Hypothetical question

If an engine (Buick 231) loses oil pressure, how long would it run before complete failure? Would it start making loud lifter, or valve or screeching/scraping noises, or would it just go...."thunk" and stop?

 

Make sure the oil pressure gauge is working / accurate. I remember chasing what I thought was a similar issue in an old pick-up only to find a bad gauge & sending unit.

But to answer your question, yes you would hear much lifter noise and bearing knock before anything breaks.

 

uuh, sounds like your Jeep day isn't going so smooth. I really hope that was completely hypothetical.

 

No, it actually is a hypothetical. My oil pressure gauge reads zero. Doesn't move or anything. Checked the wiring, messed with it for a little bit thinking it might need just an adjustment. Nope, gauge still reads zero. Engine sounds fine. Knocks a little when starting (always has), but sounds like it always has. Just making sure that it probably indeed does have oil pressure, just not showing that it does.

Things are good. It was a good Jeep day.. R)R)

 

Once the assembly lube is gone, the engine won't run more than a few minutes without oil pressure. The lifters won't pump up and the rockers will clatter.

You could take the oil pressure fitting off and see if oil comes squirting out. It could get messy...

If it's an electric gauge, I'd change it to a mechanical gauge now. This is not something you want to guess at.

 

Mechanical gauge? Do I just plumb it in to the fitting that holds the sending unit? Do you run a mechanical gauge into the cab?

Why would an engine lose oil pressure anyway? I thought the oil pump was a pretty simple system. Doesn't it run off the cam or a gear or something? I guess I need to research this somewhat. It did give me some indication that oil was wonkey. Over the last year, the pressure was always less and less. When the engine was warm, I was usually getting 5-15 psi, cold about 30-40. Sometimes when I would pull up to a light and stop, the oil pressure gauge was jumping all over the place. Bouncing between 0 and 50 psi.

 

Usual MO is the oil pressure decreases slowly over time, as the bearings wear and the clearance increases. Very seldom is there a catastrophic total loss of oil pressure, except as the result of some other catastrophe, like a connecting rod letting go. Some engines use an oil pump drive shaft, and that can break and cause a catastrophe, but it's rare compared to things simply wearing out.

No oil pressure at start-up after some major repairs is usually imporoper assembly in the oiling system - parts installed backwards, wrong parts, etc. There was an episode of "American Hot Rod" where they had zero oil pressure in a new engine; turned out to be the (new) oil pickup was so close to the bottom of the (new) pan that no oil could enter the pickup. You can also have no oil pressure in a new engine if the oil pump is full of air. The usual fix for this is pre-oiling with an electric drill via the distributor shaft, or packing the oil pump with vaseline.

 

I would agree in it sounds as if it is a bad sending unit. By chance have you changed your oil. I would change the oil and let it run into a clean oil pan, then look and smell the oil to see if anything isn't looking right.