After about 30 minutes of research, it seems like a lot of people run rottella 5w40 or some seem to run 10w30. Is there any advantages to these oils compared to 15w40 in the summer time? Does it make a difference that the motor is high millage? Thanks in advance

 

There are a million oil threads out there, choose what you want.

I run Rotella t6 5-40 and a good filter and change every 4-5k miles, mineral oils no more than 3k.

 

Clean oil. Do your oil changes on time and you're good. I use motor craft 15/40

 

Is 5w40 okay for the truck even though its not in the owners manual? Will it affect the longevity?

 

I use Schaeffer's oil. I pull heavy and all my tests on the 'other' oil showed it sheared down. The Schaeffer has moly in it and hasn't sheared down.

 

Glenn,you running the moly bond x-200? Or 5000?

I'm going to make a change in what I run as I'm having some issues.

 

There's a belief that a lot of wear occurs at cold starts and that 5w40 oil will circulate and start lubricating a little bit faster than 15w40 and will help rather than hinder longevity. I can't say for sure that this is true but there seems to be some logic to it.

If you live where it's cold in the winter, 5w40 makes for easier starting, always a good thing.

Some 5w40 oil has some sort of long chain molecule "viscosity enhancers" that allow for the wide viscosity range that are susceptible to shearing and viscosity breakdown with time. I think this is only a factor if you are trying to go with extended oil change intervals.

I think 5w40 oil is fine.

 

If I've learnt one thing, it's that any oil is good if you change it regularly.

 

Just curious what kind of issues you're having?

 

Now that it's getting warmer and I towed the camper last weekend. When it gets hot my idle quality is poor . I'm thinking a few possibilities. Oil is one consideration at this point.

 

I use the 7000 Aaron.

 

5w40 was rare at best, perhaps even non-existent, when the owner's manual was written. The owner's manual specifies an API grade that doesn't even exist anymore. I've seen 5w40 pour better at low temperature than 15w40, and with synthetics, extending the viscosity range does not compromise the lubricity the way it does with dino oil. So +1 above, 5w40 is great oil for wide temperature range driving. If you never expect to take the truck out of the south, you're fine with 15w40.
+1; I've always found that rough idle when hot, esp. when coming down from a high speed run, is like a "change oil" light.

 

The oil only has maybe 800miles or less on it. It's pretty severe and constant when hot. I have spoken with my tuner and he agrees with my plan. We will see what I find.

 

Curious what you find. That Ex built like yours has about 2500 on it now...still idles like a stock injected truck... running that t6 crap :-)

If I could get shaeffers here reasonably...I'd give it a shot.

 

So is it okay to run 5w40 even when the temperature can be up to 100 degrees outside? Or just stick with 15w40 in the summer?

Let me rephrase, any benefit when it is hot as all hell out to run 5w40 instead of 15w40?