david4451
Well-Known Member
- Joined
- February 9, 2015
- Messages
- 309
- Reaction score
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- City, State
- cotabato philippines
- Year, Model & Trim Level
- 2001 ford sport trac
I've worried for ages about my oil pressue, as slowing from high speed OCCASIONALLY my dummy oil pressure gauge bounced.
My thoughts were bad oil pump, worn bearings etc etc. However my ST uses NO oil between changes and the truck runs like a dream.
Reading another thread on bouncing gauge prompted me to dig deeper and suggested the vacuum created by the PCV could lower oil pressure at end of gallery where dummy gauge connects. This effect would be more marked when slowing as there would be less blow by at piston rings, increasing vacuum effect.
I fitted two pressure gauges 1 on block where dummy gauge connects and 1 directly to sandwich connector where filter received oil directly from oil pump. Below are results
COLD START PSI DUMMY GAUGE (block) 35 OIL PUMP (filter) 40
HOT ENGINE PSI DUMMY GAUGE (block) 14 OIL PUMP (filter) 18
Hot readings 500 rpm
I conclude that my oil pump was good and there is approximately a 5 psi drop between dummy gauge block connection and oil pump. The readings were all in driveway and I did not go on a run to increase engine temperature.
I can also confirm that the dummy gauge starts reading at 5 or 6 psi. I have a pre-lube pump that allowed my to check this, with engine not running.
Previously I fitted a gauge on a T at dummy gauge block connection that I could read while driving and at 500 rpm and fully hot engine the oil pressure was 8 to 10 psi.
To say definitely what caused bouncing needle is debatable, my thoughts are the viscosity of hot oil lowers pressure and the PCV valve has some effect lowering oil pressure along with wear and tear. I'm 100% sure my oil pump is good!!!!!!!
My thoughts were bad oil pump, worn bearings etc etc. However my ST uses NO oil between changes and the truck runs like a dream.
Reading another thread on bouncing gauge prompted me to dig deeper and suggested the vacuum created by the PCV could lower oil pressure at end of gallery where dummy gauge connects. This effect would be more marked when slowing as there would be less blow by at piston rings, increasing vacuum effect.
I fitted two pressure gauges 1 on block where dummy gauge connects and 1 directly to sandwich connector where filter received oil directly from oil pump. Below are results
COLD START PSI DUMMY GAUGE (block) 35 OIL PUMP (filter) 40
HOT ENGINE PSI DUMMY GAUGE (block) 14 OIL PUMP (filter) 18
Hot readings 500 rpm
I conclude that my oil pump was good and there is approximately a 5 psi drop between dummy gauge block connection and oil pump. The readings were all in driveway and I did not go on a run to increase engine temperature.
I can also confirm that the dummy gauge starts reading at 5 or 6 psi. I have a pre-lube pump that allowed my to check this, with engine not running.
Previously I fitted a gauge on a T at dummy gauge block connection that I could read while driving and at 500 rpm and fully hot engine the oil pressure was 8 to 10 psi.
To say definitely what caused bouncing needle is debatable, my thoughts are the viscosity of hot oil lowers pressure and the PCV valve has some effect lowering oil pressure along with wear and tear. I'm 100% sure my oil pump is good!!!!!!!
