'Listening to WSB traffic on the AM,it seems everyone in Dekalb and Fulton
are at the malls.
Today may be your historic moment to enjoy the freeway system as it was
in the '80's , before everyone in the eastern half of the U.S. moved to the
metro area.
'Just stay away from all the malls , especially town center!

My boss came out of the service dept at a Chevy store in Atlanta, and reports sludge problems with lots of cars that normally would not have an issue, due to high ambient temps and AWFUL stop and go traffic, where cars don't get above idle, they just sit there with the A/C blasting, and while they don't run up many miles, they do run up lots of hours.

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2002 Ford ZX2
2 x 2013 Honda Civics

1.Synthetic oil (AKA Mobil 1) eliminates 99.9% of the opportunity in the lube
system for "Sludging".
2.To "Sludge" , with modern, formulated, multi-viscosity mineral oils,the oil
change interval must be extended so far beyond specifications that the
additive package is completely worn out.'Running your engine and accessories
while sitting in traffic ain't good for it ; but it ain't gonna cause "Sludge".
(I am not privy to the details of your friends "Chevy" and his actual dealer
experience so I am not going to comment.)
3.A couple of years ago, Toyota had an alleged "Sludge" problem with a V-6
engine,which turned out to be a block that had not been drilled out to the
necessary diameter in the oil galleries.BUT, Toyota replaced the entire engine
for customers who could prove just ONE oil and filter change since they bought
the car. My sister took her Avalon into the local dealer for wiper blades and
the dealer said they had to rent her a car while they installed the new engine.
And she was the second owner.

Because of sludge developing using conventional motor oil on FSS, the following came about:

In September 2002, Mercedes-Benz' involvement in an owners' class action lawsuit, got them to extend the '98 - '99's engine's warranty to 10 years, or 150K miles..........--if, approved pure synthetic motor oils were used in them, citing FSS continuity.

Our '05 Toyota has a MAINT light that comes on if you exceed the oil change interval (this has only happened once). It gets reset to zero at every oil change.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma