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1998 Cadillac Deville D'Elegance
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Hi guys.... I'm the proud owner of 98 Deville and I've always used Mobil1 High Mileage 10w-30....my mechanic said if I used Mobil1 15-50 that it would help with the oil leak that all northstars seem to have.... any input on that notion????
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
Your engine doesn't require synthetic oil. The correct viscosity is 10W-30. Thicker oil will do exactly nothing for an oil leak.

There is no oil leak that "all Northstars have". Any half decent mechanic would diagnose the leak and repair it correctly.
 

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1998 Cadillac Deville D'Elegance
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Discussion Starter #3
Well I know its the rear oil pan... but it's a costly repair...was just wondering whether or not 15-50 would cause any harm to the motor
 

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98 DeVille, 97 DeVille d'Elegance
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7,345 Posts
More than likely rear seal or half case, either way not a cheap or easy fix. Thicker oil seldom helps with oil leaks.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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It's WAY more viscous than the recommended oil. Maybe, maybe not. Why bother finding out if it's not going to do nothing for the leak?

Ask your "mechanic" if he'll warranty any lubrication related engine failures for as long as you own the vehicle if you take his bad advice.....
 

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2003 Deville Base
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4,795 Posts
that all northstars seem to have.... ????
I agree that he gave you bad advice. There are plenty of owners on this forum with high mileage N*'s that don't leak a drop. Mine doesn't. Could it be he just didn't know how to do the repair, or didn't want to?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,423 Posts
15W-50 motorcycle oil is NOT recommended for your engine.

"Thicker" oil leaks just as well as thinner (recommended) oil until you repair the leak source.
 

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White Diamond '03 DHS (with DTS floor shift)
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15w-50? :shocked2: That stuff should be approaching gear lube viscosity when it heats up. I'm sure it WOULD stop leaking. :tisk:
 

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1998 Cadillac Deville D'Elegance
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32 Posts
Discussion Starter #9
Well after considering ur opinions.... I stayed with my gm recommended 10-30...thanks guys... y'all r awesome
 

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2003 Deville Base
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4,795 Posts
15w-50? :shocked2: That stuff should be approaching gear lube viscosity when it heats up. I'm sure it WOULD stop leaking. :tisk:
the 15w50 Mobil 1 V-Twin variety worked really well in my 98CI Yamaha Roadstar.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Well after considering ur opinions.... I stayed with my gm recommended 10-30...thanks guys... y'all r awesome
Aside from the leak sealing guesswork, the oil use advice is mostly fact, not opinion. 15W-40 and 15W-50 oils are reserved for some really heavy duty commercial engines as well as air-cooled motorcycle engines. The research ship that I captained for 12 years had four twin turbo Cummins V-12 diesels, 720 hp each. Those engines used Drydene 15W-40 oil and had a 3,000 hour overhaul interval. 15 gallon sumps.
 

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85 Coupe Deville 4.1 V8 & 4.3 V6 Deisel & 1970 Eldorado
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773 Posts
My MGB's used the heavest weight of any of my other cars at 20W-50. The MG's engine was built with big clearences.
I also used to use Aeroshell 100 (50 weight) in my 1951 M38 Jeep but that was because it would sit for extended periods of time and the Aeroshell would stay in the bearings and oil pump better than anything i found. (kept the dry starts at bay) But i was verry carefull how i ran it and never loaded it cold. The Willys also had big clearences. I would not recomend this to anyone else.
 

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'99 Seville STS; '96/7 ETC
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Really surprised to still see references to 10/30, as it's not been generally available here in the UK (if not Europe) for several years now.
We really have a straight choice (for this engine) between 10/40 & 15/30 - which is about 25% more expensive, presumably as it only seems to be available as semi-synthetic.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Strange - 10W-30 is probably the most common oil here, in all 3 types - conventional, "blend" and synthetic. Many manufacturers are going to 5W-30, 5W-20 and 0W-30 for their cold flow properties as well as lessened oil drag for fuel savings.

The Northstar was not designed or spec'd for anything over 10W-30, and 1998 began the 5W-30 (10-30 allowed) recommendations - sort of coincidental with the 2000 change to roller cam followers.

Can you find EURO 0W-30 or - 40 ?
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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My MGB's used the heavest weight of any of my other cars at 20W-50. The MG's engine was built with big clearences.
I also used to use Aeroshell 100 (50 weight) in my 1951 M38 Jeep but that was because it would sit for extended periods of time and the Aeroshell would stay in the bearings and oil pump better than anything i found. (kept the dry starts at bay) But i was verry carefull how i ran it and never loaded it cold. The Willys also had big clearences. I would not recomend this to anyone else.
Bearing clearance is the key. You can run thicker oil in old engines with big clearances but not in a Northstar with tight clearances. Very bad advice from the very old school mechanic.
 
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