I have a 2001 f250 with a 7.3. People have been telling me that 5 w 40 is is too thin for my year motor and I should run 15 w 40. Well I bought AMS brand 15 w 40. I was going to get mobil one 5 w 40. Is the oil I have now still a good oil and is the 5 w 40 to thin for my motor

 

Who ever told you that is wrong. Here is a quick lesson in weights of oil. The first number, in this case is 5w or 15w. That is the viscosity of the oil at cooler temps. The 40 stands for the viscosity of oil once it reaches operating temps. Both of those weights oil work great in our trucks. The 5w40 will flow better at cooler temps that the 15w40. You will get less start up wear with a light weight oil, such as 5w. When oil companies build a motor oil. They start with the first number. So they will have either a 5w or 15w to build from. They then add polymers to change the viscosity to a heavier weight when warm. I personally run Schaeffers 9000 5w40 year around. I am going 10000 miles between oil changes.

 

It also depends where you live. If you live in a cold area then 5w 40 is what you want to use. I live in south LOUISIANA and we don't get cold enough to use the lighter oil. The dino oil is cheaper.

 

I have been running rotella t 5w40 synthetic year round without any problems in fact it starts easier and faster.

 

I agree with you Jamie...I used Shell 5w40 year round.. If you have ever had the romp, romp after starting when it is cold, 5w40 will eliminate it... And it does get cold in New York where you are, FordSD250..

 

Add me to the Rotella 5w-40 list, I run it year round.

 

Mee tooooo...

Here's more to think about -- the 5W oil cold is THICKER than 40W hot. BUT, it's thinner the 15W when cold. At operating temps, they are BOTH the same weight (40W).

If you want to play, buy a quart of each and put a small amount each separate two jars and put them in the freezer. You should be convinced at that point. If you want, you can then put them both in a pan and heat them up and see what happens. To make sure they are the same temps, you could just put the jars in a pan with cool water in it. Heat to just when the water starts to boil to see what they look like then (about the operating temp of the oil). FUN STUFF!!

Of course, be careful...

 

So should i return the 15 w 40 and go with the mobil one 5 w 40 even though the parts store said that i will burn my engine up with such thin oil

 

I bet you were a hit in science lab. Probably blew it up a couple of times.

Guess you now know how much stock to put in what they say. Makes you wonder if they know so much about all the stuff they stock. By the way, 5w40 syn for me year round.

 

Servicing trucks one cold November was enough to convince me that light multi-weight oils are best for cold weather use. Keep in mind we had -30F temps, so when I brought that 55 gallon drum into the shop it was almost impossible to pump oil out. 15W-40 resembles a taffy pull at those temperatures! That was the year I became sold on Delo 0W-30.

 

Here is some more info for ya... (Mobile 1 exceeds Ford's recommendations for your engine)
Mobil 1 Turbo Diesel Truck 5W-40

 

5w-40 Rotella Synthetic now.....made the change sometime in November I think? I'll never go back to Dino now. I always ran Rotella 15w-40 before. My truck LOVES synthetic

 

I just switched to 5W40 rotella synthetic last month. It does start much easier now. How many miles are you guys putting on between oil changes with the synthetic?

 

Here we go with the dino vs. synthetic again- I'm gonna get some popcorn and pull up a chair hehe

 

I'd keep that 15-40 and run it until next fall then switch to 5-40 if you need to switch because of miles. Don't pay attention to those YO-YOS at the parts store they don't know squat, Opps did I say that out loud? Synthetic all the way. Randy