Oil for tired '98 5.7 vortec?

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stevejones

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Feb 13, 2011
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Midwest
Vehicle is a '98 K1500 with 180K. Purchased used one year ago in TX, now in the upper midwest. Unknown maintenance history.

It's my winter truck - I drive my '08 Pontiac in the summer for much better fuel mileage.

Currently the motor runs fine - only concern is the oil pressure as shown on the gage: 40psi cold, below 20psi hot. I have another 5.7 with much better gage pressure. Let's assume the gage is accurate - I'm not going to bother messing with it.

Recommended oil is 5W30; and that's what I ran last winter. I was thinking an equal mix of 5W30 & 15W40 (Rotella Synthetic) this winter. Temps can get below 0 and last winter (bad one), they often did.

Thoughts?
 
I'd run a 5w40. I had a 96' with the 5.7L Vortec and used whatever 10w30 or 10w40 I had in my oil stash
 
Run a 5w40 or 0w40. Get a UOA to make sure there is no coolant in the oil.

Run a full synth Dexron6 in the transmission. Use GM cold climate or Amsoil PSF, any brand GL5 synth gear oil.

Research the intake manifold gasket issue.

Good time to change all fluids filters for a starting baseline.
 
How about a 0w30? Mobil 0w30 is fairly thick at temperature. 10.9 cst at 100c. I would not want any 15w 40 mixed in if its below zero.
 
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Since it's your winter truck and you live in the mid-west, I'd use 0W30. Using a "10W35" concoction wont do the cam bearings any favor. Worn cam bearings in OHV engines equals lower oil pressure.
Don't add anything to the oil, period.
 
Originally Posted By: spasm3
How about a 0w30? Mobil 0w30 is fairly thick at temperature. 10.9 cst at 100c. I would not want any 15w 40 mixed in if its below zero.


Sounds good to me. Also like the idea of drain/fill trans with some newer synthetic.

Edge 0w-30 is a thick 30, hths 3.5, so if you want thicker, or not Mobil, then it's an option.
 
Oil pressure is normal for this engine/setup. I would run a name brand High Mileage Synthetic 5w-30 and not look back. These engines run longer than the rest of the vehicle will last.
 
180K miles on that engine sounds like nothing. If it's running fine,I'd just run the oil recommended in the manual/fsm and enjoy!
 
I got some of my best UOA's in my 5.7L wagon with Rotella T6 5W-40. Ran it year round, no issues in the winter. I switched just recently to Maxlife 5W-30 to slow some leaks down, I don't tow a travel trailer with it anymore either so I worry a little less about what oil is in it. Has 186k miles on it now.
 
I have a 98 z71 with 5.7 with 186k+. I bought it new. It has been decent truck but there isn't much I hadn't fixed on it except for the motor as its still original. I put a new power steering pump on it yesterday. Parts are pretty much dirt cheap for this model truck. Oil changes have been mainly 5/10w-30 conventional with occasional synthetic thrown in. I ran rotella 5w-40 for couple changes thinking it might do a little extra cleaning. Truck never knew the difference and neither did I. I think 5w-30 Dino will be just fine for winter use but spending little more for a synthetic won't hurt nothing. If you have consumption issues I would go to 40wt in a synthetic.
 
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Mine has 232k the PO used 1030 in winter and 1540 summer. I've used 1040 but am about to go back to the 5 or 1030 since I have just 1 small leak I'm about to fix and it doesn't use any oil I've noticed.
 
my buddy has a '98 GMC 1500 with the 5.7, it does the exact same, 40 when cold, below 20 when hot, it runs fine. he has 205k on it. I run T6 5W40 in it year round. Coldest it gets down here is upper 30s, and the average is in the 40s. hes never had a problem running the T6.
 
It just dawned on me my 96' was at 20 psi at idle and 40-45 while driving. That was at 144k easy miles on to 160k when I sold it.
 
Originally Posted By: WishIhadatruck
I got some of my best UOA's in my 5.7L wagon with Rotella T6 5W-40. Ran it year round, no issues in the winter. I switched just recently to Maxlife 5W-30 to slow some leaks down, I don't tow a travel trailer with it anymore either so I worry a little less about what oil is in it. Has 186k miles on it now.


Welcome, brother!
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(check sig)
 
Originally Posted By: DoubleWasp
Why not just use the 5w 40 RT6?


You have my attention now...gonna do some more research - after I put a new heater core in the old girl!
smirk.gif
 
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