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Rust isn't contagious, but it is autocatalytic.  Rusting is
a chemical reaction.  The product of the reaction - rust -
makes the reaction go faster.  Covering over the rust with
paint does little good.  You need to remove all the existing
rust, then put a primer on the metal, then paint.

Specifically which elements is the car not resisting.  I've got
neighbors with chevy, ford, GM, Volvo, Toyota and BMW cars and no one
car is more prone to rusting than the other and we live in an area
where roads are salted.  I wonder if there is not something else going
on.

"No paint on the engine block ,flat paint under the hood ."

So what.

"My Volvo 740 is rust free and 18 years old my wifes is 20 years old
no rust .My sons 240 is rust free at 18 years of wear and tear .We
don't have salt on our roads so mainly GM and Fords rust."

My 1984 240 begain to rust out around the wheelwells after 10 years,
so there is not as much predicability by brand name as you would like
to see.

"On a quiet day with clouds over head you can just about hear the GM
cars rusting .I think my Volvos will just keep rolling when the Ford
is rust bucket even if I do like the features and ride of the Ford its
very remote not a car with feeling and feed back ."

And there are old ford, gm, chevy, mercedes, etc., cars on the road
too.  And there are rust buckets of every brand if you look around.
Driving conditions, regular washing and waxing and keeping up with the
nicks and dings are probably the best ways to control rusting.

So yes my wifes wants another Volvo later on now we cured the problem
with hers stalling (wide spark gap ) as she prefers the comfort and
safety as well as the cheaper part prices.

cheaper parts for a volvo than a domestic car??? that's funny....  When was the last time you paid $45 for a brand new (not rebuilt) water pump?  Volvoo parts cost 2-3X as much than my mercury.

I own a 1991 245 with 180,000 mi on it.  Runs nice, hood paint is blue chalk, little visible rust. Upgraded with Bilstein touring shocks and iPd sway bars. Handles pretty decent, a very nice long-distance family hauler.
I also own a 1986 Mercury Capri 5.0 since 1988.  Never garaged.  Driven during all seasons, including heavily salted winter roads in coastal NJ.  Just started showing rust about 2 years ago.  Runs like a champ, very strong... tough to keep tires on it more than 20,000 mi, just smokes them.  Paint could use a good buffing, but at 170,000 miles and 22 years I'm not complaining.  Outlasted my sister's Toyota Celica and Acura Integra (consecutively), and is on it's way to out running her Nissan Sentra.  Regarding the above water pump, the original one lasted 125,000 miles on my Merc.  And when I pulled it the bearings were still tight, no wobble in the shaft, only the seal failed.  Car still has the original PS pump, AC compressor, and alternator, and all motor internals.  Got 95,000mi from the fuel pump.  Emissions air pump made it to 160,000.  I love this car because of it's simplicity -  no unnecessary electronic crap... I DRIVE it... it does not tell ME what to do, I tell IT what to do...  No traction control, no GPS, no automatic climate control, no electronic gadgets, no nothing that's not necesary.  A Speedo, tach, and a couple other gauges.  That's all I need.  Oh, and a kickin' stereo  ;-)
My 245 is actually fairly similar, if with a wee bit less power... I only drive manual transmissions, and though the M-47 is a somewhat weak tranny and has been replaced in mine, it does shift nice and when you wind it up, you get decent acceleration and quick, easy shifts with a light clutch... surprised more than one teenage rice-burner...  that B230 has lots of torque.

My point is, don't dis a car just because it's brand X (Yugo's excepted).  However, I don't seem to see many Chrysler products over 8-10 yrs old... It's quite possible my Capri could outlive my 245.  And is waaaaay cheaper to maintain.  Each is maintained equally. My last Mercury was a 1972 Montego...I put 174,000mi on it and traded it in, in good running condition, on my Capri for $400.  It was seen 5 years later still running....

 I went over my sons Ford covering minor rust here and there as theres so little paint on joins and seams and sharp edges .This car is just over 2 years old and the thin paint on rough edges just doesnt resist the elements .No paint on the engine block ,flat paint under the hood .My Volvo 740 is rust free and 18 years old my wifes is 20 years old no rust .My sons 240 is rust free at 18 years of wear and tear .We don't have salt on our roads so mainly GM and Fords rust.On a quiet day with clouds over head you can just about hear the GM cars rusting .I think my Volvos will just keep rolling when the Ford is rust bucket even if I do like the features and ride of the Ford its very remote not a car with feeling and feed back .So yes my wifes wants another Volvo later on now we cured the problem with hers stalling (wide spark gap ) as she prefers the comfort and safety as well as the cheaper part prices.