Low Oil Pressure

[bmadd2402]

OK. let me get your opinions on this. I have an s1 RB25DET in my s13. It runs pretty darn strong. but I am having this wierd phenomena with the oil pressure. When I start it, all the way up at 100psi, and everyday around town driving, it is fine, holds at 10-15 at idle and increases with the rpm. my problem is when I get to highway speeds. after an extended period of time, the needle will start to jump around erratically, and then when you go back to idle, it will read at like 5psi, and sometimes trickle off down to just above 0. the engine runs strong, it just concerns me a little. I also have a bad turbo on it right now. dont know if that is connected in any way, but the thing makes almost a screaming sound when it gets to boost. it is still making full boost (5.5, it is a turbo from an auto engine, and 5.5 is where the WG is set), but there is a bit of oil in the intake, and of course the sound. I dont know if there is any correlation. I am running Mobil1 full syn. 10w30. please let me know what you guys think.

Brendan

[Valley]

how do you know you have a busted turbo? also, turbo's scream when in boost, especially if you have a exhaust leak right after it, a dump tube, etc. also, if you still have the pcv system (hooked up to the intake) then you will get blowby in the intake. if you are getting excessive amounts, the pcv valve may be going bad.

[Tictakman]

gauge could be bad too. just a thought..

[USMCgetsome]

i'm having the same problem. Check your oil pressure switch. I'm sure you'll see some oil coming out. That is where your losing the pressure.

Mine did the same today. I plugged it in and watch it at startup at 80psi then when warmed it gets to 35psi then after i run the crap out of it. It goes to 10psi or 15psi. I then look down at the oil pressure switch where i t'd into the motor. That seems to be it. Go back and put some teflon tape over the connections and tighten it down again.

[DrifterTom]

oil in the intake is not a sure sign of a bad turbo, if you don't have a catch can it bould be blowby. i had that problem but don't have the factory recirc due to intake mani.

i have been told by a reliable source not to use synthetic on a turbo car, he said that it is too viscous and the oil is slung off of parts before it is used for its intention. when i got my gt30r that was one of his suggestions.

reliable source would be someone who builds engines and pretty much won't mess with it unless the goals are 700whp+

[Carl H]

i have been told by a reliable source not to use synthetic on a turbo car, he said that it is too viscous and the oil is slung off of parts before it is used for its intention. when i got my gt30r that was one of his suggestions.

mmm not quite there man, quite on the contrary.synthetic oil is much thinner than conventional oil and there for has less viscosity compared to regular dino oil.the reason that its not reccomended to use synthetic oil in a motor that has been run on dino is because it can seep past seals which are accustomed to the 'thicker' oil which the synthetic is not.if you were to rebuild a motor and run it in on dino then conver to fully synthetic it would most certianly be benificial especialy on a turbo motor where the oil sees high temps going thru the turbo.

[Valley]

science pwns j00.

how "viscous" an oil is shown by the numbers... you know, like the numbers in say 5w-30. 30 being its rating when cold, 5 when hot.

one thing that is different about synth oils is they have a much smaller molecule (they get into more places) and provide better protection. the only problem is if you have old seals their age shows with numerous small leaks.

driftertom. my guess is that your "reliable source" had a bad experiance with mobil 1. i heard of mobil 1 being a rare problem in the past.

[bmadd2402]

I understand the oil thing. I am a helicopter pilot in the ARMY and have extensive knowladge of turbine engines, and if you think your rb is touchy...anyways, the oil in the intake is in the tube coming out of the turbo, so I guess it could be blowby, and it is not leaking at the sender at all. the turbo scream is BAD. I dont want to get on it because of the embarrassing sound. It SCREAMS. not the typical compressor spooling sound. I was thinking it might be the sending unit since it gets erratic and "Bouncy" at speed. I am at a loss.

Brendan

[DrifterTom]

carl you are righ. when i said too viscous i meant less viscous. i was told that it was too slippery and was falling off the parts too quickly or getting slung off parts.

i was told that straight weighted oil like a 30 or 40 would be best.

[USMCgetsome]

electrical or mechanical? If electrical check the wire to the sender. Mine screams as well. But i have the exact same problem you do with the oil pressure dropping.

[DrifterTom]

i have been through two turbos on my 20. one was factory and one was cheap chinese t3/t04e. when each went out they each were kicking and SCREAMING. the factory would still build boost. but whine like a mofo. the upgrade did not want to build over 1 pound but would scream. it ended up that the sshaft bent on that one .

[noodl35]

maybe oil pressure sender is bad or the gauge could be malfunctioning. Do what those guys above said to do and check for all leaks. Do all this before driving it again IMO.

[Kansei240sx]

Who makes the gauge? I could possibly answer your question.

[Carl H]

if its not the gauge then worst case senario your oil pump may have taken a **** due to the short snout design, but leave that one as a *very* last conclusion.

[bmadd2402]

see, I dont think it is the pump because it still builds pressure all through th e rev range. it is just while I am idling where it will bleed off. and it is only while I have been driving at high speed for an extended period of time. Also it is an AC Autotechnic gauge. it probably is the sending unit. maybe could the wire be getting too hot? I dont know if those things are affected by heat.

Brendan

[bmadd2402]

bump

[Kansei240sx]

Ok since im not really familiar with that gauge, i did a search and from what i found its an electrical gauge correct?

IF SO.

1. do not use teflon tape on the sending unit2. make sure the ground is IN the engine bay close to the sending unit area, i put mine close to the passenger side strut tower near the bottom.

I have a megan racing electronic oil pressure gauge and it reads a little laggy becuase it an electric but reads accurately for the most part, mine was doing what yours was talking about untill i took it out and put in the unit with no teflon tape, the reason being, the unit itself uses the block as a ground through the threading and if you use teflon tape the curcuit can not complete itself.

[ItzGenX]

Oil pressure is supposed to drop when heated because it becomes less viscous at higher temps. On my SR, I would see 18psi at idle cruising around town, but if I go shooting at 160mph down the freeway and exit right after, my idle pressure will be more in the neighborhood of 9psi and slowly go back up as the oil cools. On a cold start I would usually see it jump to 100 and slowly go down. Your problem could be either trash in the oil galley or a bad sensor. Oil pressure never jumps up and down without rpm or temp change. A oil pump should still be able to function even when the short snout snaps the pump gear in half. The problem when it snaps is at higher rpm it should split and drop oil pressure. At low speeds, a split oil pump gear should have erratic readings, but do not jump to conclusions as someone above has pointed out. Exhaust all other bases before going deeper.

At my work place (nissanofmckinney.com), a 350z had the same problem and would flash the oil pressure light on from time to time. We've hooked up an oil pressure diagnostic gauge and drove around with it to make sure it wasn't just the sensor acting up. When we couldn't seem to find out why the pressure was doing that, tech line authorized us to pull the oil pump and inspect it. The pump gear was split in two. I ended up dropping a new shortblock into it before it was given back to the customer.

[USMCgetsome]

i agree with kansei. Seems to be the correct reason that it would do this. ground to the casing internally.