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300tdi - strange coolant issue...


Paddy_SP
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As my ground-up Defender project is taking far longer than anticipated, about five or six weeks ago I bought a very clean 300tdi Disco. How smug was I when my village got snowed in and I was still fully mobile! :)I've driven it quite a lot since, and love it. I've had no problems at all - unless you count the latch spring on the passenger door, which I fixed last week. Most of the time, it's only driven short distances - 10 to 20 miles. Last night, however, I had to trek up to Bideford from Crediton - about 25 miles into the journey I suddenly noticed that the temp gauge had hit the red...:( I coasted it to the next lay-by, by which time the needle had come back down significantly. I slowly eased the coolant cap off - there wasn't much pressure, and no sign of boiling. Just as I was congratulating myself that the level was correct, there was a loud gurgling noise, and all the coolant disappeared into the bowels of the engine. I had a 2 litre water bottle with me, so I put that in and drove to the next garage where it took most of a watering can to fill it back up. I completed the journey - albeit taking things carefully, with the temperature remaining rock solid all the way there and back...:)

So - my question for the esteemed members of this site - what are the likely causes?

1. A long-term airlock

2. Head gasket failure.

3. Cracked head.

4. Something else?

Any help would be most appreciated! :)

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I had a similar thing happen on my 110 [300TDi retrofit]. I'd had it three days and it did what you described. I refilled it carefully, following the procedure from the manual carefully to avoid airlocks, and it's been fine since. I swap thermostats twice a year [for extra heating in winter], refill carefully and it's never happened again.

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if the system had not been bled properly then it may have just been an airlock , however in my experience with 300 discos if the guage was reading red then you may expect further trouble, the 300 engine just does not tolerate heat at all

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You need to check the colant cap as there is 2 valves in it and sometimes does not hold preasure that is requred, and

will cause an airlock in the engine , if they dont seal it will push the water into the expansion tank and posibly out

through the cap, and you need to check the 2 small pipes that go to the expansion tank to se if they are blocked up,

as these pipes let the air out of the engine and the radiator to stop an airlock

one way to check your cap is after been used stop the engine and listen by the cap if you hear a slight hiss it is not

sealing and wants replacing

i have seen one vehicle that had 2 head gasgets fitted when the 3rd went it came to us and what was causing

the gasgets to go was the seals in the valves in the cap had browken up, no preasure in the coling system

causing an air lock ,when there is no preasure you think there is no problem, but thats not true

hope this will help your problem, and others need to check their caps as well as it is quite comon

GWYN LEWIS

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You need to check the colant cap as there is 2 valves in it and sometimes does not hold preasure that is requred, and

will cause an airlock in the engine , if they dont seal it will push the water into the expansion tank and posibly out

through the cap, and you need to check the 2 small pipes that go to the expansion tank to se if they are blocked up,

as these pipes let the air out of the engine and the radiator to stop an airlock

one way to check your cap is after been used stop the engine and listen by the cap if you hear a slight hiss it is not

sealing and wants replacing

i have seen one vehicle that had 2 head gasgets fitted when the 3rd went it came to us and what was causing

the gasgets to go was the seals in the valves in the cap had browken up, no preasure in the coling system

causing an air lock ,when there is no preasure you think there is no problem, but thats not true

hope this will help your problem, and others need to check their caps as well as it is quite comon

GWYN LEWIS

Many thanks for the excellent advice - that could well be the answer! :) The oil level is fine, so it's not leaked into there. I will fit a new coolant cap and check the 2 small pipes ASAP! :)

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The two pipes (one from the thermostat housing and one from the top of the rad) come together in a 'Y' piece. I've known these get blocked and the cooling system won't bleed properly. A quick check (without disconnecting the pipes) is to remove the expansion tank cap when the engine is cold. Look down in to the centre of the tank and bring the engine up to ~2000rpm. There should be signs of strong flow coming up in to the tank from the small pipe. No flow suggests blocked pipes / Y piece, or the wrong type of thermostat fitted.

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