Oil Pressure drop L03

When I had Grimace, I used to have an issue that when I would come down an off ramp and stop, the oil pressure gauge would drop to zero (engine at idle speed). tapping the accelerator would bring it right back......oil pressure would usually be around 15psi at 2000 rpm

Well, now the Blue 91 is starting to do the same thing. When I bought blue with 228K oil pressure would be indicated around 30 psi @ 2100.
Well last night I let her idle after a strong 30 minute run on the interstate (to unload my buddies stuff after our trip) and when I hopped in saw the oil light on (motor idling) and 0 pressure indicated. Tapped the pedal and it jump back up to 15. Drove it another 35 minutes home and the car ran great but oil pressure stayed around 15 psi (just changed the oil less than 1000 miles ago and plenty in the pan when cold). Got in it this morning and the OP was back up at 30 PSI. My drive to work is short (5 miles) and lowspeed (under 50), so the motor never got hot.
Turned 265K on the way home last night.

Oil pump going??? Motor has not been touched internally from what I know. How hard is it to swap one out?
Maybe time to let her go???

You sure it's not a sending unit issue? If you had 0 pressure...I don't think that motor would run very well...

John did you change oil viscosity,if the oil pressure is normal after a cold start its probably not a gauge issue?It has only done it after a longer drive where the engine reached normal operating temp and the oil is at its thinnest .Sounds like it may be a oil pump going bad or possibly a issue with the bearing tolerances getting loose.IMHO

5W30 always. I would think sending unit, but funny that two different 91 L03s acting the same way. I do have another sending unit I'm about to pull off of Ruby (9c1 cluster swap, swapped back), so I'll do that this weekend and put mine in my boy's car and see what's up with that.

Make that 3 LO3 OCCS but my gauge is the opposite.As soon as I start mine the gauge pegs and stays pegged until thoroughly warm.Once warm in drive with the AC on the gauge will drop down to a normal reading of 15 to 20 pounds of pressure at idle.As soon as I touch the gas the gauge pegs.I have the 52 dollar sending unit,just havent installed yet.There are 2 sensors on the side of the pan and naturally the sensor I need is the most costly.

Typical of many GM small block engines. Big end bearing clearances get a bit excessive and bleed off the pressure. That's not to say there is no oil flowing, just that there is no back pressure. You can install a high-capacity oil pump. You can use a thicker viscosity oil in warm weather. Or you can live with it -- after all, there's not as great a need at idle either. The real fix is undersized bearings.

Yeah, mine does this, too.

I always assumed it was excessive bearing clearance and didn't really give it another thought. Sometimes my light turns on at stoplights, but at speed it's 30-40 PSI

20w50 is a great cure for summertime heat and keeps the OP up too!

I had the issue of no oil pressure at idle in the White Elephant with an LO3. The chime would go on constantly. The engine never make a noise to indicate low oil pressure, but even a mechanical gauge said 0 oil pressure at idle, and about 10 running under throttle. My solution was to put an LO5 in place of the LO3. I now have plenty of oil pressure, and it has more git than the boat anchor. I also do not worry about the engine seizing up when I am miles from home. BTW the engine only had 95K on it.

I ran 10w40 in it when I had it....I don't think a 265K motor would need 5W30...the TBIs were never close tolerance engines, were they?

Classic symptom of Excessive Bearing Clearance is good pressure when cold, crappy when warm. Especially large swings. Time for an overhaul or replacement. Normally when a pump fails, it stops pumping regardless of RPM. Individual results may (always when on the Internet) vary.

The rule of thumb is 10 PSI per 1K of RPM so 15 PSI at 2K RPM is low.

Well I'll have to add a quart before the next change (I lose about a quart every 1500 miles) to slow leaks so I'll drop some 50W in there and then do the 10W40 route next change and see where we are.

I DID run the motor hard as I was returning home from vacation and drove out of the airport at midnight (no traffic) and hadn't driven in 6 days lol. I made an 1.3 hour drive in 1 hour   
That said, it happened once before about a month ago too.

Cant remember the last time I saw 50w motor oil so good luck with that.I just turned 75 thousand miles on the OCC yesterday.Had a turbo muffler installed and its way too quiet for my liking but I will learn to live with it.I hope things work out with the 50 weight.

20w50 is easy to come by.

I'm doing 10W40 ever since i bought her. (thats back in 04) Has 162K and is still running strong.
Pete