The engine in my 2003 G35 has been constantly maintained with oil changes and checks since it was bought by the previous owner. It has 194000 miles on it and works and sounds great. There some mild rusting on the outside of the block, but thats it. I bought this car when it has 189000 miles on it and I drive it pretty hard. I rev it to 6k RPM's a fair amount. I'm worried that I might blow it if I keep revving it so high, but I love to drive fast in this car. How durable are these engines? Should I worry too much?

In stock form very reliable. The block, heads, and a lot more are aluminum so any corrosion you see must be an accessory/bracket or possibly a coolant line. Since you haven't owned the car very long and probably have limited knowledge of the cars previous 189k miles it would be smart to keep a close eye on the oil level. I would change any fluids that you don't have a record for and you're also coming up on the spark plug interval. If you don't know when they were changed I would just change them. 100k is the interval but theres a noticeable difference if you do it sooner.

to be honest though, that's a lot of mileage on any car. You really, at this point need to be taking care of it if you want it to last. If you want to hound on it and drive it like a race car then I'd suggest getting it built up just a little. That way you can go crazy

I don't consider a 6k rev crazy since technically you're not even in the sweet spot yet but what do you consider building it up orangeNblue?

well the 6k on a DE is way more agressive than it would be on an HR seeing as how the redline is at 6.5k...the internals of that motor have seen a lot of wear and tear, at lot of friction and age. Maintenance is huge here, so first and foremost keeping your car properly maintained is his #1 concern. Now if he was wanting to seriously play with the car and extend its life, my suggestion would be to replace the internals because that'll be the first place to see failures. Also replacing all of the gaskets, etc too, to avoid leaks.

Not to threadjack, but how does the VQ35 hold up to cylinder wear? I'm eyeing up a 244k mile G35 with bad head gaskets and I don't have a problem rebuilding it. I just don't know if I'll have to have it bored out or not