Read this on another forum. In vehicles that have tell you the engine oil pressure, you can tell if the oil is breaking down or shearing if the oil pressure is lower than it was when the oil was first changed.
Even synthetic oil can have viscosity modifiers that break down. 10W40 becomes 10W10 eventually. So if your oil pressure is slightly less than it should be when warmed up at idle, then it is time to change your oil. If the pressure goes back to what it is suppsed to be after the engine warms up, then it confirms that you were right to change it.
This makes it so simple. Do they say 20,000 miles on one oil change, but the oil pressure is down slightly after 9k miles? Then it’s time to change it.
The 2014 RAM trucks have a digital oil pressure read out. I’ll have to make note of it next time I work on one.
Good point. An overheating incident can thin the oil as well, requiring a complete oil and filter renew. Besides low oil pressure, new noises from the engine can suggest an oil-thinning problem.
I do not think this is correct, and even on a vehicle with an actual oil pressure sensor, the oil pressure gauge is dampened, just like the coolant temperature gauge. And the idea of running the same oil for 20,000 miles, or even 9,000 miles is absurd, even if the “oil life monitor” allows it. If you check the dipstick (which you should be doing at least once a month) and the oil looks dirty, then it’s time to change it. Other than that, I would never run the same oil for more than 5,000 miles, or more than a year, even if the OLM says it’s ok.
The oil pressure will tell you if you need to change the oil filter if the bypass valve isn’t working, but it doesn’t tell you that you need to change the oil.
Edit: Except that if you need to change the filter, you should probably go ahead and change the oil too.
The oil on my 2012 Camry remains so clean that I still can’t read it on the dipstick just before my annual oil change without laying the dipstick sideways on a paper and seeing where the wet spot ends. Never gone over 7500 miles though. Makes it very convenient ,never have to change in the winter.
There’s that, but there’s the more basic problem-the whole idea of judging oil life using oil pressure is very likely total BS. One would have to do hundreds of tests comparing oil wear to oil pressure just to know if it works . Very doubtful some dude on the internet has done that.
I use a mechanical oil pressure gauge on my muscle car and have never noticed a correlation between oil pressure before/after changing it, I only use Dino oil in it with a zinc additive… I also cut the oil filter open to check for bad stuff… lol
Engine temp (oil temp) has the biggest effect on oil pressure…
This thread, and the idea behind it, is absolute stupidity. It simply does not, can not, will not work.
If the oil pressure control system in the engine is maintaining oil pressure at, say, 45psi, regardless of RPM and temp, how on earth would anyone gain any useful information about anything else other the oil pressure? There is obviously a great lack of understanding about how an engine works.
My 50 year old truck displays the oil pressure, and I monitor it on every drive, esp when first starting the engine and during the warm up period, then again after the drive is completed, just before parking. I can’t say I’ve ever changed the oil directly b/c of the oil pressure reading, but if it starts showing numbers that it usually doesn’t, I’ll definitely be checking the dipstick for oil level and oil color and how it feels.
