Oil weight and pressure relation

PapaBear · 08-17-2012, 09:57 AM

Guys, time to be serious lol. Here's the backstory:

I've always run 10w30 Mobil 1 in this new motor, and always have seen above 25psi oil pressure at hot idle. New cam went in with a GM performance parts oil pump and 5w30 mobil 1, and initially saw about 30-35 psi at hot idle. I drove truck back from NC and all has been well.

This morning, while on the way to work at a stop light, I saw it dip as low as 12 psi at ~800 RPM idle, but it picked right back up. Book says ~10psi per 1000 RPMs is good, but I know it should be higher with this pump.

Is it possible for an oil pump that's brand new to fail this quickly? I would have to rule out the O-ring in the pickup tube based on the initial numbers, so don't know where to point other than the pump or the oil weight.

Any suggestions? Switch to 10w30 or 10w40 and see what happens? Or proceed to tear it apart and go with a different pump? Usually this pump performs on par with Melling blueprinted pump, which is the reason I went with it due to wait time on the Melling I initially wanted.

BigdaddyDupree · 08-17-2012, 10:02 AM

12 PSI seems real low honestly. my junkyard 5.3 has never been lower then 35 at hot idle. Melling is a good pump but i can get you a GM pump probably pretty reasonable. maybe try a mechanical gauge

PapaBear · 08-17-2012, 10:05 AM

I have a stock pump with about 7k miles on it I could try, but I am really hoping to not have to tear it apart. Would going from 10w30 to 5w30 make that much of a difference?

Should I try a heavier weight oil just to see or would it be a bandaid basically?

By the way I am reading pressures on an aeroforce scan gauge plugged into OBD II port. Stock gauge of course reads 30 or higher all the damn time.

jmd · 08-17-2012, 10:17 AM

how long did it stay at 12 psi?
what psi is it doing now?
money is on the o ring.

silver455 · 08-17-2012, 10:17 AM

i had a lt1 that would hot idle 20 psi with 5w30 and 25 psi with 10w30....doesn't hurt to try

slowgreen99 · 08-17-2012, 10:23 AM

get some 20w-50. Just see if it changes a lot.

PapaBear · 08-17-2012, 10:24 AM

Quote:

Originally Posted by jmd

how long did it stay at 12 psi?
what psi is it doing now?
money is on the o ring.

It stayed at 12 for maybe 2 seconds, then picked up to 15 and then i left the light. Got to work and it idled at about 17-20.

It ran at 30-35 hot idle at the beginning of the week. Doubt the O-ring can change it's orientation in 4 days.

Quote:

Originally Posted by silver455

i had a lt1 that would hot idle 20 psi with 5w30 and 25 psi with 10w30....doesn't hurt to try

Worth a try before tearing into the front of the engine i guess. Would also give me a chance to cut the filter and take a gander at what's inside.

ForceFed4g63 · 08-17-2012, 10:25 AM

Quote:

Originally Posted by slowgreen99

get some 20w-50. Just see if it changes a lot.

X2

Also, the sending unit might be bad, might want to switch it out.

BAD BOB · 08-17-2012, 10:26 AM

The thing with these motors is you run the oil that they call for for the most part. A new gm engine should run 5w30 bc that's what the tolerances are made for. I think the alum motors will fluctuate more bc of the greater expansion rate over iron

PapaBear · 08-17-2012, 10:34 AM

Well, I'm going to throw some heavier oil in there and see.

If I have to pull it apart I'll just throw the Melling in there like I wanted to initially.

Any tips for the O-ring other than to lube the shit out of it and install on the tube not in the pump? I have a trick for removing and installing the bolt, hope it works. If I have to remove diff to pull the pan, this bitch is going 2wd.

jmd · 08-17-2012, 10:35 AM

Quote:

Originally Posted by ForceFed4g63

X2

Also, the sending unit might be bad, might want to switch it out.

this is a good idea.

PapaBear · 08-17-2012, 10:35 AM

Quote:

Originally Posted by ForceFed4g63

X2

Also, the sending unit might be bad, might want to switch it out.

I questioned this as well. Might as well replace it, could easily be a piece of trash or something in there. That might explain my high RPM low pressure readings.

Thanks guys.

jmd · 08-17-2012, 10:46 AM

Quote:

Originally Posted by PapaBear

I questioned this as well. Might as well replace it, could easily be a piece of trash or something in there. That might explain my high RPM low pressure readings. Thanks guys.

it drops pressure on high rpm runs? how low/

PapaBear · 08-17-2012, 10:56 AM

Quote:

Originally Posted by jmd

it drops pressure on high rpm runs? how low/

Doesn't drop, just doesn't build what it used to. Only gets to about 38 or 40

BigdaddyDupree · 08-17-2012, 11:00 AM

thats not good bud

BigdaddyDupree · 08-17-2012, 11:00 AM

again my junkyard 5.3 has 65-70 lbs at WOT

98z-28camaro · 08-17-2012, 11:09 AM

my milling never sees under 60 when hot......i run mobile 15w50 though......

PapaBear · 08-17-2012, 11:09 AM

I know. That's why I'm blaming the pump. Wonder if it is missing a shim on the spring. I think that's the only difference in this one and the stock one.

gearmesh, inc. · 08-17-2012, 11:55 AM

Pump gears are pretty basic. If clearances are in spec, pressure problems won't be a gear/pocket issue. I think you either have a sending unit issue, a relief not up to par, or a suction side issue.

Powerstrokes back in the day had an issue with a suction side seal. Ford recommended overfilling the pan to the point of getting the level above the suction seal just as a diagnostic to see if problems went away. You might can do this with the rear end jacked way up to get the oil level higher in the front of the pan, too.

schardbody · 08-17-2012, 02:08 PM

Don't run thicker oil to band aid a pressure problem. Thicker oil will read higher pressure only because of the restriction to flow which means less oil moving through the bearings which means more heat.

I'm with Gerald sounds like a relief issue. Suction side would usually show low pressure when cold since the oil is thicker the pump will pick up more air than oil... not always though.

First thing I'd do is talk to Alvin and see what he recommends since he was just in it.

08-17-2012, 09:57 AM	#1
PapaBear Senior Member Join Date: Aug 2010 Posts: 2,809	Oil weight and pressure relation Guys, time to be serious lol. Here's the backstory: I've always run 10w30 Mobil 1 in this new motor, and always have seen above 25psi oil pressure at hot idle. New cam went in with a GM performance parts oil pump and 5w30 mobil 1, and initially saw about 30-35 psi at hot idle. I drove truck back from NC and all has been well. This morning, while on the way to work at a stop light, I saw it dip as low as 12 psi at ~800 RPM idle, but it picked right back up. Book says ~10psi per 1000 RPMs is good, but I know it should be higher with this pump. Is it possible for an oil pump that's brand new to fail this quickly? I would have to rule out the O-ring in the pickup tube based on the initial numbers, so don't know where to point other than the pump or the oil weight. Any suggestions? Switch to 10w30 or 10w40 and see what happens? Or proceed to tear it apart and go with a different pump? Usually this pump performs on par with Melling blueprinted pump, which is the reason I went with it due to wait time on the Melling I initially wanted.

08-17-2012, 10:02 AM	#2
BigdaddyDupree Senior Member Join Date: Jul 2008 Location: MACEDONIA Posts: 4,967	12 PSI seems real low honestly. my junkyard 5.3 has never been lower then 35 at hot idle. Melling is a good pump but i can get you a GM pump probably pretty reasonable. maybe try a mechanical gauge __________________ . What you wanna do?

08-17-2012, 10:17 AM	#4
jmd Senior Member Join Date: May 2008 Posts: 3,177	how long did it stay at 12 psi? what psi is it doing now? money is on the o ring. __________________ Cadillac man

08-17-2012, 10:23 AM	#6
slowgreen99 Senior Member Join Date: Jan 2008 Location: Summerville Posts: 7,740	get some 20w-50. Just see if it changes a lot. __________________ M.R.E. Bad Bob Motorsports

08-17-2012, 10:26 AM	#9
BAD BOB Senior Member Join Date: Mar 2008 Location: SUMMERVILLE Posts: 3,681	The thing with these motors is you run the oil that they call for for the most part. A new gm engine should run 5w30 bc that's what the tolerances are made for. I think the alum motors will fluctuate more bc of the greater expansion rate over iron __________________ IM BAD BOB

08-17-2012, 10:05 AM	#3
PapaBear Senior Member Join Date: Aug 2010 Posts: 2,809	I have a stock pump with about 7k miles on it I could try, but I am really hoping to not have to tear it apart. Would going from 10w30 to 5w30 make that much of a difference? Should I try a heavier weight oil just to see or would it be a bandaid basically? By the way I am reading pressures on an aeroforce scan gauge plugged into OBD II port. Stock gauge of course reads 30 or higher all the damn time.

08-17-2012, 10:17 AM	#5
silver455 Senior Member Join Date: Jun 2008 Posts: 85	i had a lt1 that would hot idle 20 psi with 5w30 and 25 psi with 10w30....doesn't hurt to try

08-17-2012, 10:34 AM	#10
PapaBear Senior Member Join Date: Aug 2010 Posts: 2,809	Well, I'm going to throw some heavier oil in there and see. If I have to pull it apart I'll just throw the Melling in there like I wanted to initially. Any tips for the O-ring other than to lube the shit out of it and install on the tube not in the pump? I have a trick for removing and installing the bolt, hope it works. If I have to remove diff to pull the pan, this bitch is going 2wd.

08-17-2012, 11:00 AM	#15
BigdaddyDupree Senior Member Join Date: Jul 2008 Location: MACEDONIA Posts: 4,967	thats not good bud __________________ . What you wanna do?

08-17-2012, 11:09 AM	#17
98z-28camaro Senior Member Join Date: Aug 2012 Location: murder beach sc Posts: 72	my milling never sees under 60 when hot......i run mobile 15w50 though......

08-17-2012, 11:55 AM	#19
gearmesh, inc. creepy azz cracka Join Date: Nov 2008 Location: Summerville Posts: 1,587	Pump gears are pretty basic. If clearances are in spec, pressure problems won't be a gear/pocket issue. I think you either have a sending unit issue, a relief not up to par, or a suction side issue. Powerstrokes back in the day had an issue with a suction side seal. Ford recommended overfilling the pan to the point of getting the level above the suction seal just as a diagnostic to see if problems went away. You might can do this with the rear end jacked way up to get the oil level higher in the front of the pan, too. __________________ "I came into this world kicking, screaming,and covered in someone else's blood, I have no problem leaving the same way!" ÔÇ£If you carry a gun, people will call you paranoid. ThatÔÇÖs ridiculous. If I have a gun, what in the hell do I have to be paranoid about?ÔÇØ -Clint Smith, Thunder Ranch.

08-17-2012, 02:08 PM	#20
schardbody Senior Member Join Date: Sep 2008 Posts: 1,158	Don't run thicker oil to band aid a pressure problem. Thicker oil will read higher pressure only because of the restriction to flow which means less oil moving through the bearings which means more heat. I'm with Gerald sounds like a relief issue. Suction side would usually show low pressure when cold since the oil is thicker the pump will pick up more air than oil... not always though. First thing I'd do is talk to Alvin and see what he recommends since he was just in it.