If oil pressure were low(er) in a warm engine

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The oil pressure on the gauge of my Santa Fe was always higher when cold and then would drop as it warmed up. It would also be higher with thicker weight oils as I experimented.

It was rated for 5w20 but I had put in some old 15w30 I had one summer just to get rid of it. I thought the needle was going to break off the gauge.
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Yup, higher viscosity is handy:

As a teen I had a dodge slant 6, that groaned at idle - the main bearings had bottomed out
due to excessive wear/clearance and on-spec oil! Oil light was on even with a full crankcase!

Switched to 20W50, upped the idle a bit and drove it for 3 more yrs!
 
SAE60 is where it is at. I had a friend in high school ran that in his truck that called for 5w20. Blew his engine up 2 weeks later.
 
Very High Viscosity, but remember ... you may not be helping your motor that way. As long as there is an oil film on mating parts whether those parts should be under pressure or not, the oil is doing it's job. Higher viscosity oils may not be able to flow everywhere they're needed, when they are needed.

Personally, I have never been bothered by low oil pressure, as long as I knew the sump was full of oil and I had a reasonable reading. As engines wear, tolerances increase, and that is normal. Wide tolerance motors generally start easier than tight tolerance motors. In cold weather, they start much easier. This means less wear and tear on things like starters and batteries.

By "reasonable reading, as long as I have at least 10 PSI at idle, I am good to go. There is no real reason to need more, "just because".

Bends in oil lines or oil filter / cooler fittings (especially sharp bends of 90degrees or more) and various machined passages will raise oil pressure without benefitting the lubrication of the motor, in fact they are a detriment to it.

It's OK if you know the engine and it's tendencies and at that point find your oil pressure is unusually low or high, but if you are just panicking for no reason it's time to take a step back and find out what numbers you should be getting. Where you place your gauge or sender can affect the reading as well; if the numbers seem out of range, take the necessary steps to rule out unintended consequences that may be giving you an improper idea of what the pressure is at the critical areas (typically main bearings).

It's not difficult to drop the pan on many motors and have a look, do a measure, and even replace worn bearings before buttoning it up again.
 
Old vintage engines tolerate thicker oil better then new engines with much tighter clearances
and higher piston speeds where on-spec oil is needed to lube the pistons 'just right'.

While I slapped in 20W50 in a Slant 6, (that being the heaviest oil I could get in town)
I would not want to try it on a late model engine!!
 
Originally Posted By: i_hate_autofraud

Old vintage engines tolerate thicker oil better then new engines with much tighter clearances
and higher piston speeds where on-spec oil is needed to lube the pistons 'just right'.

While I slapped in 20W50 in a Slant 6, (that being the heaviest oil I could get in town)
I would not want to try it on a late model engine!!


BMW until very recently spec'd 10w-60 for their "M" engines and Ford spec'd 5w-50 for the Coyote when in "Track Pack" form, despite spec'ing 5w-20 in plain-jane GT form.

Also, temperature is a far bigger driver of viscosity than what you see on the bottle. At -30C 0w-20 is going to be much, MUCH heavier than 20w-50 in Arizona.
 
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