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15w40 or synthetic 5w40 what better to run?

9K views 6 replies 7 participants last post by  jimdawg185 
#1 ·
so I was reading on here and I am taking it as some people use synthetic 5w40 oil in the trucks? does this help or did I miss read what people were saying?
 
#2 ·
it is better.. i mean a thinner viscosity oil at lower temps will help getting the oil flowing in cold temps faser.. but when it warms up it will still keep the 40w like conventional oil. also synthetic doesnt break down as fast at higher temps like conventional 15w-40 will. So yes it is better. but its up to you weather the price difference is worth it to you. I use 15w 40 and change it every 3k miles. Once i rebuild this 7.3 and get all the bearings and clearences back to the tight side of specs ill break in the fresh engine with 15w 40 for about 10k miles and then switch over to synthetic.
 
#7 ·
A fleet I used to service ran Amsoil only. Had more than three go well over 900k and a half a dozen over 600k and still rocking. Those were 7.3's though. We still had many 6.0's run over 400k until injectors started dropping. Made cold starts much better and better mileage most of the time.

Also ran it in the transmissions, only replace trannys every 4-500k. And those trucks get beat on in the Virginia mountains.
 
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