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Unread 09-09-2013, 06:19 AM   #16
82JeepCJ7
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My 70psi at engine start up is with a stock spring and 10w40 oil. This is on a newly machined engine as well. Over time as the clearances open up a bit, I expect this to drop to around 50psi at start up and about 20psi at idle. That is what typically happens. I have around 100 hours on this motor now and those numbers have dropped off a couple PSI but nothing drastic.

As mentioned above, proper flow is important to keep the cam and main bearings happy. If you get a chance while rebuilding a motor, take your time on the oiling system and make sure the passages are clear of any casting flashing, etc. I spent close to a week on my passages. I snaked a bore brush down the passages as far as I could. I was surprised at how much junk came out of there even after having the block hot tanked. This kind of work is of no cost to the builder but time. But it's time well spent.

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Unread 09-09-2013, 06:48 AM   #17
Matt1981CJ7
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Quote:
Originally Posted by jeepdaddy2000 View Post
I'm going to be a bit of a dissenting voice here.
In my experience, a well built engine with a stock oil pump will hold a (relatively) steady pressure (usually about 40LBS) at both idle and service RPM's; hot as well as cold. This comes from the proper tolerances throughout the engine being tight enough to hold leakdown to a minimum. A stock pump will hold a steady pressure at idle when warm, with the bypass valve dumping the excess pressure at colder temps and higher RPM's.
Large fluctuations in pressure during cold operation and RPM changes usually points to some pressure leakage somewhere in the system, and 70LBS, as indicated above indicates a high pressure bypass spring has been installed. These can be bad on the cam and distributor gears due to the excessive force necessary to maintain that high of a pressure.
I am a big fan of good pressures at idle, since many of these engines are subjected to very low engine speeds during wheeling. A pressure below 30LBS at idle can become 5 or 6 LBS (or less) during a low speed lugging session in the rocks or other technical areas where the RPM's may be forced to drop well below norms (one of the reasons I run a high volume pump).
In theory, I agree with you. A properly operating system should maintain a consistent pressure regardless of engine temp or RPMs. That said, I've never seen a single AMC engine that did that.

Like 82, I spent hours cleaning and de-burring the oil passages on my 360 build. I even bored the main galley larger. I was meticulous about achieving the proper tolerance on the brand new pump. I also used the special Gyptol paint on the engine's inner castings to improve oil flow.

When it was all said and done, my 360's oil pressure acts exactly like any other AMC engine I've seen. It's 50-60# at idle while warming up, drops to around 20# at idle when warm, and runs between 40-50# while driving.

Matt
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Unread 09-09-2013, 07:35 AM   #18
LeePrather
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Quote:
Originally Posted by Matt1981CJ7

In theory, I agree with you. A properly operating system should maintain a consistent pressure regardless of engine temp or RPMs. That said, I've never seen a single AMC engine that did that.

Like 82, I spent hours cleaning the oil passages on my 360 build. I even bored the main galley larger. I was meticulous about achieving the proper tolerance on the brand new pump. I also used the special Gyptol paint on the engine's inner castings to improve oil flow.

When it was all said and done, my 360's oil pressure acts exactly like any other AMC engine I've seen. It's 50-60# at idle while warming up, drops to around 20# at idle when warm, and runs between 40-50# while driving.

Matt
Agreed...same here
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Unread 09-09-2013, 09:17 AM   #19
86cj74.2L
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I've never seen a constant oil pressure on any engine after oil is warmed up. I've seen a few.

With almost 30,000 on Grammys 258 its 65-70 warming up. 55-60 driving drown the road and idle is 18-22 depending on how hot the oil is.
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Unread 09-09-2013, 09:24 AM   #20
LumpyGrits
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I have such a set up with a buzzer & flashing light.
It's the same set up as used in semi-trucks.
LG
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Unread 09-09-2013, 09:27 AM   #21
LumpyGrits
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Quote:
Originally Posted by jeepdaddy2000 View Post
I'm going to be a bit of a dissenting voice here.
In my experience, a well built engine with a stock oil pump will hold a (relatively) steady pressure (usually about 40LBS) at both idle and service RPM's; hot as well as cold. This comes from the proper tolerances throughout the engine being tight enough to hold leakdown to a minimum. A stock pump will hold a steady pressure at idle when warm, with the bypass valve dumping the excess pressure at colder temps and higher RPM's.
Large fluctuations in pressure during cold operation and RPM changes usually points to some pressure leakage somewhere in the system, and 70LBS, as indicated above indicates a high pressure bypass spring has been installed. These can be bad on the cam and distributor gears due to the excessive force necessary to maintain that high of a pressure.
I am a big fan of good pressures at idle, since many of these engines are subjected to very low engine speeds during wheeling. A pressure below 30LBS at idle can become 5 or 6 LBS (or less) during a low speed lugging session in the rocks or other technical areas where the RPM's may be forced to drop well below norms (one of the reasons I run a high volume pump).
Maybe with a built "blue-printed" engine, you might see this for a time.
Not goanna happen with factory built, and no need to either.
LG
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Unread 09-09-2013, 10:41 AM   #22
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Quote:
Originally Posted by LumpyGrits View Post
Maybe with a built "blue-printed" engine, you might see this for a time. Not goanna happen with factory built, and no need to either. LG
Lumpy,

I think modern-day engines will keep a consistent oil pressure. My Tundra's gauge has never moved from slightly below the half way mark in 100K miles.

I just don't think the engineering on these old AMC engines was quite as sophisticated as what we have now.



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Unread 09-09-2013, 11:00 AM   #23
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I would be more impressed with how many people have an oil pressure switch installed with a horn or alarm to warn of very low oil pressure.
just saying....
No buzzer or idiot lights, but my fuel pump shuts down when oil pressure drops to 10psi... Are you impressed?
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Unread 09-09-2013, 11:03 AM   #24
LumpyGrits
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AMC engines were 'loose' to be sure.
Foreign made engines are 'tight'. One of the reasons the makers push 5W-20/5W-30 oils and such.
My CJ has only seen Castrol 20W-50, from the first oil change. 28 yrs. later, it now has 119K driven miles, and shows(hot oil)64 psi at 2500rpm/28 psi @ idle, via a FAA certified oil pressure gauge use for this testing.
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Unread 09-09-2013, 11:22 AM   #25
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Originally Posted by Spieg8 View Post
No buzzer or idiot lights, but my fuel pump shuts down when oil pressure drops to 10psi... Are you impressed?
Sure hope that engine doesn 't 'quit' when back'n down a steep incline.
You should have an 'override' built in.
LG
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Unread 09-09-2013, 11:30 AM   #26
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Originally Posted by Spieg8 View Post
No buzzer or idiot lights, but my fuel pump shuts down when oil pressure drops to 10psi... Are you impressed?
My carburetor does something similar, when the incline is too steep it stops the flow of fuel.

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Unread 09-09-2013, 12:21 PM   #27
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The grand Cherokees after 2003 kept the pressure gauge. But its now driven by a idiot switch. If pressure is above their minimum. It shows around 50psi.
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Unread 09-09-2013, 02:59 PM   #28
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Originally Posted by LumpyGrits View Post
Sure hope that engine doesn 't 'quit' when back'n down a steep incline.
You should have an 'override' built in.
LG
Yep... actually I hope it doesn't quit under any circumstances. If it ever does though, it's pretty simple to connect two wires to bypass the pressure switch.
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Unread 09-09-2013, 03:10 PM   #29
LumpyGrits
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That's why you should have an override switch in it now.
You may not have time to re-wire around it.
DOT spec for an override in commercial vehicles, BTW. That should say something.
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Unread 09-12-2013, 11:15 PM   #30
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Originally Posted by LumpyGrits View Post
Maybe with a built "blue-printed" engine, you might see this for a time.
Not goanna happen with factory built, and no need to either.
LG
Odd....
I've rebuilt a number of engines of all makes (including a 304 and 401) and have never had an issue with steady oil pressure at idle. While some were mildly "built", none were blueprinted. All main and rod tolerances were right and the cam bearing clearances were spot on. Oil pumps were bypassed at around 40LBS and the running pressure remained within a few pounds of that number, both warm and cold.
But perhaps I was just lucky.....
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