Oil pressure dropping
07-19-2020, (Subject: Oil pressure dropping ) 
Post: #1
Oil pressure dropping
Hello to all during this hot stretch,
2009, T8, ISX550, 326000 miles, 14400 hours, empty weight 52K, loaded usually 65K to 90K often up to 130K but has been up to 167K, and once 232K.
Oil pressure has been dropping last 4-4500 miles 68mph, 1700rpm oil 39psi is now 33psi hot.
Hot idle oil psi now 16psi was always over 20psi. No power difference, no sound difference.
Was ready for oil change, 10 to 12K service intervals, so changed oil, made no difference. Changed oil sending unit, no difference.
So am I in trouble just over the next hill?? just keep an eye on the oil press?? tear down the engine, pull rocker cover chk cam, pull pan chk rods and mains??
Any words of wisdom?
Thank you.


User's Signature: Heavy Towing/Recovery makes the juices flow!
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #2
RE: Oil pressure dropping
What's you oil temp been?


User's Signature: Warranty??? Yeah right, I am the warranty!!!
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #3
RE: Oil pressure dropping
What's oil pressure when cold start up?


User's Signature: 2015 Kenworth T660
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #4
RE: Oil pressure dropping
My first thought, looking at the age, weight and hours... Overhead and replace the bearings in the lower end, along with pressurizing the motor to check for coolant in the liners. I would replace the oil pump too if you roll new bearings in. If still mandated, it could also be carbon packing, or a bad delete eating the motor alive. If you have not done an EGR tuneup on that motor, you should do that regardless, along with the overhead. I would also bake and de-ash the cans if they are still in operation... I am assuming this is a CM-871?


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #5
RE: Oil pressure dropping
326k miles 14400 hrs....trucks had around 200-250k miles worth of idling and idling is 2 to 4 times more detrimental to these engines especially eating its own waste. I would bet it's carbon packed with possibly other issues.


User's Signature: 2010 Lonestar - CM871 - 13sp - 3.70s, 2016 T680 - cm2350 - 13sp - 3.36s - skateboarder
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #6
RE: Oil pressure dropping
Replace the oil pump, i had the same issue, dealership checked the oil pressure on cold engine and told me everything's fine, replaced oil pressure sensor but no luck, replaced the oil pump, my mechanic was skeptical about it, but I asked him to do it anyway everything is back to normal.
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 Thanks given by: carco
07-19-2020, (Subject: Oil pressure dropping ) 
Post: #7
RE: Oil pressure dropping
Has the Guage been verified accurate?
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07-19-2020, (Subject: Oil pressure dropping ) 
Post: #8
RE: Oil pressure dropping
(07-19-2020 )carco Wrote:  Hello to all during this hot stretch,
2009, T8, ISX550, 326000 miles, 14400 hours, empty weight 52K, loaded usually 65K to 90K often up to 130K but has been up to 167K, and once 232K.
Oil pressure has been dropping last 4-4500 miles 68mph, 1700rpm oil 39psi is now 33psi hot.
Hot idle oil psi now 16psi was always over 20psi. No power difference, no sound difference.
Was ready for oil change, 10 to 12K service intervals, so changed oil, made no difference. Changed oil sending unit, no difference.
So am I in trouble just over the next hill?? just keep an eye on the oil press?? tear down the engine, pull rocker cover chk cam, pull pan chk rods and mains??
Any words of wisdom?
Thank you.

just an FYI: If you had claimed that oil pressure comes bnack whenever the filter is changed, that is a common issue.. but you did not state this. - In the case of oil pressure falling off, then a fresh oil change and filter makes it come back, that is a sign of severe soot packing in the oil.

-- If your oil pressure has fallen off that much, and it is consistently bad ... I would pull the enigne cover and check for a spun bearing on the cams first. --Then the bottom end to ensure something is not getting beat to death, and check for debrtis in the pan. -- still nothing.... then replace rod and main bearings and replace oil pump while your at

When replacing rod/main bearings: -- BE SURE TO MEASURE all your rod and main bearings, as some ISX engines have alternate sizes and this can really screw things up. Not all ISX's come with standard size bearings from factory. They can also sometimes be different from hole to hole too.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: JimT , PuroCumminsPower
07-29-2020, (Subject: Oil pressure dropping ) 
Post: #9
RE: Oil pressure dropping
(07-19-2020 )Chamberpains Wrote:  Has the Guage been verified accurate?

No sir, but a mechanical gauge will be used soon.


User's Signature: Heavy Towing/Recovery makes the juices flow!
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