Sorry its a SBC question.... I just got this used motor. It runs real smooth, but lately i noticed the oil pressure is stuck at 30 even if i rev up to 3000 rpm while driving. It just started doing it this week, and its kinda worrying me. I know normally at idle it will be about 20-25psi, and as soon as you get off idle it should go up to about 40-55psi depending on rpm. The car never needs to go above 2000rpm so i dont think any harm was done, but im parking it till i can fix the prob. What does it mean if its stuck at 30??? Stock 1978 SBC 350. 20W50 oil used. 40ish psi when hot. 25-30 otherwise.
Could be a stuck oil pressure relief valve (oil pump), maybe a partially blocked pickup tube, could be something like a cracked pickup tube, could be some other internal leak. Try a different gage before you start taking stuff apart. Devon
You need to get rid of that oil....way to viscous....use 10w-30. Stock SBC runs a max pressure of 37 psi....your higher readings are due to the wrong oil in it....change to the lower weight oil....if your oil pressure really drops...your engine is shot......using thicker oil is way to disguise a worn-out engine.
I have used 15W50 in my engines for a long time, although the other engines were not stock.... In terms of timline, I purchased this engine. Tested compression and heard it run, it was smooth, no misses or ticks. Replaced Rear main seal, and a few external gaskets, then dropped it in my firebird. Topped it up with 10W30, and ran it for a bit. All seemed well until i noticed the pressure was stuck at 30 (didnt always do this, just started when i posted this thread). I put in the 20W50 to see if it would change. It did not. Although the starting pressure is about 5psi higher (on this gauge) when cold with the 20W50, but it drops back down to 30 when warm, just as with the 10W30. When the engine was first driven in the car, it would go up to 40psi off idle, just as expected. I guess that rules out the gauge being stuck. Although the number reading is probably incorrect, i know that its not zero, and that the gauge will go to higher readings as well. The oil pickup tube was cleaned out before i put the pan back on, i know its clean, but dont have reason to suspect its cracked. I mainly posted this thread because i dont understand how the oil is routed, and where the pressure reading is taken....? If i understood the circuit maybe i could diagnose it better. While it was apart, i had to also replace the "peice" that the oil filter mounts onto (2bolts). The old one had broken during delivery. Is it possible to install this "backwards"? Im going to take off the oil filter and see if theres anything in there that could tell me something. If not, the car is going into storage, ill tinker with it some in the spring.
The oil pressure is taken right at the back of the engine right above the pump....from your description, sounds like the bypass is stuck....check it out.
George what would cause the bypass to become stuck? I guess it could have failed due to old age, but could some sort of debris cause this as well? Im not quite sure how the bypass works, ill have to look it up. But i beleive it involves removing the pump correct?
Debris, "gummed up" due to infrequent oil changes, correct. Unfortunately the bypass is in the SBC pump. Devon
The stock bypass for the '68 up engine is mounted on the filter mounting boss. http://www.sdparts.com/product/3952...0ChevySmallBlockAnd19681990ChevyBigBlock.aspx Very easy to replace when you change the oil to the aforementioned 10w30,keep track of the two bolts,they are application specific.I would make sure that the gauge is up to par.Good luck with it.
Filter bypass versus oil pump pressure relief valve. Filter bypass shouldn't affect pressure, right? Devon
ok well i wont be dropping the pan till after the spring then. I know theres good oil in there even if its being bypassed, and the engine will only see 2500rpm max. The oil filter mount is what im talking about. 1 broke, so i took it from the other engine (1975 onto 1978) and just put it in. It only has two bolts, is it possible to install it wrong?
You are right Devon,I'm not thinking right tonight.However the pump is only about $18.00 and not too bad of a job to change on an afternoon:beer .
I am talking about the oil pump bypass.....seen this once in a Chevy that was original....the nylon material that was on the factory timing gears disintegrated and a small piece got jammed in the bypass causing it to stick. Once you drop the pan and inspect the pump, you should find the problem...would also be a good idea to check the distributor gear for abnormal wear due to additional oil pump loading.
Would a clogged oil filter do this? I figured since i changed the oil, i may as well change the filter. The car didnt warm up all the way so i still had about 30psi at idle, however when i revved it up to 3000rpm it climbed another 10psi (on my gauge). It absolutely would not change before, even if i revved to 3000...... Would stay stuck at 25psi even when warm. Maybe my new oil flushed out alot of sludge, and right into the filter? o No:
