What temperature does synthetic oil actually degrade at?

[NorthernDriver]

We all know modern API-approved oils are good to go with manufacture oil change intervals.

However is there a magical temperature that oil loses its properties at? I am asking because I’ve started to attend HPDE lapping sessions. I’m curious since the oil temp stays higher on track than steel use. Based on my research there are two camps:

1. Replace oil immediately after track day
2. Track use is easier in oil than stop and go, just follow OCI for lapping (non-race) use.

 

[Jimmy_Russells]

HTHS is measured at 150C (302F) so I would guess around there or even slightly higher

 

[Fa24wrx]

I'd do a UOA after tracking if possible and see what the oil looks like.

I see tracking as something that has several consumable expenses (oil, brakes, tires, etc.)

 

[NorthernDriver]

I'd do a UOA after tracking if possible and see what the oil looks like.

I see tracking as something that has several consumable expenses (oil, brakes, tires, etc.)

This is in the plan next season

 

[Jetronic]

Oil degradation rates go up with rises in temperature, but one oil isn't another and one engine isn't another. And we could add one event isn't another.

however the temperature at which oil dies a quick death is higher than you will see on track, I doubt the temp gauge goes high enough. Thinning might become an issue sooner though.

 

[Danno]

Interesting video stressing engine oil.. The oil light is triggered at the 21:35 mark.
Low oil pressure warning.
Would an HTHS oil rating of 3.5 or higher prevented this?

 

[gfh77665]

However is there a magical temperature that oil loses its properties at?

No, there is no "exact" temp where it degrades. For example, if "250" is the answer, that does not mean the oil is perfectly fine with zero degradation at 249, but at 251 its falling apart. Its somewhat of a linear process. The degradation process starts low, and ramps up into very high temps. A quick search tells us:

• Conventional motor oil: Can withstand temperatures up to 250°F, but starts to break down at 275°F
• Petroleum-based engine oil: Begins to oxidize, or break down, at around 240°F
• Full synthetic oils: Can handle temperatures above 300°F, and some can withstand temperatures as high as 700°

Time is a big factor. Running the oil at 275 for 5 minutes is nearly nothing. Running it at 275 for an hour is very different.

 

[twX]

The main concern with high oil temperature is oxidation. Oxidation rates roughly double for every 10°C increase in oil temperature. This starts becoming a significant factor with regards to oil life when the oil is above 120-130°C. This is based on sump temperature. The oil will be a lot hotter than this in some parts of the engine.

Here are some examples of oil life vs temperature from some studies on oil life monitors:

 

[SHOZ]

I did two track days and 5k miles on M1 5w30 when the Gen Coupe was newer. Then tested the oil and it came back still OK to use but some fuel dilution. The track laps sessions were always cut a lap short due to high oil temps nearing 300F.

 

[gfh77665]

Would an HTHS oil rating of 3.5 or higher prevented this?

Highly likely using a 5w30 this never happens.

Either way GREAT job RAM!

 

[twX]

Interesting video stressing engine oil.. The oil light is triggered at the 21:35 mark.
Low oil pressure warning.
Would an HTHS oil rating of 3.5 or higher prevented this?

The warning came on just as the idle oil pressure dropped to 19 psi. Dodge seems to have used a really conservative pressure limit for the warning, especially since the oil was only 235°F.

Most cars have a simple pressure switch that activates at 2-5 psi, and the light coming on represents a major problem. On this truck it seems like it can be more of a nuisance alarm.

I doubt 19 psi at idle is doing any harm to the engine, but yes, a thicker grade of oil would require higher oil temperatures before the pressure warning trips.

 

[The Critic]

Interesting video stressing engine oil.. The oil light is triggered at the 21:35 mark.
Low oil pressure warning.
Would an HTHS oil rating of 3.5 or higher prevented this?

Probably. Looks like the truck had almost 5K, probably original oil fill, so the oil had some degradation plus fuel dilution. So, the oil's viscosity was already on the low side. Add in high temps, and yes, I can see how the oil pressure might get a bit too low.

 

[Jetronic]

Interesting video stressing engine oil.. The oil light is triggered at the 21:35 mark.
Low oil pressure warning.
Would an HTHS oil rating of 3.5 or higher prevented this?

Just going up a grade would likely have prevented this. Rule of thumb, for what rules of thumb are worth, is you can go about 20°F higher for every SAE grade increase before you are at the same viscosity again. A 3.5 cP HTHS oil is going to be a 30 weight or up, Is that truck running a 20?

 

[Jetronic]

Probably. Looks like the truck had almost 5K, probably original oil fill, so the oil had some degradation plus fuel dilution. So, the oil's viscosity was already on the low side. Add in high temps, and yes, I can see how the oil pressure might get a bit too low.

it dropped just below 20 psi, that wouldn't worry me at idle though

 

[The Critic]

Just going up a grade would likely have prevented this. Rule of thumb, for what rules of thumb are worth, is you can go about 20°F higher for every SAE grade increase before you are at the same viscosity again. A 3.5 cP HTHS oil is going to be a 30 weight or up, Is that truck running a 20?

Standard versions run 0w20, HO runs 0w40 iirc.

 

[TiGeo]

I have done some extensive track testing...some info here. Bottom line is that I see 280+ temps on track in my Sportwagen using HPL 5W40 Euro and UOAs indicate it's just fine. Will be using all of this year so ~8 track days plus normal driving.

https://bobistheoilguy.com/forums/t...pl-longer-than-4k-ocis-with-track-use.377763/

 

[Vercingetorix]

I would be more concerned about the max temp the oil sees in the engine. The gauge reading may be 300 but the oil may have cooled down after peaking at 350.

 

[Rand]

Standard versions run 0w20, HO runs 0w40 iirc.

So upgrading the engine to the HO spec's oil grade would have prevented this?

0w20 in a TT 400hp+ engine doing a mountain towing torture test(100f ambient at start?) If I was using my truck for that it wouldnt be getting 0w20..
So I know I'll get slaughtered on bitog for it but I'd give the Ram a pass.

The Chevy with the 6.2 overheated the transmission to 300f and had to pull over.. and the Ram's trailer was 50% heavier than the Chevy's?(7000 vs 10500lb)
Obviously at low speed the trailer weight makes a bigger difference than the wind resistance (20-35mph)

Ford gave a coolant warning at 250f Seems like they need to beef up the fans.. or something.

 

[gfh77665]

Yeah the RAM just killed this test! Ford and Chevy not so much.

 

[benjy]

a lot of variables beside oil choices for sure!!! a vid by a pro Savage Geese noted even though "things" look fine including an analysis checking the engine bearings MAY tell another story $$$$.