Mixing Oils - Amsoil 0W30 (TSO) & 15W40 (AME)

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Jun 24, 2003
Palatine, IL
Well, I asked this question because I had an appt for the 7,500 mile service today (free),which has to be done before 9,000 for it to be free, and I was getting close to the limit. I thought I had 2 gallons of S2k, but one of the gallons was the 15W40, so I was in a bind. I had them put in 4 qts of S2K 0W30, and 2 qts of 15W40, and they filled the Blackstone bottle with the used. Anyone have any idea what vis. oil I now have in my crank? Have I made a huge mistake? Depending on the UOA results, I will go with either a less expensive Amsoil (5W30?), or RedLine (5W30 or 5W40). Redline gets the nod if the S2K was beaten up, and Amsoil gets the nod if the Amsoil was in good shape.
You can mix any synthetic with any oil, however, chemistries with Amsoil are all different and they don't recommend it. I was told this by Amsoil tech. It won't hurt, but your not getting the optimum benefit of a particular oil by doing this. [Cheers!]
Oh, I forgot to add that the mechanic and service advisor gave me grief for using synthetic before 10K miles. They said "Volvo recommends waiting until 10K miles before switching to synthetics". I replied, "Yah, and Volvo also recommends using dino oil for 7,500 miles on a turbo motor". The Mech replied that they (the dealership) recommend cutting the 7,500 OCI in half when using dino. The service advisor then interjected that the problem with the 7,500 OCI is that people don't check the oil, and they run them low on oil. I then stated that I thought the 10K break in rule was a load of crap. The Mech asked me if I had seen the inside of my motor. No, I replied, but I have 5,500 miles on the current oil, and the dipstick still reads full - seems like she is broken in just fine to me. I suppose the UOA will help determine if the 10K break in rule is bogus or not. [Cheers!]
I have a 1 gallon jug of Amsoil S2k 0W30, 8 qts of Amsoil 15W40 Marine/Diesel oil, and my car (Volvo S60 R - Turbo) is due for an oil change (takes 6 qts). Currently, I have no plans on using either of these specific oils in the future, so I would like to finish off my supply of both. Would it be a mistake to mix 4 qts S2K 0W30 with 2 Qts 15W40? Would I be better off with going with 6 qts of 15W40(I live in Chicago). Note that I am changing the oil mostly because it is free from Volvo. I could simply have the filter changed, and add one qt of 0W30. Your input is greatly appreciated. BTW - I will be performing a UOA on the S2k that is currently in the car (5,500 miles on the oil, 8,000 on the car).
[Frown] After reading this I wouldn't mix. Polyalphaolefin (PAO), organic esters, glycols and phosphate esters are examples of synthetics that are used to meet specific needs. Synthetics are used where the value of their special functional properties, oxidation stability, fire-resistance, etc., outweigh their cost. Lubricants made with synthetic base stocks should not be mixed with products made with mineral oil, even if they are designed for the same application. The limited exceptions include some PAO and ester-based products. Even then, compatibility is often concentration-dependent. Deposits may form because of additive incompatibility or seal compatibility may be compromised. [No no]
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