few teething issues im trying to get sorted on my ute.
driving round town, no dramas, temp needle sits about halfway, but as soon as i get on the open road(80ish kph and above) it starts to run a bit hot. ie. just below the 1st hot line.
is this a classic case of 'forgot to fit the stone guard thingy underneath'?

sounds like when the going gets tough..the tough stop working..

Sounds like a ####ty radiator.

yeah either dodgy radiator, or more likely a non proper shrouding of the radiator ie cant driect the airflow through the radiator properly. im guessing its been modified. thermos and stuff?

nah not modified, just a stock a12gx, stock rad, stock fan.
the rad was only reco'd 10000km ago, but that was 4? years ago. the only thing i havent put on there yet is the steel guard underneath.

Is it a twin core or a tripple core radiator?
twin core might be the problem.Was my problem.I replaced with a tripple core.It is now fine.Replace thermostat also.Might be old.Might also be waterpump.

Doubt it's the cover under engine that you are talking about as I tested mine with and without it. No difference in temp.

Maybe the problem is not in the cooling system because in that case the overheating would be more severe when driving slowly, I think. Could be a lean mixture which causes excess heat when working the engine harder. Whatever it is, take care of it or bigger repairs are certainly ahead.

I would tend to think that its not cooling system related as when you are traveling at higher speeds that is creating maxium air flow for the radiator......
Possably incorrect spark plugs, check ignition timing, as this could be causing too much heat in the chambers and could cause huge dramas!
Good luck with this keep us posted on your findings.

Bigger or tripple cored radiator is the only solution. The higher revs generate more heat and the increased airflow is too fast for efficiency. All the 1200s ive had standard or modified run hot on the highway with standard radiators.

Is this the twin carb A series motor that you have had for ages? Quick question. Did you replace the thermostat after it had been sitting for so long? Forgive my ignorance but I can not remember having read anything on your engine build up.

I will back up what Freak and 1200GXman said, with astock A12 newly rebuilt engine and new radiator, as soon as we went above 4000 RPM's the car ran hot...............just shy of the hot mark. Even in bumper to bumper traffic with 110 dergree Vegas heat it was fine............get on the freeway and within 1/4 mile the temp would spike. Intially we used a B210 / 120Y radiator and that helped...........the 3 core GX radiator solved it for good. Even at the track when it's 106+ and me buzzzing the engine to 8K it still stays between 180-200 degrees.

Tom