Per the manual, normal hot oil pressure is 10 psi idle and 40-70 psi @ 2200 rpm. Is "normal driving" is below that... I suggest you get her good and hot then in neutral rev it to 2200 and read the pressure. That's how the manual says to do it. I suspect doing that you will see "normal" oil pressure. The manual doesn't spec the "warmed up" oil temp and oil temp can make a difference a few psi on either side (say 150F to 180F)
FWIW I have tested the difference in pressure between 10W30 and 15W40 at the same oil temp (160F) in my engine and it was about 5 psi. In diesels, when our oil gets old and worn, it usually thicken from soot before it thins from shearing. Whenever I have run oil out too long, soot at 5-6%, the oil actually tests thicker than the new oil. In that case, old oil will actually create MORE oil pressure than new!
Bosch D+ is a great oil filter and there is absolutely nothing wrong with either oils used in the crankcase.
Depending on oil temps, you can sometimes see a drop in pressure if the oil gets really hot (hotter oil is thinner oil and vice versa) but I monitored oil temp in my truck for 10-12 years and even in the deserts and towing, I never saw more than about 220F balls to the wall with a trailer behind. In "normal" solo tooling around 150F or so... which is one reason why I now run 10W30 all the time. At 150F, 15W40 grade oil is running in 50-60 grade and that costs oil flow and efficiency (thick oil costs HP) and increases the chance of oil filter bypass (when a certain amount of unfiltered oil is allowed to pass) when you get on it.
I have a differential pressure setup on my F-150 and can monitor when the oil filter bypasses and cold oil is when that will happen. 10W30 grade oil is running in 40 grade territory at 150F. There are oil viscosity/temperature charts where you can enter in the specs for the oil you are using and you can plot the oil viscosity at any oil temp point. Cold oil doesn't flow thru the filter as well so it will "back up" at the inlet side, creating high pressure there and low pressure on the outlet side. When the differential pressure (the pressure difference) reaches the place where the bypass is designed to open, it begins to bypass the filter and allow unfiltered oil past the filter. I have never found the bypass spec for the IDI but figure it's around 10 psi. I have never tested the differential pressure on an IDI (it's quite a setup to do so) but on my 5.4L gasser, I DO NOT rev past 3500 rpm before the oil temp reaches 150F. I tried different grades of oil, 10W30 and the spec'ed 5W20, and I had to be VERY careful with the 10W30 because I could get it to bypass at high revs (4000) at 180F... which is only about 10 deg below normal oil temps. With 5W20, no bypass problems at 130F or so but I still stick with the 150F guideline. I want ALL my oil filtered ALL the time. It's ****, I admit, but I have learned a lot having 15 gauges hooked up to my truck ( : < ). I know, gaugeaholism is a disease. I need help!
