Land Rover Repair: 1997 disco Overheats, headgaskets, grey matter

Question
John, you have helped me out in the past and I really do appreciate your time.  I have another problem that keeps haunting me. "Overheating".
I replace the thermostat and had the radiator rodded out and preassure tested.  After I re-installed the radiator a couple of weeks had gone by and everything was fine.  Then one afternoon after running at highay speeds for about an hour then exiting to normal speeds the temperature rose almost to the top of the gauge.
I turned it off for about a hour to cool down then began my trek back home another hour drive and it seemed okay.  Than a couple days later it started all over again. I then pulled the radiator back out and tried to backflush it with a hose just to see if anything would come out.  Sure enough grey looking particles came out of the radiator not rusty looking at all.  I then tapped on the sides of the radiator while flushing and more and more  of this came out.
I re-installed the radiator and for about a week it ran fine until it happened again overheated.  The same routine grey particles came out.  I not sure if I should have it rodded again or buy a new radiator (very costly) the problem i am having is that is this from the radiator or from the inside the engine causing the particles to clog the radiator.  Any help or if you have heard of such a thing with the gry items before?
Should I buy a new Radiator or ????? Is there anything I can put in the water to dissolve the grey particles to help reduce overheating???

Thanks again for your help.

Norm

Answer
Hi Norm,

that grey matter bothers me.  You've flushed the system, installed a new thermostat and pressure tested the radiator.  Could it be caking deposits that have built up overtime?  IF the internals of the radiator are that bad, you should replace the rad.  

Be careful of what chemicals you use to flush your coolant.  Some are very caustic and can damage the headgaskets.  

Also, if you can, use distilled water when mixing with coolant.  It contains no minerals.

It sounds like you have caked on deposits that are causing clogs.  To verify this use an infrared thermometer to scan the surface of the radiator for cold spots. If the clogs are that bad no amount of flushing will get rid of them.

I think the fact that you pressure tested the system (for over one minute I hope) you can rule out any problems with your headgasket.  I think the deposits are fouling up the flow of fluid and causing you engine to overheat.  If you use too many chemicals to flush off the deposits (more than twice) you'll run the risk of damaging the headgasket.  Maybe its time to find a new rad.  

Best of luck,

JohnMc