Full Synthetic --- Vortec 350

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98chevy2500SS

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Update on the oil: my 98 seems to be doing fine, I don't see any leaks, so that's good. Oil pressure seems to be the same, maybe it increased 5 psi more. Overall, I am happy I did the switch, just feels good to have full synthetic running in it. Thanks again guys for the help. :)
 

Supercharged111

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I have no idea how synthetic oil can INCREASE oil pressure.

Given that it flows better when cold, I'd think it would be more likely to decrease oil pressure.

The only thing that would make sense to me is if the synthetic were thicker, merely stamping 30W on the jug does not truly tell you its weight. If I'm not mistaken Mobil oils run on the light end of their advertised weight.
 

Mildphil

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I have no idea how synthetic oil can INCREASE oil pressure.

Given that it flows better when cold, I'd think it would be more likely to decrease oil pressure.

Probably a larger volume cycling through the engine since here is less internal resistance. P=F/A, and F=ma, so if the fluids are an equal mass per a given volume, but the synthetic is able to accelerate faster (lower fiction coefficient) then the resultant force will be larger. Plug that into the pressure equation, and you will have a larger force with the same area in the denominator. This is where an increase in pressure comes from. Its the same reason why when water goes from a larger pipe to a smaller pipe, the pressure increases. the force is the same, but area decreases, resulting in higher pressure. It is also the same reason why a restriction in a garden hose, say a kink, will result in lower pressure, since the internal resistance is working against the force vector (plus area remains the same). When no variables change, Better flow= better system pressure.
 

skylark

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For what it is worth, I changed every fluid to full synthetic at 115k. It now has 134k. A month ago I had the truck on a lift doing a muffler and I noticed an oil leak by the bell housing and a slight seep at the front seal. On Friday I found a puking pinion seal, a seeping output shaft seal and a puking steering box. Coincidence? Perhaps. It does seem odd that I changed every fluid at the same time and that all of these leaks developed in the last 1500-2000 miles.
 

98chevy2500SS

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That's good to know, I will check it and see if mine does the same thing as yours in 1500-2000 miles or so.
 

delta_p

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when i replaced a bunch of original oil seals on spinning shafts recently, i was amazed at how old and crusty they were. Some were leaking and some were not. I can see changing fluids to synthetic could cause a leak in this case. I've been on a mission to try and change every seal i can get to. So far I am down to the rear main and front seal. The rear main leaks slightly.
 

Kevco2

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I have only run the Pennzoil Full Synthetic in my HT383e crate motor I swapped in a few years ago when I got my Suburban. The Chevy Performance instructions say going right to Full Synthetic 10w30 is recommended. But I have noticed that she likes to burn oil, seems every few thousand miles I have to top off
 
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