I noticed my oil got black alot quicker lately so I sent a sample off for analysis. In the middle of the report under "comments" it says viscosity was SIGNIFICANTLY low. I checked my old oil container and its Castrol GTX 20W50 like i've always used. Anyone ever run into this problem before or know why it dropped so low??? I change my oil religiously.

It's not fuel diluted because it shows <1% fuel

 

Are sure you had 20w-50 in it when it was tested? How many miles were on the oil and how hard do you run the car? Check this out, it will go over a few reasons that will cause low viscosity. http://www.machinerylubrication.com/.../low-viscosity Or who knows, maybe there was an error in there test too.

 

A viscosity of 13.3cSt@100C means that the oil has broken down to the SAE 40 range. Oh, the horror!, lol. They probably give the stat an "abnormal" rating when it drops by one SAE grade.
http://www.widman.biz/English/Tables/J300.html

FYI the color of the oil isn't such a good way to determine if oil is bad. The black color usually means that the oil is doing its job of keeping soot in suspension. Shifty auto mechanics sometimes use the "black oil" scam to convince their customers that they need an oil change.

 

Heard bad things about castrol oil. Try switching it up to valvoline or something.

 

Thanks for the good info all. I thought 13.3 wasn't bad but wasn't sure what it equated to. I checked old analysis when i had fuel dilution years ago and once i fixed that problem i had 12.96 and they said it was ok.

I've used Castrol for twenty years in this car. Castrol may be junk now but it has given me 192,000 miles on the original engine.

 

Castrol GTX is the most recommended oil brand for our engines. It has produced excellent results in my RX-7s over the past 22 years, and all of my friends like it too. I don't know where you heard that Castrol was bad, but it was probably from the Valvoline dealers, lol.

 

yea I started using Castrol GTX 20W-50 in my Turbo II after my friend bought an 86 GXL with 368,000 miles on that biatch. The original owner said the first engine lasted 289k miles and he even autocrossed it all the time, his receipt for konis and springs is dated 1991! btw, he used Castrol GTX 20W50 every oil change (which I think was every 2500 miles).

I just hope the Walmart brand of GTX isn't too different because that's what I always get, and last time I noticed the label even says Walmart on it, so it's not the same bottle that would end up at Autozone or whatever, but hopefully the same contents.

 

WOW! That's alot of miles, must have been very well maintained...

FWIW: Rebuilt 87 TII Castrol GTX 20-50w about every 2K miles. Tuning and low AFR's probably resulted in the fuel content.

 

You know I thought the same thing due to all the good things I have read about it on here.

However, the other day I brought it up to Paul of Rotorsports (30+ year rotary specialist, former mazda master technician), and he said castrol is junk and the poor quality shows after all the engines he has torn down that used only castrol. He told me for a good non synthetic that Valvoline was what he prefers.

Anyways it is just word of mouth info (which I mentioned) and I have not done any scientific experiment yet to verify it lol.

 

Come to think of it, I did buy the Castrol oil at Wal-Mart. It has to be cheaper than other Castrol's sold I'm sure.

 

I doubt that the oil is any different, just a little cheaper because they buy and sell so much, but still the same blend oil.