Fluid from expansion tank

Anyone seen this happen on a Def 90 TD5? My 2001 TD5 spits a little fluid out of the expansion tank and i am always checking the level to be half full on it. It doesnt boil up and the temp gauge sticks solid at normal but i am losing fluid somehow. I have asked in the local 4c4 garage and he says its likely to need a new head or a min of head off , pressure test and skim etc. I thik he just wants a job to fit a new Spanish made AMC replacement head at £1300 plus labour.....
I have replaced the expansion cap with a new one but it does the same.
If this was a normal car engine i would be looking at a stuck thermostat but does the TD5 engine have one and where is it located?
Has anyone had this on their LR TD5 and is the cause most likely to be the 10P engine cylinder head being cracked or the head gasket gone?
Your ideas please......

Thermostat is in a sealed plastic unit on the coolant pipes at the side of the radiator, it looks like this. https://www.paddockspares.com/pem100990-thermostat-and-housing-td5.html
It does sound like you may be getting pressure from a leaking head/gasket into the cooling system, a sniff test can detect hydrocarbons in the head tank to diagnose this, most good garages should be able to carry this out, and there are cheap test kits available if you search online. I would expect overheating if thermostat was stuck shut or running very cool if open.
https://www.google.com/search?q=hyd...bile&ie=UTF-8#scso=_wYMsYq4mtYaFsg-1nJa4AQ3:0

It's possible for a little coolant to come out of the breather in the cap on the expansion tank on TD5s, without it necessarily needing an engine rebuild. Yes of course the cylinder head and cylinder head gasket are weak points, but in this case it's possible for the weak point to be the valve in the breather. Mine's been doing this for 110,000 miles and doesn't seem to be getting any worse. A new genuine cap (not a Britpart one) solves the problem for a few thousand miles and then it starts showing evidence of leaking again. I check on the coolant level every few hundred miles (along with having a look at the dipstick, brake fluid level, windscreen wash level and suchlike), and very occasionally I put a drop more in, but it's not needed much. A few other people have mentioned this on here too over the years so it seems to be something that TD5s do.

As above. Stop topping it up and see if the level settles.

My header tank stays at around 1/3 full and if l top it up to 1/2 full or more, it loses the extra....l assume from the filler cap.

lt's been like that for 80,000 miles
2005 TD5 Defender

Obviously if the header tank becomes very low or empty then you have a problem somewhere
and will need to investigate further.

The pre-2002 10p version of the TD5 is more prone to head gasket issues.

It seems the garage i used that week for some minor work topped up the fluid in the header tank, took out the top hose bleed screw and said they bled the coolant to the right level and till no air was coming out. In putting the bleed screw back into the hose they damaged it or the thread and it leaks now. They added a brand new header tank cap for me. I didnt have any problem with fluid leaks before the garage started fiddling with it.
I have since drained out some coolant from the header and used the new cap and i took out the hose bleed screw and used some clear silicone on it and behold no more water/red coolant spraying over the turbo or manifold or the bulkhead areas.
I am about to refit / renew the top and bottom hoses and a new thermostat and have 10 litres of red OAT coolant ready to go in it. Hopefully all this will resolve the damage the garage did to my vehicle.... It was a so called Landrover 4x4 specialist in Devon as well!!!!!!

Anyone can make a mistake. Hopefully thats sorted it.

After l changed the coolant on my 110 the bleed screw wouldn't seal and l had to change it, it's only a flimsy plastic thing, maybe a metal one would be better?

Although then you'd burn your hands on it trying to bleed the air out

Yep i thought that too. I bought a nice blue metal screw for the new top hose but it doesnt fit.. It starts to screw in but then stops as i think the tapped hole isnt tapped all the way through . The metal version is a lot longer than my old plastic one so its on the shelf unused now and the siliconed plastic one is in palce and not leaking at all now. The new hoses are going on the vehicle on 28th March as the engine is coming out for a galv chassis to go on it. It will be so easy to change the upper and lower rad hoses and the thermostat and the expansion tank and its thin pipe to the rad too. It means the rad and coolant system will be drained too and flushed through so all a good thing to do. All things i doubt the previous owned did to it......

The saga goes on ... I had the system checked by a terrific LR chassis fitting company near Liskeard and they found that i was getting pressure into the water jacket which was then pushing the fluid out past the reservoir cap. So off came the head!!!!!!!! A gasket failure was expected.
Once the head was off they found the alloy head had holes in it where they shouldnt be. It looked like acid had eaten away the alloy leaving holes in the head face. See pic.
This all then meant a new head from Turners and AMC unit made in Spain. Not cheap but said to be the best and the way to resolve head issues in future.It comes with all new studs too and was fitted with new head bolts and all the recommended gaskets.
I now have rock solid temperature gauge, no more fluid leaks from the reservoir plus all the new hoses and a cleaned out rad core too that was also flushed through off the car.
The rot on the head was thought to be because of water or ordinary antifreeze being used in the engine and not the OAT version . There are warnings galore about this but it seems previous owners ignored the warnings and used water etc regardless. It is now full of the reddish OAT fluid as recommended and i also bought a spare 5 litres of it so be warned folks. It was £2,000 for the head job!!!!!!!!!!!!!
Interestingly it has done nowt for performance and if anything it goes less than before..........and thats with a stage 2 remap.

Good to get feedback/update. Glad you eventually got it sorted out.