At what temp does high quality mineral oil break d

[Francis]

SO at what oil temp would a high quality 20w 50 mineral oil break down?

 

[Francis]

Come on guy's are you all telling me that no one knows at what temp Mineral oil starts to break down in an engine?

IF thats the case then why place so much impoertance on Syn oils with there sky high break down temps???

 

[Merkava_4]

Alright I'll take a stab at it. I would say 20W-50 conventional should be good up to 300 degrees Fahrenheit. Keep in mind though that I'm just guessing.

 

[Francis]

Thats fine, so lets say that a SBC V8 being pushed a little would get up to around 240 Deg F, then there should be no issue with it breaking down under pressure so long it was changed often?

 

[Merkava_4]

I would say that's fine as long you're using at least a 40WT - and no issue at all with a 20W-50.

 

[mechtech2]

When it 'breaks down' it can thicken, not thin.
Oils generally shear to a thinner viscosity, then thicken, if they are left in there.
240 F is not unreasonable, but it IS warm!
Do you know that you can lower you oil temps about 20 deg F by using a thinner oil? It has less internal drag and friction, and less of a boundary layer insulating parts.
Do you really need that heavy stuff in there?

 

[Merkava_4]

I think it's time that you give up the ghost and tell us the engine type, the vehicle, and the cooling system it's using. Because it sounds to me like you're worried about the cooling system's ability to keep the oil cool.

 

[Cujet]

No idea on the temps. However, non syn oil always leaves (often minor) deposits on the underside of pistons. The piston underside gets fairly hot, even under moderate conditions. The use of a quality syn keeps piston undersides like new.

Not here to argue the ill effects of piston deposits, just that the dino oil does break down in this one situation in nearly all engines.

Chris

 

[double vanos]

A quick viewing of this last years UOA's shows many times dino oils having a higher flash point at the end of a run than some of these so called full tilt boogie syn oils.

I don't know if that relates to how well dino oils endure the kind of heat you're talking about..just thought I'd mention it.

 

[bruce381]

ALL oils over 200F will start the oxidation process depending on additives and base oils used the rate of oxidation will vary without any good way to know sorry.

BUt generally a full syn will last longer than a semi.
Not answer you want but no way to Grade oils versus oxidation rate based on what is published or thought to be true only way is to have private dta from Mfg or run ASTM opxidation routines.
bruce