I have owned it for 8 years and did all maintance regularly. While driving the oil pressure dropped to under 5 lbs all of a sudden and the lifters were making plenty of noise. I replaced the pressure relief under the oil fitter and the oil pump. The truck has 200,000 miles on it but runs great. At idle the pressure is still around 5 when hot and 20 cold. When reved it goes to 40 cold and 20 hot. Lucas stopped the lifter noise. I have been checking the pressure at the oil fitter with a special adapter and it’s the same as the gauge on the dash. I was told by a GM mechanic that it can’t be the cam bearings if those pressures match. I’m stumped
That engine will be looking for the Small Block Grave Yard soon. And while the cam bearings might be the most significantly worn items it is very likely that the main and rod bearings are getting thin also. You would be doing yourself a favor if you schedule replacing the engine or the truck at your convenience. When owners try to get every last mile out of an engine Murphy’s law usually comes into play.
Is it a stick shift? If so the thrust bearing could be worn (it’s one of the main bearings and it supports the crankshaft laterally when you step on the clutch). See how much in and out play there is on the crankshaft (move the harmonic balancer in and out) .003 is enough. What weight oil are you using?
STP.
Cam bearings are the least of your worries. Odds are the crankshaft bearings are worn out and possibly the crankshaft journals are worn beyond spec.
Drop the oil pan, remove a couple of bearing caps located the fartherest away from the oil pump, and you may find the cause.
And yes, an engine can run fine with no bearing knock and the crank bearings worn. With oil pressure that low odds are that something bad is going to happen at some point.
+1 to OK4450’s post.
Insightful has a point too. More viscosity might just get you years more of use before anything starts to seize. I’m an advocate of running worn out old motors until they just won’t run anymore before starting to tear into them. It can be surprising how long a tired motor will keep going with molasses-weight oil in the system. It’s possible that the compression will become too low, oil use will become untenable, the cat converter(s) will become useless, and things affected by exhaust gasses such as the EGR valve and IAC will become unusable before a bearing seizes.
You might be able to get away with throwing a new set of bearings in it. However, I’m wondering about the situation. You say that the oil pressure was fine, then it suddenly dropped. That isn’t a sign of worn bearings unless something suddenly let go, in which case it would probably be making a lot of noise. Low oil pressure due to worn bearings usually develops slowly and creeps up on you. Almost never is the oil pump bad when someone complains about low oil pressure, but I’m wondering if yours is the exception?
It’s time to start looking for a replacement engine. If it was me…I’d keep driving the truck until the engine dies. That could be years away.
200K on the engine, low oil pressure… yeah put 15W50 in it and start saving for a new truck (or a used motor)'cause this one’s time is short. If the rest of the truck is in good shape (has the transmission been rebuilt yet?), used 5.3’s are easily available with low miles. It is a lower cost fix (than anew truck) if everything else on the truck is in good shape.
It’s been a great truck.I usually drive my trucks until 300,000 until they are totally worn out.this was just a little earlier than im used to. Looks great and has a new transmission. I found a used motor with 60,000 miles on it for $1000. I decided at this point I should give in and replace the motor. ( this is my work truck . Since this problem a purchased a new truck but Its just for backup. I hope to get a few more years out of the 2004 )
I wonder about an obstruction of the oil pickup screen. How easily can the pan be dropped?
The pan can be dropped very easily. There is a small and easily removable crossmember directly under the pan. Once that is out of the way, there’s lots of room
Easy to drop. I am going to check it again but I thought it was clean
I also changed a pressure relief valve under the oil filter. I am leaning toward a spun bearing maybe on the cam that could be blocking the flow.
You’d hear a spun bearing.
If you did spin a bearing and it did “block flow”, you wouldn’t see an effect on the pressure because the system still has the other bearings to flow past. Besides, a bearing not flowing oil would probably seize pretty quickly. The cam is spinning through the sleeves hundreds of times a minute when idling and thousands when revved.
That is probaly the best course(if its an aluminum block make sure what you are getting is better then what you had) Airdoc,sometimes its hard to keep em going forever
If the truck runs well, doesn’t smoke, and doesn’t use much oil, it might be worth buying a set of rod/main bearings and replacing them if the pan is easy to drop. Bearings are meant to wear and as long as there is no mechanical noise in the engine (other than the cold piston slap that GM small blocks are known for), throwing a new set of bearings in the engine might restore your oil pressure and give you more years of service. The crank shouldn’t need to be resurfaced if there is no knock present. (obviously an inspection of the bearings is in order before making a decision)
It runs great ,doesn’t smoke or use any oil.i agree and that is my next step. I am going to inspect the bearings this week. I will post any findings.
This is my first time using car talk chat and I love the feedback.
If you are not hearing any bearing noise I would suspect a bad oil pump or cam bearings.
I just changed main crank bearings and still no oil pressure