Let's settle this oil pressure debate.....
 

As I'm about to reinstall this 6.0 after 3 years of service, here's what the bearings look like. This car makes average power (FI speaking) 750rwhp/900tq, and has 50psi oil pressure cold, and about 18psi hot in the summer. There are many who believe you need 85 psi hot in order for a motor to live, and this is proof positive that it's not true. Yes, I understand this somewhat depends on how high you twist your mill, but this motor sees 6800, and that's only sometimes. I just want this to be a data point for those who are concerned with the effects of what's considered to be low oil pressure. Bearings are absolutely immaculate, and are going back into service. In the pics, they look scuffed, but its just some of the top coating that has come off.
https://cimg0.ibsrv.net/gimg/ls1tech...e73d0afc9a.jpg
https://cimg3.ibsrv.net/gimg/ls1tech...07e049eeb1.jpg

I've been saying this for years. Oil flow is FAR more important than oil pressure.

Don't all LS motors, even factory stock always need at least 20w-50 oil, Lucas oil stabilizer to stabilize the unstable oil, a can or two of Slick 50 (the snake oil of snake oils) and at least 125 psi of oil pressure at idle?

...wink wink nudge nudge


On a serious note GameOva that's excellent documentation proving the point flow trumps pressure.

Almost forgot, this bottom end was assembled with Lucas assembly lube, and the car was started with no priming, none whatsoever. That's another myth that is alive and well, the "must prime motor to prevent instant bearing destruction". Just use a healthy coating of assembly lube on all the bearings, bust it off and roll out, it will be fine.

I still prime it first. Not for the bearings, but to ensure the oil pump is primed and working properly with oil flowing where it's supposed to flow.

Looks good. What was your clearance?

No clue, other than plastiguaging a BBC about 20 years ago, I've never checked clearance. And have yet to have a bottom end come apart on me.

Sorry but priming is just common sense, Even running for a very short time without pressure even with assembly lube can do some damage. Nobody claims instant bearing destruction but sure can shorten the life lol

Consider yourself lucky on the no clearance checking because it could have easily have came to a grinding halt, That could also explain your 18lb hot idle although that's still well within spec.

https://cimg4.ibsrv.net/gimg/ls1tech...2e4c12a1ba.jpg
Not to be argumentative, but the proof is in the pics. If your freshly built motor takes so long to build pressure, that it makes a mess of your bearings, then you've got bigger problems. And this isn't a one off example, like I said, use a good coating this here in the pic...priming is completely unnecessary.

I still recommend priming it though. If you have problem with the pickup, pump, or oil not flowing to the heads, etc... it's best to find that out before the first startup rather than after.

That's just my philosophy with everything though. Measure 5 times, cut once. Test, test, test again, and test some more just to be sure, then proceed.

What is the minimum recommended hot pressure? 18 seems awfully low when up to temps.

The thrust bearing has always been my concern, since I lost one-I thought there was a
newer one on the market, and some use tricks to get better oiling. I don't prime, but do
pack the pump with a smear of trans. assemb. grease, aids in startup pressure.
Just a thought on Slick 50, I don't use it, but a buddy races karts, usually go thru an
engine every race, was told to use Slick 50, he was able to go 2-3 races on the same engine.
After break in, I do go old school, dump in a half can of STP, since it sits a lot, helps
keep the bearings "moist".

Trust me I'm not trying to argue, We can both have an opinion and still be friends lol. Pre-priming fills all the empty spaces in the oil system so when you first fire the engine you'll have oil traveling throughout the engine as soon as it's started, Just because you see pressure at the gauge right away does not mean you have oil pressure throughout the engine.

Game ova, you were running an OEM oil pump on this setup? I've ran Melling high volume and high pressure pumps on past engines. I installed a stock GM oil pump in my current stroker.

What is your pressure at cruising rpm and high rpms?

18lbs is fine depending on the weight of oil being used. Maintaining the old Smokey Yunick theory of 10lbs for every thousand rpm is a good base line for added bearing life as is quality oil and changes with good filters.

I can't remember tbh, this motor has always had what seems to be weak oil pressure, my only guess is, the clearances are a touch loose.

I wish I had remembered to take a pic of the thrust bearing (its back together now). I TH400 swapped the car a few years ago, and have always been worried about the thrust bearing. I restricted the pump, but still. But anyway, the thrust literally looked untouched, no wear at all.

I'm running the melling 296 as well.

40psi cruising during the summer with the AC on, roughly 60psi wide open 63-6800ish. This is with water temps @ 195-200 cruising and 215-220 with in town traffic.

I like to use Rotella 15w40 in the summer, and Mobile 5-30 in the winter.

I aim for 15-20 psi at hot idle with all of my engines, which is really double what you actually need. I haven't had an oil related failure with any of my engines.

More than 20 psi oil pressure at hot idle just robs power and increases the risk of oil aeration with no benefit. Higher oil pressure doesn't correlate to higher flow. The bearing clearance, temperature, pressure from combustion, the oil's viscosity, and the oil's pressure-viscosity coefficient all dictate the flow. Oil pressure is just there to be ready to dump oil into the bearing when the wedge opens up each rotation. It doesn't take much pressure to accomplish this. It needs increase with rpm only because the time to fill the oil wedge gets shorter and shorter with rpm.

Unless we're talking about 1000+ hp engine, set the main and rod bearing clearances at .0020-.0025", put a 30 grade oil in it, and sent it.

Thrust bearing failures are commonly caused by misalignment or poor machining. Rarely is it an oiling issue. Slick 50 and STP both contain a very heavy paraffin wax. These waxes do cling to parts, but that doesn't make any difference in wear protection on initial startup, as has been shown in many SAE and STLE studies. Paraffin wax is highly viscous (100-400 cSt @ 212*F) and has poor oxidative stability and thermal stability. It will oxidize, froth, and breakdown at a much faster rate than the surrounding oil in the engine. What normally happens is when that wax coats a part, it sits there, oxidizes, and forms varnish and sludge. This is why paraffin waxes have been abandoned by the oil industry since the 1980s. Lucas Oil Stabilizer is the same thing, except it doesn't contain any beneficial additives at all. STP claims it contains ZDDP, but the concentration is so low, that it's hardly worth mentioning.

Keeping the bearings coated in an oil film for startup protection is the a function of the additive package, not the base oil. ZDDP, MoDTC, polyol esters, alkylated naphthalene, glycolated borates, and polymeric esters (just to name a few) all form polar surface films over parts to protect them when no oil film is present. When you dose the oil up with paraffin wax, you dilute that additive package and only weaken their effectiveness.

In general, if you feel like you need to add something to your oil to make it "better," then you need to run a better oil.