highway vs city miles

I have had numerous debates about this with many mechanics and all have a different opinion. This is not just related to the Porsche 996 but all cars for that matter. Is there truly a difference in engine wear on a car that is primarily driven on the highway at cruising speeds vs a car that sees primarily city driving? I am not talking about items such as brakes, suspension,etc as that obviously takes a beating in bumper to bumper traffic, just engine/mechanical. Obviously you are racking up the miles if you have a long work commute via interstate. However, you always see those car ads stating "196,000 miles, primarily highway". Would just like to hear what everyone has to say on this topic. Thanks and happy Monday!

There is no difference unless it's a Porsche because most other manufacturer's engines rarely have issues with their normally aspirated engines. If it's a Porsche, it doesn't matter as they fail no matter what! Paranoia will destroy ya......

^Says the guy who was looking at his oil filter through a microscope!

Highway miles are easier for any motor. One reason is everything gets to and stays at operating temp which isn't always the case in city driving. City driving sometimes makes the engines run hotter or colder than optimum. Another reason is there is less stress on parts if they are at relatively steady rpm's. The bottom line is that all the motors are designed to run in the cities and they will be fine, but hiway miles are easier. This is my opinion and I'm sure its not everybody's.

I've been told another way to think of engine wear is not just based on distance (i.e., number of miles), but number of hours. In city driving, you may spend an hour going 10 miles, but on the freeway, that same hour could get you 60 miles on the odometer. A low mileage car with primarily city miles may have just as many running hours (wear) as one with higher mileage.

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That is a great way to look at it. All though highway miles are easier on the engine and city miles means lot of shorter trips while temp may not even get up to proper temp, cold starts and idling. I don't believe cold starts or idling is good for our engines.

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Maybe some difference, but I think the difference is really negligible. My 2002 Boxster with over 290K miles has a good number of city miles (as well as highway miles) under its err odometer and the engine and the rest of the drivetrain isn't worn out. The biggest issue is often a city driven car doesn't get run long enough for the engine to get up to temperature. Unburned fuel, and water (mainly water) builds up in the oil and the oil then becomes thinner and may not handle high temperature high load conditions as well as it should. Also, this build up of combustion byproducts results in a build up of acid in the oil and this acid attacks the internal components, corrodes them. It is my opinion this corrosion then is wear and this works to shorten the life of the engine. With proper servicing one can mitigate the negatives to a city engine but too often the owner believes with short trips and the slow accumulation of miles the car needs less frequent servicing, not more frequent servicing.

...however a city driven car which has the same 10 mile 1 hour commute will spend approximately the same time warmed up as a car which has a 70 mile 1 hour commute. In this instance, the city driven car may experience more engine revolutions during its journey due to spending more time in lower gears. Not such a simple question.

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I agree with this also. So far everyone seems to agree highway miles are easier on the engine. Any counter arguments?

This is a prime reason to look at a 996 / 986 "hours runtime" on the DME as well as the odo reading. Whenever I have got close to buying a used Porsche, I insist on looking at the over revs and hours run time vs odo reading to give a clearer picture of the cars previous life. And its not just the engine that takes a pounding in heavy traffic - give a thought to the gearbox synchro's and clutch too....

In my opinion (closely tied to JDArthur's comments on constant/stable operating temperature) the wild card that most people might not fully consider is the number of start stop cycles in the engine's life. Every cold start creates more wear, and the number of times an engine (over a given number of miles) is subjected to heating and cooling from being turned on then shut down, cooled off and restarted, will stress the case and the components more than an engine that has more miles but fewer start/heat/stop/cool/repeat cycles....And, given that performance engines are manufactured to much tighter tollerances, and with more different types of metals (which contract and expand at different rates) than mass market engines, thay are particularly impacted by the heatng and cooling cycles. For that reason, I always ask a seller to tell me about how they used their car day to day...Just my $0.02...

When I was shopping years ago, I brought a "clone" durametric with me to check for Type II overevs....which to me was more telling about how the car was driven vs. than the numbers on the odometer. I did not put much faith in ads that read: used on weekends only, mostly freeway miles, driven by/like a grandma, etc. since anyone can make those claims and I have absolutely no way to verify the same.