Oil Change Mix-up
 

Couple of weeks ago I decided to pick up some oil and a filter at Autozone. I use the Castrol Syntec blend, 10W-40 for winter and 20w-50 in summer. This time I let the oil sit in the garage for a few weeks before I got around to changing it. All went well as usual, except as I poured in the last quart, I happened to glance at the jug. It said 5W-30. I looked at the other containers and found four of the seven were 5W-30 and the other three were 20W-50. I remembered when buying the oil there was none on the shelf, so I asked the girl stocking filters to get me the 20W-50. Guess I should have checked her work.

So, the question is, what is the effect of running this oil? I have noticed a decrease in the indicated oil pressure on my gauge. Normally, because I have a bad sending unit, the pressure stays at 3 bar from idle to redline. Now I am down around an indicated 2 bar at idle. Do you forsee any potential risk? I'm at about 83,000 on the odo. Thanks a bunch.

Dave

Sounds like it averages out to a 13W-42. No need to worry!

Duke

I wouldn't worry too much, but maybe this would be a good time for a cleansing oil change. If you were to do an overnight drain after getting the engine piping hot, it would cleanse the inside of the engine really well and give you peace of mind after getting in your favorite brew and a fresh filter.

Good luck,

Dave, I'd recommend changing over to the 20W-50 ASAP.

Duke: remember that the viscosity scale is not linear,
 

but sort of logarithmic: if you have a shelf with some 30 and some 10 and the customer says he wants 20, you need to put in two 30 and one 10 to get 3 qts of 20 (not 1 and 1/2 of each). It used to happen all the time at the Porsche dealers in the far north 40 years ago, where the factory said use straight 10 (multigrades were verboten, but that's what I used in mine, and got excellent wear) in the winter in that climate, but customers with their owners' manuals in hand would insist on 20. Of course, the interactions of multi-grade additives from two different types may complicate the picture even more.

Good Lord:eek: Oil weight cannot be mathmatically averaged like you just did. The viscosity(flow rate at a specific temperature) and additives generally determine the weight. You simply cannot mix a 30 weight and a 10 weight and call it a 20 weight. You can start blending your own oil if follow your suggestion ;)

Duke:

I think most of us here understood your sense of humor. Thanks for saving me from doing the math myself.

Dave

Why 20W-50? will 15W-40 works?

Oil viscosity selection is based on the lowest and highest anticipated ambient temperature during the period the oil will be in the crankcase.

Manufacturer's recommendations vary slightly, and in recent times they generally recommend lower viscosity oils than twenty years ago, but as a rule a 20W is okay to 20F, 10W to about 0F, and 5W for below zero, except arctic winter climates where 0W is the best choice. Using the logrithmic mean of 10W and 20W, 15W is okay down to 7.38765 degrees F. The lower viscosity range recommended by many OEs nowadays is an attempt to lower internal engine friction and eek a slightly higher number on the EPA mileage rating.

At the high end for summer temperatures the viscosity should be 30 or greater, but some manufacturers are recommending 5W-20 for year round use in all climates.

All owners manuals have recommended viscosities for expected temperatures, so if you want authoritative information for your specific make and model, consult the owners manual.

Duke

I looked at the user manual for 1988, 300E. From looking at the diagram that shows oil viscosities, 15W-40 is okay for southern california weather.

The problem is every mechanics I go to, he uses 20W-50, even the dealer uses 20W-50. I am trying to use the Chevron Delo 400, but they only make 15W-40? Is is okay for southern california weather?


Thanks a lot for de-confusing me..

The 15W-40 grade seems to be unique to the CI-4 rated HD diesel engine oils. Though I DO use 15W-40 Chevron Delo in my vintage cars that do no not have catalysts due to its higher concentration of detergent, dispersant, anti-wear, and anti-corrosion addtives, I DO NOT use Delo in my "modern" cars with catalysts including my 190. For these cars I use a conventional API SL 20W-50.

Modern cars do not need the additional additive concentration from the CI-4 oils because they have precise fuel control, which reduces crankcase dilution. Also, some of these additives are not kind to catalysts. Given that oil consumption increases with age and the 103 engines are already on the ragged edge of CA's ASM emission test, I continue to use SL oil in my Mercedes and recommend this practice to other owners.

On balance, I believe the potential pitfalls of using CI-4 oils in these cars outweighs the potential benefits.

Duke

oil ratings
 

An SL rated oil is an SL rated oil. I have never seen anything that said SL rated, but do not use in a car with a cat.

Just for fun I have used Shell Rotella T in my 94 Ford escort with 170K miles, mostly because I also use it in my 01 Ford explorer and my boat's diesels. I buy it in 5 gallon buckets and it makes my shopping list shorter.

I pulled the head on the escort the other day. Shiny and clean as the inside of beer can. Not a trace of sludge or mud or tar. Zero oil use. I had it smogged today (thank you California) and it was still at the minimums for everything except Hydrocarbons. New injectors needed maybe? But there is not a hint of problem oil related. I still think that I would have the same results had I used the house brand oil from WalMart, Kragen, etc. and the dreaded Fram orange can filters , which I did for the first 100k miles before switching to Motorcraft.

Use the most modern rated dinosaur oil appropriate for the climate, and change it every 5 - 7k miles.

Re: oil ratings
 

WHAT... are you talking about? Have you ever read the API label on a bottle of oil?

Duke