Hi there,

Been wanting to ask these questions, particularly the first two, for quite some time (like nearly 10 years):

1.) I used to work as a lube tech. Diesel passenger pickup trucks had to be filled up to about 14qts of engine oil. We would start the engine up to conduct a basic pressure test, and then once in awhile we might have to drop half a quart or so. But why does the oil go in yellowish, yet in that 30 seconds, come out black like it's been used?

People have given me a number of theories, but no real explanation -- such as "It's dirty inside and it's picking up contaminants." ??? If it was that dirty inside, how could it even run? Crank bearings, valve guides, piston rings, hydraulic lifters, tensioners etc would be TOASTED.

The rest of these questions are more generic, but I don't want to create additional threads for relatively easy questions.

2) At the typical running temperature of an engine, which is about 190-200 deg F, if I am running 20W-50, what might be the "viscosity" of the oil right then and there? 50 weight? 40 weight? 45? 30? What about 10W-40 -- might it be maxing out at 40 weight?

3) I have run Castrol GTX (non high mileage) for all my prior BMWs and my present 'yota. Is it "decent"? "Good enough"? I just put in 10W40 in the 'yota (1991 2WD pickup with the 2.4L 22RE mill) and I heard that that is *bad* for that motor. (I used 20W-50 in all the BMWs, they were E30 325e, 325i and 325is models.)

4) One last real off-topic question. If I run aftermarket lights, can't I be stopped by LEOs to make sure the lights are DOT/SAE rated? If they don't have DOT/SAE markings, am I supposed to carry paperwork to prove that they are rated as such?

Thanks!


Edited by Raven (12/02/13 05:34 PM)