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300 tdi auto cooling issue bugging me...

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Hi Guys,

Hope you may have a suggestion for this little concern please....

'Mumf' our 1994 D1 (auto) 300 has never over heated and her cooling system has been bled properly by me (cabin heater works at about 3 miles) but she does seem to smell like she's running a little on the hot side when hammered for long spells. :excl:

Still never over heats even in the recent hot weather (got to have a good memory for that!) with cabin heating off.

(It's a shame there no easy replacement for the silly standard VDO guage that is not reflective of conditions by sensible increments)

Thing is that the header tank is one of those 'blingy' Alisport ones and it never has more than about 3mm water in there when cold but fuller when hot (Maybe it sits higher??).

From start up the water is flowing through the self bleed branched return pipe to header and the header gets very, very hot and you think it's going to boil.

The stat opens up and the top and bottom main rad pipes get hot but never as hot as the header tank. That's how it feels anyway.

Just wondering if this self bleed pipe thingy could be blocked on its other branch or the header tank cap may be fubar'd or not able to seal against this blingy header. Dunno.

My old 96 disco had a standard plastic header and was always around half full of fluid and never ran this (apparently) hot even when towing diggers up hill!! :o

I'm not sure if water is dispelled after running hard but I never seem to get a zizz of pressure or steam when I catiously release header cap with rag in hand.

Is it normal for a fast flow via this self bleed return? - quite a significant flow when revved before the stat opens.

Is it normal for header to be that hot?

Anyone else had experience of this or of a blingy header?

Everything seems iin order but yu know.... :rtfm::unsure:

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In our parts where it gets quite hot we add an after market digital industrial thermometer that sits on the cylinder head and gives us an extra reference. These are very sensitive devices and show centigrade by centigrade variations in real time. Mine has saved the day on more than one ocasion once when the main belt gave way on a highway where other indicators such as failure of pas pump did not come in to play. In most cases by the time standard coolant indicators register over heating the cylinder head has already sustained damage. We also add a buzzer that self activates at 106 so even if you are day dreaming you notice.Highly recomended add on !


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I fitted one of these to my Dad's camper, as he managed to cook the head badly when the hot water heat exchanger failed, it has a warning at 120C, as well as the digital readout, good for peace of mind:


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Point well made and thank you 'NegevLandRover '. Boy it must be hotout there! Makes my concerns fade..... :o

Thanks for the link 'Bowie69' neat - I will seriously consider fitting something to show what's actually going on in terms of temperature. :i-m_so_happy:

Anyone had experience of or would also like to comment on the notes and queries? :mellow:

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If you fill the system and get all the air out, then the header should be half full when cold. If the header level subsequently drops, you are losing coolant and need to investigate where. I recently had a tiny gas leak from the cylinder into the water system via the head gasket on a 200 Tdi (very similar internal configuration which shares the same head gasket as the 300), which caused the coolant system to pressurise. The leak was small enough that the coolant stayed pressurised as the engine cooled, the gas being trapped in the header tank until the cap was unscrewed. This leak cased a small amount of coolant loss. Check yours for any signs of coolant leaks or contamination of the oil with coolant or the coolant with exhaust gas (you can buy a chemical tester kit which changes the coulour of a sample of coolant you draw from the tank if gasses are dissolved in it).

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