Originally Posted by barnym17
I was baseing the temp on the fact GM turns on the electric fan at approx.235 degrees in many newer vehicles including the 3rd and 4th gen F- bodies.Again 210 is just about perfect as the oil temp must be over 200 to rid itself of harmful moisture etc.
The factory runs 220 and up coolant temps and 5W-XX Energy Savings oil strictly to meet EPA/DOT fuel economy standards. These things have no relativity beyond that to the real world. The engines are still principally made of gray iron which isn't anymore friendly to overheat temps today than is was 50 years ago.
Back in the Hyper aircraft engine era of the late 1930s and early 40s the Army Air Corps tried to run up engine temp into the 300s F and it didn't work with motors built from billet chrome moly steels and forged aluminum/magnesium alloys; so why people today think that something magic has happened with the auto-industry's wonder metal, cast iron, and it's limited use of cast aluminum is beyond my reckoning. Physics hasn't changed the limits of these materials that I'm aware of.
I rather think that a 180 thermostat with a hot day coolant temp of 190-200 is plenty high enough. As was stated the oil is running 20 to 40 degrees more which for mineral oil at 220-240 is getting edgy. Plus at those temps, 5W-XX mineral oil has the consistency of hot water. Synthetic oils are more tolerant of these temps, but still that's plenty hot. If the slightest thing goes wrong you can be over the edge in an instant and from the number of toasted engines I see, it happens a lot especially with trucks and SUVs hauling the family on vacation.
One has to be careful about OEM oil coolers, since the 90s the factories have run engine oil into a radiator mounted heat exchanger as they do with auto tranny oil. This however is not done to cool the engine's oil; quite the opposite, it's done to heat it so the engine warms faster so mileage improves sooner and the emissions come down faster by eliminating time it's on cold enrichment (choke). While there are some striking advantages to doing this, there is no way that you can depend upon this system to protect your oil from overheating, especially when the engine is working hard or is running in slow moving traffic on a hot day. To truly cool engine oil you need a stand alone cooler. To take advantage of the OEM system to shorten warm up time and keep the engine oil cool the way to replumb this is take pressure oil into the factory heat exchanger. Coming off the exchanger flow into a thermostatic bypass valve. When under 160 degrees the oil is returned to the pan, when hotter the valve routes the oil to the external cooler. On a hot day this will take 10-20 degrees off the cooalnt temp as well as keeping oil temps around 210-220. Plumbing the automatic transmission the same way will do similar things to the engine coolant and tranny fluid temps as well.
I won't run Energy/Fuel Savings oil in anything whether it's mineral or synthetic base, the thinnest I'll put in an engine is 15-40, for myself 20-40/50 the year around.