Jeep_junkie

I switched from 5w30 Mobil 1 in my 156k mile 94 LT1 to 0w30 Mobil 1 to help with a bit of a cold weather tick from the top end. The motor now runs a lot smoother and get this, leaks less too! I was usually losing about 1/2 a quart between oil changes earlier. The oil level is now where it was the day I filled it up and much fewer oil spots on the ground too.

Here's the dilemma; on 5w30 the oil pressure would never drop below 40 psi on the move, even at 50mph in 6th gear, but never go much further than 45-50 psi no matter how it was revved. On 0w30, I didn't notice any difference in cold weather but now that the ambient temperature is higher, I need to keep rpms around 1500 all the time to maintain 40 psi, but it idles fine at 20 psi and never goes any lower. The needle on the gauge also dances around a bit at times.

AFAIK from my research about engine oil, 0w30 is supposed to flow better at cold temps but behave like a 30 weight oil at operating temperature. However, in my case it's behaving like a much lighter weight oil when hot. Now which grade of oil would be best for this motor? 0w30 Mobil 1 is highly recommended for LT1s, but I don't want to spin a bearing to find that it wasn't right for mine.

1994Z28Lt1

iTrader: (1)

if you have 20 psi during hot idle with a stock internal engine and oil pump you are in good shape

according to gm specifications as long as you have more than 6 psi at 1000 rpm on a hot engine you are in good shape

you wont spin a bearing with 20psi at idle, dont get too hung up on the psi because there is a difference between volume of oil being pumped and the pressure

just as a comparison what you describe is exactly how my oil pressure as acted for the last 70,000 miles i have put on my car

ss.slp.ls1

iTrader: (36)

+1. Mine would straddle the red hash mark like ~20 psi at idle in my old engine. That's fine for LT1's.

My new engine sits at 30psi hot idle and 60psi at WOT.

My95Z

iTrader: (8)

You are right the oil should be the same as a 5W-30 when up to temp, did you change oil filter brands?

You are still well within spec though so I wouldn't really worry about it.

Derek98z

iTrader: (55)

So is it okay to run the car to 5500 rpms if it only sees 45 psi at that point?

ss.slp.ls1

iTrader: (36)

The rule of thumb is 10 psi for every 1000rpm. So that seems low. But I think that's what my car got with my old engine. Hopefully someone else can chime in.

Jeep_junkie

I'm confused. GM says at least 6 psi at idle on a hot engine and you're good, and then I keep hearing 10 psi per 1000 rpm, which is quoted most often when talking about oil pressure. So which is it?

ss.slp.ls1

iTrader: (36)

The GM spec is correct. Rule of thumb doesn't always apply. Who knows, you might be fine with 45 psi at 5500rpm. Hopefully someone else knows for sure.

My95Z

iTrader: (8)

I would not be comfortable with 45 psi at 5500rpm, but does that mean their is a problem, no. The stock gauges suck so it could be reading off you don't know unless you have a mechanical gauge. I've seen some SBC's go on and on with hardley any oil pressure especially at idle, it just depends.

I would switch to a slightly high viscosity oil if i were you, (10W-40) especially in the warmer months. What pressure do you have at hot idle?

Jeep_junkie

It's very possible that the oil pressure sending unit could be junk since the needle does jump around sometimes. The motor holds 20 PSI at idle without any problem. It just seems to have trouble building oil pressure as the revs climb and never goes above 40 PSI when hot, no matter how high the revs. It wasn't going much higher than 40 PSI even with the 5w30 but it was at least getting to 40 PSI at anything above idle.

Low N Slow

iTrader: (4)

Mobile oils test a little on the low side of the vicosity range for 30 weight oils. Try the Mobile 0w40 it will act more like a real 30 wt oil.

Derek98z

iTrader: (55)

I ask because my LT1 is the exact same. I see 20 psi at idle and goes to 40 with any amount of throttle. But it will never go above 45 even if revving it high. I personally don't want any spun bearings but it has been a long time since I have owned a LT1 and didn't know if it is common

Jeep_junkie

My old LT1 used to go all the way to 60 psi at redline on 5w30. Never used anything else in it. I guess the next course of action is to try 0w40 Mobil 1 and see if that helps.

buffman

iTrader: (9)

probably not. M1 0w40 is known to shear, and it will shear in our LT1s. I have 13K worth of driving with m1 0w40( 3 OCIs), and it's not all what it's cracked up to be. Not in our LT1s at least. IMO don't trust a electric sending unit gauge especially a stock one.

BTW I dont think GM has a spec for oil pressure over XX rpms. Anything over Xpsi at XXXXrpm then you're good to go. I dont think they have a spec over 3000rpm.

the m1 0w30 iirc is meant for fuel economy? Green accent bottle? probably on the thin side to begin with.

Jeep_junkie

Yeah it's the jug with green accents. FWIW, I didn't notice any improvement in fuel economy but that wasn't my reason for switching in any case. I searched the forums for the best oil for LT1s and it turns out that Mobil 1 0w30 is highly recommended. However, Mobil 1 5w30 doesn't fare well in LT1s and UOA results back up this claim. 0w30 should behave like a 0 weight oil when cold and like a 30 weight oil at operating temperature, but the Mobil 1 stuff does seem a little on the thin side when warmed up.

You say Mobil 1 0w40 is known to shear. Do you have evidence like UOA results to back it up?

buffman

iTrader: (9)

I think if you reaad this forum, you'll find made in Germany Castrol Syntec 0w30 is the LT1 recommended oil...

I have evidence on my UOA that the m1 0w40 sheared. in 3,000 miles. it sheared quite a bit on the 5K run, but fuel dilution (at least in the sample) was present. the 3K OCI had no fuel dilution present. The middle sample had an increase in viscosity because of VSOT that I added part way through. If you want I will post up the UOA. There are a few on BITOG that show it shears.

Jeep_junkie

I meant the M1 0w30 is highly recommended compared to the 5w30 M1. I do know that the made in Germany Castrol Syntec 0w30 is the ideal choice for Lt1s, but availability depends on where you live. No shops carry it around here.

How many miles on your LT1 and which oil are you using now? How is it holding up?

caldercay

Same with me on the 160+K Z. Actually, things got better when I switched
from Mobil-1 to Royal Purple.

96capricemgr

iTrader: (1)

The stock oil pump relief spring is I believe only supposed to be 45psi new which would not upset me at WOT but these days stock springs are quite old and could be opening early. I did put a 65psi spring in the stock pump though more to put a new spring in than for the higher pressure.

There are a lot of antiquated "rules" based on no real information that folks like to follow. The 10psi per 1000rpms is one of them.

Far as the M1 oils, if you did meaningful research I don't think you will find results for any of them that would suggest they are worthwhile for an LT1. For the results they give you could just use an oil half the price.

buffman

iTrader: (9)

I have 175K miles on my LT1. 130K of those miles was the previous owner and conventional oil.

I am running German Castrol right now, but don't have any Good UOAs to show for it. Mainly because a powdercoated intake I isntalled apparently had leftover blasting media in it, even after I cleaned it out, and dumped a LOT of silicon into the engine.. I've been doing some 1K OCIs to wash it out.