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Old 08-04-2012, 06:39 PM   #1
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Default Straight 40 weight oil vs

5w40. Is there an advantage to running a synthetic straight weight oil on track?
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Old 08-06-2012, 10:49 AM   #2
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http://www.bobistheoilguy.com/

I learned quite a bit reading all the arcicles on there after getting in a argument with Hustler.
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Old 08-06-2012, 10:54 AM   #3
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5w40. Is there an advantage to running a synthetic straight weight oil on track?
5w40 vs w40?


it's the same oil. just one has additives to help in colder temps.
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Old 08-06-2012, 10:57 AM   #4
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Take it back a step, if both oils are synthetic the straight 40 and the 5w40 are the same oil except the 5w40 doesnt get as thick when the engine is cold. If the 5w40 is dino oil then they are not the same, its actually a 5w oil with additives that make it act like a straight 40 once up to temp.
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Old 08-07-2012, 10:45 AM   #5
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I use synthetic, so you pretty much answered my question.
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Old 08-07-2012, 11:49 AM   #6
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I use synthetic, so you pretty much answered my question.
Right so you want to run the synthetic 5w40 over the synthetic straight 40. I'm not sure the car will even be able to crank with straight 40 in it.
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Old 08-07-2012, 11:55 AM   #7
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it'll crank but it wont lubricate anything for like 20 minutes while the oil is warming up and can't flow.
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Old 08-07-2012, 12:02 PM   #8
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Right so you want to run the synthetic 5w40 over the synthetic straight 40. I'm not sure the car will even be able to crank with straight 40 in it.
Different oils behave differently over time (and some is pure snake oil).
Some argue that a straight oil live longer at higher temps (theory being that the visco modifiers break down with heat/time). At the same time you don't have only 100 degrees C (spec temp for the higher viscosity number) as the max temp in the engine.
120 in the pan is not uncommon and should not be alarming. That means you can have 140-150 elsewhere (still no alarming temp for a good oil).
How the visco curves looks at 150 degrees C (think rod bearing oil film thickness) can vary some between straight 40 and 5W40 (and they can differ up there too).

I'm not arguing for one over the other but cold start viscosity is hopefully not the only prio in this subforum. Oil pan preheating is the norm, right
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