Just bought a 2004 GTS, Previous owner was a just put in whatever is cheapest kind of person. The two things I know are incorect is generic power steering fluid being used instead of Dextron II, seals are leaking and I will have to tackle that eventualy. Cheapest unleaded fuel was also used, instead of 91 Octane. Dont know what problems that may cause. Pretty sure 5w-30 was always put in, just varying between Synthetic blend, Conventional, and full synthetic. Anything else I should look out for or do?
The Celica GTS with 2ZZ engine is a very reliable car. I put in 330K hard driving miles on my 2002 GTS Auto, average 15K miles a year, with lots of neglects abuses. Car was overheated 3 x, but it still runs smooth and strong, nothing is broken, compression is strong on all cylinders.
How many miles does it have?
Do a compression test of all cylinders as a baseline.
Power steering leak may be sealed with a chemical. Fix the seal before flushing and replacing with new fluid.
I ran the car 200K miles with the cheapest 87 Octane fuel. Sometimes it would knock when stressed at low speed but never at high speed and is mostly OK. I usually drive at high speed, climbing steep hills ect. No problems. Sometimes I would add $1 Octane boosting fluid to the tank.
Check the radiator and all cooling hoses for any leaks or cracks. Run engine to op temp, shine a bright beam of light into engine bay. Any leaks or steam would show up. Fix the leaks, replace cracked hoses, then flush coolant and bleed air. Buy Toyota's red coolant ($25 a gallon) and dilute half and half with distilled water, cheaper. Replace the thermostat, since if it fails you would have to replace it and rebleed air, takes about 2,3 hours.
Mine Had an oil leak from the front timing cover. Took a shop 10 hours to remove and reseal it. I use Walmart 20K miles synthetic oil. Engine is smooth like silk. I cruise at triple digit on long trips often. No problems. It eats about half a quart every 10K now, at which point the oil looks dark and I would change it.