Bungwacker

Change oil 4.0 Grand Cherokee. 10w/30.
for the first time I installed an oversized Purolator L30001. Because I read better flow more filter media etc etc.

I think the oil pressure is higher and stays higher at idle, than before. Wondering if it is not safe. Cold Start up pressure is 50-55 PSI idle. Warm idle it drops and stays steady at 40-43 PSI. Running any acceleration approx 1500-2500 rpm 60-65 PSI. Shall I put a short filter back on ? Im really only concerned about the idle pressure. Seem kina high ? doesnt drop below 40 psi even warmed up. thoughts ?

dave1123

First of all, IMHO you don't need 10W-30 unless you never see temps lower than 60*F.

My WJ 4.0 runs 5W-30 synthetic with 168K on her and my normal cold start-up pressure is 55 psi that drops to 40-45 warm. It runs 55 at 65 mph and holds 40 when hot at idle. I use a Mopar #05281090 filter, have replaced the oil pressure switch with a Mopar one, and use Valvoline Syn-Power oil which I change every 5K miles. When I replaced the valve cover gasket, everything was clean and wet without any sludge or deposits.

I'm happy.

Bungwacker

Thanks for your reply, My pressure seems to be near exact what yours is. I have 173k on it and it is still relatively quiet except the usual start up very minor/(not loud) sewing machine lifter noise. Manual calls for 10w / 30. I run 10/40 in summer and 10/30 in winter. last month ran about 12 oz of Marvels in with the oil for 1000 miles. I think it cleaned it out pretty good. Oil was blacker than usual on oil change. again thanks for reply, good to know theres another 4.0 with similar pressure readings.

dave1123

I had to get out my manual and check that out. You're right. It recommends 5W-30 from 32*F and below, and 10W-30 from 0*F to 100*F. I switched to 10W-30 once and that's when my pressure gauge **** the bed. I started reading 80 psi all the time. I changed back to 5W and replaced the sensor. I do get a bit of valve rattle, but hey, all 4.0s rattle.

twinkiedooter

My 97 ZJ runs at a very low pressure. Even going down the road at 50MPH it reads 40 some Pressure....and not much higher regardless how fast or slow I go. Hmmmm. I use synthetic high mileage oil with a shot of Lucas Oil Additive. Keeps the ticking stuff away...... My 94 ZJ would run anywhere from 50 to 70 pressure.

sycoglitch

first off. 40psi is in spec. Spec is anywhere from 10 to 60 hot idle iirc. Second, high psi does not equal lubrication. People need to read up on this. The higher the psi doesn't mean it's better. In fact it means oil is possibly flowing less

kgm

Like blood in your vessels, pressure isn't what is needed.

bigbadon

Impossible for filter to increase pressure b/c sensor is downstream

Bungwacker

Yes downstream from the filter, but if its less resticted coming out of filter, and more flow, wouldnt that make it easier on the pump and put your pressure somewhat higher ?

dave1123

Consider this, the sensor may not be telling you what the pressure really is. Put a mechanical gauge on it to find out. Also, pressure is controlled by bearing clearances and limited by the pressure relief valve in the pump. At high engine speed, the maximum flow can sometimes overpower the relief valve and actually increase the pressure by about 5 psi. Thinner oil will leak past the bearings more easily and drop pressure. You only need enough oil pressure to maintain the oil film that prevents metal-to-metal contact on the bearings. 90% of bearing wear occurs before pressure comes up, so don't wind it up until then, especially after changing the filter.

Some full-blown race engines use an oil pressure accumulator which is a cylinder that holds pressurized oil to flood the bearings BEFORE it lights off. We made them from small fire extinguisher tanks with a solenoid valve on them. The instant you start cranking the engine, pressurized oil charges the bearings. This is a little extreme for street use, but it's just to show how important protecting the bearings is.

From my experience, if I've got 40 psi at idle hot, I'm happy. If it gets down to 20, I begin to worry and start checking if that reading is accurate. If it never goes above 40, it's okay in my book. Except for full throttle, 40's okay any day.

Bungwacker

Thanks for replys. Im ok with my pressure at this point. When fully warm it goes / drops to 35-38 idle. . and when driving about 55-60. gauges Im sure are not exact measurements / just close. Anyway, yeah I think its pretty good for 173,000. thanks again.

bigbadon

Maybe. BUT the pump is a positive displacement pump which means it will push the same volume through the filter...the pump will be harder to turn but the same flow will go through the filter UNLESS it is restricted enough to open the by-pass valve on the pump.
Less restrictive/high flow filters reduce hp and improve gas mileage! There is also a high pressure by-pass on most filters.