Mobil 1 oil change and new recommendation.

Well, it's a fantastic oil, so pretty hard to go wrong with.
Got a jug stranded from when we used it in a turbo Cruze RS … only 5 quart engine I have is a Pentastar ?
(older 5.3L just started 5W30 - new one on dealer OLM plan with tire rotation) … ?
It may be a significant drop in viscosity, but I have to ask: Do you know for sure that your hot oil pressure would drop at idle? You've been using the M1 HM EP 5w30 for quite a while, so you must be happy with it. Your engine sounds pretty healthy and you may be jumping ship prematurely seeking another oil recommendation, but obviously you do whatever you need to do. It's just that people seem to get caught up in solving problems that they don't have.
You're probably right DGXR. Im sure the oil would still be acceptable. However, as mentioned in an earlier post I get nervous when specs change especially when getting thinner. Im sure thats to meet some new emissions regulation. Just because engines are design to last long now with new thinner oils does not mean it will always be the best for older engines with more milage.

Yeah I do know the pressure drops at idle. I also saw this on my 93 jeep. Pushed it way too close to minimum hot oil pressure on a long trip with it. Again, only change from normal was fresh m1 10w30hm. That got dropped at an advanced auto mid trip for 0w40.
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I put the 0w40 Fs in this afternoon and I'm happy with the results. Its odd because it seems like the engine revs smoother despite the thicker oil. It also seemed like I was accelerating more on light throttle after TC lock up. This is particularly noticeable as TC lock up is around 36mph and I typically drive around 40mph.

Oil pressure is up, but I didn't get a good heat soak today. I think this will be a winner unless mpg tanks.
No need to look back from here
I agree. Mileage on a 1000mile trip was some of the best and relatively consistent with full load, different drivers, and serious hills (34.5-36.5mpg over 3 tanks).
It appears the viscosity of many of Mobil 1s oils have changed based on the provided viscosities on their website. For example high milage 5w30 used to be 11.7-11.9cp at 100C, but is now showing as 10.1cp.

I reached out for confirmation from Mobil 1 since this isn't an insignificant change, but got no response of value.

Anyways, now im looking for an oil recommendation for my 03 celica (1zzfe) with 190k miles. My oil pressure is fine (13psi max heat soak with ac and 55-60psi at 3krpm) with Mobil 1 5w30 HM EP, but I believe its the previous formulation with higher viscosity. I dont want to go lower with viscosity to maintain healthy pressure at idle.

I have a jug of 0w40 mobil1 fs for another vehicle, but am concerned it may be too thick at 12.9cp. Im looking to stay with Mobil 1 if ththere'a good fit since ive used Mobil 1 with the car for 88k miles. I need the oil to perform well at 100F and occasional periods down to -10F.
Let go over some facts. The drop in viscosity was likely attributed to meeting the latest specs. For a time, Mobil 1 held back doing that and stayed thicker. Considering all that, there is not much to worry about with a 19 year old, 190,000 mile vehicle. Either the Mobil 1 5w30HW or 0w40 will work in that car. If you don't want to go lower, then use the 0w40. If you don't want to go out of spec, then use the 5w30HW. Take your pick.
Possible unpopular opinion here that you could mix the 5W-30 HM EP with the 0W-40 to have some sort of inexact middle ground, also because the are both Mobil 1.. however, you should be fine with either or. The 0W-40 may very well be very good. (*for your engine.)

The 1ZZ-FE 1.8L has been prone to oil consumption, something about the rings.

KV100 is 13.5
HTHS a nice 3.6

Properties and Specifications​

GradeSAE 0W-40
Total Base Number, mgKOH/g, ASTM D289612.5
Ash, Sulfated, mass%, ASTM D8741.2
Flash Point, Cleveland Open Cup, °C, ASTM D92233
Kinematic Viscosity @ 40 C, mm2/s, ASTM D44577
Hi-Temp Hi-Shear Viscosity @ 150 C 1x10(6) sec(-1), mPa.s, ASTM D46833.6
Kinematic Viscosity @ 100 C, mm2/s, ASTM D44513.5
Density @ 15.6 C, g/ml, ASTM D40520.839
Viscosity Index, ASTM D2270180
Mini-Rotary Viscometer, Apparent Viscosity, -40 C, mPa.s, ASTM D468428200
Pour Point, °C, ASTM D97-45
*Ash over 1% is not good for the DI engine owner crowd.