dickey Posted April 23, 2019 Share Posted April 23, 2019 just bought this 1994 dump with e7 400 the thing runs excellent,no blowby,no smoke pulls great, oil pressure 56lbs at 1650 but at idle 8 lbs bump it to 800 rpm and its 30lbs ,,,oil pump??? already changed filter,oil,and put manual gauge on it,,,???? Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/ Share on other sites More sharing options...
AZB755V8 Posted April 23, 2019 Share Posted April 23, 2019 19 minutes ago, dickey said: just bought this 1994 dump with e7 400 the thing runs excellent,no blowby,no smoke pulls great, oil pressure 56lbs at 1650 but at idle 8 lbs bump it to 800 rpm and its 30lbs ,,,oil pump??? already changed filter,oil,and put manual gauge on it,,,???? Roll in some new main and rod bearings. Probable has over 500K miles on it. Oil pressure is OK at 1650RPM so pump should be fine just replace pressure spring. Or... put some 90 weight in it and the pressure should go up for awhile....😀 Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421214 Share on other sites More sharing options...
JoeH Posted April 24, 2019 Share Posted April 24, 2019 Just fired up my 1995 e7-350, "cold" it's running 75psi oil pressure at idle. After a few minutes running it's at 60psi, pressure goes to almost 90 at 1600rpms. Maybe your pressure relief spring is fatigued or broken. Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421261 Share on other sites More sharing options...
dickey Posted April 24, 2019 Author Share Posted April 24, 2019 im ok with doin the bearings but idk about 90 weight ,yea it has 673,000 ,how many miles are these usually good for Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421269 Share on other sites More sharing options...
theakerstwo Posted April 24, 2019 Share Posted April 24, 2019 Set the idle to 700 rpm Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421278 Share on other sites More sharing options...
JoeH Posted April 24, 2019 Share Posted April 24, 2019 Mine runs 20 psi at idle and about 65 psi at 1600 once the engine is hot. 251k miles, 18,700 hours. Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421279 Share on other sites More sharing options...
dickey Posted April 24, 2019 Author Share Posted April 24, 2019 i understand my pressure is low,thats why i was asking for input,i was thinkin bearings but thought maybe someone else had same problem Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421283 Share on other sites More sharing options...
JoeH Posted April 24, 2019 Share Posted April 24, 2019 Put a reman oil pump in? Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421286 Share on other sites More sharing options...
AZB755V8 Posted April 24, 2019 Share Posted April 24, 2019 (edited) 4 hours ago, dickey said: i understand my pressure is low,thats why i was asking for input,i was thinkin bearings but thought maybe someone else had same problem Oil pressure is not an uncommon problem with a lot of engines. I was making a little fun of adding 90 weight, do not do, but if all else is OK the fix is lower end bearings and pump spring. Not knowing any more about your engine or service, maintenance that can add to the issues the fix is straight forward and would take about a day or so to do labor wise. The V8's were harder on bearings than the I6's and if not replaced at every 250K the engine would be toast. If done with proper scheduled maintenance a million miles before rebuild could be had on the V8. Some others here would probably say a longer interval on a bearing roll on the 6 cylinder engines. I think 670k miles is pushing it though. Edited April 24, 2019 by AZB755V8 Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421289 Share on other sites More sharing options...
dickey Posted April 24, 2019 Author Share Posted April 24, 2019 no im gonna put mack oil pump with mack bearings if it turns out to be bearings when i get it apart Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421293 Share on other sites More sharing options...
Mack Technician Posted April 24, 2019 Share Posted April 24, 2019 (edited) Pull the oil pump relief cartridge. If it’s galled clean it with a fine grit. Check the seating face seal taper. View it as valves in a head.... is it clean? and even halo where it engages the seat? no erosion or pits? Keep a sample of the oil and send it in to see if you have presence of soft metals. If your pressure is low, and your pump looks ok, you may have spun, and may not especially be main bearings. Pump’s rotating group rarely fails, have seen parts of pump fail on multiple occasions. Lot of folks buying junk engines these days sold by people who oil test. In other words “people who know exactly when to sell”. Edited April 24, 2019 by Mack Technician Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421296 Share on other sites More sharing options...
Lmackattack Posted April 24, 2019 Share Posted April 24, 2019 sounds like a weak pump or you have an internal leak such as a piston cooling nozzle has come louse? Quote Link to comment https://www.bigmacktrucks.com/topic/56865-help-with-low-oil-pressure-only-at-idle/#findComment-421301 Share on other sites More sharing options...
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