motor would be blown by now if the pickup tube was at fault.

look at it this way... the turbo needs oil and it had a short life cycle. you have a valid oil pressure complaint
did you pull the relief valve out of the oil cooler and take a look. maybe it has a broken or weak spring..

other than that you have to be an old fashioned mechanic and start taking things apart to verify WTF happened which is going to involve removing the oil pan... and then the front cover if nothing is obvious on the bottom end. maybe the oil pump itself is slipping on the drive gear.. but nobody can guess their way to what is obviously a mechanical problem..

 

[AH64ID]

With initial pressure and then dropping are you sure there is enough oil in the pan?

The cold oil relief valve could be weak, but should still let some oil thru, and have some pressure.

The filter bypass wouldn’t have that effect if stuck open.