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3416H

Simplicity 7790 diesel motor oil?

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3416H
Hello, I just picked up a 7790 diesel and i'm going to change the oil. I was going to use 5w40 mobil 1 synthetic diesel motor oil. Is that a acceptable oil for summer use? Any thoughts and opinions appreciated. Thanks, 3416H

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BLT
Here is the recommendation right out of the operator's manual -4 deg F and below - SAE 5W -4 deg to 32 deg F - SAE 10W 32 def to 68 deg F - SAE 20W 68 deg and above F - SAE 40 Zach's VW was probably desinged around 15W40, the engine for the 7790 was not as 15W40 was not available 25years ago. 10W40 in Diesel engine industry was almost a complete disaster, I couldn't beleive 5W40 would be any better.

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427435
quote:
Originally posted by BLT
10W40 in Diesel engine industry was almost a complete disaster, I couldn't beleive 5W40 would be any better.
Was the 10w-40 oil dino oil or synthetic oil??

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BLT
quote:
Originally posted by 427435
quote:
Originally posted by BLT
10W40 in Diesel engine industry was almost a complete disaster, I couldn't beleive 5W40 would be any better.
Was the 10w-40 oil dino oil or synthetic oil??
Dino. Synthetic wasn't on the drawing boards in the mid 80's for our industry and there was a gray area about using it and getting warranty. The whole industry for the larger trucks seems to be on 15W 40. Most Diesel engines today were and are designed around it and have fared well. An engine today in class nine trucks will get about 600,000 miles or better life to rebuild under normal maintenance, 20,000 - 25,000 mile oil changes using dino and having oil analysed periodically. Engine people don't recommend any extended oil change intervals using synthetic, so there no cost advantage. Also, Diesel engines start better now in cold weather then they used to.

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427435
The problem with wide viscosity range dino oils is that they start off with an oil of the low number (a 5 weight oil for a 5w-40) and then add lots of viscosity index improvers to keep the viscosity from falling too far as it warms up and be at a 40 weight viscosity at operating temp. These VI improvers shear down with use, however, and the the 40 weight at operating temp becomes a 30 weight and then a 20 weight as the oil is used. A good synthetic oil doesn't use many (if any) VI improvers and doesn't lose its operating temp rating as it is used. In other words a 5w-40 dino oil will likely become a 5w-20 oil before a normally scheduled oil change. A 5w-40 synthetic will still be a 5w-40 oil after extended use (or very close to it). The other issue with a wide range multi-viscosity dino oil is that after enough VI improvers are added to make it a wide range oil, there isn't much room left for other additives like detergent and acid neutralizers.

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