Low oil pressure but runs fine

[USAF Bus]

Hi all, c7 KAL48435

Low oil pressure alarm at startup and at stop lights and stopping in general.

Did not drive for a long period of time, just to troubleshoot this.

I checked indicated pressure at the T, within 5 psi.

Oil dirty, but needs to be changed (will do) i know how picky c7s are about their conventional oil.

Oil level good.

Cant check for active diagnostic codes, don't have a Cat ET.

Can someone take a picture of their c7 engine oil pressure sensor so i can see how its supposed to be installed i cant verify if its right and the C7 troubleshooting manual doesn't have a reference picture.

Thanks,
USAF bus

[cadillackid]

ive driven a couple C7s that ran low oil pressure... there are many different reasons for why it can be low.. the most troublesome is if the engine bearings are worn out and the journal tolerances are wide and letting oil by too fast...


other reasons.. dirty oil filters - most diesel engines measure their oil pressure after the filters so clogged filters can run low pressure....



diluted oil - bad HEUI injectors are notorius for dumping fuel in the oil which dilutes and makes it thin..



bad sensor.. soundsl ike you ruled that out by testing with a mechanical gauge at the T where the sender connects.



bad turbo - loose turbo journal letting lots of oil by (not leaking into the intake or exhaust) but back into the return..


clogged oil pickup - debris in the pan clogging the oil pickup.


bad pump or relief spring - issues with the oil lift pump..



most of these are rare.. although in the case of one of the ones i drove ,its service history showed where several injectors had been replaced due to a driver complaint of smoke and oil level going up.. it apparently had been driven that way for awhile.. it had quite a but of blow-by ran high oil temps and low oil pressure.. so the previously bad injectors had munched the bearings....



another i drove clear across the country.. highway speeds the gauge read 25 PSI.. at a stop light it went down to like 5 and the alarms went off.. I dumped a gallon of lucas in it and it at ;east ran 30 highway and about 7 or 8 stopped (no alarm).. as far as i know that bus is still being used as a church bus and hasnt blown up several years later...



first thing Id do with yours is a oil / filters change and use Rotella T4 standard oil and see what you get.. you may want to save some of your old oil and send it into blackstone.. they can give you an idea if its got fuel in it.. metals that resemble bearing inserts, etc...

[USAF Bus]

Originally Posted by cadillackid

ive driven a couple C7s that ran low oil pressure... there are many different reasons for why it can be low.. the most troublesome is if the engine bearings are worn out and the journal tolerances are wide and letting oil by too fast...


other reasons.. dirty oil filters - most diesel engines measure their oil pressure after the filters so clogged filters can run low pressure....



diluted oil - bad HEUI injectors are notorius for dumping fuel in the oil which dilutes and makes it thin..






bad sensor.. soundsl ike you ruled that out by testing with a mechanical gauge at the T where the sender connects.



bad turbo - loose turbo journal letting lots of oil by (not leaking into the intake or exhaust) but back into the return..


clogged oil pickup - debris in the pan clogging the oil pickup.


bad pump or relief spring - issues with the oil lift pump..



most of these are rare.. although in the case of one of the ones i drove ,its service history showed where several injectors had been replaced due to a driver complaint of smoke and oil level going up.. it apparently had been driven that way for awhile.. it had quite a but of blow-by ran high oil temps and low oil pressure.. so the previously bad injectors had munched the bearings....



another i drove clear across the country.. highway speeds the gauge read 25 PSI.. at a stop light it went down to like 5 and the alarms went off.. I dumped a gallon of lucas in it and it at ;east ran 30 highway and about 7 or 8 stopped (no alarm).. as far as i know that bus is still being used as a church bus and hasnt blown up several years later...



first thing Id do with yours is a oil / filters change and use Rotella T4 standard oil and see what you get.. you may want to save some of your old oil and send it into blackstone.. they can give you an idea if its got fuel in it.. metals that resemble bearing inserts, etc...

Thanks big time for the info.

I agree on the first move being an oil change, ill give that a shot this weekend. Im hoping its not the Turbo or HEUI, but ill deal when i get to that.

From your experiences, i have the same issue with that church bus. What lucas product you throw into the oil? Just incase.

Really appreciate the help. All sounds like expensive fixes minus the oil.

[cadillackid]

if the bearings get washed it may not even be something current... the first C7 had injector issues previously and they were fixed.. and the bus driven as a route spare by the school till it went for auction (and sold for next to nothing).. the HEUI issues were fixed and it actuallyu ran really good despite the draft tube leaving a good smoke trail esp on the highway.. I have no idea of the current whreabouts of that bus.. it was originally bought for its A/C and MD3060 to go into his project.. his other project got destroyed by a derecho storm so he sold the bus..


the church bus didnt have near as bad blow-by.. i had forgotten my bluefire on that trip so I couldnt read the oil temp.. Oil temp can be a telltale.. with conventional oils, the hotter the oil the thinner it gets and it loses its ability to maintain good pressure.. oil pumps are gear-type pumps designed to pump thicker liquids...


its normal to see oil tenps 10-15 degrees above coolant temp.. maybe 20 if you are pulling hills.. but if your poil temp is way the heck up there 240-250 then its either the oil cooler is not doing its job or there is so much blow-by its heating the oil up..


the lucas i used was the standard oil stabilizer..

[Albatross]

Originally Posted by USAF Bus

What lucas product you throw into the oil?

https://www.autozone.com/motor-oil-a...gal/169274_0_0

You should be able to find it just about anywhere, especially where big trucks go.

Get in the habit of adding this stuff to your oil in recommended dosages. It is magic. And it's how I keep stuff running for far longer than it is 'supposed to last'.

[sportyrick]

If your oil pressure goes up as the oil get warmer it's a clogged oil pick up screen, if goes down as the oil warms up bearings would be my first inclination.

[USAF Bus]

Hey all an update.

Changed the oil, pressure shot up while hot to 35 psi or greater at idle.

I figured out why the oil loses lubricity quick on this engine.

So, when the engine gets warmed up it operates just under 210*F (at the high end when at my max speed of 55 mph) which is way too hot for this engine. For reference, i live in Central GA.

I cleaned the radiator(s) with simple green and pressure washed them and it didn't really make a difference.

So I think I need to change the Change the coolant, then thermostats, and check the water pump. The fan turns on and moves when it needs too.

Thinking of grabbing this kit and just swapping them out. I think one of the two thermostats dont open correctly https://www.raneystruckparts.com/cat...RoCuOUQAvD_BwE

Any idea which coolant to use? I checked the troubleshooting PDF i have for on road c7/c9 and its not clear. (I have all the pdf books from cat for our engine if anyone needs) Same with thermostats.

I appreciate your guys help.

USAFbus