I need to drive from Adelaide to Sydney in my 91 KR auto, I have serious doubts that it can make it that distance without something dying on me in the middle of nowhere. Can anyone tell me just how resilient a 6G72 is, I just bought the car for rather cheap so i don't know its history such as last oil change, belts, etc. Gear changes are a little rough, especially when disengaging overdrive. Sometimes while driving the car will be doing say 2100rpm, all of a sudden it will drop to about 1100rpm and the shoot back up to 2100rpm, hence why i have doubts about whether it can travel such a significant distance or not. Help this brother out friends!

this is a difficult question over a forum because we cant see

looking at a 14 hour trip- 1400 plus km each way

can you afford to get a minor service before you travel
at least that way a "mechanic" will cast an eye quickly over the magna

oil plus filter / tune / coolant/ windscreen wipers

RPM drop of 1000 rpm in that middle range cant be ignored
any ones guess plugs / leads /02 sensor / idle control valve/ MAF / Coil.

6G72 >these motors will not stand over heating
timing belt break means 95 % chance bent valves and piston hit

unknowns

all coolant hoses
timing belt
tranny oil and smell
oil leaks
tyres and spare
brakes

A bit of a lottery, but if you prepare it the best way you can, should be ok

Keep the speed down.
Highway driving is less stressful on an engine anyway, so unless it has major problems that you haven't noticed driving around town, you should be ok.

Keep the speed down.
Highway driving is less stressful on an engine anyway, so unless it has major problems that you haven't noticed driving around town, you should be ok.

Agree, keep speed down, go easy on the throttle to minimise stress on the car. Have a few breaks so its not driving continously for hours on end.

Getting a service done beforehand would be ideal and tell the mechanic that you plan to drive a long distance and ask whether he sees any major issues with the car.

Some one close might offer to drop by just for a look and give advice on the car

cant find any auto special service deals around adelaide today

I've taken my 91 TR from Brisbane to Sydney and back and done some other 200+ km each way runs. The car loved the highway, much better fuel economy than city, and the overdrive clutch stopped shuddering after a decent run. Check coolant and all hoses very thoroughly and if possible do a flush prior to the trip. Fresh engine oil and filter is always good, and cheap. A car doing a lengthy highway trip in one hit will not hurt it as much as stop/start driving provided you're not flogging it. At speeds under 80km/h turn the overdrive switch to off, to reduce stress on the overdrive clutch.
How many KMS on the odometer?
Check the water overflow bottle frequently for it using any water, if it does check the oil filler cap for any grey/white milky residue. An unmaintained 2nd gen 6G72 quite commonly rears a failed head gasket after time.
Check transmission oil level when car is hot to be sure it has sufficient oil, check colour of the oil too, it should be a dark pinky/red colour, if brown/black it's well overdue for a flush. Check power steer fluid level.
But provided there is sufficient oil in the engine, no water leaks, the transmission holds and you're gentle with it, it could potentially surprise you. Start out very gentle with it and get to know it's characteristics.
A good example is my TR, I thought my transmission was cactus, it commonly takes up to 5-6 seconds to engage fully into reverse/drive when cold, but I allow it time to engage itself slowly and don't accelerate until I'm sure it's in, and the overdrive was shuddering didn't give me confidence but I have done 15,000km since then and it's still a good daily car.

I've done that trip about 20 times in my 6G72 Gen 3. A very reliable engine generally and doesn't seem to have many unpredictable or catastrophic 'mechanical' issues that would leave you totally stranded. A busted timing belt is usually my main fear if I am feeling a bit paranoid. But electrical problems can be a whole other ball game. I'd not do it until you get that rpm issue sorted out, or unless you are prepared to just 'walk away' from the car if it breaks down.