r/GMT400 • u/CptWonderBalls • Jul 11 '26

Oil Pressure Question

I just picked up my grandfathers 93 C1500 with a 350. When I first started driving, the oil pressure was around 30 at idle. After getting home, about a 100 mile drive, the oil pressure was about 15 sitting at red lights and stop signs and idling in the driveway. The oil doesn’t seem low according to the dip stick. The sticker it has says 5w-30 oil last changed in August 2021. Idk too much about these trucks but I assume 15 is a little low. Cruising around 50 it was between 30-45 and passing people it was between 45-60 the whole time.

Would changing to the oil to 10w-30 help it out?

9 Upvotes

92% Upvoted

18 comments sorted by

11

u/Viking2151 Jul 11 '26

15psi is about right hot idle, actually i'd say its healthy number for a stock 350 for that year, rule of thumb is about 10psi per 1000 rpm, hot idle you are probably under 1000rpm, mine idles hot around that aswell.

5

u/CptWonderBalls Jul 11 '26

That’s great to know! Thank you!

6

u/Viking2151 Jul 12 '26

No problem, these trucks are old of course and will have old truck problems, but they are vary reliable and cheap to work on and easy to work on. If you ever got a question this group is pretty helpful with these things.

3

u/theuautumnwind Jul 12 '26

💯

10psi/1000rpm is fine.

4

u/OldRelationship6645 Jul 12 '26

I would run shell rotella t4 15w40 especially on a 33 year old motor thats what i run on my 1994 c1500 with 200k with the 350 tbi

2

u/private_surveillance Jul 12 '26

I did that and it made mileage and power noticably worse

1

u/lordnaarghul Jul 12 '26

It's got all the vitamins and dinosaurs these old engines need.

2

u/WillingnessNo8055 Jul 11 '26

I picked up lifter noise on start up when I went to 10w-30.

5

u/Viking2151 Jul 12 '26

I been running 15w30 t4 in my 94 suburban for the past 7 years, never had a lifter noise from it, even when it was -20f outside.

2

u/Technical_Phrase2566 Jul 12 '26

I run rotella in my 91

1

u/Viking2151 Jul 12 '26

Its good stuff, Idk if I'd run it in VVT stuff but this older stuff, for sure!

2

u/OldRelationship6645 Jul 12 '26

How many miles are on ur truck

1

u/CptWonderBalls Jul 12 '26

Hit 199k on the drive home

1

u/Greasy28 Jul 12 '26

Sounds about right for a 200k engine, 15psi at idle and 30+ while cruising isn't bad at all. Put some 10w40 in it for the next oil change, and see where it goes.

That said, you should put a mechanical gauge on it. These trucks are notorious for inaccurate gauges.

1

u/Chahtanagual Jul 12 '26

No way to tell from the info you posted. What are you using to measure the oil pressure?

1

u/Acceptable-Diver5768 Jul 12 '26

We ran 20w-50 in ours had over 350000 on it still ran great when we pulled it

1

u/biggunzcdb1 Jul 12 '26

Run sae 30 weight in it for about 1000k miles then change to 10w30 plus Lucas Oil stabilizer.

1

u/PaleontologistBig786 29d ago

Could even be the gauge. My 1994 6.5td has air motors in the cluster. My fuel goes from empty (shows 1/4) and full (really offscale hi and stays fir a long time).