Doing a little spirited driving today (and it as quite hot out... for here, but nothing like Texas or Florida conditions), keeping between 3500 and 4500 in third gear (I have a 5-speed) and the oil temp quickly rose to 220degF. Water temp stayed steady at 180degF.
That oil temp is not uncommon, but usually occurs when driving in town with traffic and hardly moving. Today was different as I kept the rpms up, which I don't usually do.
I'm running an Aviad pan (9 qts there-abouts) so it won't cool as quickly from air underneath due to the volume, but still....
Am using 15W50 Mobil 1 synthetic and bearing clearances are 0.0025"
I am wondering if the thick oil is getting hot due to friction from viscosity, or is it just absorbing engine heat that is too high for some reason. Engine runs great otherwise.
My concern is my oil prssure at 2000 rpm is usually a bit over 40 psi, but it dropped to about 35 due to the temp. No doubt it won't hurt, but I never liked oil pressure that drops for an unknown reason.
I wonder if I should be using a thinner oil to reduce friction, but then again, when the 15W50 thins out, it would be close to 10W30 anyway, so why doesn't it stablize a bit cooler? Such a drastic difference between water temp and oil temp... so I'm confused.
By the way, when I rebuilt the engine, I used Castrol GTX 10W40 for break-in, and I noticed the oil pressure was a bit higher, most noticeable at idle. Don't remember the temps, but I never drove it like I did today.
This message has been edited by Argess on Jun 25, 2012 7:35 PM
Yes, the 220 doesn't bother me very much; It's the difference between water and oil temps that I find a bit of a puzzle. It's probably just due to the 9 qt pan not being able to get rid of the heat, but I was wondering if there was any other causes.
Also, as I wasn't pushing things too much, (just keeping the rpms up a bit), I was wondering where the oil temp might stabilze if I really pushed the engine hard for a while.
When working a engine hard it is not unusual to see oil temps 40 deg higer than coolant temps. We see this all the time on large trucks, That had engines that lasted 1,000,000 miles before doing a inframe overhaul on them.
I have two Detroit Diesel powered gen sets, one is a 2-53 @ 20kw and the other is a 2-71 @ 30kw both @ 1800 rpm. The little set has 30 wt oil and the bigger has 40 wt oil (have to run low ash single grade oil in Detroits!!). Oil temps from an IR type gun run about 190 to 215F or a little higher at the pan under slightly less than full load. According to the factory specs, this is normal and expected. The factory operations manuals warn about running the engines too cold, and the issues that are caused by this (short sleeve life, piston varnish, valve varnish and carbon buildup, fuel wash down of the pistons and rings, etc). Both sets can and will run non stop for 3 24hr days at full load with no issues. And in a Detroit, all the water goes from the pump outlet directly into the oil cooler first and then through the engine block, up through the head and back out to the radiator. The oil cooler in effect, pre-heats the water going to the block. If everything is right & new and the engine is clean to start with, the oil stays quite clear, like a newer gas motor. This is because a Detroit will re-burn its own blow-by waste gases past the top rings through the air box and back up to the combustion chamber.
Not a GM car guy, but these 2 cycle engines, considering that GM started building them in the late 1930s, are really well engineered, have the most intricate iron block castings of their vintage and are very adaptable to all types of uses. Consider that MTU is still building 6v53TTIs for the US Army that put out 400+ hp from 318 cid in a tracked off-road troop carrier (last of the M113 family). Not too bad for a 70+ year old design.