Engine Oil

I do not switch to synthetic til the engine is broken in. I have been using Amsoil and one year had to do a valve job on a Subaru engine with over 100,000 miles. There was no ridge in the cylinders and the hone marks from the origionaol build were still faintly visible.
I switch to all shynthetic oil, engine, transmission, differentials and in this kind of weather, single digit and below zero it is worth a couple of mpg because of a lower pour point. It also has higher tolerance for heat before coking. Subaru #11 went to the junk yard with over 300,000 miles and these are a high RPM engine.

I use Mobil 1 in MH and change oil once a year. Usually no more than 7,000 miles between changes. Unlike Gonzo42 I buy mine at Wally world.....5qt jug for #25.17 and 1 qt bottle for $6.36. Never had any problems. Happy travels.

My vote is for Mobil 1, I have been using it since 1999 in all of my vehicles.

Bob

Blend

I run Full Sythetic when I'm towing, because I run pretty heavy (22,000 combined typically) and drive it pretty hard (Ave speed across the midwest is usually 85 MPH). But mostly because when I'm towing I'm putting on a lot of miles, which means 10-12,000 miles between oil changes.

When I'm not towing, I just run MotorCraft 5W-20 Synthetic blend, because not towing means more short trips, and I like to change it at 5,000 miles under those conditions.

I'm just shy of 373,000 miles. Still runs great!

My Sprinter-based class C requires synthetic per Merceded-Benz and I got mine from Amazon.

Valvoline SynPower Full Synthetic Motor Oil SAE 5W-40 - 1 Quart Bottle (Case of 6). $45.48.

If you don't mind changing your own oil and filter and can wait a few days for delivery, this could work for you. I think the price is quite good, and shipping is free for orders over $35.

I don't have near the mileage success of TucsonJim but have been using Mobil 1 in my RV's since 2008, never any problems. Nice thing about synthetic oil is that you can go 5-6000 miles between changes or more (assuming that you're on a long trip). Otherwise probably should change every year or less if you're not putting much mileage on.

I've used full synthetic on all my gasoline engines for the last 30 years. I've never had an engine malfunction in that time. Here is the mileage when I traded them in or sold them:

1984 Mitsubishi Montero - 235,000
1994 Chevrolet 1500 - 175,000
2002 Chevrolet 1500 - 38,000 (Transmission failure at 37,500 - traded for 3/4 ton)
2004 Chevrolet 2500 - 130,000