Coolant Loss on 300TDI engine

Singr07 · Jul 2, 2025

Hope everyone is doing good. Please advise on coolant loss on this 300Tdi Engine. There is no coolant mix in the Engine oil and it does not misfire. P Gasket was replaced about 300 miles ago and there is no sign of coolant leak there. In the winter exhaust does spit out some water, soon as the engine warms up then it stops.
I tested the coolant leak with this coolant pressure tool on 20PSI then discovered coolant was leaking from 2 hoses, after tightening the jubilee clips it fixed the leak.
But it was still loosing some coolant about 50ml every 40-50 miles. When I went under the vehicle for inspection I discovered small amount of coolant runs below the gearbox. Which made me think it may be leaking somewhere from the back of the Engine.
With a endoscope help, I discovered that middle core plug (behind the Turbo) is badly rusted and noticed some coolant leak there. After removing th

e Inlet manifold and turbo, I tested it again with coolant tester tool on 20PSI. Then one of the exhaust port from left to right number 5 started leaking too as in the picture. Does that mean cylinder head has a minor crack or advise otherwise please?

D1Nut · Jul 3, 2025

There is another one of those welsh plugs at the back of the motor - which would leak down onto the g box

tottot · Jul 3, 2025

The exhaust port seep could be just a tracking leak from a waterway through the head gasket to exhaust port but the only way to know is head off.
Can see other core plugs have been renewed and the heater transfer pipe has been replaced with copper tube.
All sign's that engine has spent time with just water in cooling system with no corrosion protection.

tottot · Jul 3, 2025

D1Nut said:
There is another one of those welsh plugs at the back of the motor - which would leak down onto the g box

Just out of interest @D1Nut but where does the name "welsh plug" for what we call "core plug" come from. Cheers.

Wimblowdriver · Jul 3, 2025

tottot said:
where does the name "welsh plug" for what we call "core plug" come from.

Something to do with leeks?

I'll get me coat ------

Singr07 · Jul 3, 2025

tottot said:
The exhaust port seep could be just a tracking leak from a waterway through the head gasket to exhaust port but the only way to know is head off.
Can see other core plugs have been renewed and the heater transfer pipe has been replaced with copper tube.
All sign's that engine has spent time with just water in cooling system with no corrosion protection.

Thanks for your reply, I have been trying to restore this vehicle from last 5 years gradually. From last year or so I am trying to fix things on my own as I have a garage and tools now. One of the core plug were replaced my myself without removing the manifold and turbo about 2 years ago. At the time maybe the middle core plug wasn't leaking but can't remember exactly. I made a
Copper pipe myself as the original one was badly crowded. I do not do lots of mileage on this maybe 1000 miles a year That's all. But I can remember exhaust were always spitting out some water on cold start. I am going to dismantle the Cylinder head and going to watch some instructions on YouTube and on the Manual. I will keep it posted here

D1Nut · Jul 3, 2025

tottot said:
Just out of interest @D1Nut but where does the name "welsh plug" for what we call "core plug" come from. Cheers.

Alway's been called that in saffaland

Singr07 · Jul 3, 2025

Please advise, What would be the consequences of running the vehicle as it is with coolant leak from the valve port with new core plugs ?

D1Nut · Jul 3, 2025

What is a valve port ?

tottot · Jul 3, 2025

The leak to the exhaust is likely only to get worse over time. As a short term repair [ months] you could put in some rad sealant, like Kseal [other makes available] Advertised as permanent repair but in my experience that is not so and will give up eventually.
Be careful as 300's are not tolerant of low coolant levels because of high coolant pump position on engine and unit will soon overheat.

tottot · Jul 3, 2025

D1Nut said:
What is a valve port ?

The hole where the exhaust gas comes out or air goes in from manifold.

Singr07 · Jul 3, 2025

Does anyone know if ERR5025 Cylinder head is the same as the old one with Landrover stamp HRC2666?

D1Nut · Jul 4, 2025

tottot said:
The hole where the exhaust gas comes out or air goes in from manifold.

Didn't know it was possible for water to leak there

As mentioned the water pump sit's high and the dash heat gauge is useless as by the time it moves it is tickets allready

I run a water level sensor in my expansion tank and has saved me many times from overheating

tottot · Jul 4, 2025

Water level sensor is a good mod.
Head Gasket leaks usually result in pressure in the cooling system but can go other ways

Singr07 · Jul 5, 2025

Here is the picture of Head and block. I have already installed a coolant sensor and clear coolant reservoir. I think it didn't had head gasket leaking but may be cracked inside by the valve seat

Singr07 · Jul 15, 2025

tottot said:
The exhaust port seep could be just a tracking leak from a waterway through the head gasket to exhaust port but the only way to know is head off.
Can see other core plugs have been renewed and the heater transfer pipe has been replaced with copper tube.
All sign's that engine has spent time with just water in cooling system with no corrosion protection.

First Welch plug on the left was replaced by myself. Which had some sort of glue on the leaking hole to cover it but I missed the Welch plug under the Turbo was not visible to me. Middle welch plug had same temporary treatment with some sort of glue on it. Now I can view the right side of the welch along with rear welch plug on the engine. These two welch plugs don't seems to have any leaking holes. I am thinking to change all of these welch plugs at the same time.

I am wondering if there is a way to replace the rear welch plug without removing the Engine as rear welch plug only have 3-4 inch space between the bulkhead

Chris95 · Jul 17, 2025

Singr07 said:
Here is the picture of Head and block. I have already installed a coolant sensor and clear coolant reservoir. I think it didn't had head gasket leaking but may be cracked inside by the valve seat

In the second picture there looks like there is some corrosion on the gasket around the water port which could be enough for it to seep out.

Singr07 · Sunday at 22:40

Hi Chris I have noticed corrosion on head gasket ports too, but head gasket wasn't leaking. Cylinder head had a crack internally, coolant was seeping into inlet manifold port 4th from the right. Coolant was also leaking from the Core/Welch plug Small amount of Coolant was also present in the crankcase breather hose and into the air filter housing. I've been told its not worth fixing this internal damage. With this new Cylinder Head refitted, I tested it again with coolant pressure tester while manifold remains off. At 15PSI luckily it has no coolanr leak anymore. Injectors and glow plugs needs to be put back on as I am working on it gradually.
I am thinking to use the Prestone coolant flush, then flush it again with water then new coolant will be added on. It has conversion engine from a Disco engine number starts with 21L. I am bit confused which coolant shall I use (Granville Rapid Cool Red Antifreeze/Coolant Concentrate OAT) or Blue one?

tottot · Monday at 10:15

K-seal in the system will sort minor leaks for a good time. Can be used with Blue antifreeze.

Coolant Loss on 300TDI engine

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