OK, I'll fess up. I run 15w40 diesel oil in my truck in the summer. Come winter it comes out and 10w30 goes in. Well we had a bout of early near 80 degree weather recently and the old engine wasn't sounding happy on the low viscosity oil. So, since I'd just changed the oil in a couple tractors and used the last of the Delo, and I had a small bottle of STP on the shelf. Well yes, yes I did put it in the 51. And yes the old viscosity enhancer did quieten things down nicely.
I'll pick up a few cases of Delo in the near future and change the STP contaminated out for Delo and summer driving.
RonR
