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Interesting overheating problem on the 300Tdi

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jnoshea:
On the weekend we drove up to Creswell Crags (about 35 miles or so). The truck was fine all the way up and the heater was working nicely. Shortly after leaving Creswell the engine started to overheat and at the same time only cold air coming out of the heater. Pulled over for a while and started again. Same problem. This also happened a week before but suddenly corrected itself. Now it seems permanent. So when hot water is going through the heater everything is fine, when it's not the temp gauge shoots up really quickly. The coolant pipe that shoots straight over the top of the cylinder head underneath the rubber cover is cold, the radiator top hose is hot and the radiator itself is hot. Any ideas what's causing it?

Pete:
 First thought would be an air lock, or crap in the system, causing an intermitant blockage. A system flush and refill is cheap, if it works, it saves time and cash on a system strip down.
It would be the first thing I would try.
 Pete.

jnoshea:
Thanks Pete, I'll try flushing the system first on saturday. A bit of crap does sound likely. The efficiency of the radiator has been getting worse over the last year or so with a tendency to overheat onthe motorway above 60 mph in the summer unless I had the heaters on. Maybe a bit of radiator has come loose inside. Since the heater doesn't work at the moment I guess the blockage could be somewhere in the heater matrix.

jnoshea:
After the last overheating problem the system was low on water. I filled it from the rad and the expansion tank, then took it for a spin. Everything was fine and the heater worked as normal. The next day I notice some water around the expansion cap, took it off to find the water level was right to the top (Not where I had filled it the previous day). Opened the filler on the rad to check water and in doing that the level in the exapansion tank dropped to normal. So now I think the system is getting pressurised and is pushing the water out of the expansion tank. I guess this can only be the gases from a combustion chamber leaking into a coolant channel somehow. I'm hoping that it's a head gasket. Don't want it to be a cracked head. What are the chances? There is also a little bit of grey smoke at low revs and it doesn't feel as smooth as it used to. :'(

Digsit:
James

My previous 300tdi showed the same symptoms when the head gasket went...take her for a spin to get her warm then take off the oil filler cap to see if you have any creamy emulsion inside the rocker cover ( one indication of failed head gasket ). If it has gone then its a good idea to get the cylinder head tested while its off.  Mine was cracked and had to be replaced. You really don't want to change the gasket only to have to take it all apart again  ;)

On mine, the gasket failed after the engine overheated due to a leaking heater matrix. Fixed that and then found a leak in the radiator....fixed that and also found another leak in the expansion tank.......the moral = check everything cos by the time you notice the overheating prob it could well be too late to save the head  :evil:

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