Re: [Amc-list] My two cents on oil weights

[Frank Swygert <farna@xxxxxxx>]

Dave, the Chrysler reps from the engine plant were in Kenosha a few years back. A mechanic walked by and saw the new V-6 cut-away engine they had on display and remarked to his buddy that they were junk, he'd already replaced a few. The rep responded that the engines were specifically made to use 5Wxx oils, and what was killing them was people running run-of-the-mill 10Wxx, especially in winter, but even in the summer when the engine is first started. Running thicker will take a lot of miles off those engines. 

On the flip side, if you're talking specifically about AMC engines, or any older ones, you're absolutely correct. They were designed to run thicker oils and thinner may take miles off instead of adding. The same with oil changes, even with synthetics. If the engine is kept in good tune you can get by with extending past 3K miles, and running 6K with a filter change and top-off at 3K should be fine. But it doesn't take much for a carb/points engine to get out of tune. The oil has to be watched. 

Modern EFI cars are different. Most of what dirties oil is residues from unburnt fuel. Carbs are designed to run a little rich, as that's better than too lean. Carbed engines dirty the oil much faster than EFI engines, unless of course something is wrong with the EFI. Since the computer is monitoring the mixture a lot more precisely than a carb possibly can, and changing tune as conditions and climate changes, it can run a lot cleaner and longer between changes. There's no reason to change the oil in a good running EFI car at less than 5K miles. If the oil is getting dirty before then something is wrong. At 5K miles the oil might still look clean, but there's all the unseen thing in it and it's a good idea to change it. With the extended drain oils that are specifically designed to go longer (up to 10K miles), a filter change and top-off is still recommended every few thousand miles -- even with a double filter system like the AMSOIL "never change the oil" system. It works, b
 ut you still have to change the filters and top-off, so it's more like a "constant change" system than "never change". 

-------------------
Date: Fri, 11 Apr 2008 21:57:26 -0400
From: David Crooks <david.crooks@xxxxxxxxxxxx>

The whole 5wXX thing has come from the desire to improve CAFE fuel  
mileage.  I've heard of a fair number of "off the record" suggestions  
from factory shops saying that you're better off running 10wXX unless  
you're operating in cold winter conditions.  And that only applies to  
fairly new engines, that are machined with modern tolerances.  
Personally, I'd never go lighter than 10w in an AMC.

The same theories hold true in Trany oil.  The old school was 90w, but  
a lot of trany's are now calling for standard engine oil.  You have to  
read the specs.  You can kill a trany that needs 30w by putting 90w  
into it, and the opposite is true as well.  Again, part of the reason  
for the lighter weight is fuel economy, but don't go overboard!  Some  
parts need a certain amount of drag in order to function properly  
(like syncro's).

  And last by not least, change your oil (engine, trany, diff) often,  
and don't cheap out!  Just because a synthetic oil maintains it's  
grade longer doesn't mean you can stretch the change intervals  
(inspite of what most people tell you).  The oil may be good, but it's  
also full of crap that you don't want to keep in your motor! And if  
you do the math, a few more oil changes over the life time cost of the  
vehicle is chump change.

I'll step off my soap box now!
Dave

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)


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