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Author Topic:   oil pressure drop after warmed up
rockafellz
Gearhead

Posts: 1250
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 04-07-2003 11:32 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
The problem is with a '89 Mustang 5.0

When the car first starts up it has normal oil pressure.When it warms up(after about 5-10 min) the gauge drops to zero.But when you give it any amount of gas/throttle the oil pressure jumps right back up.A new oil pump was installed but it still seems to do it.The motor doesnt make any lifter noises or knocks.

Any ideas as to what it could be?

The mods to the car are: Jet Performance Chip,2 Chamber Flowmasters,March Underdrive Pulleys.

Thanks in advance.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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SteveLaRiviere
Administrator

Posts: 32655
From: Saco, Maine
Registered: May 99

posted 04-07-2003 11:50 AM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Tired engine with excessive oil clearances, I'm afraid. It's bearings time.

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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rockafellz
Gearhead

Posts: 1250
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 04-07-2003 12:01 PM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
Thanks SteveL, Could you emphasize a little on what part of the engine has excessive clearances. Is it the cam bearings? Crankshaft bearings? Oil piston rings?

Continually learning so I'm trying to picture which part of the engine has wore out.

Thanks in advance.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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SteveLaRiviere
Administrator

Posts: 32655
From: Saco, Maine
Registered: May 99

posted 04-07-2003 12:24 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Sorry about that. The most likely culprit are the crankshaft main bearings and/or connecting rod bearings. As they wear, the oil clearance, which is the space between the crankshaft journals and main/rod bearings gets larger and allows the oil to bleed out, and that's how you lose your oil pressure. When the engine is cold, the oil is thicker and doesn't bleed out as quick.

It may be possible to fix this without a rebuild. It all depends on the condition of the crankshaft journals. You need to remove the oil pan, and remove and inspect each bearing and journal. If each respective journal still looks good, {no bad scoring or rough surfacing} you can try replacing the bearing {look at the back side of each bearing to read what undersize it is} and see what you end up with for oil clearance using Plastigauge, which is a type of clay string you lay across the engine bearing, reinstall and torque the bearing cap, then take it apart again to compare the width of the crushed Plastigauge to a scale and determine oil clearance.

{This was a common job for me at the Buick dealership, as the guys that grind crankshafts in Flint seemed to smoke lots of reefer. }

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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Tim Cash
Gearhead

Posts: 228
From: Clarksville, TN, U.S.A.
Registered: Dec 2001

posted 04-07-2003 10:05 PM     Click Here to See the Profile for Tim Cash   Click Here to Email Tim Cash     Edit/Delete Message   Reply w/Quote
Erik, I had a very similiar (Almost identical) problem with my 88GT. It is/was exactly as Steve stated in respect to my car.

On the brighter side, the wife has let me go ahead and purchase a new engine in lieu of rebuilding the old one with limitations.

Good luck
Tim

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Moneymaker
Administrator

Posts: 19611
From: Lyons, IL, USA
Registered: May 99

posted 04-07-2003 10:22 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Are you using the original factory guage for testing? If so, I would try a mechanical guage test before you condemn the motor.

------------------
Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00,'01,'02,&'03
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com

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rockafellz
Gearhead

Posts: 1250
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 04-08-2003 12:58 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
Thanks for the in depth description SteveL!! One more question. Where is the oil pressure "information" collected? Does the oil get pushed through the insides of the crankshaft, thus building oil pressure (readings)? Do the bearings serve as somewhat of a "cap" to prevent oil from leaking out of the journal/bearing assembly, explaining the reason why the loss of oil pressure? I hope I got that right.

Alex, the problem is on a "prospective" fox body car that I was eyeing.

Thanks in advance. Again.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

[This message has been edited by rockafellz (edited 04-08-2003).]

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rm302 boss
Moderator

Posts: 578
From: Austin Texas
Registered: Dec 2002

posted 04-08-2003 02:10 AM     Click Here to See the Profile for rm302 boss   Click Here to Email rm302 boss     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Moneymaker:
Are you using the original factory gauge for testing? If so, I would try a mechanical gauge test before you condemn the motor.


Just what i was thinking, hook it up to a good oil pressure test gauge. Don't condemn a motor for a bad gauge or sensor..

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rm302 boss
Moderator

Posts: 578
From: Austin Texas
Registered: Dec 2002

posted 04-08-2003 10:43 PM     Click Here to See the Profile for rm302 boss   Click Here to Email rm302 boss     Edit/Delete Message   Reply w/Quote
You have a 5.0 in there?? If so i would say cam bearings.... i have seen it a bunch..
Rene

[This message has been edited by rm302 boss (edited 04-08-2003).]

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SteveLaRiviere
Administrator

Posts: 32655
From: Saco, Maine
Registered: May 99

posted 04-09-2003 09:29 AM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Alex is right, you should verify the pressure reading first, although varying with temperature sure points a finger.

Think of the oil clearance as a controlled leak. When the clearance gets too large, the pressure drops. In fact, one of the things I used to do to quickly find a bad bearing is I used to pressurize the oil system and gm actually had a drop-per-second spec that would help you pinpoint the bad bearing. You usually didn't even have to count, the bad one would usually squirt. All you did was hook an air line at the oil sender port and hit it with 20-30 psi. That would also point out the cam bearings if they were bad.

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

Please remember our sponsors,
Mustangs Plus, NPD, Osborn Reproductions, MyFordPerformance.com, and FordRamAir.com

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Moneymaker
Administrator

Posts: 19611
From: Lyons, IL, USA
Registered: May 99

posted 04-09-2003 05:46 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
My own McLaren had very week indicated oil pressure via the factory guage and sender.
I replaced the sender to no avail, then tested the guage and replaced it.
We plugged a mechanical guage directly into the block and it would never drop below 25 lbs hot at idle.
Problem turned out to be the hexagon tube extension that screws into the block for the bell oil sender. Something had partially plugged it and caused a restriction.
Put a new tube in and drove the car on an 800 mile round trip to northern Michigan.

------------------
Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00,'01,'02,&'03
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com

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