300TDI overheating headache?!?!

my 300tdi (78,000 miles) keeps boiling, i did the headgasket 2000 miles ago, iv removed the thermostat, and put a new waterpump in it, and it still over heats, but its strange, i can leave home, it'll get up to temperature within 2 miles, then sit fine for maybe ten miles, then boil? almost like a thermostat closing but like i say its removed?

you can tell when its about to boil because the heaters go freezing cold and it goes from normal to past red in a matter of seconds?

last night i drove 15 miles with no issues, got back in the car to drive back and it boiled in 5 on the way home?

any idea's?

thanks in advance

plastic impeller on waterpump?

the lack of heat means air lock or no flow

big air lock?

try bleeding it again, squeeze the pipes and fill from the top hose.

I put a brand new water pump in it last night, and iv bled it several times?

Bypass the heater matrix, which probably has the airlock, by linking the input and output feed at the engine bulkhead. If it doesn't overheat, you know where the issue is. My old 300Tdi had a blocked heater and it seems any issue with the heater flow will affect the main system.

lukespeed said:

I put a brand new water pump in it last night, and iv bled it several times?

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you haven't done it right then

it does sound like a classic air lock.

if you are doing the usual thermostat and rad plug, try undoing the disco expansion tank fixing bolts and raising it above the engine and let it get upto temperature.

i've also driven up sides of hills to try and dislodge bubbles before. you can tell if it works as the level drops in the tank.

when i did mine i found plastic valve on pipe to header tank was u/s its the pipe from thermostat housing header tank hope this helps

Cheers il try bypassing my heater matrix, and bleeding it whilst on ramps at the front with the tank raised lol

anyone ever taken their radiator off and tried cleaning it out with plug hole stuff for kitchen? I took off the pipe from the thermostat to the tank and blew down it, it was blocked and when i blew harder some brown sludge that looked like brown silicone came out? Just wondered if my radiator is full too!

just take top and bottom hose off put hose pipe in see if that will flush all brown crap out

yeah see if your main rad is blocked, flush it and then reverse flush it with a hose till it runs clear both ways

Check rad isn't blocked did you skim head wen you replaced gasket ?

no but i had the head checked and it was fine, iv flushed the system out, and iv bitten the bullet, gonna do the headgasket again because it was pressureising and spaffing coolant out before it boiled :-(