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Low oil pressure at idle when truck is hot


chana1634
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I been having problem with my e7 350. I check rockers plugs but i did not see any leaks  remove and replace rod bearings main bearing oil pump, i notice that crank was cut ones before main bearings are p10, rod bearings still standard some mains when in tight and some when in kind of easy, install oil pan add oil and oil press when up, from 60. To 70 with new bearings and pump, but when driving truck weather was around 80 degree, oil drop around 15 psi this with no load on truck. Now i was told that cambushing if they never been change can make oil pressure drop while hot. Is this possible or is something that i over look.

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Cam bearings are popular on that vintage of engine. Usually you could drive through it, except you lose your engine brake around 1,100-1,000 RPM as you descend. Mack came out with a spec for gauging acceptable loss vs rebuild time. Oil at a certain temp and RPM at a specific rate should create “. “” “”” psi of oil pressure. I don’t remember “” “ “ psi.  

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7 minutes ago, theakerstwo said:

If you do cam brgs then get the acc drive bushings also.Did you plastic gauge the mains also?Reason i ask is most people grind the mains when the rod throws are done.

Original post says mains turned and rods standard 

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No i did not plastic check the mains just rodbearings . I got the truck running but will drive for a while and then do bushings on cam. And now that i was looking at the bearing that we remove I'm more convince that it was not done right and that dirt was all over. The bearings that i posted are from 1 year ago. Pressure is nice while cold but once hot just won't hold up  goes to low and when i stop for a while it goes up, 

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Before I’d go to the trouble & expenses of cam bearings, I’d probably try to shim up regulator & relief valves to try to get more psi. If (I) was going to do cam bearings, I’d pull engine & polish crank & have tolerance checked.

 

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I realize there's more to it than this but a bad or plugged oil filter will definitely lower your oil pressure. When I started driving I worked at a place where maintenance was not so good. I remember my oil pressure dropping one day I got back and reported it. They spun a new set of filters on and it was back to normal again. And yes all they did was filters no oil change

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10 hours ago, chana1634 said:

No i did not plastic check the mains just rodbearings . I got the truck running but will drive for a while and then do bushings on cam. And now that i was looking at the bearing that we remove I'm more convince that it was not done right and that dirt was all over. The bearings that i posted are from 1 year ago. Pressure is nice while cold but once hot just won't hold up  goes to low and when i stop for a while it goes up, 

You can’t plasti the mains in chassis, you can do rods. If your creative you may load the crank upwards with a porta power to try it. 

Edited by Mack Technician
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15 minutes ago, Mack Technician said:

You can’t plasti the mains in chassis, you can do rods. If your creative you may load the crank upwards with a porta power to try it. 

I and many mechanics have did it for years.Two ways to do it and one is to use a jack and jack up the weight of the crank but i always remove front and rear main cap and  double up some paper and put on the lower brg and then tighten up the main cap.I was in involved in a deal just like this one but it was a 8.3 cummins in a bus.The mechanic that did the over haul put standard main brgs on a .010 010 crank and got the right rod brgs in but std mains in it.Same deal it had low oil pressure.The lead man at a truck dealer made the call to pull engine and send crank out for more measurements.I was asked that evening for my 2 cents worth.I showed him how to plastic gauge the crank and found the mains were standard after checking it.Come to find out he had check the new rod brgs for size but did not check mains.Some one there sure did like me for a few days.

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glenn akers

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Lol, yup, you porta power the crank up you’ll find a 0.010” under mishap!! Heck, you probably can save money and use the same piece of plastigauge for the whole thing!

In the dealer world Mack wouldn’t allow us to machine the crank. Only Remack cranks. Machine shops don’t ease the corners of journal cuts and it predisposes the journal to crack. Don’t suppose that matters as much at 350HP, but 12 liter cranks turning 480HP May be a little more critical. 

On the rare occasion it was needed we used a porta power. Seems like the weight allows for a lot of sag distortion if shimming. We’d generally, 99%, check to make sure crank was std, and if polish was good, it got a shell. In most cases main failures destroyed the block. 

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i like to know were is the , I’d probably try to shim up regulator & relief valves, in this engine, and i notice that this engine on top of cover, says that is remack engine . now the relives valve and regulator is in the oil pump, well i install a new pump, well today drove and work with truck, got load it and work ok, but weather was not that hot, like 80 degrees, waithing on thursday weather look like is going to be on the 90 degrees, well will let you know if repairs will hold up.

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not for nothing; reading all the technical ideas that  are on track ., did anyone consider maybe  the brand of oil being used isn't holding up . the pictures show a definite problem with foreign matter raising havoc with bearings etc; the oil itself may be breaking down ,,

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