kermit_rr said:

does it actually unscrew, or is it popping off the thread? if its a replacement cap then it could just be a poor fit

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tony109 said:

Trouble with small header tanks, don't need to loose much water to have serious problems. Do you have a separate overflow catch tank, or does it vent to atmosphere? Maybe seal the header tank treads with PTFE tape, will stop the lid coming loose, then feel for pressure and water loss.

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lynall said:

I would try new tank and cap before doing any engine work, I have had cheap header tanks with poor fitting caps,(not tdi though)
How hard is the top rad hose after a decent run?

Pretty rare for a 200 head gasket to fail pressurising the coolant system, in fact I have never seen one do that myself, 300 on the other hand! the 200 head gaskets normally fail at the back of number 4 cylinder allowing exhaust gases to take the paint off the bulkhead.

Still got viscous fan?
Could be over heating and your gauge is lying?
Is this the series< might be your hose routing?

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cornish rattler said:

Yeah i was thinking of trying a 90 / 110 header tank with a twist cap first and see how that does, hose routing, larger hose from header tank joined into a heater hose and small hose from tank to rad, does that sound right

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lynall said:

Is the tank bolted to the engine or the car? thinking engine vibes.

Small hose to rad top is just an air vent, ie it vents air from the rad to the header tank, think bottom tank large hose should go lower on the engine, my 90 has it Teed into the rad lower hose, I am not sure if Teed into the heater hose would make any difference though, as I assume the header tank fat hose just keeps the system topped up.

My series tdi uses the original series diesel rad, ie no separate header tank.

The twist cap tanks are approx 1/2 the size of the screw on cap tanks capacity wise.

Pic is hose runs on a 90, I guess disco is much the same.

View attachment 293097

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cornish rattler said:

Yes its more or less the same setup other than the large header tank hose that moulded to the bottom hose goes into a heater hose as there isn't much room with a tdi in a series as regards the bottom hose and made a bottom hose that just went from the water pump to the rad

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lynall said:

I reused the original series diesel rad with my tdi.

Have you had a feel down the back of the cylinder head when she's running?

I would still try a new tank and cap, then if it still happens you know you have an issue.

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cornish rattler said:

Yeah i've ordered a used 90 / 110 brass header tank, new rad cap and bracket should be here early next week but will need a clean up and re-paint before i fit them

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cornish rattler said:

Thanks guys,
My new to me brass header tank and new cap are on and i've just been out on a road test up and down the Mway with no problems

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lynall said:

Is the tank bolted to the engine or the car? thinking engine vibes.

Small hose to rad top is just an air vent, ie it vents air from the rad to the header tank, think bottom tank large hose should go lower on the engine, my 90 has it Teed into the rad lower hose, I am not sure if Teed into the heater hose would make any difference though, as I assume the header tank fat hose just keeps the system topped up.

My series tdi uses the original series diesel rad, ie no separate header tank.

The twist cap tanks are approx 1/2 the size of the screw on cap tanks capacity wise.

Pic is hose runs on a 90, I guess disco is much the same.

View attachment 293097

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miktdish said:

I like all tye little red bits, is that wee a plastic cover on the end of the jubillee clip ?

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