Low Oil Pressure???
 

I met a guy here in Beaufort that bought a replica with a Roush stroker and auto trans. He said it runs great but the oil pressure was only about 15 PSI and wouldn't go higher until he changed the oil??:confused:

At that point it went to 40-45 PSI but in time it fell back to 15 or so!!:mad:

He changed it again and back to 40-45 PSI but after 500 miles it falls again.....What could cause this??:confused:

Mine stays at 35-40 PSI hot at idle and 65+ at 2500+ RPM's....I guess the bypass opens at 65 PSI?? **) **)

Coosawjack:D

Has he hooked up a mechanical gauge to the engine? If he is using a electric sender it may be failing. 15psi is not near enough to be running the engine.
He needs to look closer as to what is going on before he spins a bearing.

It could be many things. Lets assume it isn't the bearing clearances, althought that is the biggest cause for low oil pressure in high mile worn out engines.

It could be the gauge. Try a second. It could be a tired oil pump. Many "rebuilt" engines get used oil pumps or pumps of questionable heritage. A good standard pump will get you 35 pounds at idle hot maybe up to 50 at speed.

A high volume pump will get you 35-45 pounds hot and as much as 60 pounds at speed. High pressure pumps will get you 50-60 pounds hot and as much as 100 pounds at speed. All this is predicated on prober bearing clearances, oil viscosity, and oil temp.

I had a recently rebuilt 428 in my CC when I bought it. It had 25-35 hot and 50 pounds at speed. I had no reason to suspect the bearings but was really concerned about the 25 pounds at idle (which is really ok for an average engine).

I was planning an oil pan change anyway so while I was in there I put in a new Melling 57HV oil pump. Same engine, same oil I alway ran. The pressure went to 40-50 pounds at idle hot and 65-70 at speed.

It may not be that simple for your friend, but with 15 psi you'll want a new oil pump to go with whatever you have to do next.

I suggest installing a windage tray while you are down there. It is about $40 and can net you 10-15 horse power.

Is it the oil change causing the pressure to increase or the filter change? What happens if only the filter gets changed? Is there lots of junk in the system whcih eventually clogs the filter? Just a thought.

Bob

I don't know what all he's tried but thought it was interesting that new oil (or filter) brings it back up!!

I'm going to talk with him again this week to get more details.

Coosawjack:(

I can't imagine how junk in the filter would cause a drop in pressure? Unless eventually all the oil got stuck somewhere and the pickup was sucking on air...??

I have been experiencing similar issues lately, but the gauge appears to be functioning in the proper manner. Is it accurate? I do not know. Is it doing the right things? Yes.

Hot idle.... I've actually seen 15 PSI...
Up to speed.... 45 PSI...

I've talked here about it before and have moderately wide clearances... .0025 - .003" Not HUGE, but still a moderately loose motor.

My question is - if my pressure is coming up no problem and holding a very steady 40-45 PSI at anything over 2000 RPM, am I in danger of anything?

I am running a pretty bone stock 5-qt. Canton pan. No windage tray, standard volume oil pump, fairly loose clearances.

I KNOW the rule...10PSI for every 1000 RPM and KNOW I'm not getting that. But I've also heard from plenty of reputable builders that pressure is pressure...and if it's coming up with revs, then things are working right.

I'm considering replacing the 5qt. pan with a 7qt. pan this off-season and while in there, will probably replace the pump as well.

But for the time being... is a 15PSI hot idle going to kill me? Should I not be running the motor?

BTW, it fires up to a 55 PSI cold idle but after some hard driving, eventually drops to the 15-18 PSI I was mentioning.

J.P.

Ok lets try to put this to rest. Would you run your engine with 20psi at 8,000 RPM? No way. Why not? Because at higher RPM's the load on the engine is higher. If the oil pressure is not high enough to over come the added pressure put on the rods and crank to keep the bearings off the crank what happens to the engine? How about spun bearings thrown rods piston scrape and all kinds of other not so great things.
You need to have higher pressure to over come the high stress put on the engine at higher RPM's to over come the forces that are trying to force to oil out of the way.
Glad I got that out of my system!
Ok now on to your question. First I have a few for you.
1. What weight oil are you running. If the enigne was put together loose you will need to run a heavier oil to help over come the added space.
2. What oil pump are you running? If you run the enigne on the loose side you need to have a pump that can move enough oil to over come the want of the engine to push it out of the way. i.e. HV HP style pump.
3. Are you running an external oil cooler? If so what size lines are you running and are you running a stat in the system so it does not let the oil flow to quick and not cool?
4. Did you check the pick up to pan clearance to be sure it is not to close or to far away? To close and at high rpm's it will not get oil to it. To far and and it could be sucking air.
If you start it cold and it shows 55psi it sounds like the oil is to thin after it warms up. Try a SAE40 to see if it makes a change. 15 at idle is fine but it needs to get up to 10psi for every 1,000 you rev it to or you will damage it. Maybe not today but it will happen.

Bruce,

Not sure why you had to get the lecture out of your system for my regard... I understand all of those catastrophic failures and the need for additional pressure at higher RPM (not to mention WHY the need). But I'm glad you feel better, now!! And I'm so glad I could help!! ;)

Anyhow...

1) Mobil1 15W-50. Have considered a straight-weight SAE40 or 50.
2) Melling M83 Std. Vol. pump. It is what the shortblock builder sent with the shortblock. I do not have ANY idea what their reputation was. They had no complaints with the Bureau, seemed fine, etc... won't get into all the reasons they were chosen. I don't understand why the SV pump came with the fairly loose clearances, but it did. Plan to change it.
3) No.
4) No, however I've never seen a loss of pressure when winding the motor up...ever. Also never seen a loss of pressure at sustained higher RPMs.

Now back to my questions one more time... I have some new ones.

Some people have claimed to get higher pressure with lower viscosity oils. I'm supposing that would NOT happen in my case because of my particular setup (loose).

I'm assuming the Viscosity Index of a straight weight SAE40 or 50 is such that I would not be thinning the oil as much when it is running 200F. The flash point of dead dinosaur is lower, right, but...purely from a viscosity (and resulting pressure) standpoint, it should be better.

I understand the nomenclature of the oil weights, but I want a little refresher... 15W-50 pours cold like a 15 but will pour hot like a 50 would pour hot? Is this entirely true, though? If so, why would I be gaining anything by going to the SAE40 or 50? I'd think my cold idle would jump up in the 65-75 range but my hot idle would remain the same (as well as my hot cruise PSI).

Just trying to get some more info. Thanks....

J.P.

Sorry for going off. It was not you I was after but all of the other folks out there that read these post. I see the same question about pressure all the time and it just got under my skin this time.
Now back to trying to help.
20w-50 "should" flow like a 20 weight oil but lube like a 50. I have never been much of a fan of multigrades in performace engines. The straight grade will hold the same weight across the board and thus should hold the pressure the same after warm up. Plus the heavier oil will in my view do a better job of staying put. Try it you have nothing to loose and it my help your problem.
The pump will control the max pressure you will see by way of the valve built into the pump. Again if however the engine is built on the wide side it will take more oil to full the space and thus more volume will be needed.
Just for the record I am no fan of syntetics. Sorry. I am still waiting to see a side by side done for wear at 1,000 hrs to show me if one is really better than the other. In 20 plus years I am still waiting.
I run straight 40 in all of the perfomance engines I build and have never had a failure.
We can talk about this more if you like. Just give me a call at my shop and I will try to get into more detail if needed.
407-857-8587 Mon-Fri 9:00-5:00 est.

You're right, the straight weight oil should do nothing for hot conditions. The split grade oils have a higher viscosity index (around the 150's) as compared to the straight weight oils (in the 100's).

I think the whole point behind the multi-vis is the cold "drag" losses. It provides easier starting and less losses when the oil's cold. At the same upper temp, the viscosity is the same as the straight weight.

Seems to be an issue with supply and demand. The closer the flow potential equals the flow from the pump, the lower the pressure. When revving, there should be little change in flow potential as the orifices and drain holes stay the same diameter (the only increases are from the increased speed of the bearings, cam, etc.), but the flow from the pump increases significantly.

I'd say that a new pump would do the trick. One question that comes to mind is - do these pumps have a relief circuit? Or can you (in an extreme case) put all kinds of restrictions with a high volume pump and run at 250 psi?

MidOHasp, I think the real problem is too many charity rides in London! :)

I HAVE ALSO SEEN THIS OIL PRESSURE QUESTION COME UP TIME AND AGAIN. I, TOO HAVE RESERVATIONS ABOUT SYNTHETIC OILS AND DO NOT PREFER MULTI-VIS OIL. I HAVE HAD VERY GOOD RESULTS WITH CASTROL 30WT. IT HOLDS UP VERY GOOD IN PERFORMANCE ENGINES AND HAS HIGH RESISTANCE TO THERMAL BREAKDOWN. MY 2 CENTS ON OIL...

AS FOR THE PRESSURE.. I THINK YOU ARE FINE ON THE CLEARANCES... (A WHOLE OTHER DISCUSSION) BUT SOME PEOPLE ARE VERY PICKY AND WOULD NOT ACCEPT AN ENGINE WITH A .003" CLEARANCE. AGAIN, JUST MY OPINION, BUT I PREFER A "LOOSE" MOTOR WITH QUALITY OIL AND A HV PUMP. EVEN WITH THE .003" CLEAR, IF YOU RUN A HV PUMP AND DECENT OIL, YOU SHOULD HAVE AROUND 20 PSI HOT IDLE AND UPWARDS OF 60 AT SPEED HOT. I'VE BUILT LOTS OF FE'S THIS WAY AND NO PROBLEMS YET. MY PERSONAL FE IS A 390 WITH .003" ROD, .028 MAIN CLEARANCES, MELLING M57HV PUMP, RUNS LOW 20'S AT HOT IDLE, HIGH 60'S TO LOW 70'S AT CRUISING SPEED. IT'S BEEN RUNNING FOR 6 YEARS THAT WAY.

AS FOR A MINIMUM PRESSURE, I THINK THAT YOUR 15 POUNDS AT IDLE IS PROBABLY NOT GOING TO KILL YOUR MOTOR - SO LONG AS IT DOES, IN FACT, RISE AS SOON AS YOU PICK IT UP OFF IDLE. I WOULD BE MORE WORRIED ABOUT THE CAM THAN THE BEARINGS AT 15 PSI THOUGH. I BET IF YOU REPLACE THE PUMP WITH A HV ONE THE PROBLEM WILL BE SOLVED.

I think I am going to do this:

1) Drain the Mobil1 and replace with a SAE40 or 50. Nobody should be sorry for not liking synthetic oil. It's a preference thing. Speaking of preference, what 40W do you use, Bruce? You can tell me offline if you are against bowing to a particular brand, etc...

2) Replace the M83 w/ a hi-vol pump. Can't see how it can hurt. Although, have had lots of people tell me I'm going to wear out the distributor gear w/ the hi-vol pump. I have a steel gear, though. Should I really be worried about that? (Steel gear and hydraulic roller cam)

3) Give fewer charity rides in London next year! (Nuke...what was I supposed to do? It was for the KIDS!)

Thanks to all for the insight.

No worries on going off, Bruce... I know the same question comes up over and over and over and it must get frustrating. 15 was a new "all-time-low" I saw, though.

I would really like to see the hot idle never go below 25 (hell....20!) and the hot cruise consistently over 50...and even over 60 at higher RPM applications. I'd feel better about the life of my motor.

I will post results as soon as I have any. Rest assured....

JP :)

J.P

I like Valvoline and have used it for years. Anything that says Ashland on the bottle is Valvoline with out the name.
The bit about wearing out the gear has come up before to but don't worry I will not go off again. I use HVHP pumps in EVERY performance engine I build and after 20 + years of building engines I repeat I have never had one of my engines come back with an oil related failure, or for that matter ever come back for more than an adjustment or two, tune ups and oil changes.
I have never had one eat a gear or spin a pin on the distributor shaft.
Install a HD oil drive shaft when you swap the pump.

I purchased a drive shaft from ARP when I put together my motor before installation. Is there a specific shaft that is marked HD or should the ARP driveshaft be HD already?

Funny... I had a case of Valvoline SAE50 race oil sitting in the garage and then someone convinced me to stay with the Mobil1 15W-50. Took the Valvoline back. :)

Will make the change here some time... maybe once the season winds down a little bit...and let you know how it went.

Thanks for all the info!

JP

Just talked to the guy and found that his fuel pump was bad and leaking into the crank case!!!

New pump and a couple oil changes andhe is fine!!

Coosawjack:MECOOL:

Hey Coosawjack:
This problem is not about the oil. Don't think that replacing the 15W-50 you now have in there with some parafin 40 or 50 wt. will solve the problem, it won't. The fact that the oil pressure steadily reduces over time tells me it's not the oil or oil pump.

Bob

Well, I use the 15W-50 Mobil 1. I run around 30 to 40 PSI at idle and 75 to 85 ( peggs the needle ) at high Rs.

Everyone has an opinion, the great thing about this site is, you can, and usually do, get everyone's opinion.

Here's mine. 15 or 20 PSI is too low to safely run an engine.

J.P

That ARP shaft is HD and will work fine.
Let me know what you find out.