These forum members would have agreed with you, until their plastic broke.
BMW MOA 696, BMW CCA 1405
My fiance's grandfather didn't believe me when I said that 10 years might be too old for tires no matter how good the tread and sidewalls look, even if he hardly drives the truck and it's almost always in the garage, even if he never drives on the highway.
About 2 months later, the tread separated at 35 mph and was flung into the wheel well so hard that it dented the fender.
It's not really about the the mileage, even though heat and heat-cycling are also hard on the plastic. It's a chemical reaction. Plastics and a lot of other petroleum-based products have a"short" lifespan because the properties that make them so good are unfortunately also linked to oxidizing and rotting.
BMW plastic, rubber,etc...are notorious for short service life.
It has generally been agreed upon on all BMW forums I have visited,
that ~5yrs~60,000mi is the recommended timeline to consider a cooling system refresh.
I personally have had a plastic expansion tank burst open at 5yrs~66,000mi.
Replaced that only, connected all associated hoses, which looked good, but felt soft,
only to then have leaks at the hose ends, and at the coolant temp sensor, due to failing O-rings.
When you are the mechanic on these cars, DIY or otherwise,
you can see and feel the deterioration from new, up close.
We can go on with other notorious plastic, rubber failures like-
Third brake lights, windshield cover trim, cowl, rubber intake boots, vacuum hoses,
the list goes on, they are mostly cosmetic, but a cooling system failure is engine threatening,
Hence the importance of preventive maintenance.
The simple truth is:
If one component of the cooling system has cracked-burst due to heat and age,
what do you suppose is the condition of the rest of the system if similarly aged?
But then again, everyone is free to do as they please maintenance wise, and as budget allows!
Look, there's two different approaches being represented here: repair vrs preventative maintenance. Some advocate only replacing a part when it breaks. Others advocate replacing parts before they break. I happen to fall into the preventative maintenance camp, but there is no right or wrong way--it's a matter of preference. For me, the issue is time, not money, so if I have to remove a bunch of parts to get to a repair, I'm replacing everything I touch in the process; if I can identify a part that is coming up on the end of its useful service life, I'm replacing it when I have the time, not waiting for it to break. Heck, I'll replace a part just because I found something better, even if the part replaced is relatively new. For other's it's a matter of cost--of keeping the total cost of vehicle ownership to a minimum--"if it ain't broke don't fix it." Both ways are right for the particular owner's circumstance and preference.
In responding to this thread, my particular bent is that I don't want my Z overheating under any set of circumstances--not for a millisecond--I'm paranoid about overheating. I replaced the entire cooling system--every piece of it except the block and the heater core--and then upgraded my replacement with oil cooling and a Zionsville custom radiator, shroud, and Spal. But that's just me. I maintain my cars with the aim that if I wanted to, I could just jump into one and drive it right to California and back--across endless plains, over mountain ranges, through deserts, high sierra, cities, and emptiness--and not need anything but gas. This idea makes me happy. Just replacing parts when they break would drive me mad--I'd be constantly attuned to every little noise or bump analyzing what just broke and how long I had until it left me stranded--not for me. But then I completely ignore things that would drive another saner man crazy--like the speed limit, fuel economy, and the opinions of my wife (as to my driving). À chacun son goût is what I say.
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