TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC V8 Engine Repair and Modifications
  New Posts New Posts RSS Feed - Oil Pressure Temporarily Drops On Acceleration
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Oil Pressure Temporarily Drops On Acceleration

 Post Reply Post Reply Page  123>
Author
Message
Rebel Machine View Drop Down
AMC Addicted
AMC Addicted


Joined: Jul/03/2007
Location: Western Il
Status: Offline
Points: 4712
Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Topic: Oil Pressure Temporarily Drops On Acceleration
    Posted: May/13/2022 at 7:02pm
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-

Back to Top
Boris Badanov View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Dec/14/2013
Location: NH USA
Status: Offline
Points: 4020
Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 7:39am
Oil stacking up at the back of the oil pan is the likely culprit.
My guess is the pick up needs to be a tad closer to the rear of the pan.

I would not panic.

Gremlin Dreams
Back to Top
Trader View Drop Down
AMC Addicted
AMC Addicted


Joined: May/15/2018
Location: Ontario
Status: Offline
Points: 4447
Post Options Post Options   Thanks (1) Thanks(1)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 7:49am
Beyond agreeing with Boris, why do you only put seven quarts of oil in an eight quart oil pan?
Back to Top
BassBoat View Drop Down
AMC Addicted
AMC Addicted


Joined: Aug/29/2008
Status: Offline
Points: 1481
Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 3:04pm
I saw the heading on your topic, I had exactly that problem on my AMX.  However the cure in my case was the Canton pan.  I think Boris and Trader are on the right track.  I have an old Milodon with external lines and swivel pickup that chases the oil.  440 source makes a swivel pickup that is about half the cost of the Milodon.  A pickup that swings back on accel and forward on deccel might solve your problem.

Back to Top
Rebel Machine View Drop Down
AMC Addicted
AMC Addicted


Joined: Jul/03/2007
Location: Western Il
Status: Offline
Points: 4712
Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2022 at 8:35pm
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-



Back to Top
JGRANTAMX View Drop Down
AMC Addicted
AMC Addicted


Joined: Jun/02/2017
Location: NH
Status: Offline
Points: 990
Post Options Post Options   Thanks (0) Thanks(0)   Quote JGRANTAMX Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 10:39am
 IIRC your engine RPM limit is about 5800? So if you bring the RPM's up a little slower and hold 5800 for a few seconds does the pressure dip? If you duplicate the quick RPM wind up in neutral from holding 3500 to 5800 does the oil pressure dip then, does it matter if you are going up or down a hill? These are some of the things I would try to narrow down the problem before taking it apart.

J


Edited by JGRANTAMX - May/15/2022 at 10:43am
Back to Top
Red Devil View Drop Down
AMC Addicted
AMC Addicted


Joined: Jul/10/2007
Location: Canada
Status: Offline
Points: 1707
Post Options Post Options   Thanks (0) Thanks(0)   Quote Red Devil Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 2:32pm
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




Edited by Red Devil - May/15/2022 at 2:53pm
Back to Top
Trader View Drop Down
AMC Addicted
AMC Addicted


Joined: May/15/2018
Location: Ontario
Status: Offline
Points: 4447
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 2:56pm
I have 3 dipsticks here and all are different lengths, 24" Jeep, 20-1/2" and 20-1/4" AMC. All different to full mark also, but within a 1/4".
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.

Back to Top
Rebel Machine View Drop Down
AMC Addicted
AMC Addicted


Joined: Jul/03/2007
Location: Western Il
Status: Offline
Points: 4712
Post Options Post Options   Thanks (0) Thanks(0)   Quote Rebel Machine Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 3:51pm
Originally posted by JGRANTAMX JGRANTAMX wrote:

 IIRC your engine RPM limit is about 5800? So if you bring the RPM's up a little slower and hold 5800 for a few seconds does the pressure dip? If you duplicate the quick RPM wind up in neutral from holding 3500 to 5800 does the oil pressure dip then, does it matter if you are going up or down a hill? These are some of the things I would try to narrow down the problem before taking it apart.

J


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-










Edited by Rebel Machine - May/15/2022 at 3:55pm
Back to Top
Trader View Drop Down
AMC Addicted
AMC Addicted


Joined: May/15/2018
Location: Ontario
Status: Offline
Points: 4447
Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2022 at 5:24pm
Another possibility would be rush of oil to the rear of the rocker covers and the front head oil returns are not doing anything going uphill. 
Also applies to the valley return holes.
So momentary oil starvation until oil starts returning via the front head/valley oil returns.
Back to Top
 Post Reply Post Reply Page  123>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.078 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or