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After sitting down for about 6 months, I started driving my Evo X again. After a week of short trips, I took a long and spirited drive in the thing and by time I was returning home, I noticed my oil pressure at idle went from roughly 15-20 psi at the start, to about 10, then finally about 3psi when I started babying it back home. This was read from AEM oil pressure gauge, even at its lowest, my dummy CEL never turned on, though.
When babying the car back home, I would get about 30psi when driving around 2-3k rpm.
Drove it again today, it started perfectly fine, read 60psi to 70 when driving around, but after a bit my idle psi dropped down to 3-5 again, but cruising stayed around 60psi.
Any idea what could cause this?
I looked at info from my last oil change, which was shortly before I garaged it, they put in 0w-20 oil.
Could this low oil pressure at idle be caused by the overly light weight oil? Maybe that combined with it sitting down for so long?
I'm going to change the oil tomorrow and use 10w-30, and hoping this will fix my problem.
I'm running FBO, mhi, pump gas.
Any ideas would be appreciated.
 

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Discussion Starter #2
I forgot to mention, my oil level looked good after I initially saw the low pressure. I parked it, then drove it 30 minutes later and my idle oil pressure read 15-20psi and driving read 60-70 range.
I also changed my AEM oil pressure sensor on the block, as the old one was leaking a couple weeks ago. I drove it a bit after initially installing it, but didn't notice the low readings until a few days ago.
 

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Low oil pressure at idle after the engine warms up is normal. Your oil viscosity weight, sea altitude and outside temperature will play a role in your readings also. As long as you are not at low readings while the engine is under load, you're fine. I get the same numbers ~10 idle(engine warmed up), ~75 cruising highway, at around 80 degree F weather in MN.
 

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Discussion Starter #4
Alright, that's a relief. I was worried when I noticed it hit like 3-5psi at one point a couple days ago.
I just got an oil change today, switched to 10w-30, even on a hot day and getting on it, my idle pressure never dropped below 9-10 psi. Felt a lot better with that.
Appreciate the input
 

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You idle oil pressure should never be that low. The off idle oil pressure seems fine. I agree with your assessment that the 0-20 is just to thin. These car require 5W-30 synthetic. The recommend brand is mobile 1. I use a store brand that is relabeled castroil. I have tried 5W-50 in my car and can tell you that at operating temperature the oil is to thick. I only ran the thick oil for about 10 minute before changing the oil back to 5w-30. Change that oil now.
 

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Discussion Starter #6
Yeah, I got it changed yesterday with 10w-30, it seemed much happier. Went on a decent drive, got it up to temperature, got on it a little, and idle pressure stayed around 9-10 psi.
I'm guessing between having that oil that was too light and maybe having it sit down for about 6 months while I was gone, breaking the oil further, might have caused the low idle pressure?
 
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