what have i done to my rad?

[hobson]

OK, this has been niggling me this evening so been out to check and not happy!

i flushed my radiator and intercooler whilst doing the waterpump, all's well, but noticed earlier on getting back from shopping that there was a hissing and bubbling coming from the header tank, going on for a while after turning the engine off.

i refilled the cooling system via the instructions in the tech archive:

Take the cap off the thermnostat, refill the header tank until you can see the coolant in the thermostat, replace cap, then run the engine, and refill a litre.

did that, but somethings not right.

just been out and checked, took the cap off the radiator and found a fair size air gap at the top, same with the thermostat housing, lots of air.

so topped up both openings and put caps on, to find the header tank is now quite above the fill level.

so have i just moved the coolant into the header or something? it's been a long day. can anyone please tell me what's wrong?!

[Maverik]

Just sounds like you've got an air lock somewhere, what engine are you running?

[hobson]

300tdi, i think it is an air lock, but i'm surprised as i did the refill exactly as described.

have to wait until lunchtime to see if i cured it last night as my wife has the car now.

will it do any damage if it's an air lock?

[Maverik]

The problem with an air lock is that when the engine gets hot the air expands and pressurises the system making it a bit more "volatile", meaning be very very carfull taking the top off the header tank while its hot as it could spit a fair ammount of hot water at you. (as you depressurise the sytem, the air lock will have wanted to expand, but will be kept compressed by the closed system, so as soon as you open it, it will expand, its ok if the air is at the top of the tank as you just will hear a woosh, but if its behind some liquid, i.e. in a pipe, it will push that liquid out as it expands)

As long as the system is still cooling the engine (not in the red) then you wont have a problem and you'll find the air lock will probably sort itself out, just keep an eye on the coolent level in the tank.

Did you bleed the system with the engine up at temp (i.e. when themostate is open and water flowing through the rad)?

On my 200tdi, I think Haynes suggests it, when the car is up to temp (not red hot from motorway driving, but from a nice idle start up as it where) you carfully - and I stress that! unscrew the radiator filler cap and "bleed" it. I always wear some goggles and gloves for doing this as don't want hot water where it hurts. All you usually have to do is uncrew the plug until the last few threads and like a house hold radiator it will spit water at you and some bubbles/air then you'll start to get a steady stream, then you screw it back in.

[cookie64]

300TDI airlocks are the bain of my existance

fought with my engine since january when it froze up and blew the p gasket.

since then have changed the head gasket, replaced the heater, the water pump, radiator, and various pipes but luckily is working perfect now

by the sounds of it you have a small airlock somewhere, probably in the heater. i found the best way to gget rid of this airlock is to remove the heater pipe that goes vertically into the head at one end when the engine is running but not too hot,the water should come up out of the head, stick ur thumb over the hole then hold the pipe up in the air, your airlock should come out then lots of water, now quickly get the pipe back onto the head. (dont forget the pipe clip though or youll be taking it off again.

always do this as the last bit of bleed as its the highest up so most of the time the airlock gets stuck here.

tom