Re: [GMCnet] Tid Bits: Oil consumption. It's all in how/where it's consumed. [message #336506 is a reply to message #336505] |
Wed, 29 August 2018 14:12 |
GMC.LES
Messages: 505 Registered: April 2014
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Thicker oil generally means a thicker oil film on the cylinder walls. It is my belief that the thicker oil film can overload worn or stuck oil rings, increasing consumption.
I’ve actually seen a few engines where a thinner oil helped reduce oil consumption. Didn’t get to pull them apart for a proper diagnosis, so I can’t say if it was the guides/seals, or rings that were worn.
Thicker oil can also overwhelm the pcv system on engines with excessive blowby. Seen this happen a few times on some worn out engines.
Les Burt
Montreal
'75 Eleganza 26'
> On Aug 29, 2018, at 2:22 PM, James Hupy wrote:
>
> My 403 when I first got it, had 87,000+ miles on the clock. P.O. had been
> using 10w - 30 dino oil in the engine. Consumption was 800 or so miles per
> quart, which I thought was a bit high. My mechanical fuel pump gasket was
> leaking a bit of oil, so I fixed that and cleaned up all the surplus stuff
> on the outside of the block. Ran long enough to tell that oil consumption
> didn't change much. Darn. So, I decided to change to Valvoline 20w - 50.
> Oil consumption changed to a quart every 1200 to 1500 miles. That is where
> it is today with over 125,000 miles on the engine. Compression is
> consistent at 150 psi across the board. So, the old girl is going to be
> driven like she is, until something changes dramatically. Factory says that
> a qt per 500 miles is acceptable. I think that borders on excessive
> consumption, while the factory is covering their butt on warranty claims.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
>> On Wed, Aug 29, 2018, 10:41 AM Bob Dunahugh wrote:
>>
>> Sully. Don't know when most of the oil consumption would occur. Never even
>> saw a hint of oil smoke ever. Thought that the 50 might help some. It did.
>> Bob Dunahugh
>>
>>
>> ________________________________
>> From: Bob Dunahugh
>> Sent: Monday, August 27, 2018 9:53 PM
>> To: gmclist@list.gmcnet.org
>> Subject: Tid Bits: Oil consumption. It's all in how/where it's consumed.
>>
>>
>> 6 years ago. I knew someone that got very upset that their engine
>> consumed one qt every 300 miles. So we looked at the spark plugs. All the
>> spark plugs showed about the same as to discoloration/deposits. The
>> compression test came in at reasonable numbers. At 115 to 123 psi. Not
>> great. But not bad. Inspection camera showed oil washing around the edges
>> of the pistons. All washing on all pistons was about the same width. Again.
>> Not a great sign. But not bad. Just expected. Put a dial indicating
>> micromotor to the top of each rocker arm. Just looking for consistency
>> between all the intake. Then all the exhaust. Looked good. But that test
>> doesn't show how much the lifters are dished. Or how much of the cam lobes
>> are gone. Again used the inspection camera to check the cam gear/chain. Had
>> been changed at some past point. Warm oil pressures were13psi at idle.
>> 21psi at speed. This is a candidate for a high volume oil pump. But the
>> pump could over load the piston oil control rings. That are already over
>> loaded. Thus it could up oil consumption. I suggested running it as is. And
>> run a heavier oil. He's been using 20W50 oil. Still running well. Oil
>> consumption has been at about 400 miles per qt. If the engine had all the
>> oil consumption issues in just one or two cylinders. That's time for a
>> rebuild. As for what's best for you. Not my monkeys. Not my circus. Bob
>> Dunahugh
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