Originally Posted by
DGMFORD
when started in the morning and cold outside, the truck runs like crap, seems like when I first got it back, it ran good, but it was still warm outside. It takes a good 5 to 10 minutes for it to really warm up and start running good. All other starts from that point are good unless it sits all day. One last thing, if I plug it in and start it the next morning, runs like a top.
So the truck starts good when it's warm out. If it's cold it has to warm up. And if it's plugged in all night it runs fine in the cold morning. Sounds like the oil is to heavy for the cold weather. So let me explain oil. Multi weight oils are made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number (15) indicates the viscosity of the oil at a cold temperature ( W= winter), while the second number indicates the viscosity at operating temperature (40). So if you're using 15W in your diesel in the cold and start your truck the oil is very thick like honey vs. 5W which will be thinner like water at cold start but once at operating temperature will still be 40weight just like the 15W40..... The viscosity rating is basically just the fluids resistance to flow.