Thanks for all the comments. I'll switch to the 5W30 synthetic. But I'm still wondering about the rear differential and using the 75W140. My RPO codes from the vin say G80-Rear Axle - positraction-limited slip, G75-4:10 ratio with a MT1- 4sp auto tranny THM R2(4L80E). I'll attach some photos of...
When I first got the unit I learned that a K3500 HD had the option for the heavier oil. Since I was running with such a heavy load I figured it was the safest thing to do and easier on the diff under load.
I've experienced a similar issue and even heard the sound of sloshing water when making turns or lane changes. I pulled off the wiper arms and cowling and found the water drains that drain to the inner fender. They were clear and the water flowed unimpeded. My water issue usually occurred in the...
My 1997 Sierra SLE 7.4/454 dually calls for 5W30. I've been using conventional oil and it purrs. I always have the Big-Bigfoot camper on it and it comes in at 12,000lbs when I cross the scale. It has 260k/160 miles. I use 75w90 in front diff and 75w140 in the rear diff. Minimal mileage so I oil...