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Old 08-17-2013, 02:08 PM
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engine oil cooler potential pressure loss

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


WARM ENGINE
5-7 PSI 750 RPM
15 PSI 1000 RPM
20 PSI 1500 RPM
42 PSI 3000 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.

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Old 08-17-2013, 03:59 PM
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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.

Last edited by jokerZ71; 08-17-2013 at 04:15 PM.
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Old 08-17-2013, 04:19 PM
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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...

Last edited by jeepers creepers; 08-17-2013 at 04:24 PM.
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Old 08-17-2013, 04:33 PM
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Originally Posted by jeepers creepers View Post
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.
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Old 08-17-2013, 04:39 PM
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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.
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Old 08-17-2013, 04:40 PM
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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.
i agree, i'm looking at videos i made just after the rebuild and oil pressure was just an hair higher than today, i personally changed the cam bearing, guys at the machine shop didn't , i remember that i found the new bearings on the shelf! i made a tool to change cam bearing and worked great, they have holes to be oriented in a specific way to ensure proper lubrication.
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Old 08-17-2013, 04:53 PM
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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.
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Old 08-17-2013, 05:05 PM
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Originally Posted by jokerZ71 View Post
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?
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Old 08-17-2013, 05:19 PM
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Quote:
Originally Posted by jeepers creepers View Post
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?
That would only make the bypass open @ a higher psi,which if high enuff,could cause problems or leaks.The bypass shouldn't open unless you exceed 60 psi.Mine will hit 60 & flicker there until temp gets up.A new pump should have no problem building 60psi with cold oil.20 psi @ idle on cold oil is extremely low'IMO.The fact that you only see 60 psi @ 4000 rpms on cold oil tells me you definitely have something goin on.
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Old 08-17-2013, 06:03 PM
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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.
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Old 08-17-2013, 06:17 PM
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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.
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Old 08-18-2013, 08:10 AM
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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.
thank you, i can get here the Shell Helix 10w60 or Bardahl same grade, what do you think?
I think is not a bad idea to keep the 5w50 for the wintertime and put the helix 10w60 during the hot months.

I torn down oil pan today, oil pump looks perfect, i dismantled it to check gears and they look like new, no dirt, no shavings or weird shiny stuff in the oil, i also took off a mani cap and bearings are ok too.
Maybe the machine shop left clearances on the "safe side" wich is not really that safe...
I don't like high volume oil pumps, the put too much load on cam/distributor gear and there's a chance to wear them out prematurely.

The only thing i' m thinking about is to put a thicker oil...
I also raised the engine idle to 850-900 RPM,that seems to raise oil press to about 10 PSI when warm.
Thank you guys.
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Old 08-20-2013, 05:27 PM
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You ahve enough oil pressure. It don't need fixing.
It don't need different oil. A oil cooler helps keep the oil, cooler.
Thats all.
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Old 08-21-2013, 07:09 AM
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Originally Posted by F-BIRD'88 View Post
You ahve enough oil pressure. It don't need fixing.
It don't need different oil. A oil cooler helps keep the oil, cooler.
Thats all.
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.
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Old 08-21-2013, 09:42 AM
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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.

That part of the auto machne shop's CYA program.
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