Gapimpin

I just purchased a 98 z28 M6 126k on her but I know the guy that owned her since new and he changed the oil religiously with mobil 1 since he drove it off the lot in 98.

The oil pressure on cold start is a little under 60 but once warm at idle it drops to a bit over 20psi. It gets up to 40psi while cruising around 2000rpm but does not go any higher than that. I took it up to 4000rpm to test it and the needle stayed at 40psi.

I live in texas so its about 104 right now running mobil 1 10w30. This is my first LS1 so im not sure if this is normal or not. Is this common or should it be going higher than 40psi when hot?

Gapimpin

So I noticed today that if I take it to 4k it sits at 40psi then when I shift it jumps to about 45 and then drops.
Ive read about 98's having faulty pumps and from the mechanics of it im wondering if it could be a weak bypass spring when the rpms get high its bypassing then when I shift it snaps shut and pressure rises for a second?

Its all speculation I know but Id like opinions before I just dig in and replace a pump that may not be the issue.

crainholio

iTrader: (2)

Electric oil pressure sending units can generate strange readings when system voltage fluctuates. I wouldn't try to address the ~5psi spike during shifting without verifying oil pressure using a mechanical gauge.

The pressure readings you're getting other than the spike don't seem abnormal for a car of this age and mileage, given the heat and relative thinness of the oil you're running.

Personally, for street use I like Mobil-1 0W-40 better than their current -30 products...more zinc and phosphorous anti-wear additives. It's a proven oil in the LS engine and holds up very well to heat. For hot weather or road course use, their High Mileage 10W-40 has done well in mine also.

I'd consider switching oils if you're concerned about the hot idle pressure readings.

Gapimpin

Thanks for the response I may check into that on my next oil change.
At this point Im a little more concerned with my pressure not going up at all from 3-4thousand rpm. I dont romp on it a lot so I dont usually take it that high but oil pressure not going over 40psi hot makes me wonder

farmington

iTrader: (14)

for what its worth, when i did a cam change I put in a new LS6 oil pump and I picked up about 10psi of pressure. Only drops down to 35 hot idling with 10w30 Mobil 1

crainholio

iTrader: (2)

I'd say given that your pressure rises from ~20psi at idle to 40psi at 2K, your pump and the bypass mechanism are working properly.

What oil filter are you running?

It's likely that your seeing a combination of:

a.) thin, hot oil.
b.) increased bearing clearances due to normal wear.

Higher viscosity oil as mentioned above would be my next step, maybe a different oil filter depending on what you have now. Wix (NAPA Gold) is my favorite low-buck choice, K&N if you're willing to spend extra. Both are proven to flow enough volume to generate normal pressure readings...some others restrict flow enough to show up on the oil pressure gauge.

s346k

iTrader: (4)

my ta is like that. it has 96k miles on it and i run 5w30 castrol synthetic. it shows somewhere around 25-30psi at HOT idle and goes up to 40ish between 1200 rpm and 4k rpm. however, it will clip 60psi up around 6k rpm.

the oil pressure going up on decel is simply mechanics. apparently it's like loading the engine makes everything expand or stretch and unloading it tightens it back up. seems typical on a motor with any kind of use on it. you can create the same effect (much less of course) cruising on the interstate and playing with the throttle.

i think everything looks ok except maybe for the fact that it won't build over 40psi above 4k rpm. perhaps it is the extremely hot temps.

Darkman

iTrader: (2)

I used to run Mobil-1 0W-40 in some non-LS engine applications that required a 40 weight. I ultimately switched because, based on used oil analysis, the Mobil-1 0W-40 sheared very quickly to a 30 weight equivalent.

Gapimpin

I may try changing the filter I purchased a puralator but accidentally got the wrong one. Asked the girlfriend to stop by the parts store on her way home and get me a new filter and she picked up an STP. Never looked at the reviews on them but it looked to be made crappy. Maybe I should change the filter and check it again?

crainholio

iTrader: (2)

Filter change wouldn't hurt given it's an STP on there now, but I wouldn't expect much of an improvement.

My thinking on oil is changing quite a bit lately. API SM spec, and now SN, really put a nosedive on anti-wear additive quantities in xW-30 and thinner oils. We seem to be seeing a lot more noisy engine/lifter complaints here and on other LS boards lately. API says the extra zinc and phosphorous aren't needed in modern engines with roller lifters, but their testing is laboratory based and may not fully reflect real-world conditions.

I've recently changed to Red Line 5W-30, and after nearly 400 miles of commuting and abuse including a 5-session autocross it's still right on the dipstick's full mark...and the engine is the quietest it's ever been. Costs more but appears to be worth it thus far. I'm usually adding ~1/2 quart after a good afternoon of autocrossing...sustained high RPMs usually make my '01 engine drink oil, and I'm turning 3K and up for a full minute each session. I may pop for a Blackstone lab analysis after more miles.

01ssreda4

iTrader: (96)

Stock oil pressure gauges are not real accurate, take their readings with a grain of salt.

Your pressure sounds pretty normal. If you are hell bent on increasing it, install a Melling 10295 pump. It would probably be good insurance anyway as stock oil pumps have been known to take a crap.

Gapimpin

New issue presented today oil pressure was steady at about 30psi at 2k did not move while accelerating but once I let off the gas at 3k it jumped to 40psi. Does that point to a gauge issue or is that the bypass on the pump?

98z-28redcamaro

iTrader: (3)

check oil level........make sure its not draining the pan......if oil level is right then the sending unit is not hard to replace....its behind the intake and the oil pump isnt bad to replace either....

usmcz28

iTrader: (3)

ZINGER..............Check it wil a mechanical gauge to be certain.

Gapimpin

where can i hook up a mechanical gauge? is there a port thats easy to get to?

01ssreda4

iTrader: (96)

There is an oil pump plate directly above the oil filter. You pull it off, drill and tap for your mechanical gauge, run your tests, then put a plug in the hole.

Gapimpin

Well I suspected a pump issue its the stock 98 pump with just under 130k on it. I replaced it this weekend with a new ported pump and bam pressure jumped from just over 20psi hot idle to just under 40psi hot idle. It also goes up to 60psi by 3k. Super happy I fixed that before it died and took the motor with it. Now I just have to deal with it blowing out the oil pan gasket.... Doh

01ssreda4

iTrader: (96)

Glad you got it figured out.