May not be related but my D6 9U started getting hot, shut it down and let it cool, started discing again, slowly got into the hot zone again. Next day got hot quicker than the day B4, finally had to stop discing, cooled it down and checked everything, could not find and problem other than the fan belt was not as tight as it should be. Tightened the fan belt back to spec, overheating stopped for a few days. 5th day slowly started to get hot after discing for 3-4 hours. Replaced the fan belt 3 years ago, no problem since and I have worked her hard pulling a big plow in adove, still does not overheat. Hope this helps.

Need to check out what the problem is before just throwing parts at it.
Find out what is needed then we'll see where the parts can be located.

Clean and check that valve assembly, they get plugged with mud duabers, the valve is still available from Cat, I also use stainless bolts on the cap.

check the fan belt tension.

wash the rad clean of dirt and dust check behind any fan shroud or screens they can hide dirt build up and damage.

check the hoses for crud buildup as hose can be failing internally and look ok on the outside.

some times a reverse flush of the rad can help clear some of the debris
try a bottle of radiator flush.

Sounds like the first thing i should do is tighten the fan belts,thanks to all for the helpful tips.The belts are really loose,i just have to work out the set up on it,and go from there.I also may have been over doing it greasing the fan pulley,causing grease to spit out at the bottom of the radiator so maybe needs a good clean.
In 3 years of owning it,it has never looked at even getting hot,even in summer,always about less than half on the temp gauge,even working it hard until now ,so hoping it might be just the belts.I have been working in sand ,so probably does'nt help with dust.
The valve assembly on top of the radiatior does'nt look like its been touched for years so will check that out,hoping if i don't break bolts and definitely look at getting stainless,Rome K/G.
You are right about finding the problem first Old Magnet,i was already looking at replacing the water pump first off,i even managed to loosen every bolt on it without breaking them,then thought maybe its not that and would be expensive to replace,so will look at the fan belts first,cheers all.

Here again since a different vintage of engine, but check the gas bubbles in radiator first.

D6 9u started spraying water out of water pump lost a lot of water fast. Rebuilt the pump, part of a day of use and it is spraying again. Took the apart again, as don't consider myself a great mechanic. Took it a better mechanical minded person, he suggested the pre cups, which was the problem.

So I suggest you do the cleaning and tighten the belts and see what you have then.

Try the easy fixes first before ripping parts off, though my RD6 managed to rot off both the drive pin and key in the water pump a few years ago, so the impellor wasn't spinning on the shaft!

Thanks for everyones advice,i'll have a look on Sunday and see if i can tighten the belts.I managed to stop my 63 cadillac coupe deville from overheating,i actually thought the worst with that too,a head gasket or worse,but replaced the radiator,waterpump,thermostat and cap and it runs cool now, so hoping it might not be too much with the dozer,otherwise it could be expensive.

mike i think you meant turning with the shaft.
simple things first.
greasing the pump should be a one shot every x hrs deal the schedule is in operators book. note the fitting with no ball is a relief point it may have a little dick valve in it just to keep dust out if grease appears here you are greasing slightly to much check no one has changed it thinking its broken excess grease pressure will pop the shaft seals.
heres a tip a old mechanic told me apply a little anti-sieze or even just grease to bolt threads it makes em easier to work on next time as things aren't rusted tight and one of the best penertrants ive found is a product called penertrene availible in spray bottle, 5 or 20lt drums or spray can

I went up to my block today, where my dozer is to see if i could figure out why its overheating. I started it up and with the radiator cap off let it warm up and did notice the coolant rising then would see it bubbling then again the coolant would drop and build up again and cause bubbles till it basically wanted to overflow as it warmed up,this was after about 10 minutes.
I put the radiator cap on and took it for a 5 minute drive and pushed a little dirt,the temp gauge showed under quarter,but the pressure gauge was starting to rise fairly quick and coolant was running out around the cap as the water pressure gauge was rising,then i parked it up.
I guess its not a good sign and maybe looking like a head gasket but not sure. The motor starts easy, and sounds fine,no white smoke.
I have noticed a lot of condensation build up on the dipstip when i check the oil,which i didnt get before, but the oil looks fine and not milky. The filler cap had milky residue and water dripping but does'nt look like coolant,maybe water got in somehow when i powerwashed it or even from the constant rain we've had lately.I need to drop the oil i think.
I did check the radiator temperatures with a infra red gun as it was idling for 15 minutes and it showed 112 degrees F at the top tank and 60 degrees F at the bottom tank, and 135 degrees F at the thermostat and waterpump area.
A few things i need to sort out,i can turn the fan quite easy by hand so will tighten the belts and the radiator overflow pipe must be blocked as no coolant coming out,only from around the cap as the pressure rises.
The coolant in the radiator is as clean as it can be and not brown or rusty looking and no oil contamination.
So at this stage,the water pressure is getting way too high and its spewing water out of the cap even when the temp gauge is only about a quarter.
If anyone has any ideas on what the problem could be,your help will be greatfully appreciated