cat 3126b low oil pressure

[jesse beiler]

i am working on a c7500 with cat engine 3126b with heui injection system, oil pressure is fine at startup ,as engine warms up oil pressure drops til engine warning lite comes on, checked with mechanical gage, it matches dash gage,replaced one injector for high oil flow , had broken o ring , replaced rod bearings, although it did not change , shimmed oil pump relief valve, it raised cold oil pressure, but not when hot ,

 

[Nige]

Engine Serial Number please, and what maximum cold oil pressure @ Low Idle and @ High Idle do you have..?

 

[jesse beiler]

7as28667 cold idle 55 psi , 60-70 psi i put a shim in oil pump releif , before fully warm it was down to < 5 psi , as oil pressure drops < 10 heui pressure starts cilimbing as high as 3000psi on mech gage, then stalls

 

[jesse beiler]

hi idle 70 psi thanks

 

[Nige]

Are you sure you don't have a major leak that develops somewhere in the HEUI system when the engine warms up..?
One thing we used to use was a Portapower full of engine oil that we'd hook up to the injector actuation oil inlet at the cylinder head, then pump the f**k out of it (4,000+psi) with the valve covers off and look for where oil was spurting - and FYI it usually wasn't that difficult to spot. Try getting the engine warm then do that test and see where it gets you.

 

[jesse beiler]

I did run the engine with the valve cover off is earlier found that I had a major leak on injector number one with broken o-ring which I replaced I had thought of rigging something like that up but I didn't

 

[Per Eriksson]

Much more fun running them without a valve cover and have oil spray all over the place....no?
I don't think the issue is in the heui system, that pump doesn't have the capacity to "starve" the lubrication system in my experience but if you feel adventurous it can be tested by towing it in gear with ignition off, then the heuisystem isn't consuming any oil.

Are you sure the pump is in good working order?
No suction leaks?
Piston jets was all in place?

 

[jesse beiler]

Actually running it with the valve covers off there's hardly any oil flying around the way it acts when it is sitting there idling reminds me like it's getting air into the oil on the pump suction side or something it'll start and run nice as it warms up the oil pressure will start to climb and it'll start acting a little funny and then finally stall out and the pressure will be up to nearly 3,000 meanwhile the engine oil pressure code is that a nice 50 and steadily drops do below 5 PSI which is Wendy computer turns on D warning light

 

[jesse beiler]

i did the portapower style test, was fine , removed oil pump and found pickup tube gasket was bad ,also pickup tube was warped, sanded to get a flat surface, plan on reassemble tomorrow and start and see what happens

 

[Per Eriksson]

So, was that the problem?

 

[jesse beiler]

sorry you all for not finishing the thread, i replaced the lower oil pump , hot oil pressure came up to 20 psi at idle, 55 psi above 1500 rpm the engine sounded quieter and smoother at idle