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Arlene Spadaro, Electrical Engineer - Automotive
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Engine runs ok but after probably 15..misfiring..oil change..tanks

Customer Question

engine runs ok but after probably 15-20 minutes oil ligth turns on but car still working propertly,after
another 20-30 minutes of driving it start misfiring
or failing I just did the oil change and spark plus replaicment
but still have the same problem tanks.
Submitted: 11 years ago.
Category: Car
Expert:  Arlene Spadaro replied 11 years ago.
You will need to get a real oil pressure gage and install it to see if the oil light is correct.



As engines age , oil pressure will drop due to th oil pump wearing and
not pumping as much oil as it did when new and the engine is wearing
allowing oil to pass in larger volumn and might lower the oil pressure
where the light will come on.



A typical oil pump in a car engine is a constant volumn with a relief
valve.  When the engine is new , the pump will pump more oil than
the engine can pass and so the pressure will build until an internal
relief valve will let the excess pass.  The relief is set at a
particular pressure so oil pressure will not exceed this setting. 
The temperature will cause the relief to be slightly higher when
cold.  In a worn engine condition , the pump pumps less and the
engine pass more to where the oil pressure drops.  Revving the
engine will increase the pressure but will go low when back to idle.



A real oil age will give you an accurate reading to allow you to
determine if it is possible to repair.  I had an old engine that
would run just fine on 3 pounds of oil pressure.  It was worn out
but I was young and didn't care as long as it got me to school and back.



You can replace the old oil pump with a high volumn replacement from the auto parts store.



I can't see where the misfire is related and think it might be a separate problem.

If you are loosing oil noted by gray smoking from the exaust , it might
be burning it through the cylinder and fouling the spark plugs . It
might be difficult to see the smoke as today's caytalic converts would
try to burn the excess oil/ smoke  before it gets out through the
tail pipe.  You might want to disconnect the converter to better
see the exaust as a test.

Check the plugs for wet oily condition.  There used to be adapters
to help oil fouling but I can't say that anyone sells them today.

---

Ron




















Customer: replied 11 years ago.
Reply to Arlene Spadaro's Post: Ron thanks for your answer you have been very clear about that I need to do but by mistake I
send the same question twice and allready pay
for the firs answer wich it was allmost the sa-
me answer as well once again thankyou

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