Jianis,
I use straight 40 in my truck year round. 30 leaks out with too much enthusiasm.
Now, when it gets cool outside, below 5 degrees celsius, I use a block heater, and most importantly, a magnetic heater on the oil pan, to warm the oil before starting.
Even still, when first started, the oil pressure is 15 or more pounds at idle. Just like in the manual, when you start out driving in the cold, you want to keep the engine rpms low, and keep the oil pressure below 30 pounds.
Cleaning the pan out is a great, and easy way to judge the condition of your engine. I imagine your fleet master is similar to my Pontiac, you have to undo parts of the steering to get the oil pan off it. Cleaning the pan out with kerosene after its removed is quick and easy. If you don't have time to do that, just use non-detergent 30 oil. The manual for my Pontiac recommends a slow switch from non detergent, to detergent oils. I always go by the book, I figure that the engineers who built them, knew what they were doing. I think a bigger risk than having some sediment in the pan and dippers, is having sediment in the rocker tube. When I took the rocker arms off of my truck, I was surprised to see that the tube was half full of sediment.
