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MAC

20W-50 Oil

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I decided to give 20W-50 oil (Mobile 1 Full Synthetic) a try in my '05 STS.  I'm dealing with leaking, plus no doubt burning oil with almost 300K miles.  I know that some will tell me that I am looking for trouble; however, my high mileage engine no longer has tight tolerances, so this heavier weight oil should lubricate.  The oil pump should handle it.  I recently put in 4 quarts of 15W-40 and it seemed to me the car ran better.  Probably less oil burning helped?  I will see how it goes, particularly if I have to top off less. Between oil leaking and burning, I was topping off too much.  In fact, it was almost like not necessary to change oil because I was topping off so often.  I changed oil today and used almost all 20W-50, except for about 1 quart of 5W-30, just to get rid of it.

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Keep us posted. What have you got to lose.

On a side note I have 2 nissans. 1 with 315k miles, uses no oil at all. other has 220k and uses about a quart between changes.

Completely different engines I know but still impressive. Both run like new. No major issues with either

 


GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I have an 02 Deville and it has an oil consumption issue with 145K. In the summer I change the oil and put in 15w40 rotella from meijer 10$ for a gallon x2. The oil cuts consumption to zero the car burns no oil. It was going through 2 1/2 quarts every 2K miles of highway driving. I install a thinner oil in the winter 10w30. 

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I would feel comfortable with a 15W-40 oil in a Northstar engine since the Guru once told me it wouldn't harm anything if I found it hard to find a 10W-30 to my 1993 STS.  (I would on the other hand not gain anything). If you look closer in your user manual they also mention other viscosities for other cases/temperatures but 5W-30 or 10W-30 is the best all-round solution. Cadillac specifically states "do not use heavy weight oils such as 20W-50". Next time I change oil I'll switch to 15W-40 because my baby has developed an oil addiction too.

I understand what you are saying MAC, after almost 300k the car has probably greater play between many bearing surfaces and thus can handle a heavy weight oil. But there will probably be bearings with larger play and there will be bearings which still have factory specs in your engine and the possibility is that they will suffer from oil starvation on cold starts.

If 15W-40 won't harm a "normal" Northstar then I would stick with that to be on the safe side. If the oil burning comes from stuck rings, leaking valve guides or the crankcase ventilation the heavier oil will probably cure the symptoms but the rest of the engine may suffer. Just my two cents.

 

rockfangd and cdgrinci like this

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I drove almost 800 miles over Labor Day and, so far, no issues.

Thanks Jan.  I will probably use either 15W-40 or 10W-40 during winter.  

BodybyFisher likes this

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22 minutes ago, MAC said:

I drove almost 800 miles over Labor Day and, so far, no issues.

Thanks Jan.  I will probably use either 15W-40 or 10W-40 during winter.  

MAC, did you mean 10W30 in the winter?


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

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10 hours ago, BodybyFisher said:

MAC, did you mean 10W30 in the winter?

If it's better to use 10W30, then I will use it.  I just want to curb oil burning and hopefully oil leakage.  I am now looking to maybe buy a STS AWD-V8.  I have been looking for a few months.   But I have said that I want to run and run the STS I have until it can't run anymore.  But the V8 Northstar in it just keeps going and going.  If I solve the oil leaking chances are oil use will be cut quite a bit.  I just haven't had the time to get underneath and see what's going on with oil pan bolts--maybe they are loose.  Then again, oil leaking is a problem with these cars, so it is likely that I need to replace several gaskets, especially with almost 300k miles.

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MAC, Well 10W is the cold viscosity, so I suppose 10W30 and 10W40 act the same when cold.   But I wouldn't use 15W40 in the winter months.  

I will let others state their opinion but, I recall that even with the Northstar, the guru would say 15W40 in the summer ok, but drop to 10W30 in the winter but he was speaking of Rotella for the NS, with the higher zinc content. 

What oil are you using in the Northstar?   The leak you are experiencing with the NS is probably the case half seal at that mileage but it doesn't hurt to have a look.  Your STS probably has an oil cooler in the radiator, check the cooler hoses, and orings, oil filter adapter seals, and oil level sensor and oil pressure switch.


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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What engine, and under which operating conditions is 20W-50  Mobil 1 even called for? Maybe a Porsch Turbo with 200,000 miles in, say, the Mohave Desert? Possibly racing engines? Just trying to learn here.

I can tell you that the Mobil 1 0W-40 European Formula is called for year round in passenger car (V6) service. Complete with meeting fuel economy specs for those cars.

My point is, sometimes you give up certain oil qualities for specific applications. Racing oil doesn't require much detergent, some diesel oils require more dispersents, Oils designed for higher mileage vehicles contain aromatic hydrocarbons in order to swell seals. To me it would seem prudent to understand exactly what I am giving up before I made the switch.


Never underestimate the amount of a persons greed.

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I tend to agree with Jan and JohnnyG, why push beyond 15W40?  

The same thing crossed my mind that Jan brought up, yes some clearances widened but, some didn't.  

It would be interesting to see what your actual oil pressure is with 15W40 and then 20W50.  My feeling is, if 15W40 made a marked difference why push it?  

Have you tried removing the plugs and adding upper engine cleaner and letting it soak overnight to clean the rings?  Someone here will know the procedure, know it, so that you don't hydrolock the engine.  KHE knows it I know


Pre-1995 - DTC codes OBD1  >> http://z-cut.de/US/dtcobd1.html

1996 and newer - DTC codes OBD2 >> http://carprogrammer.com/Z28/PCM/OBD2/On-BoardDiagnosticTroubleCodes(OBD-II).mht

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The GM top engine cleaner can be used to un-goop rings - I did it 10 years ago.  You will need several containers of the top engine cleaner.  I jacked the front of the car up when I did the front cylinders to get as much of the cleaner in contact with the rings as possible.  I let it soak overnight (The guru suggested the overnight soak vs. the dealer bulletin of 2 hours), then vacuumed it out of the cylinders with a Mityvac vacuum pump.  I then raised the rear of the car and repeated the procedure with the rear cylinders.  I then unplugged the ignition control module and cranked the engine (with all 8 plugs out) to remove any residual solvent, then installed the plugs.

The oil needs to be changed immediately after this procedure as some of the solvent will find its way into the oil pan.

When I started the engine, The exhaust was like a mosquito fogger!  It took a couple of miles of driving it hard for the smoke to subside.  The engine oil and filter should be changed within 200 miles of performing he procedure.

rockfangd and BodybyFisher like this

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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On Wednesday, September 7, 2016 at 11:06 PM, BodybyFisher said:

I tend to agree with Jan and JohnnyG, why push beyond 15W40?  

The same thing crossed my mind that Jan brought up, yes some clearances widened but, some didn't.  

It would be interesting to see what your actual oil pressure is with 15W40 and then 20W50.  My feeling is, if 15W40 made a marked difference why push it?  

Have you tried removing the plugs and adding upper engine cleaner and letting it soak overnight to clean the rings?  Someone here will know the procedure, know it, so that you don't hydrolock the engine.  KHE knows it I know

I haven't tried adding upper engine cleaner.  I have used Marvel Mystery Oil figuring it may clean internal parts including rings.  I also did a bit of research and someone said 15W40 did not increase oil pressure--at least anything worth noting.  As far as 20W50, that may be a different story? 

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I haven't seen anyone mention volume here in this thread so I thought I would give some food for thought....Unless you were experiencing a dramatic oil pressure drop I don't see any reason to go over a 40 weight oil. Pressure is a measured resistance and is based on engine bearing Clearances and oil pump tolerances (worn high mileage pump=less pressure than a new tight pump) and because the oil is thicker you tend to see a pressure increase but what I would be more concerned with is volume. High pressure alone isn't always a good thing you need volume too. Somewhere I had seen a chart that was done on minimum oil pressure vs engine rpm and can't find it now, but actual oil psi requirements per thousand rpm were not as high as you might think. If I can find it I'll post it up. 

Edited by CTS V
Missed adding engine bearing clearance

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All my life I've heard 10 lbs per thousand rpm. 10 lbs for 1000rpm, 20lbs at 2000 rpm etc.. I have never read anything proving that, just hot rodders lore.

 

CTS V likes this

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