My coolant level on my TD4 always sits between min and max. I asked my dealer about this and they told me this is normal, dependant on the type of driving you do. Apparently motorway work will cause the coolant to drop a little?! Anyway I topped it up a couple of weeks ago and it's back to sitting between min and max. It doesn't seem to drop any further, so I don't think there's any mechanical issues, but it seems a bit odd.

Anyone else's do the same??  Gone - TD4 XS Auto, Sumatra Black, Mud flaps and side strips, clear indicators, private plate, privacy glass

It's normal to drop a little when engine is hot because of the pressure that builds up inside the cooling circuit.
Remember the laws of thermodinamics: same volume, increased temperature -> increased pressure.
It's a pressurized cooling circuit because in this way water inside will boil way over 100*C (212*F).

alex_pescaru wrote:

It's normal to drop a little when engine is hot because of the pressure that builds up inside the cooling circuit.
Remember the laws of thermodinamics: same volume, increased temperature -> increased pressure.
It's a pressurized cooling circuit because in this way water inside will boil way over 100*C (212*F).

Fair enough, but it does it on a cold engine too. Hot or cold, makes no difference  Gone - TD4 XS Auto, Sumatra Black, Mud flaps and side strips, clear indicators, private plate, privacy glass

If the pressure inside the cooling circuit is over 1.45 bars, then the water/pressure surplus is released ouside the circuit. This could be an explanation for founding again the water between the marks after a while.
For sure the level when hot is lower than when cold. You can try it by CAREFULLY and SLOWLY unscrew the expansion tank cap when engine is hot and see how water inside will rise a little.

alex_pescaru wrote:

For sure the level when hot is lower than when cold. You can try it by CAREFULLY and SLOWLY unscrew the expansion tank cap when engine is hot and see how water inside will rise a little.

I'll give it a whirl - cheeers Alex  Gone - TD4 XS Auto, Sumatra Black, Mud flaps and side strips, clear indicators, private plate, privacy glass

alex_pescaru wrote:

For sure the level when hot is lower than when cold. .

it's been a while since i sat A level Physics but i am sure it's the other way round. As it heats it expands then as it cools it contracts therefore the level will be lower when cold. 

Hmm, I need to read my owners manual. I may well be wrong but as a rule of thumb for all vehicles I always thought you used the lower mark when checking expansion tank water level COLD. As the engine warms up and water expands, the bottle then provides the room for the excess water, the expansion 'space' is what is between minimum and maximum marks. As the engine cools down and the water contracts, water is drawn out of the bottle back into the circuit. If the expansion bottle gets too full, ie above the maximum mark, then the cap valve lifts against its spring and allows excess water down the overflow pipe.

So if you are filling the bottle to the high mark, then the bottle will empty the excess everytime the engine gets hot and probably leave you with somewhere between mim and max. Which is exactly the characteristics your experiencing. Look for water witness marks out of the overflow pipe.

Some systems might appear to be expansion tanks but are in fact header tanks and work differently. Header tanks require the bottle to be the highest water level point, whereas a true expansion tank can be anywhere, above or below. Can't say I've ever looked closely at my LR to determine which it is. 58 HSE, auto, lago grey, tints. Mine and my dogs Storm and Sky
TT Quattro, black. Ers.
AC Cobra rep in build. Ars.

christian138 wrote:

it's been a while since i sat A level Physics but i am sure it's the other way round. As it heats it expands then as it cools it contracts therefore the level will be lower when cold.

On PRESURIZED cooling systems the level on expansion tank when hot is lower than when cold.
On ATMOSFERIC cooling systems the level on expansion tank when hot is higher then when cold.

On FL2 there is a PRESURIZED cooling system. Because of the pressure AND because the hoses are flexible, the pressure will build up in expansion tank and will lower the fluid level and expand/harden the hoses.

Sorry for my poor english, but I believe you will understand what I've meant.

je comprende tres bonne At work
At home

"I can't always believe facts I read on the web" - Charles Dickens

winner by default of the tractor vs caravan race

Sorry Alex,

Hot water expands, its a fixed law of the universe. As you say pressurisation is used artificially to raise the boiling point.

When you first start the engine there will be a number of different things affecting the water level, the pump starts to generate pressure, and yes there may be some very small hose expansion (but its very small) the thermostat position etc. So the water level may change but you won't see it by naked eye, its millimeters.

(If hoses are found to be panting a great deal then the design and quality are dangerous and should be changed ASAP. replacing straight sections with pipe may help)

As the water heats up it then expands. The ONLY place it has to go is the expansion bottle, which is why the water level rises.

Normally the cooling package will reach equilibrium with the heat generated by the engine, the temerature and the water level will stabilise.

If you unscrew the cap on a hot running engine (not advisable) then the water will dramatically rise. This is simply because of the pressure differential created by the pump/cap, not because hot water contracts.

NB the manual says to fill the tank between mim and max marks. 58 HSE, auto, lago grey, tints. Mine and my dogs Storm and Sky
TT Quattro, black. Ers.
AC Cobra rep in build. Ars.

I always thought on starting from cold the coolant went round and round the engine until it was warm then the thermostat opened to allow water into the radiator to help cool the engine.

Or am I living in the dark ages?

Yse thats how T stat works. 58 HSE, auto, lago grey, tints. Mine and my dogs Storm and Sky
TT Quattro, black. Ers.
AC Cobra rep in build. Ars.

stormsky wrote:

Hot water expands, its a fixed law of the universe. As you say pressurisation is used artificially to raise the boiling point.

stormsky wrote:

As the water heats up it then expands. The ONLY place it has to go is the expansion bottle, which is why the water level rises.

stormsky wrote:

If you unscrew the cap on a hot running engine (not advisable) then the water will dramatically rise. This is simply because of the pressure differential created by the pump/cap, not because hot water contracts.

Ok I see where you are coming from.

Although by design the water level should rise in the tank, in reality due to hoses excessive expanding or panting it actually drops a mm or two.

Never noticed on mine but will have a look next time I spend some time cleaning her inside and out. Sounds like LR have used cheap and nasty hoses. If thats the case might be worth a chat with my nearest Samco dealer... 58 HSE, auto, lago grey, tints. Mine and my dogs Storm and Sky
TT Quattro, black. Ers.
AC Cobra rep in build. Ars.