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MercianRover



Member Since: 07 Apr 2022
Location: Culworth
Posts: 138

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
300TDi very slow coolant loss
I'm slowly loosing coolant in my 300TDi, maybe 0.5 litre over a month or so. Next time I top it up I'll make a note of the mileage and date so I can see what the loss rate is.

There is:
No evidence of coolant on the ground after a run.
No white smoke.

I fitted a header tank level switch after reading horror stories of sudden coolant loss, I'm more concerned at the moment about where else I could look for the leak, the heater doesn't smell of coolant either.
Post #1040414 20th Jul 2024 9:26am
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landy andy



Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5563

2006 Defender 110 Td5 USW Zermatt Silver
Is it falling below the low line on the reservoir?

Years ago I was frequently topping up the coolant on a vehicle to the max line, only for it to drop to the min mark after a while. Eventually I found that the system was pushing some out when hot and low mark is where it wanted to be. It never went below that level.

Just a thought.
Post #1040415 20th Jul 2024 9:37am
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MercianRover



Member Since: 07 Apr 2022
Location: Culworth
Posts: 138

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
That's an interesting thought, maybe I'll see what happens when it gets to the low level.

The only concern I have is the Land-Rover header tank cap / level switch isn't adjustable so I was using that as the set point for "not enough".

That said the warning light only illuminated when the vehicle was parked on the drive (sloping) so maybe the level, although low, is actually OK.

Slightly off-topic I can post the wiring diagram and parts used if there is interest - I bought the cap / level switch separately, use the "transmission temp high" light to warn (because it's red and looks a bit like a water pump) and have a latch / timer with a delay (I think 5 seconds) to prevent false alarms. Only change I'd make is to add a buzzer.
Post #1040417 20th Jul 2024 9:43am
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I Like Old Skool



Member Since: 23 Feb 2015
Location: Manchester
Posts: 791

United Kingdom 1994 Defender 110 300 Tdi ST Coniston Green
P-gasket. Search it, it's a common fault. Leaks when warm and engine heat evaporates the dribble before it is visible. My 300tdi was doing the same for ages until I tracked it down. Such a slow loss of liquid it makes you doubt if you even have a leak......[/url]
Post #1040420 20th Jul 2024 9:57am
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Chicken Drumstick



Member Since: 17 Aug 2020
Location: Near MK
Posts: 668

United Kingdom 
Re: 300TDi very slow coolant loss
MercianRover wrote:
I'm slowly loosing coolant in my 300TDi, maybe 0.5 litre over a month or so. Next time I top it up I'll make a note of the mileage and date so I can see what the loss rate is.

There is:
No evidence of coolant on the ground after a run.
No white smoke.

I fitted a header tank level switch after reading horror stories of sudden coolant loss, I'm more concerned at the moment about where else I could look for the leak, the heater doesn't smell of coolant either.

I wouldn’t worry too much. The Tdi is a stout and very simple engine. If the leak isn’t obvious just chuck a Radweld or similar in it and only sort it out if it becomes a bigger problem down the line.
Post #1040425 20th Jul 2024 10:20am
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Mdm



Member Since: 11 Sep 2013
Location: Sunny Lancashire
Posts: 1570

United Kingdom 
small leaks can be hard to find . pinhole in a pipe , leaky p gaskets are quite common.

easiest way is to pressure test the cooling system. most 4x4 garages will have a tester and dont charge a lot to do it.
if no visible leaks then a sniff test or coolant test to see if you have a blown head gasket.

im not a fan of radweld etc as a 1st line of fixing a leak.

its a temp solution and is know to gunk things up, small water ways etc.

if i was to use it i would drain the coolant.
use product until leak stops.
drain system and add fresh coolant.
Post #1040476 20th Jul 2024 3:28pm
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TomB8



Member Since: 17 Nov 2022
Location: West Sussex
Posts: 115

United Kingdom 1994 Defender 110 300 Tdi HT Arles Blue
If you've checked everything else thoroughly, I'll second the p gasket recommendation. I wasn't going to go that far when I replaced my water pump but glad I did as the p gasket was original and in a bad way.

There was no obvious signs of leaking as shown on YouTube videos, just a very slight loss of coolant over time - not as much as you're reporting.

The gasket is about £1 and takes a couple hours so well worth it to eliminate that as a point of failure. For the sake of a few more quid you could go ahead and replace all the coolant pipes... Sounds obvious but make sure none of them touch pulleys. Found one of mine almost worn through and I'm pretty anal.

The other place mine likes to leak is the bottom rad hose if the clip isn't tightened right down, no idea why it needs to be so tight but there we go.

You could modify your old coolant cap and make your own pressure tester if you are so inclined.
Post #1040578 21st Jul 2024 11:43am
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Mo Murphy



Member Since: 01 Jun 2008
Location: Letchworth Garden City, Herts
Posts: 2170

United Kingdom 1984 Defender 90 200 Tdi HT Pennine Grey
P gasket or core plug would be my first places to look.
Mo The Land Rover 90 - Many are called, few are chosen.
Post #1040643 21st Jul 2024 7:51pm
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MercianRover



Member Since: 07 Apr 2022
Location: Culworth
Posts: 138

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
It's the P gasket, I stopped a trickle this morning.

Thank you for the interest.
Post #1041110 27th Jul 2024 12:45pm
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sako243



Member Since: 08 Jul 2014
Location: Wales
Posts: 1203

Wales 1994 Defender 110 300 Tdi CSW Alpine White
Re: 300TDi very slow coolant loss
Chicken Drumstick wrote:

I wouldn’t worry too much. The Tdi is a stout and very simple engine. If the leak isn’t obvious just chuck a Radweld or similar in it and only sort it out if it becomes a bigger problem down the line.

I wouldn't bother, Radweld and similar are supposed to be put in then have the entire system drained and refilled so it doesn't clog up the internals of the cooling system. They're not difficult engines to diagnose or find issues on and they're pretty robust so just find and fix the issues properly. Ed
82 Hotspur Sandringham 6x6
95 Defender 110 300Tdi
Post #1041112 27th Jul 2024 1:17pm
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MercianRover



Member Since: 07 Apr 2022
Location: Culworth
Posts: 138

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
Predictive text replaced "spotted" with "stopped".

I spotted the leak by the P gasket.

Since it needs surgery at some point to cure an oil leak in that area I'll get that fixed at the same time.
Post #1041120 27th Jul 2024 5:10pm
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I Like Old Skool



Member Since: 23 Feb 2015
Location: Manchester
Posts: 791

United Kingdom 1994 Defender 110 300 Tdi ST Coniston Green
MercianRover wrote:
It's the P gasket, I stopped a trickle this morning.

Thank you for the interest.


I would like to say I told you so Thumbs Up
Post #1041148 27th Jul 2024 10:31pm
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