Hello everyone.
I have one question about the l98 engine. I am planning to buy an 89 trans am gta and it currently has 185, 000 miles on it. Everything is good and I was just wondering how long does these engines last before I need to replace or rebuild it. Sorry if this a stupid question and also how high is your mileage?

 

It just depends, could last 30,000k or 300,000k. there is no set rule.

 

I'm no expert, but I did a lot of research on this while I was looking to buy my 3rd gen. The most common problem I saw on "high mileage" L98's was they start to burn oil because of leaky valve guide seals. Generally, this seems to start to show up in the 120,000 to 130,000 mile range. The bottom end of the motor seems to hold up pretty well to 150,000 miles and beyond if it's not been abused and well maintained. But unless you know the history of the car, I would assume the worst.
I would do a compression test on the engine, check for blue smoke on cold start up, listen for unusual engine noises.
My Formula 350 just clicked over 119,000miles. So far, it's not burning any oil that I can detect and the compression is good.

 

Yup depends on its history. I passed on a car at 90-ish K miles because it seemed to leak fluid from everywhere. Then found a mint 89 at 131k miles but single owner who had regular maintenance and highway driven. Bone stock. I beat on it for another 30k miles with bolt ons and still ran hard. Never burnt oil. Did develop intake gasket oil leak but i fixed that and no motor issues. Pulled it at 166k miles i believe. Ran 12's with just bolt ons so motor def held its compression and tolerances. Cam bearings did show good wear but other than that it lasted a while. I think it would have stayed strong to 200k

 

Like everyone else says, "it depends".
I bought a '91 TA with 196,000miles on it, but I did so knowing that the engine could go tomorrow. I planned on having to rebuild/replace the motor, so my buying price reflected that.

 

Thanks everyone for the replies. It gave me some insight on the engine and what things to look out for.
Chances are I might get the car once I have enough money.

 

One more thing that's quick and cheap, check for oil in the coolant and coolant in the oil. It could help you spot a cracked head or bad head gasket.