Disco 300 Tdi coolant loss - Slice
Suspect I'm not going to like the answer to this one, but here goes.

The 300Tdi engine on my Discovery (127,000 miles) has suddenly developed a raging thirst for coolant - about 1 litre every 70 miles or so.

There are no visible leaks that I have been able to find and there are no obvious symptoms of a blown head gasket - no white smoke, no water in the oil. The head gasket was replaced and the head skimmed about 11,000 miles ago just before I bought it.

Finally, even after it has sat for 24 hours, on removing the pressure cap, the system is still pressurised.

Disco 300 Tdi coolant loss - Aprilia
Well, the water's got to be going somewhere....

If there is no sign of an external leak (don't forget the heater matrix) then the loss must be internal. If its not going into the crankcase then I would suspect its going into the combustion chambers.

Start the engine from cold. It the hoses pressurise quickly (i.e. whilst the coolant is still cold) and/or there's bubbles in the header tank then HGF is most likely. Given that the Disco is one of the most unreliable vehicles on the face of the earth (other than a Freelander), HGF would be my immediate 'remote' diagnosis, but it could also be crack in the head.
Disco 300 Tdi coolant loss - Slice
Thanks - suspected as much.

BTW, I haven't found it to any less reliable than I would expect any 10 year old vehicle to be, even given the current problem - there certainly seem to be plenty of other contenders for the accolade on this forum.
Disco 300 Tdi coolant loss - Cabsusa
Has to be a headgasket, I am afraid, especially as you say elsewhere that it had a relacement before. Had the same thing with a Ford - after about six months of topping up (sometimes it would not need this) - it eventually got worse and failed completely. Went again about two years later, and again (terminally) about two years after that. The scrap yard engine then fitted was perfect for 3 years and needed NO topping up at all.

You might find it cheaper in the long run to do the same thing: it was costing £400 - £500 to do the head gasket, the scrap engine was £190. (Plus fitting). But, a Ford DOHC petrol.

Or, stuff it full of Radweld, and flog it.

Incidentally, before Land Rover haters start chortling, my son in law bought a 3 year old Toyota Amazon which did exactly what you describe: this was just out of guarantee. Toyota did not want to know. It turned out to be a faulty cylinder head. They knew very well there was a problem with this model, but refused to own up.

It was entirely due to publicity from Honest John that he learned he was not alone, and after some threatening noises Toyota refunded the £2000 repair bill.

I doubt a Discovery would be that expensive to fix; still, nice one, Honest John.

AS
Disco 300 Tdi coolant loss - Slice
Yes, it's comforting to know that other vehicles are capable of breaking down - often at greater expense, although Tdi engines do seem to have something of a premium on them.

I've tried the Radweld solution, to no avail. Think I had been trying to live in denial re: the head gasket.

Now, where's that piggybank...

Disco 300 Tdi coolant loss - Brummig
I've just had this problem with an otherwise excellent old car. Apart from getting through lots of water it ran almost perfectly right up until one day I found the engine oil was an emulsion. My research suggested that even if I did get the head gasket replaced it would likely as not fail again in a year or two. Since it still started and drove, I subtracted the book price of getting it fixed in a garage from my estimate of its value and flogged it at that price with an honest and open ad in Autotrader - I knew a DIY mechanic would pick up on it as an absolute bargain, and that is what happened. It got the thing off my drive, saved me the cost of unexpected complications, and was a big weight off my mind.

A friend also had this problem, and his solution was to flog it at a car auction before the car became undrivable. Naughty, but it solved it for him.

I would suggest flogging it - one way or another.
Disco 300 Tdi coolant loss - Aprilia
Once the HG goes on these they never repair up quite right. If you fix it, my bet is it will go again within a year. You may even find its on its second or third HG.
Disco 300 Tdi coolant loss - vmturbo

Yup I got conned with one of these as well. It was bought when my twin-cam had bust its cambelt 180 miles from home. At that point I discovered that the "Full Recovery" that I thought my insurer had provided (still have the booklet!) was just a first year introductory offer and it had now been watered down to a tow of up to 20 miles. To recover the car would be £436 and the RAC man suggested that it might be worth thinking about scrapping it on the spot. My Rover 800 diesel that had been hit by an uninsured 40 ton artic was still not fixed so I was down to Shanks's Pony. The big attractions of the Disco were (1) mature owner (2) new timing belt and supposedly fully serviced but things are not always what they seem. The legal owner had bought the car for his 17YO son who had used and abused it (including off-roading) for eight years!

It lasted me for two and a half days. A universal joint failed at 50 miles, it was bone dry and red rust powder was puking out of it. How can that be serviced? I bought grease and a grease gun, greased the UJs and soldiered on. A new joint was purchased later but could not be fitted until I had obtained circlip pliers. After this the car ran more smoothly but doing the job at the roadside was a devil of a job. On my trek I visited the twink and removed its trailer in preparation for recovering it. Alas once the Devon hills were reached overheating set in and there was a drought - no water anywhere! Several bottles of lemonade were on board and by nursing it I did get back to Cornwall but only just and the head gasket has gone. Note that the temperature sensors on these are not made from Bakelite. Instead they use a plastic which melts and the actual sensing element then falls out and measures the temperature about an inch away from the head. This gives the impression that the engine is now cooling. Duh!

The consensus of opinion is that with the 300TDi a NEW radiator is a must. Mine only had its pipes left, all the fins had corroded away. The other consensus of opinion is that overheated heads invariably crack and that repaired heads are not worth messing with. A new bare head (with valve guides) was bought for about £250. Its genuine LR from South Africa. A new ALUMINIUM radiator with a 10% uprate was bought for less than £100 including carriage. With these parts I might be in with a chance of success. Hopefully an alcohol metal bellows thermostat can be fitted as these fail in the open position unlike the modern wax versions. Aluminium rads don't corrode like copper rads so a ten year life is easily possible. Copper radiators soon loose their fins unfortunately.

Incidentally by the time that the Disco failed I was in the position of paying tax and insurance on three dead cars but having to walk everywhere. This new "Continuous Insurance" is the pits and there is no discount for non-runners.

Disco 300 Tdi coolant loss - vmturbo

Blown head gaskets on LR 300TDi engines. There are one or two excellent Land Rover specialists in Cornwall and they all say the same thing about the 300TDi Discovery. "Lots of people replace head gaskets and cylinder heads but they never replace the radiator and it blows again". (In actual fact the new South African300TDi heads are only guaranteed if the radiator, thermostat, and water pump are all replaced)

IMHO if one comes across a 300TDi where the heater has been left at full blast its because the tightwad seller didn't want to buy it a new radiator.

Disco 300 Tdi coolant loss - Peter.N.

The reason you can't find a leak is because the pressure in the cooling system is blowing the water out of the overflow or filler cap, if you look around that area you will probably find signs of dry antifreeze.