Is this normal for GXP's??

[sethjamesrimrodt]

When I first start my car in the morning I have about 50 psi at idle and it stays that way until it is warmed up. Once the car is up to temp the oil pressure drops to about 25 psi at idle. Is this normal and why does it do that?? I do not know if it has 5W30 or 10W30 in it I haven't changed the oil yet.

[CMNTMXR57]

Yes, every engine has higher oil pressure when the oil is cold vs. once it's up to operating temp. Cold to oil is still in the low 100* areas. Imagine a cold sump when it's 0* outside...

A heavier oil will only exagerate this, but yes, it's normal.

[00Beast]

It's not abnormal. How many miles are on the oil? I recommend a good synthetic, I have had good luck with Pennzoil Platinum. Not saying any conventionals are bad, but 4-5k changes versus 7-10k, plus better lubrication? I'll take that, lol.

The other variable is the filter. Make sure it's a good brand (NEVER FRAM). AC Delco, Wix/NAPA Gold/Carquest, Mobil 1, K&N (pricey), Purolator PureOne are all good filters. Your filter choice is much more important than your oil choice. I'd rather run bargain-shelf store-brand oil through a good filter (those I listed) than the best oil on the planet through a Fram.

[CMNTMXR57]

LOL at 10k oil changes, conventional or synthetic...

I've changed my oil at least three times by the 10k mark. I don't give a crap!

Food for thought, the density (or commonly referred to as Specific Gravity) for a synthetic and conventional are below;

Pennzoil Platinum Full Synthetic 5W-30: 880 - 890kg/cm3 @ 59* F
Valvoline Conventional 5W-30: 856kg/cm3 @ 60.1*F

With that said, at cold start up, they're nearly identical weights at pretty much the same temp, which means a virtually non-existent difference to GM's oil pressure system and what you would see on your gauge. If anything, the regular old Valvoline conventional actually performs better at this stage...

These numbers are taken straight off their respective MSDS sheets (both on page 9);

Pennzoil: http://www.epc.shell.com/Docs/GSAP_msds_00092901.PDF
Valvoline: http://www.canyonstateoil.com/msds-shee ... 2_1_QT.PDF

[sethjamesrimrodt]

The dealership said the oil was changed when they got it, I have put 1,500 miles on it so I would assume the oil doesn't have much more than 1,500 miles, they put an off brand filter on it (NOT FRAM). I use Napa’s highest line of filters and I'm planning on using synthetic. Maybe the gauge in my 2000 didn't work too well it was pretty much always at 40-50 psi and the engine had 220,000 miles

[CMNTMXR57]

First off, you're comparing two different engines with two different oiling requirements. The Northstar also uses 2+ more quarts of oil (for the DOHC's), than a 3.8L V6 does right from the start. As such, once up to operational temperature, it may not require the additional pressure.

Secondly, too high of oil pressure is a bad thing too! Without knowing the condition of your previous engine, it could've been a number of things, starting with the simple things, a faulty oil pressure sending unit could definitely cause this, or heck, even a bad gauge in the instrument cluster. Moving on to more serious items, it could have been a faulty pump (or the pressure relief mechanism on it), or were your oil galleries somewhat plugged from age/mileage/oil used over that mileage, etc...

Once again, comparing apples to oranges. Once up to operating temps, where your needle is in the first picture is what I would consider normal, and a sign of a properly operating oiling system, provided when you increase RPM's, the pressure goes up to a certain level, as it should.

[repinS]

My oil pressure is identical to yours, and I'm on 5w30.

I see ~50psi under load and while driving, ~25 at idle. When cold it'll more or less stay at ~50. It's a good indicator as to when I can take it easy and when I can punch the throttle since things are up to temp.

[CMNTMXR57]

You guys would crap a 24k brick if I told you how much mine puts out for PSI even warm under throttle...

I think I saw 124psi one day...

That's actually normal for this particular engine.

[sethjamesrimrodt]

That makes me feel better thanks guys

[00Beast]

Lane: that's why I also brought up the filter. A crappy filter will cause lower pressure.

[CMNTMXR57]

To some degree, yes. And then it depends on what you're defining it as "crappy". Crappy, because it offers NO filtration and basically a pass through. Or crappy, because it's a high restriction unit which would increase pressure.

[dpnewfie]

Well, mine is the same and has been the same since new.

Lane, I just crapped that brick when I saw the 124psi you stated. dang!

[bigwiteboy07]

Yup, my GXP does the exact same thing with 63k and about 1k on the castrol syntec in her. Nothing to worry about.

[CMNTMXR57]

Well, mine is the same and has been the same since new.

Lane, I just crapped that brick when I saw the 124psi you stated. dang!

Was it a 24k gold one though? If not, I'm not even acknowledging this...

Seriously though, the LC3 uses a gerator style oil pump that flows an insane amount of volume and pressure through the oiling system. It is done so as to keep tension on the cam drive chains. This is why I am so specific about using the OEM AC Delco oil filter on it. It can actually filter that volume and pressure of oil, wheras others are in "by-pass" mode.

[dpnewfie]

Was it a 24k gold one though? If not, I'm not even acknowledging this...

Nah, it was pure lead. Must have came from my foot when I kicked myself in the arse for buying this car. lol

[00Beast]

[CMNTMXR57]

Was it a 24k gold one though? If not, I'm not even acknowledging this...

Nah, it was pure lead. Must have came from my foot when I kicked myself in the arse for buying this car. lol

I am very familiar with that feeling.


And as crazy as I am, I'd do it again...

[dpnewfie]

Me too. Sounds crazy but its true.

[MotorheadV8]

My 05 GXP reads similarly to your gauge. This is normal. However, I change oil in a car when I buy it. That way I know the filter ius new, isn't a junk one like Fram, and my motor isn't running on junk oil like Billy Bob's non detergent special. Its too easy and cheapto pass up and too important to mess up. I change my GXP between 2 and 3 thousand miles with a filter, and use Lucas oil additive to help with starting. I also put oil in the filter before putting it on so it doesn't run dry on the initial start up. I've got 108k on the motor and it runs great.

Somewhere I read that for every 1,000 rpm the oil pressure increases so much, but I can't remember the formula.

[01bonneSC]

My 05 GXP reads similarly to your gauge. This is normal. However, I change oil in a car when I buy it. That way I know the filter ius new, isn't a junk one like Fram, and my motor isn't running on junk oil like Billy Bob's non detergent special. Its too easy and cheapto pass up and too important to mess up. I change my GXP between 2 and 3 thousand miles with a filter, and use Lucas oil additive to help with starting. I also put oil in the filter before putting it on so it doesn't run dry on the initial start up. I've got 108k on the motor and it runs great.

Somewhere I read that for every 1,000 rpm the oil pressure increases so much, but I can't remember the formula.

10psi for every 1K RPM.

And thats a lot of oil changes(read wasted money) You can run synthetic with a good filter for about 6-7K miles. But of course it is YOUR money. Also the oil life indicator works really well in these cars.