Normally sits around half way on the gauge of my defender depending on how warm it is out side, forgot to clean my rad after a Pay and play and next time I went out I was driving and glanced at the dash and noticed it nearly in the red, it did it in the way home to never got in to the red, there happened to be a pup on the way back to stop at,

I've heard that the heads warp easly could it have damaged it or does it have to be well in the red?

its not unusual for engine temp to rise slightly under certain circumstances , blocked rad will definitely make it run warm but generaly unless you boil up the coolant and by this i mean water and steam coming from header tank and loss of coolant .. if its just warmer than normal it should be ok !! clear out the dirt from rad and intercooler and check coolant level when cold top up as required , warm up engine with cap off header tank to bleed out any air trapped in heater matrix
( itss quite high up in relation to the tank air rises) check your temp etc check heater blows hot and if theres no problem youre good to go !! if all is good then undo a hose and let some water out and refil with antifreeze!! i 50/50 fill it slowly with engine ticking over!! filling too fast with a hosepipe usualy causel air lock problems .. good luck

Firstly, Landie heat gauges are virtually useless. Get a proper one from a spares shop that uses the same wiring and probe thread 3/8 NPF. Now you will get a realistic indication of cylinder head temp. Secondly, you should see only very small varations in temperature, normally a slight rise on highway drving at speed. The only time I ever got sudden leaps on the heat gauge was when a cylinder head crack (one of twelve at the time) finally penetrated a water jacket. Cylinder head cracks are common on all diesel engines with aluminium heads after about 300,000km, Landies are no exception. What gives the head crack away is bubbling in the header tank. Funnily they don't let water into the oil initially. Maybe because it requires pressure to open the crack, and that only lets gas out and not water in. Not a big deal if you catch it early.

Everyone jumped in saying heads gone mate, but no mayo in oil and not blowing bubbles in tge header tank, not boiling just almost in the red sarmt there for 2 hours on tge m1.

I removed the rad and intercooler. I clean it every time I got off roading it looked clean but in the middle it wasn't, was blocked solid in most places, also found the header tank to head pipe was blocked, good clean of rad and pipes and s flush and all is sorted now,

Good that you sorted. I run 2 110 tdi's (actually 3 - I bought another yesterday) and they don't do the same thing with the heat gauge. Both original heat gauges been slung out and replaced with accessory types.

Car A hardly ever moves from 89 degC. Only on the steepest hill hauling a big load on a hot day will it creep a few needles widths to 93 degC max. This car has new aluminium rad.

Car B has original rad in good condition. This one moves the heat needle a lot. High speed driving (110 km/h indicated) on a hot day moves the needle to 110 degC and even a tad beyond on extreme days, but immediately retreats towards 90 degC when the speed comes down. On heavy hauling on a hot day needle stays close to 90 degC mark

Conclusion: brass rad is less efficient at speed ie heat transfer does not increase linearly with airspeed and heaviest demand is placed on rad at high speed rather than high load.

To address the rest of your comment - the term "head gone" is a loose one. A head may be bent from heat or it may be cracked. A bent head will be indistinguishable from a leaking head gasket - you will get immediate mayo.

A cracked head be dfferent. Cracks develope in a head over a long period of time and only become critical when the propagate into a water jacket. Many heads are out there with cracks that the owners don't know about - yet. Cracks are caused by thermal stress at the combustion chamber surface mostly at the webs between the injector passage and glowplug hole, also at the narrowest part between the valves - the aluminium cracks but the valve seats remain intact. The last head I changed had 12 cracks growing but only 1 was through to the water. They were evenly spread over all 4 cylinders and some were obviously much older than others.

Once the crack propagates into the water jacket it does so as a pin-hole initially. The hole grows over several hundred kilometers of driving and stays one-way for a long time ie gas gets out of the hole but water cannot get in - yet. In my experience when you first hear bubbles in the water you have 200kms+ to get to a new head. Where I live I'm over 1000kms from help and there be no tow-trucks. As long as you keep going no water will get in to the oil, but you need to just take the cap off to header tank.

Also the sudden jump of the heat gauge is caused not by boiling or over-heating but by the heat probe being enveloped in hot gas instead of water as the gas bubble passes out of the head into the header tank.

its common for 300 tdis to have warped head or even just poor gasket for it to pass gas from cylinder to water way without producing any signs apart from pressurisation,

Ok, on the assumption the standard temperature gauge is a pile of ****, this may be a worthless post but...

This was a my temperature gauge about 1.5 miles into a 2.5 mile hill, on the motorway, with foot buried at 50, with a 1.8 ton trailer behind, on a hot day.

The thing that struck me was the speed at which it rose, it seemed to spike a little from halfway where it usually sits, then climbed steadily to the point pictured, at which point I backed off.

Should I be worried, or given the load it was under not worry too much given the circumstances. The rad is in good order and clear.

Definately thinking its time to pull the head for its 150k health check.

Thanks

James

is rad hot all over its core surface ,is system full checked by removing bung on thermostat housing

Not checked rad surface, but before the trip did check all the obvious things like oil, water and pulled the thermostat cap off to check there was no air in there.

That's about where mine was sat. The breather pipes where blocked off the rad an head to the tank. What condition is the inter cooler in? And is the rad clean? Mine looked it but wasn't was full of mud in the middle.