I have just about made the decision to drop some $$ and go for one of these:
https://www.allisport.com/shop/performance-products/tanks-and-reservoirs/header-tanks/range-rover-p38-v8-discovery-2-v8-late-td5-header-tank/

They are doing a re design to allow the use of the stock cap, so still a few weeks out for ordering.
This looks like the gold standard.....is it?
I do really like the idea of a low water alarm for obvious reasons.
The pinhole in the brand new plastic tank really spooked me. If it was the wife driving, I would be looking at a serious overheat instead of just a new tank! Spendy, but cheap insurance.

The sight gauge faces into the engine bay so you have to look at it from the far side.

I am going to get the one with the low level switch and no sight glass.
Less to go wrong, and I will install a nice loud alarm and light for low coolant warning.
Good for peace of mind knowing when the coolant has suddenly made a break for freedom.......From wherever!

Allisport one seems to be the best option at the moment I think.

Sorry for the great delay, but only this week I've managed to accomplish this incredibly simple task which I've delayed weeks ... so here it is, the "tee" added to the return hose to the expansion tank:

I had a welder (my welding skills are very ... primitive) add a "bung" there and then attached a hose from the TBH return outlet. Would have wanted a thinner silicon hose like the one mentioned around here, but at the time seem unavailable. Since I grow impatient to move on with the build, I just snatched the first hose available and route it unceremoniously around the top of the engine, trying to keep it at the level of the "top hose" and the expansion tank itself ...

Et voila'! Engine running couple times for at least 15/20min, no leaks so far, very happy.
I've concluded my cooling circuit saga.
In time there are the LPG pipes to replace, and I want to add a Thermo Top heater, but this will be down the line...

Well, I was finally able to order my Christmas present to self this evening.......
Allysport got their welder back from sick leave and caught up with back orders.

To replace the nice new German plastic tank that proceeded to split at a seam within 30 days, (Got my 89 bucks back from Parts Geek)
I have dropped $299 Yankee dollars into the UK economy (Glad to do my bit to help out!) to procure a new header tank with float switch!
Lot of $$ for a header tank, but you look at the number of times that an overheat due to loss of coolant
has triggered a series of expensive repairs, or in a few cases I know of, the final trip on a flatbed to the
knackers yard for an otherwise perfect P-38......I recon it is a cheap investment to be able to eliminate one more possible worry.
Now to figure out which section of the cluster to use to install my indicator.....Thoughts?
I also have a sonalert which will go under the dash and should wake you up quickly if the coolant level drops.
Cheers!

Bolt, the tank does look very nice. I am surprised it is hand welded, I would have thought Allisport would be more automated.
The genuine BMW plastic tank is the best part of £100.

It has been a while since I did it, but when you take the speedo head out and take it apart you will see pockets or recesses behind the front panel where bulbs stick through. There is a thin black sheet in front with symbols etched into it for the various warning lights. If you hold it up to the light you can see them. I have a few spare speedos and they are all slightly different. Petrol or diesel, manual, early or late but there will be unused ones or just make a hole and stick in an LED. I used the one with 2 gear cogs. Is that traction control? Anyway it was not used on mine. There was no bulb behind it.

The one with two cogs should flash while the transfer box is changing from low to high and vice versa so should have been used. There are a couple of other blank spaces though.

The $10 alternative. It might be worth considering.

Coolant level switch

$300 dollars give you a lot of options?

Marshall8hp wrote:

The $10 alternative. It might be worth considering.

Coolant level switch

That would indeed be an option, and I shall get hold of one to put in the Black plastic header tank on the 85 Classic
the next time I am in Oz..........The black one I have on the 300Tdi are a MUCH tougher plastic than the white ones.
The major problem from my standpoint is that I have had 4 tank failures on 3 vehicles in the last 15 years.......
I count myself lucky that each time I caught it before anything overheated.
I cannot see spending about the same amount to get an Range Rover branded plastic tank, although
it would probably be fine, I know this one will not leak, or suddenly burst on me. (Do it once, and do it right!)
Honestly, I am a bit surprised that there was never an option for the switch from the factory. I believe I read somewhere that there is provision of some sort in the Becm for low coolant, but they must have run out of I/O spaces on the CPU and dropped the switch option.
Even tho' I will be a bit poorer in the $$$ department, I shall be a happy camper when I get this installed!

Mad-as: For $300 bucks, I get the tank, and a low level float switch, and about $75 dollars shipping charge.
I will post the results.......
:

its a bit more than just a tank and a level switch bolt , its a purpose built unit to fit and thats exactly what you would expect for that money , but when your a cheap ass like me you always look at something and think, i could make a bracket for that ....

In terms of catching a loss of coolant, I have an alarm fitted, which is bolted to the cylinder head. It gives a constant read out and you can set the alarm to sound at whatever temp you like. Unlike a sensor in the coolant, which will drop if you have coolant loss, the cylinder head temperature increases, so you get a warning pretty quick. Comparing this sensor to the water temp sensor, they are usually within a couple of degrees.

Engine Guard

That would be a good option as well, and a bit less dosh! Could I trust the wife to heed the advice?.....Experience says a loud alarm and flashing light is what it takes to get the "other drivers" attention........
With the level switch, I will have a warning that the temp will rise SOON if I do not address the issue.
However, I look at this as an investment in my cooling system, and a way to eliminate what has been for me at least a very vexing problem. I just have very little faith in the currently available plastic tanks with all of the cheap Chinese knock offs out there.......
Mad-as.......Please do not misunderstand, I am as mean a bugger as they come!
I will however happily pinch a penny till it screams and in turn, buy something which I find to be good value!......Hang the cost!
A hand made, bespoke, "Custom" part like this? I could not do one myself, and I know it would be a bunch more if I commissioned a one off.
Cheers!

Bolt, for the Classic with the black plastic tank, if it has a screw cap and not a standard bayonet fitting pressure cap, then the cap incorporating a level sensor as fitted to later Classics will fit straight in. Part number for it is PRC7925 (https://www.lrdirect.com/PRC7925-Expansion-Tank-Sensor-Late-Rr/). Looking at LRCat, it appears that the earlier Classic had either a metal header tank with a bayonet pressure cap or the black plastic one with a screw cap. If you've got the screw cap all you need do it fit one of them and wire in a warning light (which my 93 Classic had as standard).

As for the P38, a catch tank on the overflow with a sensor is one option but that will only tell you there is a problem if coolant is being pressurised and blown out, not if you have a leak somewhere else and the level is dropping. I'd be wary of drilling a hole in the side of the header tank to fit a float switch in case I introduce a leak there and make matters worse. I'd rather find something that can detect the coolant level from outside, but not sure how yet. If the header was completely clear, shining a laser at the surface of the coolant would be a way to do it.

my 83 classic has a brass tank , the only thing wrong with it is the paint is flaking off and thats nearly 40 years old . i do understand the crappy plastic problems , especially the Chinese rubbish and if i was to spend that amount of money on a tank it would look just like the one you going to purchase , i do like shiny things to . i tend to make alot of pieces from stainless steel ,polish the welds clean it all up, and then paint it black . i am a little surprised the rover dosnt have a low water alarm its got everything else that gets hot. its whatever gives you piece of mind Bolt and sometimes its good to get something that just fits and works , and thats why you pay a little extra . it is a good looking tank and it will be interested to see the finished product in place. it looks a more compact unit so it might make working in that area easier , maybe.

Gilbert: Thanks! Of course, that would be the easiest solution.
The 85 did have a brass tank with the petrol motor, however when we dropped in the Tdi 300, we used it's tank as well.
Thus, I will want a tank cap for an Disco.

Disco 1 and later Classic used the same tank so the one I linked to will fit your header tank on the Classic.

Well CRUD! 300 bucks down and I am still using plastic!
I got my new Allysport tank just fine.
Took out the old one, fitted the sleek silver beauty, connected the hoses, filled, bled.......................Annnnd......
Discovered that the filler neck will in no way accept the stock cap!
The 1 1/2 month delay I experienced was due to the tank undergoing a resign to allow the use of the stock cap.
As they did not provide the cap, I figured that this is what I had. Nope, did not check first........
I have contacted them to ask what next.
On a side note, the return for the radiator bleed is on the side of the tank not the neck, so the pre formed
hard black plastic tube is not a nice fit and there is no provision for an overflow tube.
Possibly they just flat out sent the wrong tank??
Anyone used one of these?
Awaiting further developments......
Cheers!

EDIT: I looked at the part number I ordered, and it appears they dispatched the wrong tank!
Only has 2 nipples, not the three I need. Now to see how they handle this one!
Sighhhhh.........

Hi Bolt, just installed yesterday one of this redesigned tanks in the P38 of friends. . The bleed pipe is really a bit too long. I made long holes in the bracket and moved it a bit inwards. (LHD)
Mine came with a cap and it was the right one.
My experience with Allisport customer service is really good / great. Feeling sorry for You.