Originally Posted By: simple_gifts
There are boatloads of different stainless steels. Stainless steel doesn't guarantee it doesn't rust.
No, there aren't. There are only 5 basic classifications of Stainless:
https://app.aws.org/wj/1998/11/kotecki/
The most popular for auto exhaust systems is 409. Any 400 series stainless (any type of stainless beginning with a "4" such as 403, 405, 409, 410, etc., is easy to identify on the car because they are SLIGHTLY magnetic. 400 series will also RUST, but it will take longer than plain old A36 steel. (A500 pipe is structural equivalent of A36
http://msc.aisc.org/globalassets/modern-steel/steelwise/022012_steelwise_spec.pdf See Table 1 on page 2) 400 series stainless is the least expensive stainless. Think Walmart made in China steak knives.
Mr. Delorean used 304 steel. 304 stainless is COMPLETELY nonmagnetic. It is HIGHLY corrosion resistant and used in chemical plants, food processing, medical and dairy equipment. It will hold a high polish and is used for expensive and long lasting exhaust systems:
http://www.exhaustvideos.com/faq/stainless-vs-aluminized-steel-exhaust-system/ I disagree with this column; I believe 304 stainless exhaust will outlast any car in any location, even if you wanted to store the car under salt water; the exhaust would be the last thing to succomb.
But going back to the OP question; I warm my car up ALWAYS in the winter. My car spends the night in a heated garage. My morning routine includes warming the car fully up to operating temp of 180-185. I have a 180 thermostat and a driver information center. COLD engine oil pressure is 66-73. I like to wait for the oil pressure to drop to less than 60 at idle, letting me know that the OIL is STARTING to warm. This can take place while I'm drinking coffee and shaving. I do not drive a cold engine, I'm not a tree hugger, nor do I give a **** about wasting a quart of gasoline. I do UOA and I KNOW the internal condition of my engine and oil.