Hi guys,
i have a mildly GM SB 350 on my Jeep, weather it's pretty warm here and i'm experiencing low oil pressure when warm, stock gauge is not accurate at all so i checked pressure with a mechanical one, this is what i read:
COLD ENGINE
20 PSI idle
43 PSI 1500 RPM
60 PSI 4000 RPM
Engine has run for about 20 hours after the rebuild, runs great, no smoke, never heard noise of any kind, changed the oil 2 times and i didn't find a single metal flake or shaving.
I made a groove on the distributor shaft to increase gearS lubrication, don't know how much it would affect pressure, i also took off all the casting flashes into the oil pump and polished them, pump is the stock Melling 55, i also made a custom bracket to keep oil pick up in place, honestly i don't remember main and rod/ bearing clearance but was within the limit, checked with plastigauge.
I went from a Catrol Magnatec 5w40 to a 5w50 Mobil 1 and oil pressure when warm seems slightly better, engine runs the majority of the time under 3000 RPM and just off idle, i'm thinking about put an oil cooler to keep the oil a bit colder that also helps to stabilize whole engine temp, said that ,i'm concern about the oil pressure loss due to the flow restriction caused by the cooler itself, i'm wondering if the benefit of a colder and maybe slightly thicker oil would be invalidated by the pressure loss due to the system restriction.
I'd like to get a sandwich adapter with thermal bypass or an external one.
Any opinion and real life experience with the engine cooler? Would be great to know also the sandwich model and cooler to, i want to get an high flow one.
Thank you in advance.
Your warm psi is almost identical to mine.However on a cold start,I have 60psi @ idle.The big difference is,my engine has 287,000 miles.I'd say you definitely have a problem somewhere.Are you sure guage is accurate? Where are you reading psi from? Did you put new cam bearings in during rebuild?These are often overlooked & big contributor to low oil psi.I don't think adding an oil cooler will help,or,hurt psi.Actually low psi is a result of little,or, no resistance.You must have resistance to build psi.Worn damaged bearings have more clearance which lowers resistance & there4 creates lower psi becuz the pump can't pump enuff to build the required psi.I wouldn't run a thicker oil to increase psi.You risk potential increased wear,especially on a cold start up.With only 20 hrs on a fresh motor your oil psi should be a lot better.It will only get worse & cause more damage if you don't deal with it now.
i didn't find any metal shaving in the oil so i'm assuming bearings are ok, may be i'll take the pan off and see what's going on, hope bearing clearances are ok...
Yes all new bearings all around , cams included...
The absence of metal shavings just means that nothing is galling,or, doing anything to create shavings.You can still have excessive clearances on rod,main,cam bearings,etc.Were all bearings replaced & clearance verified on ea & every bearing.As I said,the cam bearings are often overlooked during a rebuild.They are also the hradest to insatall & most likely damaged during installation if the proper tools are not used.
On a fresh engine,i'd say you should have a minmum of 25 to 30 psi on a warm idle.1 psi for every 100 rpms is said to be a minimum requirement.You are just barely getting that on a new engine.I'd make sure the guage is accurate & take another reading.
Another possibility is a bad,or damaged oil pump.Did you do any welding on the pump ? Some ppl spot weld the pickup to the pump.You have to remove the bypass spring during any welding,brazing to prevent damage.If the bypass doesn't close off,pump can't build adequate psi.It should only open if psi exceeds 60 psi.Normally @ a cold start.During you flash removal,is it possible you got debris in the pump,or,is it possible that you maybe removed a little more than needed,creating excessive clearance in the pump?It doesn't take much.Just a thought.
i didn't make any welding or brazing, i just made a bracket to keep the pick up in place but i TIG welded it on the bench than mounted on later on the pump, may be i'll remove the oil pan tomorrow and see if there's anything wrong, what about to put a washer on the relief spring of the pump to increase pressure? Does that affect at low RPM too or not?
hi , i don't think you have any issue , if it was me i would go to a thicker gade of oil as the oil you are running is very thin. i have just build my engine with oil pressure at 21 when hot. the grade i run is 10w30.
21 psi is on a warm idle is perfectly fine.That's 3 X's the psi he's getting.Granted,the oil he's using is relatively thin,I don't see 10W30 increasing it by 3 times.I have better psi on an engine nearing 300,000 miles.His has 20 hrs.I have ran 20W50 in extreme southern heat to try to raise mine & it only made 3 to 4 psi difference.
Apprecciate your response so much, that's the kind of answer i was looking for, i know you'got a lot knowledge, so thank you.
About the cooler, i'm not sure if pros are more than cons with that, anyway, i'm looking for a high flow model with the fan, so i don't have to put it in front of the radiator and make all those loops with the hoses plus fittings and so on, Derale makes a nice one with the fan that i can put on close to the sandwich adapter, short hoses, less fittings means better flow and less pressure drop.
I'll keep you tuned, thank you.
Production engine builders usually install the rod and main bearing clearances on the loose side because they do not know how the vehicle is going to be used, no matter what the owner says. The shop prefers to set the rod/main oil clearances at .002"/.003" if the shop thinks the customer does not have an oil pressure gauge.
Just increase the oil weight. The 350 is not a modern engine, these 5 weight oils are really too thin for it. It has the wrong type oil pump for moving light weight oils that being spur gear at half crankshaft speed versus the almost universal use on contemporary motors of gerotor or vane pumps often driven at crankshaft rather than camshaft speed. With a spur gear pump you shouldn't drop below a 10W-xx oil and preferable 15W-XX.
Secondly is a rebuilt engine, seldom do nor can engine shops perform machining to the quality of original specifications unless you pay really big bucks. This is also a limitation of selected materails used in the original parts, again the Gen 1 is an old design that tends to depend upon what today are seen as excessive clearances. These type clearances and this is everything not just journals to bearings do not function properly when a spur gear pump and light weight oils are used. They simply bleed too much volume not only against the pumps output but also how this type pump builds a pressure against RPM curve.
For engines with spur gear pumps the output curve is too low at idle and builds in a concave curve as RPMs rise which will show low oil pressure (though usually adaquate) in the mid RPM range. The upper curve is fully recovered and not something of concern.
The 350 as I build them with the specified 15-40 to 20-40 oil I use will show cold idle at 40 pounds which quckly rises to the the relief valve pressure of 55 to 75 depending upon the set up I install. Fully warmed idle pressure will be 17 to 23 pounds, mid RPM will be 40-45 pounds and 2000 RPM up will be on the pressure relief valve at 55 to 75 pounds again depending on the set up. This is with a standard output pump which depending on the characteristics I'm after will have a relief valve spring calibrated for 55 to 75 psi max. street cruisers get 55-60 on the relief; heavy duty for campers, mild off road, street strip get 60-65 psi relief; full tilt motors for constant heavy duty use including snow plowing to circle and road course racing get 65 to 75 psi.
The oil is not only important for lubrication but is vital to cooling interior engine parts that do not have direct contact with the cooling jackets, that includes all the crank and cam journals and bearings, the cam lobes to flat tappet lifters, and the underside of the piston which is critical to piston cooling in heavy duty and competition use.
Maintaining good oil pressure in the GEN I and II engine is critical to connecting rod life, This engine tends to distort the big end through the seperation plane of shank to cap under heavy loading and high RPM. This wipes the lube off the rod journal and bearing leading to overheating and sudden failure of the rod bearing and or rod. High quality aftermarket rods with ARP bolts or for milder builds the use of select stock rods with ARP bolts
is quite an improvement but this has always been a sensitive area in the Gen I and II motors when high power loading and high RPMs are combined. Lots of high pressure and high quantity oil flowing through the rod journal to bearing interface goes a long way toward keeping this oil wet and cool.
Thank you for your response Bogie, so much apprecciated, what do you believe would be the right oil weight?
There are a couple of things i want to discuss about, a 5w50 like the one i'm using right now should an high flowing rate at low temps compared to the
10w-xx wich i think is great becacuse thinner oil would go to lubricate even the farthest tiny hole in the block better than i thicker one does ,but having a 50 grade at high temp it should be even better that a 10w40, is that correct?
I know there's some "grey" on the oil test and their related viscosity, i mean that a 5w50 is probably very close to a 10w40 weight but i'd like to hear that from you.
Last thing, i use to put ZDDP in the oil, do you believe there's the chance to find oil with the right amount of ZDDP that doesn't need any add? actually i'm not even sure i ZDDP is needed or not, i just don't want to be the one who wiped a cam lobe and discovered that ZDDP was needed...
Diesel oil use to have more ZDDP and anti-scuffing additives, maybe the solution, ZDDP is basicly impossible to find here in the old stinky italian boot, i get can that from the UK but i just want to know if it is mandatory or not.
Thank you in advance.
What brand filter are you running. If it is a Fram, get rid of it and get a Wix gold. Fram filters are worthless.
I am not in agreement that your pressure is OK. In my opinion it is to low. All the SBC's I have had are at around 60 PSI cold idle and usually at least 20 PSI or so warm idle.
I run 10w40 Castrol in mine
I think it's low also.Especially for a fresh engine with only 20 hrs on it.SBC's are somewhat known for having low warm idle psi,but,the cold idle psi should be higher than he posted.The psi he is seeing is adequate per the minimum recommended 1 psi per 100 rpm,but,on a newly rebuilt motor w/ a new oilpump,he should have a lot better psi.He probably should switch oils,but,I don't think that'll solve the problem.
i have a Wix filter on, doesn't have the antidrain valve but i believe is not a big deal because is perpendicular to the engine.
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