Engine low oil pressure (dominator???)

low oil pressure (dominator???)

I have ran Mobil 1 full synthetic 5W-30 since 7000 miles with either Toyota or Purolator oil filters. The car is a 2003 Corolla CE 5-spd with 57,000 miles. During the last winter, I installed a mechanical oil pressure gauge and ran 55psi @ 3000rpms (consistently) when at operating temperature. However, since the weather has gotten warmer, if I rev the engine or drive any faster than 75mph for any length of time, the oil pressure drops to around 45psi @ 3000rpms. Idle psi also drops from the normal 15psi to around 10. Oil pressure typically maxes out @ 65psi @ anything higher than 4000rpms. However, when the pressure drops, the max oil pressure also drops to around 60psi.

The culprit seems to be revving the engine and heat. If I slow down and feather the throttle, oil pressure will slowly come back up to 50psi @ 3000rpms.

So, the problem is 1 of 3 things:

1 - oil pump (pressure relief valve, perhaps???)
2 - bearings
3 - the oil itself is getting WAY thin when it heats up (is this typical of synthetics or Mobil 1 full synth??)

I actually bought another gauge to make sure it wasn't a problem with the gauge - they both gave the exact same readings. I change the oil every 5000 miles and this particular oil has about 1000 miles on it. The engine uses about 1/2-3/4 quart between oil changes (a.k.a., the oil isn't low...I check it meticulously).

Any advice?? Think I should just scrap the 5W-30 and go with a 40 or 50 weight oil?? Different brand? Any advice is GREATLY appreciated because this stresses me out....I don't want to throw a rod and I'm afraid that's what will happen.

Late,
Trav

ok I tryed something with mine . It cost me almost $14 but it is called lucas synthetic stabilizer. Its worked great for my 01 .I have almost 4500 on my engine and was haveing oil presure issues. Now oil pressure picks up great. Now I idle at 19-20 psi while hot. I might be a band aid for you but give it a try.