Oil pressure drops as it warms up?

[willua11]

I ran Purolater filters for a long time and then the #8 piston started knocking and I had the engine repalced. That's when I saw that Purolaters' restrict oil flow on start up.

 

[SunlitComet]

A week later and still no more pressure issues. I really think it was the crappy quality oil filter that caused my oil pressure to drop so low. Running at 60mph on the highway, my oil pressure sits at 40-45psi. Even goes up to 50+ if I jump on it. At idle I'm sitting at 20psi. I think I'm gonna run 10w40 for the rest of its' life. Maybe switch to 30 weight in winter if the 40 doesn't want to flow well.

much better numbers and more then sufficient.

 

[ccapehartusarmyINF.(ret)]

always use royal purple filters theyve tested the shit out of them and they always come out on top

i believe as long as it stays between 10 and 20 PSI at a idle and you dont hear any extra noises like lifter noise when there dry you should be good

 

[Big Roller]

Well I figured I'd update on how the Tahoe is running... Oil pressure has dropped back down again. Now it's running around 12-15 at idle and fluctuates between 25-35 when I'm running down the interstate at 70-75mph. Same problems as before -- cold start, it'll go up to 55-60psi at idle. As it warms up, it slowly drops down to 20, and even down to 15. Driving has the same problem. Starts around 45 or 50(I let it sit and warm up a few minutes before I take off in it), then bleeds off to 25 as I'm driving. Sometimes it even dips down to 20 as I'm driving. But here's the kicker... If I get it up to 3000rpms or above, my oil pressure jumps up to 40+psi. What's going on with this thing? Oil pump going out? Worn bearings? Has anyone else ever had this problem?

And now I'm pretty sure that I've got a knock in the bottom end... Not 100% sure because of it basically being straight piped with the glass packs on it and it being pretty loud. Any ideas? I really don't want to start throwing money at different things without knowing for sure. I'm gonna put a mechanical gauge on it tomorrow to see what readings I can get. Maybe the original gauge is wrong? Wiring gone bad over time?

 

[2000tahoeZ71]

Mine is always at 40 when it first starts, after it warms up it will drop to around 20. No problems. I have heard that 10psi per 1000RPMs is sufficient, not ideal but sufficient.

 

[laredo1307]

Well I figured I'd update on how the Tahoe is running... Oil pressure has dropped back down again. Now it's running around 12-15 at idle and fluctuates between 25-35 when I'm running down the interstate at 70-75mph. Same problems as before -- cold start, it'll go up to 55-60psi at idle. As it warms up, it slowly drops down to 20, and even down to 15. Driving has the same problem. Starts around 45 or 50(I let it sit and warm up a few minutes before I take off in it), then bleeds off to 25 as I'm driving. Sometimes it even dips down to 20 as I'm driving. But here's the kicker... If I get it up to 3000rpms or above, my oil pressure jumps up to 40+psi. What's going on with this thing? Oil pump going out? Worn bearings? Has anyone else ever had this problem?

And now I'm pretty sure that I've got a knock in the bottom end... Not 100% sure because of it basically being straight piped with the glass packs on it and it being pretty loud. Any ideas? I really don't want to start throwing money at different things without knowing for sure. I'm gonna put a mechanical gauge on it tomorrow to see what readings I can get. Maybe the original gauge is wrong? Wiring gone bad over time?

Sounds like it's operating pretty normal to me. I think the old rule of thumb is that you want 10psi for every 1K RPM. The fact that the oil pressure goes up when you step on it is a good thing. Mine generally is around 60psi at start-up, 20psi at idle, and 35-45psi on the highway. I wouldn't suggest using heavier oil to raise the psi. While the pressure will go up you might actually have less oil flowing to the top since it is thicker. If you're running synthetic oil then this is probably why you're getting lower psi. In general synthetics are thinner than dino oil. So while the psi may be lower with synthetic oil your probably getting more than enough flow to the top.

Here's a really good article on the topic of oil. It's lengthy but definitely worth reading.

http://www.ferrarichat.com/forum/faq.php?faq=haas_articles

 

[Big Roller]

Well after hooking up the mechanical gauge that I bought, it is reading around 12-15 at idle, 23-25 at 1000rpms and 38-40 at 2000rpms. But after raising rpm levels, my idle pressure drops down to 8-10. According to that article you posted Laredo, this would be sufficient because the engine isn't stressed at all. I'm using Mobil 5000 10w40, dino oil. BUT, I don't think I have a knock after all. I think it's just an exhaust leak. Could be wrong. It's more of a tick than a knock.

It also takes a few seconds for the oil pressure to build up at startup. I've ran 10w30 and 10w40 in it and it still takes a few seconds for it to build up. I guess I'm just going to drive it until it dies, then I'll know what was wrong with it. I don't want to throw money at it, but I also don't want to worry about it if it does in fact have enough oil pressure to safely operate.

*Edit*
I put a new oil pump on today, and I looked at the rod bearings while I was under there... I could move them side to side(very little travel, though) but I couldn't get them to move up and down like I've seen in countless youtube videos describing bad bearings. But, according to my mechanical gauge, there is no pressure change. There was also a lot of metal flakes in the pan. I'm planning on towing a trailer down to Panama City Beach in july for my church's youth camp... Should I trust this motor or start looking for another one?

 

[rayninglead]

Sounds like the sane thing that just happened to me with my Yukon oil pressure was reading on the low side and went to pull a buddy out of the snow and spun a bearing, so if your bearings have play and your psi is lower than usual be easy on her lol. I have the same readings you do for psi at idle and start up metal in the pan and everything I'm swapping motors this weekend.

 

[Big Roller]

That's probably what has happened to mine. Now after it warms up, it drops to zero at idle and it stays anywhere from 20-35psi while driving. Just depends on how many rpms it's turning. So I'm assuming it's on its last leg. I don't hear any knocking when it drops down that low, but I can hear what sounds like a lifter ticking. Maybe I can get another year out of it before it finally gives up.

 

[memphisrains423]

My two cents: Bearings are failing. Oil pressure is generated by bearing clearances.