Defender 300Tdi Overheating

Here's my tale of woe!
'P' Reg Defender 90 with 80k miles on clock (well I think so!); had it for 6 months without undue trouble, but noticed temp guage always showed on warm side of normal. Uses very little oil, no coolant leaks (fresh antifreeze 3 months ago). 8 weeks ago moved to Devon, involving towing Ifor W. twin axle stock trailer up and down the M5, then onto the hilly bits.With 2.5 tons on board the temp guage goes into the red, and cab smells of hot wellies. I pull over check water; sure is hot (but stopped before actually kettling), but no loss or leaks. After allowing to cool, I proceed gently, and on every steep climb when the throttle is on the floor, we run into the red, so my journey is slow, (as is that of anybody else heading through North Devon behind me).
On arrival home, I hose out system with Holts speedflush; - no result.
Checked into local non-franchise landrover specialist, who logically substitutes the following components in ascending order of cost:

1. New theremostat
2. New guage sender
3. New guage
4. New Visco fan
5. New Radiator

Still no benefit; temperature still shows red when towing on hills, and emits a smell of hot rad hose.

The next rungs on the ladder of substitution could get costly, so I would be grateful if anyone has encountered this problem before.
Expert says engine shows no excessive wear, and water pump OK, no sign of gasket blowing. His proposal is to start stripping the pump/thermostat/head area, and probe for possible physical blockage, resulting from possible earlier boiling, (or sparows nest?)
Anybody have any ideas please??

Try removing front grill and powerhosing the radiator and intercooler as these can become clogged up and cause overheating problems. B-B

Did you stick a hose into the cooling/engine parts untill it ran clear? This could dislodge things, will also give you an idea it the water will go in and happily come out the other side or if there is an obstruction.

I would not pay land rover to strip the water pump, I would do that myself, retain gaskets or get some new ones before you start.

Thanks - I'll try the hose -regret I have private water supply which has dribble pressure, so maybe I'll sneak someone's from in town!

Hi Stephen, I had a similar problem with my 300 TDi. I re cored the radiator and changed the water pump - no more problems. I live in Zululand which is only about 3 degrees cooler than hell and often travel with a full load...

Cheers
Wayne

Hi Wayne,
I have replaced the radiator - so that's not it; the water pump looks Ok, but I think its the next candidate fro removal close scrutiny, and maybe replacement. Thanks for your help - I'll keep you informed

Something else you may want to check - if your TDi is blowing oil all over the place (I know Landy's don't leak oil, they only mark territory) you may be building excessive crankcase pressure and need to replace rings etc. This can cause overheating under load conditions... Seems you've eliminated all the obvious causes!

Cheers

Wayne

as a temporary measure, take the stat out. that should help.
otherwise drastic action is to take the head off and inspect. you can get a blown gasket which doesnt always show up on a normal test.

Rather than take the thermostat out, cut the spring out of the stat. This ensures that you still get the benifit of an "open" thermostat whilst still retaining back pressure in the water jacket. This way you get cooling around your number 4 pot. This was a tip given to me by an old school mechanic - from the days when they still fixed things!

if you find it runs too cold without the stat, drill a few holes around the stat rim and try that.
we used to make our own plates with various size holes to replace the stats in our rally cars.
just change the plates according to temp required. time of year etc..

Yeah,
I wish I could get that running too cold bit!
My money is still on something like the water pump (Or is that just because I hope its cheaper than a head/ring problem).
No time to do anything yet as its peak lambing time - yes I know its late, but we've moved!, but hope to get the marigolds onto something more metallic next week - will keep you posted Thanks for all the responses