Low oil pressure

[dunk]

''

 

[AcIdBuRn02ZTS]

Mine runs 18-22psi hot idle... 40 or so hot running down the road. 45 cold idle... 60+ cold running down the road.

I'd say you've got a stuck bypass as you suggested. Did it just happen all of a sudden like?

 

[dunk]

Only got a gauge with numbers on it this past week. It started acting up several months ago when I noticed above a certain RPM for an extended period of time and the factory gauge would drop lower, slow down a bit and it would increase. Prior to that gauge indicated as I would expect, mid scale on cold idle, a bit lower hot idle and higher on the scale at higher RPM. Now that I think of it I believe the factory gauge used to read higher than it does now when cruising on the highway.

When looking up oil pressure on here and other forums it seems most people say these are low pressure high volume pumps and the oiling system is made to run low pressure. In that regard the 32 psi at speed doesn't bother me as much as having under 10 psi at idle. Thanks for letting me know your numbers, that confirms that mine is a bit low across the board and especially at idle.

I'm due for an oil change soon, think I'll change it and poke around at the valve. Maybe I can tell if it's stuck or free it up. Either that or I'll just get an o-ring kit for the cooler, pull it, and thoroughly clean and inspect the relief valve, maybe shim the spring with a washer for more pressure. I'd imagine I should just be able to stake it in place when reassembling as the factory did.

Another thought, I'm tapped into the fitting off the rear left side of block for both factory and aftermarket gauges, on the same line that feeds my turbo. I'd assume this should be the absolute lowest pressure anywhere in the system, so hopefully the mains have been getting a little more than at the end of the line. Either way when I do my ZF swap I'll be pulling the engine and inspecting the bottom end for bearing wear and clearances.

 

[Shawn MacAnanny]

I have the exact same pressure as you. I have a tee coming off of my turbo block with both the factory sensor and my electric pick up in it. I am using a GlowShift gauge. When it's colder out say 30-40 i see 10-12psi at idle, now that it has warmed up 70-80if i and cruising down the highway for 10 minutes or so, it cruises at 30psi at 2000rpm, 32psi is the max i ever seat hot. When i come to a stop i can see it drop at low as 6 psi and i've even seen 4psi, but i've never see the factory low oil light come on. I am going to try to check the position of my oil pressure regulator next oil change and also switch from the rotella 5w 40 to delvac 15w40. Since temperature seems to affect it so much i am thinking the 5w 40 synthetic might actually be too thin.

 

[dunk]

Interesting. I was wondering if the synthetic would drop the pressure a bit. On my 460 running synthetic definitely lowers pressure as compared to dino. That engine pegs it on the relief at 75 psi on cold start and I don't start moving until it drops off the relief valve. Hot idle on that is maybe 20-25 psi, quickly goes up to maybe 40-50 with any appreciable RPM. Not sure 100% on numbers since I haven't driven it in a month or two. That engine has a high volume pump and fairly tight clearances.

Acidburn, what oil are you using? If dino 15w40 then maybe syntehtic is too thin. Another thing I notice with the IDI having a real gauge now is is takes a couple seconds on cold start to get oil pressure... Longer than I would consider normal for a healthy small block or 385 series, but not alarmingly long. A relief valve stuck cracked open could certainly cause that. It doesn't make any noises like it isn't getting oil, but I'd be more comfortable with 10+ psi at idle.

 

[IDIoit]

replace oil cooler header, or gamble on the spring mod.

i too had an issue with low oil pressure at hot idle.
it happened all of the sudden in my 87.
went from 20 @ hot idle, to 5 @ hot idle.
i thought my bearings **** the bed.
i rebuilt the entire engine.
bearings spec'd out perfect (w/ plastigauge)
i used the old oil cooler.
to my surprise, when i got it running and it got up to hot idle, oil pressure was at 5 psi @ 200*
shut it down and changed oil cooler, hoping for the best results.
i swapped it out, and now i have 17 psi @ 200*

there is a shim and spring mod we can do to these, but my inexperience said to just swap them for now.

i look forward to finding @typ4 or @icanfixall thread on how to do this.
i dont know if they exist, i havnt searched.
but i still have a header that has a *****'d bypass valve.
low pressure high volume for sure,
but i speculate the timeframe i had a lack of 15psi + oil pressure is the reAson i cracked a head
never mind the 1300 EGT's

 

[Koch13351]

I have a mechanical oil pressure gauge on my truck with the sender inline on my turbo feed line, which should be the lowest pressure in the oiling system as previously stated. I see about 42-43 psi cold start idle, 20 psi on fully warmed up idle, and 17-18 psi at idle after giving the engine a good workout. Whenever my engine is above 1000 RPM, it's always a steady 40 psi no matter what the engine temp is. I don't drive my truck when cold until about 2-3 minutes after high idle shuts off or my temp gauge shows 160°F, and by that time the oil pressure is still at least 35 psi at idle. I run regular Delo 400 15w-40.
I'd definitely look into the oil bypass valve as an issue. Even if it doesn't seem to be malfunctioning, give that shim fix a try.

 

[Shawn MacAnanny]

I'll be changing my oil this weekend anyway, so I'll try a different weight oil and see what I can see about the regulator. I had found this article and was going to try to reach it with a pick and see what I could feel, maybe try to look with a bore scope. If that doeant help I'll pull the oil cooler when I replace my steering box and shaft and try the shim

http://diezelcrazeesidipage.homestead.com/oilregulatingvalve1.html

 

[Shawn MacAnanny]

TypeFour also mentioned in another thread that some turbos have a 1/4" NPT oil inlet at the turbo block and some have a 1/8" NPT. Mine has an 1/8" NPT which would mean reduced flow through the turbo block, the other side of that block has my factory oil pressure and electric sending unit. With less flow there would be less pressure seen since the oil would be going through the turbo bearing bleeding off pressure. I wonder if maybe Kotch13351 has a 1/4" inlet on his and Dunk and I have 1/8" oil supplies which would also make a difference.

 

[whiteboyslo]

I'm using an Autometer digital gauge with the sender in the turbo (Banks). I regularly see 6-7 psi at idle once warmed up and it's been that way as long as I've owned it. Truck only has 92Kish original miles and runs like a champ. Running down the road, it's in the low 30s.

Mike

 

[jhenegh]

I have the exact same pressure as you. I have a tee coming off of my turbo block with both the factory sensor and my electric pick up in it. I am using a GlowShift gauge. When it's colder out say 30-40 i see 10-12psi at idle, now that it has warmed up 70-80if i and cruising down the highway for 10 minutes or so, it cruises at 30psi at 2000rpm, 32psi is the max i ever seat hot. When i come to a stop i can see it drop at low as 6 psi and i've even seen 4psi, but i've never see the factory low oil light come on. I am going to try to check the position of my oil pressure regulator next oil change and also switch from the rotella 5w 40 to delvac 15w40. Since temperature seems to affect it so much i am thinking the 5w 40 synthetic might actually be too thin.

I'm exactly here too. My Autometer gauge senter is T-eed into the oil inlet at the turbo with the factory sender. I figure with a 1/4 line feeding that high on the engine, that is the place where oil pressure will be the lowest. I never see below 7-8 at idle, and never above low 30's cruising. Which makes me a bit nervous to be at 2700rpm sometimes pushing 10psi boost and only at 32psi oil pressure

 

[icanfixall]

Where you take pressure readings off the turbo supply line is what the mains are seeing. That line to the turbo is the same pressure as is the rest of the block. As for the 1/8 or 1/4 supply ports. They will both supply the same amount of oil to the turbo. The bearings in the turbo are a sleeve bushing type bearing. We do not have the needle or roller bearing type shaft. Banks found the 1/8 supply line gives plenty of oil to the turbo. Otherwise they would get plenty of warranty work... And they did not. So it works fine.
Usually oil oil pressure is because the actual spring in their rear cooler header has worn thin. It drags on the valve and gets thin so then the spring pressure drops. No amount of shimming can change that. there are no replacement springs either. I suggest replacing the rear header but that is costly too. About 9 years ago I paid around 400 bucks for a new rear header and added 60 thousands shim under the spring. You need to remember adding too much shim can lift the oil supply bypass in the rear cooler header too. I feel 60 thousands is as much as we should go. Oil engineers designed the bypass to supply dirty oil to the engine if the oil filter fails. Dirty oil is much better than no oil. Ever wonder what happens on a cold strat.. Say around 20 degrees with 15W 40 oil.. You bet its in bypass..

 

[OLDBULL8]

Just to compare a New/Overhauled engine using New 15W40 Vis. oil and filter, the oil pressure is ~7 PSI @190* @650 RPM Idle, and ~30 PSI @190* @1500 RPM, and a max of ~70 PSI @190* @3400 RPM measured with a analog gauge. Any gauge has a +/- accuracy. A Digital gauge is more accurate.

These IDI 6.9 and 7.3 engines are designed to run on oil volume for cooling purposes, not so much on oil pressure. Dropping 2 to 4 PSI @idle RPM from above data, means there is a greater volume of flow due to bearing wear.

An engine with 100K 200K miles on it and the oil PSI was close to a new engine pressures, I would be more concerned that the oil cooler is partially plugged. Seen lots of threads/posts of oil cooler partially plugged when replacing the O'rings.

A sudden drop in pressure could very well be a partially stuck open pressure regulator.


EDIT What Ican says above is true. The oil pressure is the same through out the whole system, a 1/8" port is large enough to not act as an orifice to show reduced pressure.

I'm a hunt and punch slow typer.

 

[dunk]

If there are no new springs available, where can I get a new rear oil cooler header?

 

[OLDBULL8]

They are on ebay for around $400.

Don't get paranoid, your oil pressures are OK for a 86.

How many miles on it?