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Oil pressure light at higher speeds - Eagle |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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Good oil pressure at low RPM but not at high RPM tells me that either your oil pickup in the oil pan is plugged/restricted, or the oil drain passages that drain the oil back to the oil pan from the cylinder head are plugged/restricted. This happens a lot on Eagles because of the plastic valve cover. The valve covers leak a lot, so people paste obscene amounts of silicone sealer on them in an attempt to make them seal. The sealer breaks loose and plugs things up.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Plastic valve cover depends on the year. Not all years had that...... luckily.
I've seen one other thing do this - short drives, lack of oil changes. I wish I had photos of the cars where I'd pull a valve cover and oil would pour down the head. The oil had turned to a caked-on mess up in the head and it happened with cars that seldom saw long drives (short commutes, no thermostat or a cold thermostat) and infrequent oil changes. in one case it was so bad I had to use a long drill bit and drill through the crud, then flush things out several times. It was almost like carbon plugging the oil drain-back holes in the heads. |
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73Gremlin401
Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 946 |
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I've had this occur on 2 AMC 6 cyls, 1 a 77 258, the other an 84 258. in one case, it was the sending unit, in the other it was the drainback holes in the head being sludged up with broken umbrella seals, and a heinous amount of blue RTV from the PO trying to seal up....you guessed it...the plastic valve cover. I've never had an AMC 6 oil pump fail me, nor have I ever had an oil filter on an AMC 6 clog up, but that's certainly not out of the realm of possibility. So I do agree with several of the other suggestions - swap out the oil filter, put in a new sending unit, check your engine ground strap, and if the light still comes on at speed, I'm going to go with 99.5% certainty that most of the oil is sitting inside the valve cover at high sustained RPM due to the drainbacks being clogged with crap. Another good clue to this possibility would be an air cleaner full of oil from the valve cover breather backing up and letting excess oil get pulled up into the air cleaner.
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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Actually a well-built, or rather properly built, AMC 258 will put a LOT of oil up on the top end in short order.
When I built my 4.0 (same as a 258) I used a speed handle and bit to run the oil pump by hand and achieved 50 psi turning it by hand and had oil literally flowing over all rockers and streaming down pretty quickly. That's by hand. So anything like bad valve seals (broken up and plugging holes - yeah, that happens a lot) or sludge, whatever, means you have a lot of oil up on the head at highway speeds. The oil is running off these pretty fast and I was turning the pump by hand - |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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AMC's have big oil pumps. They are good at emptying their oil pan faster than the oil can drain back into it.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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73Gremlin401
Supporter of TheAMCForum Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 946 |
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A trick I learned from the Team Highball guys back in the late 70s was their rather ingenious, near-zero cost oil control 'kit' - when installing the pushrods, they would stuff a pipe cleaner up inside each one. That created just enough resistance to slow the flow up to the rockers, without stopping it completely. I did it to 2 motors I built, and it worked like a charm. On the first try, a few of the pipe cleaners got pushed through the oil hole in the rocker arm an inch or two over a couple thousand miles, but didn't stop the flow of oil - there was still plenty of seep-through to keep everything lubricated. The 2nd time around, I kinked the pipe cleaners a little as I shoved them up through the pushrods, and never had that happen again.
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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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A trick I learned was that AMC engines built to the tight side of specs with no physical issues and good maintenance was that I'd never have oiling issues.
Seriously, never had any issues with any AMC 6 (other than in the very old days, like in the late 60s, early 70s, when there were the shaft rockers and short drives and oil not as good as it is today - we'd have old people bring in their Ramblers that had in-town driving only and a highway drive was maybe 50 mph for a half hour) As long as the oil is clean, the filter is quality, the engine is build to specs, I prefer to go the tighter side when I have complete control over it, an AMC 6 just won't give issues until or unless something extraordinary takes place or goes wrong. So I've never seen any reason to do amy sort of mod to any AMC 6, and frankly, on the 8s it's just a matter of attention to detail. Maybe that's my secret - all of my bosses over the years in every case on every review I was rated high on "attention to detail" - sometimes it drove them nuts because things had to be perfect, but hey, like my wife says - if it's worth doing, it's worth doing right.
So I've had no reason for any restrictions or mods on rocker arm oiling (again, other than EARLY Ramblers, but then even AMC talked about that) IF the engine is right and in specs and things are as designed, there won't be issues like this. The OP is dealing with a fault, something wrong, not a design flaw, so has no reason to modify anything, only check the pressure with a gauge, etc. (we have had a couple of guys talk about filters coming apart inside, so we did mention "could be filter) IF there's "too much oil" on top, then there's a fault or issue somewhere that needs to be fixed, causing that oil to stay up there. |
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Midnight Rambler
AMC Addicted Joined: Jan/17/2011 Location: SoCT Status: Offline Points: 1670 |
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It was just the sending unit on my 4.0 that has 204K on it. Cheap, easy, and can't hurt.
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'66 American 440 Convertible 290/M-40/AMC 20 3.15/PS/PB '04 Jeep Wrangler X Rocky Mountain Edition 4.0 5sp |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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Aren't the new lifters for AMC engines a thousandth or so smaller than the original lifters and allow more oil to leak between the lifters and their bores? I seem to recall seeing that somewhere. Of course, worn lifter bores don't really help and not too many people are re-machining the lifter bores in their block to fix that.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16611 |
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