Oil temp and viscosity

PeteF · #1 (**permalink**) 03-22-2012, 03:17 PM

I have a 351W rebuilt by Jasper Engines with 41,000 miles. I have had a concern with low oil pressure at idle, around 12 psi when fully warmed up, but the engine has been this way for the 4 years I have owned the car, and has not caused any problems. For my spring oil change, I decided to run Castrol 10W40 instead of the Castrol 10W30 I had been running previously (both conventional dino oil). I expected to get some increase in oil pressure with the higher viscosity. I did get a slight increase in oil pressure at idle, now around 15 psi, but I was surprised by an increase in oil temperature. Previously, with the 10W30 oil, my oil temp would run only around 160 deg F in normal driving, and maybe 180 - 190 when I worked the engine hard. ( I previously removed the oil cooler trying to get oil temp up). Now, after only the viscosity change, normal driving oil temp is 200 deg F, and 210 - 220 working it harder. I am surprised at the 40 deg F increase in oil temp. I attribute the increase to reduced oil flow rate due to the higher viscosity, where the oil is picking up more heat and carrying it to the pan (where the oil temp sensor is). I always thought oil temp should be around 200, to boil off any moisture, so I am OK with this new situation. Does anyone think I am giving anything up, or have similar experience to share. Thanks

JBCOBRA · #2 (**permalink**) 03-22-2012, 05:15 PM

Don't worry about the low pressure at idle. Mine was making about that much at idle. The bearings were great when we took it apart. How much pressure does yours make while driving?
My pressure gauge reading is on the light side by 3lbs. Maybe your is too?
You are correct about additional heat also.
JB

PeteF · #3 (**permalink**) 03-22-2012, 05:47 PM

Oil pressure starting cold engine is 60 psi, then about 35 - 40 psi when warmed up at speed. I always have more than 10 psi per 1000 rpm, that I read was enough (old Smokey Yunick rule). I think I'm ok. Thanks

RWD · #4 (**permalink**) 03-22-2012, 07:01 PM

You may want to check-out BITOG (bobistheoilguy.com) - the Motor Oil University articles discuss how oil viscosities (dino and synthetic) vary with temperature.

JBCOBRA · #5 (**permalink**) 03-23-2012, 07:48 AM

You are fine. Flow is way more important than pressure

That is where mine was and the bearings were perfect.

Quote:

Originally Posted by PeteF

Oil pressure starting cold engine is 60 psi, then about 35 - 40 psi when warmed up at speed. I always have more than 10 psi per 1000 rpm, that I read was enough (old Smokey Yunick rule). I think I'm ok. Thanks

Gaz64 · #6 (**permalink**) 03-27-2012, 04:41 AM

Quote:

Originally Posted by JBCOBRA

You are fine. Flow is way more important than pressure

That is where mine was and the bearings were perfect.

Great to see others say the same thing.

Flow is more important as it's keeps the bearing lubricated and cooled.

Tight bearings, less flow, less lube, next to no cooling, then overheated bearings, then bearing failure.