Got a strange thing happening with my AMX. When rolling along slowly I'll drop it in 1st and stomp the gas. About one second afterwards the oil pressure drops from 56 lbs to 40 lbs for a split second then the pressure recovers. It's never done this before. I've got seven quarts of oil in a Canton eight quart pan. Also has a windage tray.

I find it hard to believe in that short time the pan gets emptied into the valve covers. This engine wraps RPM pretty quickly as it's supercharged.

Possibly the overpressure valve is opening too far? Maybe the oil is aerating somehow?

Ideas anyone?

Thanks,

-Steve-

My guess is the pick up needs to be a tad closer to the rear of the pan.

I would not panic.

I have the Canton eight quart pan. The dipstick shows full with seven quarts. Should be more than adequate. Never had trouble with a stock pan.

This may require a teardown. Might be a few LS engines in the local salvage yard.

-Steve-

Momentary pump cavitation, pressure drops, then quickly recovers?   Does it happen at a specific oil temp? 

Any changes to crankcase venting, oil grade/brand, oil filter recently?

Assuming still reading pressure at stock location after the filter?   Does it have the stock filter bypass, plugged bypass, or filter with a bypass?  Filter bypass is there to handle sudden oil surges / cold oil that the filter can't handle, to prevent starvation (pressure reading in bypass would be lower ... but pressure would have dropped already due to filter restriction for it to go into bypass).

Also of interest, the relief valve spring cavity is vented to the oil pump inlet (pump suction).   Theoretically, if the pump could momentarily pull full vacuum, the relief would open at 14.7 psi lower than normal and pressure momentarily drop.  Note the stock relief starts to crack open around 40-45 psi.  FWIW, I changed the relief spring cavity venting on my stock pump years ago to vent to crankcase instead of pump inlet, but can't say for certain if it made any improvement (shared details on Fran's Forum).

But if it only drops momentarily and quickly recovers, don't see a big concern.   Owner's manual actually says a momentary drop in pressure is normal under certain conditions - likely to keep the Service Department from being inundated by owners who notice pressure fluctuations ... and why actual gauges were eliminated in newer cars.

But if it's something new that hasn't happened before, can understand the concern.   Especially with your history of multiple engine builds chasing an ideal pressure.  Best to check for any recent changes and maybe fit a new filter as the most economical option.

Hope this helps, RD

Don't go by the dip stick unless you know absolutely it's original.

An 8 quart pan should likely have 8 quarts in it. Likely 1/4" higher then the full mark on your dipstick!

Oil pressure fluctuations are also normal, so if you want to run 7 quarts, then that's fine.

Replaced the oil pressure gauge with a spare, same thing.

Took it out and tried your tests. While driving at 30 MPH I slipped it into neutral and wrapped up the RPM north of 6,000. No pressure drop.

Uphill acceleration showed a larger drop in pressure versus downhill so that suggests the rush of oil to the rear of the engine is the cause. So that being said how is it related? Aeration from the oil hitting the crank suddenly? Starvation? The pan has spring loaded internal baffling, maybe it's fallen apart?

Since the engine has the internal oil line I have to trim out the center of the intake gasket so it fits. Done this on multiple engines in the past so I doubt that's part of the problem but thought I should mention it.

Here are some reference photos.

-Steve-

Also applies to the valley return holes.

So momentary oil starvation until oil starts returning via the front head/valley oil returns.

J

Tried that too. No change. Starting to wonder if this has always been happening but I simply never noticed. Also wondering if a stock type pan baffle in the Canton pan would be helpful.

-Steve-

Are there trapdoors on those baffles?  My pan has no baffling down low. I don’t have any pics but seem to remember a shelf like the stock pan at the rear of the sump. I can’t see how you could be draining the  pan on such a short rpm blip. I’ll run the 1/4 in a rpm range of 6500-7400  the whole time. No pressure drop or drain back issues. What weight oil and filter and in stock location?

As others have offered, try a bump in oil level. That is easy. Sure windage blah blah, but really, your issue seems less likely to be windage or drainback. It’s an instantaneous thing, and those above mentioned things would take more steady state operation to occur. 

The oil will stack up at 45 degrees under your anti gravity launch. (@1G) and with the car lifting the front a bit, and the sudden surge, you can bet that oil slams aft and then sloshes. All while drawing serious gulps of oil from the pickup, creating a vortex that may exceed the sloped slug of oil. 

To me, the baffle you show in your pic seems inadequate, IMO.

The idea of moving the pickup aft as suggested, to me, may also be a good idea, but more difficult. Maybe canton could do better there too. Possible. 

I do think it’s possible that your relief spring is weak, and may not recover quickly once you blow it off a bit with a quick rap.

That was my thought.  I know there are a few common sticks with different full lines on them.  If the pan is 8qts, I'd do an oil change with 8 qts and put a new "full" indicator on the stick.  It would seem most likely to be that or the baffle.

This is the Canton pan: http://www.jegs.com/i/Canton-Racing-Products/074/15-554/10002/-1" rel="nofollow - https://www.jegs.com/i/Canton-Racing-Products/074/15-554/10002/-1

Using their pickup tube: http://www.jegs.com/i/Canton-Racing-Products/074/15-555/10002/-1" rel="nofollow - https://www.jegs.com/i/Canton-Racing-Products/074/15-555/10002/-1

I believe it has spring loaded trapdoors. 10W-30 oil. Purolator filter in the stock location.

-Steve-

Are the 7 quarts with or without the filter?

They built the pan and doubt they would mislead on how much oil the pan holds installed on an AMC V8.

Running sticky Mickey Thompson rubber, car hooks pretty good even on the street. It'll pull the front wheels and inch or so on a prepped surface.

Tried the extra quart of oil, no change.

Think I'm just gonna run it. If I hear a rod knocking I'll tear it down.

-Steve-

When I first got the Canton pan I put water in it a quart at a time to check the level.

Four quarts:

Five quarts:

Six quarts:

Seven quarts:

Eight quarts:

So you may be running at the 6 quart level in your pictures.

I think its good that several people have indicated not to worry about it.

Mike

J

bwamx wrote: Nobody has asked I don't believe . Did you check or verify the location of the oil pickup to the bottom of the pan ?

Yes, used clay to measure and make sure it's not sitting against the bottom of the pan.

-Steve-

If he has 56 PSI and it drops to 40 PSI when he floors it, please explain how the pressure relief spring is an issue?  (it's not)  It was just 56 PSI two seconds prior.