I just purchased an 89 IROC with the 350 TPI. Vehicle is all stock with 77K. Previous owner was using Valvoline conventional 10W30. Vehicle had great oil pressure (30-60). I took it in for a full tune up an flushed out all oils replacing with synthetics. I used Royal Purple 5W30 with a NAPA Gold (Wix) oil filter. I took the car out for a cruise yesterday and the oil pressure kept dropping till it was finally at 12 to 14 pounds @ 2000RPM and ZERO at idle. I turned it off and let it sit for an hour. When I started back up, it was a little under 30 but kept dropping till it was again at zero when idling. Oil level was perfect on the dipstick. I'm not experiencing any pings, knocking or any other abnormal noises and the car runs extremely smooth and strong.
What seems to be the issue? Oil weight? Sending unit? Pump? Will Seafoam help? Any ideas?
I used the same oil and filter in my 87 Vette with the similar L98 and 80K on the odo with no problems. Any help would be appreciated. Thanks.

 

I would never use 5w oil in a 350. I would recommend replacing the oil with 10w-30.

It's my understanding that the oil pressure will go down a little bit with synthetic.

Just my 2 cents. Hope this helps.

 

5w-30 shouldn't cause that much of a change in oil pressure. I would get a mechanical oil pressure gauge and hook it up to see if your oil pressure is really that low or if the gauge is not reading correctly due to something like a bad oil pressure sending unit. Then go from there...

 

Yeah, check it with a mechanical gauge, if you really had no pressure you would know it.

I agree the 5w30 isn't the problem and i wouldn't feel bad using 5w20 in a pinch especially on cooler days.

 

the oil press. sensors on our cars are well known for in-accurate readings . try a new sensor , you may be suprised . good luck .

 

Every time I've had an oil pressure sensor go bad on a 3rd gen it was mysteriously right after I changed the oil. Sometimes it would fix itself and start reading correctly again, sometimes not.

A new OPSU is not that expensive and would be the first place it'd go to if the engine is not showing signs of ACTUAL low oil pressure.

 

Thank you to all. I will take it in this week to manually check the oil pressure and change out the sending unit if need be.
Happy Motoring.

 

Sending unit is only like $15... cheaper than most gauges.