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Oil pressure drops at idle

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DoctorC
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Oil pressure drops at idle

Post #1 by DoctorC » Fri Aug 30, 2019 2:57 am

Hi all,
So a couple hundred miles ago I put in ~40% of a can of seafoam in the oil and ran the engine for about 100 miles over a week. Then i changed the oil. During that week I noticed that, once the car warmed up, the oil pressure would slowly drop to the min on the gauge when at a stoplight. The pressure would quickly return to normal (~30% on the gauge) once the revs came up. Next stoplight, same thing.

I assumed the seafoam had worked some gunk loose, and was highly diluting the mix making it too thin. I assumed this would normalize after the oil change.

I changed the oil and filter and it's still going on. Oil level seems fine. And it only happens after the car warms up. I'm running Napa 10W40.

In all fairness, it may have been happening before i just never noticed. I'm rather new to the car. When i pulled the valve cover, it does not appear starved since there was oil on all the springs.

Should I be worried?
1967 Cherry Red Mustang
Weber 32/36,
MSD 6AL+MSD Coil,
Duraspark 2 dizzy

chero1369
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Re: Oil pressure drops at idle

Post #2 by chero1369 » Sat Aug 31, 2019 7:07 am

So,what are you calling min.?30# 15#? And how old is the build?
Had a 144 run for a year with rod knock and 50w oil,before I tore into it.
Check gauge and line for air first.

I replaced an oil pump I didn't have to because of a China gauge.
Joy!

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chad
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Oil pressure drops at idle

Post #3 by chad » Sat Aug 31, 2019 9:22 am

to me the oil pressure drops BECAUSE it's at idle.
Isnt that normal?
Is this a "idiot' guage or duz it have actual gradients?
Duz it have actual Lbs Pressure? or just a needle w/colors behind?
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

DoctorC
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Re: Oil pressure drops at idle

Post #4 by DoctorC » Sat Aug 31, 2019 11:19 am

It's the idiot gauge. Standard 67 mustang stuff. All the gauges are guess gauges :bang:

The engine has been rebuilt, and from the looks of the cylinder head, recently. When I bought it I had a mechanic drop the pan and he said there was no sludge and that it looked very clean. I only did the sea foam cuz I had a tick. Whatever it was it went away with the flush.

Maybe it ended up in the pan? Clogging the filter? Another option I've been reading is that my engine wants a different oil grade.

Maybe it's too thin when hot?
1967 Cherry Red Mustang
Weber 32/36,
MSD 6AL+MSD Coil,
Duraspark 2 dizzy

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bubba22349
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Re: Oil pressure drops at idle

Post #5 by bubba22349 » Sat Aug 31, 2019 11:47 am

:beer: Yes in my opion you would need a different oil grade, these old engines when new used a straight 30 weight. Their bearing clearances tend to be a bit much even when being rebuilt to be using the thiner modern oils designed for the tighter bearing clearances of late model engines. Then on top we also need to add into the mix the ambient air temps in the area where the cars engine is operated. Good luck :thumbup: :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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wsa111
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Re: Oil pressure drops at idle

Post #6 by wsa111 » Sat Aug 31, 2019 10:06 pm

Put a real oil pressure gauge on your engine & let us know the readings.
If your idle oil pressure goes below 10 psi when hot.
As Bubba stated go with a heavier oil or overhaul the engine with tighter tolerances.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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DoctorC
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Re: Oil pressure drops at idle

Post #7 by DoctorC » Tue Dec 03, 2019 5:51 pm

Update:
So I changed the oil to 10W30 (from 10W40) to see if that helps. It didnt. Then I drove 500 miles to Napa. Halfway there my oil pressure went to zero. Boom. I panicked, looked in the rearview mirror dreading a giant black line behind me. Nothing. Engine sounded fine.

Pulled into the next Autozone and bought a new sender. Done. Was just a bad sensor. Correlation, not causation.

So, now I know that, should I go back up to 10W40? Or keep the 10W30 on the next oil change? I read somewhere you should always gofor the thickest you can get away with...
1967 Cherry Red Mustang
Weber 32/36,
MSD 6AL+MSD Coil,
Duraspark 2 dizzy

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wsa111
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Re: Oil pressure drops at idle

Post #8 by wsa111 » Tue Dec 03, 2019 7:19 pm

If your oil pressure is back to normal, just stick with the 10W-30.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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StarDiero75
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Re: Oil pressure drops at idle

Post #9 by StarDiero75 » Wed Dec 04, 2019 3:59 am

DoctorC wrote:Update:
So I changed the oil to 10W30 (from 10W40) to see if that helps. It didnt. Then I drove 500 miles to Napa. Halfway there my oil pressure went to zero. Boom. I panicked, looked in the rearview mirror dreading a giant black line behind me. Nothing. Engine sounded fine.

Pulled into the next Autozone and bought a new sender. Done. Was just a bad sensor. Correlation, not causation.

So, now I know that, should I go back up to 10W40? Or keep the 10W30 on the next oil change? I read somewhere you should always gofor the thickest you can get away with...

Correction, run the thinnest stuff you can get away with. Heavier oil takes longer to reach the top of the engine and it takes longer for it to start circulating. But too thin is not good due to larger tolerances. Thats why the older stuff usually runs 10w30/40 and not 5w20 or 0w-20.
--1965 Ranchero w/1966 200, dual friction diaphram 9" Modern Driveline clutch and billet flywheel all balanced, 1985 SVO WC T5 with front shift, 1966 2.8 Ford 8", Weber 32/26 with VI adapter, CRT Performance HEI.
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Econoline
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Re: Oil pressure drops at idle

Post #10 by Econoline » Wed Dec 04, 2019 3:22 pm

StarDiero75 wrote:
DoctorC wrote: I read somewhere you should always gofor the thickest you can get away with...

Correction, run the thinnest stuff you can get away with. Heavier oil takes longer to reach the top of the engine and it takes longer for it to start circulating. But too thin is not good due to larger tolerances. Thats why the older stuff usually runs 10w30/40 and not 5w20 or 0w-20.


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DoctorC
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Re: Oil pressure drops at idle

Post #11 by DoctorC » Wed Dec 04, 2019 4:42 pm

Thanks guys!
1967 Cherry Red Mustang
Weber 32/36,
MSD 6AL+MSD Coil,
Duraspark 2 dizzy

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chad
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Re: Oil pressure drops at idle

Post #12 by chad » Wed Dec 04, 2019 4:55 pm

Econoline wrote:+1

ahhahahaaa I wuz thinkin "pressure all ways drops @ idle"....
"Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt" turbo2256b » 1/16/2017
Chad - '70 LUEB on '77 frame (i.e. PS, D44, trapezoidal BB 9", 4.11), 250, NV 3550 & DSII to B transplanted, "T" D20/PTO, 2" SL, 1" BL, 4 discs, 33"X15", tool boxes, etc. Seeking: Hydraulic gear motor for Koenig pto. chrlsful@aol.com (413) 259-1749

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