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Old 10-02-2005, 07:28 PM
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Oil Pressure

Hi,

I am running a 330 HP 350 from GM. I am using an oil filter relocation kit with single filter and an oil cooler in front of the radiator. After I broke in the motor with petroleum 5/30 oil I switched to Mobil 1 5/30 oil. I also installed a new Auto-meter oil pressure gauge & the pressure switch in the kit and noticed that cold start the oil pressure is 50 PSI. Once fully up to operating temp at idle I see 12.5 on the gauge @750 RPM and 40 PSI when cruising @1500+ RPM. The motor is new with now about 3,000 mile on it.

Is this normal?

Thanks,
Rusty

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Old 10-02-2005, 07:39 PM
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It should have more oil pressure than 12 and a half pounds at idle especially a new engine. Maybe the Auto-Meter guage is bad. I think I would check it with another guage.
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Old 10-02-2005, 07:46 PM
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Actually, that's not unreasonable. My dad's 350 with the M55HV high volume pump is around 50 psi cold around 35-40 cruise and high teens low 20's at idle when hot. I have the factory guage that just shows I have oil pressure (of sorts). It registers no less than 25 at all times.
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Old 10-02-2005, 07:50 PM
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Quote:
Originally Posted by 1982 SS
Actually, that's not unreasonable. My dad's 350 with the M55HV high volume pump is around 50 psi cold around 35-40 cruise and high teens low 20's at idle when hot. I have the factory guage that just shows I have oil pressure (of sorts). It registers no less than 25 at all times.
OK, I am confused now..... You say high teens to low twenties at idle hot....Then you say it never gets less than 25.
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Old 10-02-2005, 07:52 PM
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Sorry, I should have said different cars... One has an Auto meter and the other has the factory guage. Make sense?
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Old 10-02-2005, 08:02 PM
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An old rule-of-thumb is, 10 lbs pressure for every 1000 rpm. I've always considered that as a minimum-hot-pressure.

Measuring pressure accurately is a tricky thing. Of course, the oil temp is a major factor. Less commonly considered is the point along the oiling circuit you take the measurement. The pressure as it leaves the pump will be highest. Measure it at the crank and it will be considerably less.
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Old 10-02-2005, 08:05 PM
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OK 1982SS I got ya now, my bad.
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Old 10-08-2005, 12:19 AM
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Quote:
Originally Posted by gazrnr
Hi,

I am running a 330 HP 350 from GM. I am using an oil filter relocation kit with single filter and an oil cooler in front of the radiator. After I broke in the motor with petroleum 5/30 oil I switched to Mobil 1 5/30 oil. I also installed a new Auto-meter oil pressure gauge & the pressure switch in the kit and noticed that cold start the oil pressure is 50 PSI. Once fully up to operating temp at idle I see 12.5 on the gauge @750 RPM and 40 PSI when cruising @1500+ RPM. The motor is new with now about 3,000 mile on it.

Is this normal?

Thanks,
Rusty
*********

Ok here is the key to all this.

He has 50 when the oil is "cold", I conclude 70* ambient..(?) When the oil gets up to temp (xx? he has a cooler) the pressure is low..... so it is probably NOT THE GAUGE, huh?

I'll bet it has a high volume oil pump. That explains the jump from 12 to 40 in from only 750 to 1500 rpm increase.

5 weight at 70* is still more viscous than 30 weight @ 200*.

I have 20 yrs experience with Mobil 1, and this is TOO LOW idle pressure for even Mobil 1. The 40 @ 1500 seems OK.

I don't know how tight the pistons are fitted, but I would consider trying a heavier viscosity oil as a test. What viscosity does GM recommend for that crate engine?

I'd try 15-50 M-1 and see what the pressure difference is.

I had one engine that hit the 60 psi pressure spring at 2200 rpm with 5w30, and at 1800 with 15w50.

I have an assembly line stock 5.0 Mustang with 55,000 miles that idles at 50 when highway-hot with 10w30 M1 (uses the police car water/oil cooler).

Let us know.

Last edited by xntrik; 10-08-2005 at 12:27 AM.
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Old 10-08-2005, 06:09 AM
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oil pressure

That is too little oil pressure. I have a race eng that at the end of a pass that has more oil press than that. what has piston clearence have to do with oil press? the oil press by pass spring may be too weak.
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Old 10-08-2005, 06:42 AM
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You are getting way too many conflicting reports on your oil psi.
One thing has been stated. GM recommends 10 psi per 1000 RPM,if you are more than that,it is ok,UNLESS you have put in a high volume oil pump.The GM crate motor you are describing probably has a standard volume oil pump installed in it.Therefore you are running correct.Fresh oil is ALWAYS going to allow for higher PSI at start-up,due to the fact that it has not been broken down or thinned out any from heat and use.
What a Ford runs on PSI is no way concerned with what a GM runs on oil PSI. Two different engines,two different recommendations.
Rings have nothing at all to do with oil pressure.They are designed for compression,your lower ring scrapes remaining oil from the cylinder wall on the downstroke.That is way it is also referred to as the oil scrapper ring.
12.5 @ 750 is fine,40 psi @ 1500+ is fine also. If you are spinning 2000 PM's per GM specs,the minimum should be no less than 20 psi,which you have exceeded.


For a STREET MOTOR you are fine.

Last edited by RCastle; 10-08-2005 at 06:56 AM.
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Old 10-08-2005, 06:53 AM
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your lifters will let you know when you have a pressure drop. oil flow/volume is more important than pressure. as rcastle said for the street your fine.
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Old 10-08-2005, 07:23 AM
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Thanks to everyone for their input. The manual for the engine calls for 5/30 oil. The oil pump is stock in what comes in the GM 350 HO crate motor. Is the Mobil 1 "thinning" to the point where it could be the problem? Should I switch back to a petroleum based oil and will this give a different result?

The idle is good...no ticking from the engine. The motor has good power and runs freely up to 5500 with no problems and cruises at 70 MPH at 1800 on the tach with a steady 40 PSI on the oil pressure gauge.
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Old 10-08-2005, 07:28 AM
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pressure drop with mobli 1 is normal. less friction = less pressure.
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Old 10-08-2005, 07:36 AM
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Exactly as Shine stated.Your oil pressure is fine. I would not worry about it. You are using something differnet from what you first used and it is just worrying you a little bit.Change your oil at regular intervals,and you will be ok.Oil preferrance is just a matter of opinion. I use regular petroleum based oil because I am cheap.I keep it changed,and am fine on mine.I drive the crap out of my SBC.My OP at idle is around 13 psi,40 to 50 psi @ highway speeds which are 2500 RPM's for 65 MPH.I built my motor almost three years ago,and lately have not been using it as my DD,simply because the cost of fuel has gone up so much since these last couple of months.
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Old 10-08-2005, 08:15 AM
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about 4 years ago I put a 300 hp gm crate motor in a 57 chev for a guy. It did the same thing. 45psi cold 15psi hot on 5/30 or 10/30 I don't remember which weight oil it called for. it had vdo gauges. I put a mechanical stewart warner on it and confirmed the reading. It scared the hell out of me. I thought there must be prob w/ oil pump or bearing clearances. My buddy at the dealership said run it, as those pressures are typical. That motor has about 40k miles on it now and is still together.I think if it were mine though I'd want a little more than pressure than that. I would dump the stock oil pump and put a high volume pump on it. at least you won't be looking at the gauge all the time expecting the worst. Don't put the high pressure spring kit in it though or you will replace distributor bushings on a regular basis and the pressure will be sky high. I put one in my blazer's 350 and saw 35psi at idle hot with 10/30. cold it pegs the gauge. Hot @ 2000 rpm it pegs the gauge .It is the stock mechanical gauge with no numbers. I would assume the upper mark is 60psi. I don't even want to know how high it goes when it's cold @ 2000 rpm.
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