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Schrade | Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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Q: If I go heavier viscosity, will I get less oil burn-off @ start-up?
'90 LT-5 was assembled withOUT valve stem seals. The oil burn @ start-up, even after ONLY overnight sitting seems common, EVEN IN LOWER-MILE CARS - 30-50k. Mine has 37K. I didn't notice it in mine when I got it. But soon after first oil change (I went 5W-30 Syn, when most recommend HEAVIER weight), I noticed it. Now, with headers + 3" OPEN pipes all the way back, I see a little more... --------------------------------------- There's a 'confederate' factor here to consider, about where it's coming from: LT-5 pulls LOTS of oil through the PCV, into the plenum. I saw this FIRSTHAND. After I did top end rebuild, I did 2 0r 3 Closed Loop idles in garage. THen I pulled the TB, and saw a small pool of NEW OIL @ the PCV-to-PLENUM inlet. Posted a snappic on Z boards. Everyone said NORMAL!!! They also said put in a catch can. So, ... thoughts? If I go heavier weight, will I get less oil through the valve stems, after overnight sitting? And, might I get less oil pulled through PCV??? |
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Posted on: 2015/5/26 23:39
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bogus | Re: Start-up oil burn; should I go heavier visc? | ||
Grand Imperial Pooh-Bah
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going heavier would have a negative effect on bearings and things.
I would go maybe 10-30, and leave it at that. |
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Posted on: 2015/5/26 23:41
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Schrade | Re: Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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Negative effect ?
I'm not understanding? Only negative I could see is gas mileage??? |
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Posted on: 2015/5/27 0:37
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EngineDoctor | Re: Start-up oil burn; should I go heavier visc? | ||
Master Guru
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No Valve stem seals??
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Posted on: 2015/5/27 0:55
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EngineDoctor | Re: Start-up oil burn; should I go heavier visc? | ||
Master Guru
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Just to add....Your oil viscosity is relevant to your bearing oil clearances! What are those clearances?
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Posted on: 2015/5/27 0:59
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bogus | Re: Start-up oil burn; should I go heavier visc? | ||
Grand Imperial Pooh-Bah
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that's not what I was always told... if bearings are close, putting in 20-50, say, will cause dry spots...
please correct my error then! |
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Posted on: 2015/5/27 1:00
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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EngineDoctor | Re: Start-up oil burn; should I go heavier visc? | ||
Master Guru
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Andy, The more oil clearance you have, the thicker the viscosity needed, The tighter clearances require thinner viscosity.
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Posted on: 2015/5/27 1:07
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Schrade | Re: Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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Correct engine doc; '90's LT-5's were built w/OUT valve stem seals.
I don't know spec clearances; but the heavier stuff IS recommended by Haibeck, and others, 'in the know'... I follow now there Andy. But back to the original question here, about DECREASED oil burn @ startup... ? |
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Posted on: 2015/5/27 1:56
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Schrade | Re: Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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With heavier stuff, will LESS oil make it's way down the stems?
And would heavier stuff be LESS likely to pull through the PCV plumbing? |
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Posted on: 2015/5/27 1:59
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EngineDoctor | Re: Start-up oil burn; should I go heavier visc? | ||
Master Guru
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I know they were built with out V/S seals , But I always machine & run seals on the Intakes As for as what viscosity oil for you to run , Idk , without knowing your valve to guide clearances , etc...Sorry.
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Posted on: 2015/5/27 2:17
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CentralCoaster | Re: Start-up oil burn; should I go heavier visc? | ||
Senior Guru
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The cold viscosity rating is at 32F. So it doesn't mean squat except for that first 30 seconds of run time.
Also keep in mind that all oils thin out as they heat up, some just more than others. An oil that maintained same viscosity after warmup would have to be rated a 10W700 or something ridiculous. I would expect thinner oil to always smoke more on startup. I don't think there's much harm in running a thicker cold weight. Don't hit WOT in the first 30 seconds and you don't have to worry about bearings. I run 15W40. Also, I've noticed the cat burns oil hot enough that you can't see it. So an engine could burn oil when warm, but not show it with the cat installed. I did valve seals on mine, but it still smokes when warmed up after idling a few minutes, such as at a slow drivethru. I've read that this is because the combustion chambers cool off and don't burn the oil completely. This is without a cat installed. |
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Posted on: 2015/5/28 0:22
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Schrade | Re: Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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Quote:
That's MY thoughts too... But NOW: I'm not getting the heavy start-up burn. And I'm knowing why. For 2 weeks, I had the car OUT of the level carport on the down-hill pointing part of the driveway. That's when I noticed it was worse. Parked back in the carport, level, and it back to a slight puff @ start-up, like it was years ago, when I got the car (shortly afterward). This one is solved withOUT doubt.................... |
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Posted on: 2015/6/6 14:15
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CentralCoaster | Re: Start-up oil burn; should I go heavier visc? | ||
Senior Guru
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I'll check mine, it's been pointing steep downhill for a week now, and the valve guides are shot. It does have new seals though which seem to have stopped the startup smoke. On level ground anyways. I thought the heads had drain holes at the very front corners, but maybe it's pooling up in there close to a valve.
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Posted on: 2015/6/8 18:19
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1985 Z51, ZF6 |
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BillH | Re: Start-up oil burn; should I go heavier visc? | ||
The Stig Moderator
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Both my 92 LT1 and my Silverado blow a puff when parked down hill. Never do it parked flat.
The Vortec in the Silverado's been doing it since I got it and at 165,000 , only uses 1/4 qt. between changes. |
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Posted on: 2015/6/9 13:41
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Schrade | Re: Start-up oil burn; should I go heavier visc? | ||
Elite Guru
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Quote:
VERY interesting there Bill... 2 vehicles that do it. Don't motors have a (+) Pitch, to keep motor torque out-of-plane with suspension? So oil drain holes in heads are in rear? ??? |
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Posted on: 2015/6/10 16:45
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