c-mac Posted July 11, 2018 Share Posted July 11, 2018 I'm not sure whats going on here. I though I recognized the tractor number. I looked through the service history and saw where another tech replaced the oil pressure sensor, then a month or so later in May I had it towed in due to low oil pressure. I put a manual gauge on it and it got down to 15psi at Idle and 35psi and dropping at WOT. Driver said the shutdow light came on at highway speed. At that time I remembered another guy had the same problem after injectors and cups. Turned out he had cut the oring on the engine brake oil control valve tube where the tube goes into the rocker shaft. I checked this one and the oring had a notch cut out of it. I replaced both tube orings and I thought it was fixed. The oil pressure was good. Now, two months later we have the same problem. I have already had the pan off to inspect the screen and it was all good. I think that I'm about to pull the valve cover and check the oil control valves orings again. Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/ Share on other sites More sharing options...
Mackpro Posted July 11, 2018 Share Posted July 11, 2018 Check the o-ring on the bottom of the engine brake valve where it bolts to the head as well as the o-rings on the tube. Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/#findComment-402296 Share on other sites More sharing options...
c-mac Posted July 12, 2018 Author Share Posted July 12, 2018 looked ok about to go back with all new orings, thanks Quote Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/#findComment-402335 Share on other sites More sharing options...
turckster Posted July 12, 2018 Share Posted July 12, 2018 There are cup plugs on the engine brake valve as well, make sure they are not loose or missing. Make sure the cup plugs on the rocker shaft are not missing or loose. Also, make sure all rocker shaft bolts are tight. It could also be an issue with the CCV spinner. There is a brass nozzle that sprays oil at the CCV spinner and could be loose or missing. Verify low oil psi with a mechanical gauge. Seen this issue several times on mp8 engines and response from e-service after checking everything was to replace the oil filter housing and that may be where you are headed. Attached is a PDF for low oil psi on a D11/MP7 engine, some of it does not apply to the D13/MP8 but it still has good info in it. 11 liter Low Oil Pressure Diagnostic Process_D11_Nov 2016.pdf Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/#findComment-402340 Share on other sites More sharing options...
c-mac Posted July 12, 2018 Author Share Posted July 12, 2018 OK, I"m kinda embarrassed to say I think I have figured it out. when I started the engine cold it stumbled for a second which seemed odd, the oil pressure looked good 45 idle and 75 running high, then started dropping back to what it was prior to attempted repair. To make a long story short, fuel is getting into the oil ..how? past a bad injector oring? Thats all I can come up with anyway. I work on a fleet of 150 2008 and up macks eveyday and haven't ran into this problem. I've had fuel in the coolant several times, but not this. This engine has had cups and injectors about 1000 hours back. Do you think I can get away with just injector orings or maybe ya'll know of something else that may be the problem? Quote Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/#findComment-402347 Share on other sites More sharing options...
turckster Posted July 12, 2018 Share Posted July 12, 2018 If you have fuel jn the oil it could be a leaking o-ring or through the injector plunger and or body. To determine which, remove supply and return line fittings, plug one and apply no more than 20 psi air to the fuel galley. Use soapy water to find leak. Quote Link to comment https://www.bigmacktrucks.com/topic/53777-2011-mp8-intermittant-low-oil-pressure/#findComment-402351 Share on other sites More sharing options...
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