Engine oil temps

[gunt]

i know its 20yrs ago and oil tech has come on a lot but so has engine tolerances , but i was always thought 175 - 150 was the working range of oil

[Belgian1979]

I see my dd get to about 212°F not much higher, lower when outside temps are lower. My Corvette runs oil temps which are a little higher than water temps, so in the 195-200°F but I have never seen it climb above that.

[peejay]

i know its 20yrs ago and oil tech has come on a lot but so has engine tolerances , but i was always thought 175 - 150 was the working range of oil

Modern oils, especially ACEA rated oils and some of the manufacturer specific standards, work just fine when hot. They want the oil hot so any fuel or water contamination boils right on out.

One major thing most new cars have are oil coolers... or more precisely water/oil heat exchangers. When the oil is cold but the water is up to temp, the coolant heats up the oil. When the oil gets hot on its own, it gets hotter than the coolant and transfers the heat back to the coolant where it can be shed by the radiator.

[hoffman900]

Besides oil technology, CFD and it’s ability to model fluid flow has undoubtedly helped the OEMs and high end race programs. A lot less guess work and more knowing how heat flows between the materials, where it needs to be, and how to get it there.

[ptuomov]

i know its 20yrs ago and oil tech has come on a lot but so has engine tolerances , but i was always thought 175 - 150 was the working range of oil

Modern oils, especially ACEA rated oils and some of the manufacturer specific standards, work just fine when hot. They want the oil hot so any fuel or water contamination boils right on out.

One major thing most new cars have are oil coolers... or more precisely water/oil heat exchangers. When the oil is cold but the water is up to temp, the coolant heats up the oil. When the oil gets hot on its own, it gets hotter than the coolant and transfers the heat back to the coolant where it can be shed by the radiator.

We run an air-to-oil and an engine-coolant-to-oil heat exchangers in series. There’s an oil thermostat and an engine coolant thermostat so we don’t get the oil heating effect though.

[bentvalves]

hot oil (212-220) and cooler water (170-180) is where a racing engine is happiest as far as I know.

[Steve.k]

All good info everyone. I’ll definitely have to rethink how i was setting up things. I was waaaay on the cool side by looks.

[Schurkey]

540Rat does temperature-testing of various oils, the better ones seem to be ok at 270+ F. That might mean 200--240 in the pan, because the oil coming off the bearings is likely considerably warmer.

https://540ratblog.wordpress.com/2013/0 ... t-ranking/

[BigBlockMopar]

Just curious... why would one want to have overly hot engine-oil temps?
Only thing I can think of is first, proper evaporation of unwanted moisture (but that also already happens at 180°-200°F), and second is to just lower the viscosity of the oil, freeing up internal drag and friction of the moving parts.

Downsides I think of:
Heat-energy transfer gets to be less from metal to oil if the oil is already hot to begin with.
Service life of engine gaskets and seals are shortened by hot temps.
Parts get baked easily with contaminants when oil isn't serviced on time.

[Belgian1979]

Water evaporates at temps lower than 212 °F (100°C). So, when driving long enough it would be so much of a problem.

[ptuomov]

My thinking has always been that one wants to boil water out of the oil as quickly as possible before any load is applied. That would argue for 212F+ in the sump. This is because if there’s still water in oil when it’s lubricating a high pressure metal to metal interface, the result is hydrogen embrittlement.

[Steve.k]

I always figured the metal surfaces in engine would likely be hotter than 220 even when oil temp is lower. That would get rid of any moisture would it not?

[ptuomov]

I always figured the metal surfaces in engine would likely be hotter than 220 even when oil temp is lower. That would get rid of any moisture would it not?

I don’t know. But I am thinking that I don’t want the water in oil being under pressure in gears or under cam lobes or whatnot, so safer to boil the water out in the sump?

[Kevin Johnson]

... As shown in Figure 1, the saturation point will also change with temperature, as fluids absorb more water at elevated temperatures (i.e.the water solubility increases with temperature).

The diabolical nature of physical chemistry and combustion by-products: aligning the forces of the cosmos against the engineer at every step. Bwahaha.

https://www.machinerylubrication.com/Re ... minant-oil

[ptuomov]

The safe maximum temp of motor oil is high enough that it’s just simplest to boil the water out of the oil.

As was mentioned above, vacuum helps. Alternatively, if vacuum is not used, positive breather system helps by pulling dry outside air into the crankcase and pulling wet air out.