My recent oil analysis


Irregularly I send off oil samples. Attached is the latest one. Oil is Brad Penn 20W50, an highly respected oil among oil geeks. IIRC this oil has 14 track days on it which was 6 track weekends and a couple Friday’s. I told Blackstone 20hrs. I’m pretty sure I changed the oil last Winter. I wish I was more positive about that tho. It would make a big difference in how this oil report is interpreted. If I was too lazy to change the oil load last Winter then this is the first oil load this bottom end has seen, not counting it’s break-in oil.

This is one of the bottom ends I built at Metric Mechanic. Except for some gouges in the cylinder walls and having to hone them a little big to mitigate, it’s a helova bottom end. The bearing clearances and static balancing were done tighter than OEM specs. Premature bearing wear on this motor would be an irksome surprise.

The head and cam has 2.5yrs on it, except Rich Bratton and I lapped the valves last winter.

Things to note.

  1. High iron, copper and lead. That’s worrisome. Iron means rings and cylinder walls. Lead means bearing wear, copper means serious bearing wear. Understandable if this is the first real oil load the bottom end has seen. Not so understandable if it’s the 2nd oil load. The fact that my oil pressure is still pretty good, I’m hopeful that my bearings are indeed ok. And if not there’s 2 more bottom ends in the garage ready to go.

  2. Low moly. Brad Penn oil is not a high moly oil like Royal Purple and some race oils.

  3. High silicon could be my racy air filter not filtering as well as an OEM air filter.

  4. High calcium content probably indicates that there’s plenty of detergent left.

  5. Zinc and Phosph, indicative of ZDDP, is mid-range. BP oil has a lot of ZDDP but it’s consumed by both mechanical action and also the calcium. The oil probably started out with 1400ppm of each. The reduced ZDDP indicated here would be a reason to change this oil load.

  6. Visc 14.65. This is mid-range for 40W. The visc of BP 20W50 (20 cSt@100degC) is at the high end of the 50W band so I’ve lost a fair amount of viscosity. That is to say, my oil became thinner. This indicates a fair amount of “shearing” of the long carbon chains. This syncs with the fact that I’ve observed less oil pressure (55psi) at red line over the last couple of events vs. earlier in the year.

  7. Fuel <.5%. This indicates my injectors are not leaking…a common problem with cheap or cleaned injectors.

  8. No water. Always good.

  9. Low insoluables. I use the Purolator Pure One oil filter. You won’t find it spec’d for our car. Instead, get the one for the Audi TT.

  10. TBN. Total Base Number. This is a measure of the acidity of the oil. The oil’s detergent keeps the acidity down. When the acidity # gets down to 1 or 2, your detergent is pretty much consumed. My oil started with a TBN of 10.2 so at 4.2 now more than half my detergent has been consumed.

Why change this oil load. #1 is that the Zinc and Phosph #'s that have dropped a bit low. The loss of visc isn’t a crisis, I’d be comfortable with another couple of weekends. With the viscosity going down the High Temp Shear (HTHS) #'s are sure to be going down too. BP oil has fabulous HTHS #'s, which is a reason it’s well respected, but if visc is going down, HTHS is sure to be going down too. I just don’t know how much.

TBN. I’d have run another of weekends with that TBN. Acids are still being consumed.


Viscosity chart

Brad Penn specs


WAY too long on oil change…I change mine every 2-3 races and I hold 11 quarts. I also always add extra MS02 when I change. How long do you go on trans and diff oil???


I disagree. This is longer than I’ve gone in the past between oil changes, but I was curious as to what I’d find in terms of the oil’s remaining life. I don’t see anything in this report that tells me my additive package is entirely used up, nor my oil worn out.

I’ve been changing tranny and diff oil every 2yrs.


How does this compare to other samples you’ve sent in the past? Same oil brand and type?


It’s hard to compare analysis results because I’ve played around with so many engines. The last several years I’ve used Brad Penn 20W50 oil.


Thanks for the tip on the Audi TT Pure One filter.


I would think running oil that long on the track would be comparable to 50k street miles! Would also indicate to me lack of film maintenance in the bearings, maybe oil pressure fluctuations not caught by monitors? Has hot OP dropped the last couple of races?


Hot OP has dropped a bit. Maybe from 65psi at RL to 55psi.

All: The drop of hot oil pressure is to be expected because visc dropped from 20 to 14.65 (cSt@100deg C), likely do to shearing of carbon chains and the wearing out of visc modifiers. 20W oil + visc modifiers = 20W50. As the visc modifiers wear out the oil becomes 20W40 then 20W30. One of the charms of a full synthetic oil is reduced reliance on visc modifiers.

The unknown is how much HTHS dropped while the visc dropped. Crappy oils depend on high visc for decent HTHS #s. Good oils tho manage good HTHS #s w/ less visc. That is to say crappy oils need to be thick to protect well, but a person can go thinner on good oils.


I change every 2 weekends and use oem filter, Rotella with zinc added…

Trying some of that fancy French oil next race…

I have Cat lab check my oil…$16



Ranger – what’s the model year to use to find the correct Audi TT filter?


Not sure. I’ve never paid much attention to that. I just pick and older model and it’s always resulted in the right oil filter. I just looked up the part # from my notes. PL20252.