Kubs

Last fall I developed a low oil pressure issue on my new engine. The car would idle at <10psi. It had good pressure when I built it (30-35psi at idle) and increased with RPM. The low idle press happened after 6 laps of evaluation in track. I did not push it hard, just kind of drove around. When the engine cooled a little bit idle pressure was around 20psi, but did not climb very much. I figured I would start with the easy stuff and tired 50wt (it had 30wt in it before) oil to see what would happen. Cold idle was now 10psi, but started rising slowly as the car idled for several seconds. I decided to pull the pan and check out the oil pump. I was epecting to see a broken or weak pressure spring. I took it apart and did not see anything bad. I sent it to Melling who checked it out and said the pump was fine, but sent me a brand new one anyway. They said my pump had 34psi idle pressure and the bypass opened at 64psi. Same as the new one they sent me.

Today I installed the new pump and a new filter, thinking a clogged filter (engine assebly lube) might cause pressure issues as well, and ran it again with the 50wt oil. The idle pressure is better, around 30psi, but when I rev the engine it dips DOWN! So pressure is not building. What would cause this? There are no external leaks. What else should I be checking?

Here is a video of the idle and some small revs. Notice the pressure drop when RPM goes up. Ignore the water temp gauge. The coolant needs to be filled more and it was running for less than a minute.

bjankuski

I would suspect your main bearings are toast.

Churchkey

Did the new pump come with a pickup tube/screen or are you using the same one?
I always cut the pick up tube @ a 45* angle then use a long drift etc to roll a flare on the end. Form a sock from metal screen & hose clamp it to the tube.

If the oil pressure gauge is mechanical remove the pressure line & check for an obstruction. If no obstruction check pressure with another known good gauge. If the gauge is electrical remove the sender & check pressure with a known good mechanical gauge.

If the on board gauge, sender, line etc check out ok suggest checking bearing clearances
however & hard to tell from a vid but the motor does not sound like it has been oil starved

What brand E- tach are you using?

Kubs

Can you explain why? I'm not doubting you I would just like to understand. There is no metal in the oil.

The gauge is mechanical going to the port behind the intake. It is in the OEM tee fitting where the original sending unit with the fuel pump switch. I took the line off the gauge and oil flowed out while cranking.

I had to make a pickup for this pan and pump combo. I took and existing one and just re clocked the screen to have the correct cleance. I used the same pickup on the new pump.

The engine was not starved of oil at all. I also have a 3 quart accumulator to help prevent thst, but like I said all my laps were cruising.

The tach is an Auto meter carbon fiber series 5".

If it were bearing clearance wouldn't it stil, build pressure just not as much or not enough? Why would it go down?

Churchkey

Pressure going down is the reason I suggested checking the line to the gauge. A restriction in the line could act like a one way "flapper" valve. The mechanical gauge could be checked with regulated air pressure.



Thanks for the tach info.

WW7

Kubs, I have also heard from mechanics I trust, that if the engine is under load ( as in going up a hill) and you press on the gas, and the pressure drops , that there's a possibility your main bearings are going bad....I would definitely hook up another oil pressure gauge first to make sure that's not the problem before jumping to conclusions...I have had pressure gauges go out in 2 of my cars, so it's not a rarity for this to happen..I have to say the motor sounds like it's running ok.....WW

LTxDave

You said something about a clogged filter and assembly lube. Did you change the oil and filter after initial startup of this engine?

C409

..... By your description it sounds like the pump may be sucking air ... which pump are you using ? and are you certain that the pick-up screen is positioned correctly in the pan ? and certain that your modified pick-up has no pinholes or voids ?

leesvet

You HAVE to start at the pump and think each step thru like oil as it travels and see what the oil will see/ go thru.

The Pan....holds the supply like a tank. It has trays or baffles so the "supply" will stay where it can be picked up by the p/u tube to feed the pump. The sump can store all the oil in a place that's not so easy for the pump to suck up....be sure of the correct pan.

You state your eng run time was some gentle laps then a cool down... then you noticed the problems...
This pan has a tray inside>? could the oil have been slung against the sides and away from the p/u tube/screen ? IF that happened you should have noticed a serious loss in pressure as the pump sucked air.....aka cavitation.
THAT is how we toast mains and other bearings,...Mains need a constant supply of fresh oil....or

Could a bearing have moved? spun? that's usually accompanied with noise...knocking or bumping sounds,.

Rod bearings too....if its so loose that the pressure is escaping....its loose enough to rattle. You'd hear all about it.


next, is the p/u tube in the proper location? depth? is it TOO high off the pan bottom? is it flat against the pan so it cannot pick-up any oil? Is the tube leaking at the mount? the pump body? ANY tiny bit of a leak at a suction line will ruin the pumps ability to move oil. Air is much easier to suck than 50wt.

Now, viscosity...
going to 50 wt...bad idea IMO. IF the pump or pick up was struggling to suck up ANY oil, then making it thicker made it even tougher.

Now the common things...
the pump bypass.....oil that's too think OR has too much pressure against it will be dumped off thru the bypass. This is just a relief valve designed to dump excess pressure so things are not blown apart...filters mostly. If you did not have any kind of bypass....your filter would explode from the high pressure from the thick oil each morning. I've seen a filter that was plumped up like a keg from too much pressure trying to go thru the fine filter medium. Many filters also have their own bypass...
This effectively throws away most of the pressure. Volume too. The engine gets whats left...not enough to survive on for long. This cycle ends when the oil thins enough to flow freely again so the bypass allows it to circulate instead of going straight back to the pan.

If the oil is/was too think to be pushed thru the system, it would NOT BE SEEN AS VERY HIGH PRESSURE on the gauge. Because....the bypass is at the bottom of the system...the gauge is at the top. The gauge would never see or know that there WAS excess pressure because that pressure was dumped long before it ever got close to the OP sensor where it could be measured.... You'd never know. This happens every morning according to the experts. That's why/how cold start is responsible for 80% of all engine wear. The oil is not flowing...yet.

The gauge sensor at the top of the oil system is almost the last place the oil goes before the fall to tank (pan) again. if you see 50 psi from the gauge, the pressure below that at the mains is much higher. Maybe as high as the pump can produce...as the oil travels it looses some pressure everywhere due to "slippage", meaning bearings that ooze a little, seals, valves that all weep oil that's under tension. That's normal.

The oil viscosity changes a BUNCH with temps. AND the trash suspended in the fluid.

50 psi cold WILL certainly be 20-30 psi at normal op temps...or less IF there is wear present. Even when new...parts are not 100% perfect mates...there is always someplace for oil to weep out.

Oil pressure that FALLS when the RPM goes UP indicates a pick-up problem. The pump is unable to get a "bite" on the fluid and move it. That means there is a void being moved thru the oiling system until the pump can once again get a good bite and push more fluid. This is a dangerous time since critical parts are suddenly having to move without the aid of a fresh layer of lubrication...not to mention the heat that instantly builds up when there is no oil (fluid) to collect and carry the heat away for dispersal.

Then the sender(s). These electronic OP sensors can cause as much trouble as they eliminate.
Remember that each of these many sensors are just a measurement of electrical resistance that the dash interprets and displays as numbers. If the resistance is high the dash shows high oil pressure. If the CONNECTION to the oil pressure sensor is dirty and has MORE resistance in the circuit...the dash SHOWS HIGH OIL PRESSURE AS WELL ! Some are the opposite...a broken circuit can show "good" on the dash.

Default for this OP circuit is 80 psi when the wire is d/c. That tells us that dirtier the connection the higher the OP should read.

So, the issues to investigate:
pick-up screen/tube height and tube seal to pump.
pump bypass (unlikely in new pump, same symptoms)
filter bypass, filter housing seals, housing bypass spring
viscosity and temp of oil
sensors/gauge

Always confirm Oil pressure with mechanical gauges. IIRC there is a fitting/port on the filter housing that will accept a mechanical gauge so you can see what the filter is getting....and then compare that to the normal OP sensor port up toward the end of the oiling system.

If it were dangerously low, lifters would rattle, there would be "noise"...
D/c the fuel relay and see what happens. I know that's NOT in the book....but seriously low OP should have trouble setting the OP switch that allows fuel pump operation IF the fuel relay is bad....might help in diagnosing.

and last, pull a main cap and start looking.

My guess is that somewhere in what's been mentioned there is a simple fault...probably in the electrical, sensors, wire, plugs...

Hope something here is helpful.



MORE thoughts...

Does the PSI JUMP up as the throttle is tapped? and falls immediately as if were part of the tach? Instant response to rpm changes? That's a good sign,. Indicates a good tight system. It shows the system is intact with the exception of the leak...that can be anywhere.

Pan is correct? baffles/trays in place?
Seals on/around the oil filter/cooler housing in place? The fittings IN the housing adaptor are all ok and sealed?
Screen not plugged or obstructed with debris?

IIWM,
my next step would be to pull a main cap/bearing and inspect it...see what the bearing looks like and do it NOW before any more damage takes place. IF you have proven to your satisfaction that all the above possible points of failure are OK, then its time to prove that there actually IS a problem and IF it has progressed to doing physical damage to the new parts.

Churchkey

Sucking air = good point.

Had one gen 1 engine with a weird low pressure problem. Turns out the proud owner installed the oil pump using a short corner head bolt. The bolt bottomed in the main cap = the pump was not tight to the cap.

Kubs

Its not under any load, just trying to idle with a little rev. I will look into the gauge for sure. Mine is mechanical though. Have you had electric or mechanical ones go bad?

This is now the 3rd filter on the car. I initially ran the car with break in oil for a little bit, then drained and put in racing oil with new filter. Now I have changed that filter and put fresh oil in. No signs of metal in the oil that I could see.

I am using a Melling Select 10552C. Yes the pickup is positioned properly. When I measured the pickup on the initial assembly it was 3/8" off the bottom of the pan.

I have a Canton RR pan so it does have baffles. I cleaned the pan out before putting it back on and all the baffles move freely the way they should. Like I mentioned already the pickup height is good, and I doubt there would be that much veriation in pump body height that I would have to change the pickup each time I change the pump so I did not check it again.

No knocks, rattles, ticking, or any other noises of concern. It seems to run fine just show low pressure.

I could try 30wt again and see what happens. That would be simple enough. There is no longer a bypass by the filter, just the one in the pump. All the seals are good and nothing is leaking outside the engine.

I have a mechanical pressure gauge and the fuel wiring is all been redone. It would help to confirm it with another gauge. The oil pressure switch directly runs the fuel pump now. I have a toggle switch in the dash for the pump which sends the signal to the pressure switch which then goes through the fues panel to the pump.

Yes the oil pressure change is an instant response to rpm changes. Same time RPM goes up pressure comes down.

Another thing I notice this morning as I tried to show the issue to a friend, that when I shut the car off, the fuel pump kept running for about 5-6 sec AFTER the gauge showed 0psi. As mentioned before the gauge and the switch are reading from the same port, but if the gauge read 0psi why the pump continue to run? The OEM switch (which I am using) shuts off at 7psi correct?


I have an ARP stud holding the pump in place and it torqued down nicely to 45ft/lbs and sealed on the cap. I can investigate further if/when I take the pan off again.


I think I am going to try to go back to 30wt and another new filter and see what happens before I take things apart again.

Thanks for the list of things to check.

fredd1

PVC valve?

Kubs

Removed. Both valve covers vent to a vented catch can.

Kubs

Well, I think I found the issue.... Went to change the oil, and it looks pretty glittery. I didn't notice it before, but the old filter had some bearing material in it as well as the one I just put on. Looks like I'll be doing bearings soon. Thanks for the help guys. Ill be sure to check out all the things you listed while I am under there again.

cohocarl

I e-mailed ARP's tech support about a month ago regarding the depth of the stud going into the cap and possibly bottoming out on the main bearing because when I measured the stud threads, and the threads in the bearing cap, they were very close to the same. Their reply was: "It is ok to back the stud out a little, just don't turn it out an eighth of an inch or more and you should be ok.", so when I torqued the nut down, it didn't bottom out the stud on the bearing.

leesvet

Bunmmer...

sorry to hear that.

But, I have a thought that might be worth your time to follow up on and see. Its a little "after the fact" but it might help prevent a 'next time'...

Its never happened to me, but I have known people that this has happened to...

There has always been debate over high oil pump pressure & volume. One concern was that too much pressure kept the bypass open and flow was lost to the upstairs.

the vol argument might be appropriate in your case......

sometimes, in a very fresh, clean, well made system where everything works right, (assuming that usually not everything does) you can get the fatal effect of the pump moving TOO much oil TOO fast and creating STARVATION IN THE PAN. May be a big pan, but if that pump has it all up top, ............

The argument against high vol pumps is that they CAN move so much oil so fast that the oil does not have time to drain back into the pan for pick-up again...and the pump cavitates and sends bubbles thru the oiling system as it waits for oil to drain back.

The most common solution is a larger capacity pan. That solves the problem in most cases...but the other solution can come in the form of a simple orifice to maintain pressure after the pump, but reduce the vol from the pump. There will be flow, but it will be calculated to match the pans capacity and the engines requirements.
Your pump mfg should be able to help with that. It takes a calculation that I damn sure don;t wanna do...
This is an option because you get to keep the high vol, but you can adjust it down if needed. Some folks just get a lower vol pump...but then that's all it will ever do...can't make it go faster.

The effect of over-pumping is always smoked bearings. First to feel the effect of no/low oil flow, first to fail.
I"d be willing to guess that it only takes a very few seconds of no pressure at 4 or 5000 rpm to skin the mains real good...That microscopic layer of lubrication is so critical at high rpm and heat...

That's the selling point of all the snake oil additives...they can still supply lubrication without flow, for quite some time due to the smaller molecule that can be hidden in the cyl walls and bearing surface even when there is no oil flowing. there IS some science to that stuff...

if you see the silver paint in the oil that you drained...just plan on pulling the bottom apart.

You say the OP moves right with the tach...instant, stable, not sluggish. Tight. You may be the victim of everything working right...and doing what it should....Sounds like its just a good tight system that starved briefly. Unfortunately, that's all it takes.

hate to hear of this happening to anyone....
Good luck ! I'm sure it'll work out

Cliff Harris

The OEM switch closes at 4 PSI according to my FSM. A friend of mine lost all his oil but the oil light never came on (he ran over a large rock on a dirt road in an old Chevy pickup truck). His theory was that the oil pump was putting out more than 4 PSI even though it was pumping air.

Does that gauge actually read zero PSI? Many gauges/senders are very inaccurate at the very low end and sometimes they put a pin in the gauge that the needle hits. I've seen gauges where the lowest they would read is 10 PSI, for example.

C409

..... When you put it back together , make sure the oil pump pickup screen is 1/4" - 3/8" off the floor of the pan , not just the pickup assy but the screen itself , especially if you're using one of the OEM style round pickups that Melling sells for those pumps ... watch the angle of the pickup as well .......... the screen should angle down slightly if at all and never up .....

leesvet

That's a good assessment of the electrical gauge/sensor accuracy...

As long as the circuit is showing 4 psi (whatever measure of resistance that amounts to) the OP switch is gonna stay closed and you get power to the pump. 4 psi ain't much.

These things have such a large 'window' for the scale of measurement that they are more of an approximation than an accurate measurement.
I've had brand new senders show 4 to 12 psi as soon as they were plugged in the harness ! Some times static elec in the harness will make it show 9 psi or more, just at Key ON. Funny thing, its got 17 psi without running but the instant it fires the psi finds a place and levels out...sometimes less than the "off" pressure.

For those that STILL wanna think that's a safety shut-down for low oil pressure.....you're gonna be waiting a good long while for that OP switch to break the circuit when/if you ever lose the oil pump....I wouldn't hold me breath!

Kubs

Thanks for the replies. The pump is only 10% more volume than stock so I doubt if it pumped it all to the head. I have a 7 quart pan and a 3 quart accumulator so that's a lot on reserve. I am going to check the ARP pump stud for sure when it comes apart.

As for the gauge it has a 10 psi mark and a 0 psi mark then a pin to hold the needle.