Citroen Synergie HDI pressurising coolant, ignore or fix?

[citronut]

the guy I spoke to reckoned the problem wouldnt get any worse?

well if it is H/G failure it can/will only get worse,

if a H/G completely fail's on a diesel it will gush coolant out of the header tank with the cap off and the engine from absolutely stone cold

[citronut]

Im happy to have a go at bleeding the system, can anyone recommend a step by step guide to this?

firstly locate all/any bleed screw/vavles,

on XUD's ( cant remember if this is similar on the HDI's ) i remove the bung/plug at one end/top corner of the rad, then fill the header tank till coolant comes out of the top of the rad and stops sinking,
then replace the rad bung/plug and open any other bleed screw/cap and keep filling the header tank till coolant comes out of these,
if it doesn't at the point start the engine and bring the revs up till you get coolant coming from the bleed screws/caps,
refit each bleed screw/cap as you get a good flow of coolant coming out of them,

once all the bleed screws/caps are refitted continue to run the engine ( checking coolant level all the time ) till the level seem steady, now refit the header tank cap and continue running the engine till the fan/s cut in and back out, then gently open the tank cap, they sometimes erupt the first go round, so just go through as much or little as you need again to the point the fan/s cut in and back out, then check how calm the coolant is

[mrtee]

The heating is working OK, if there was air in the system would this still be the case?

[Peter.N.]

It will work OK all the while there is coolant in the system but will fail as soon as there are sufficient combustion gasses to fill the heater matrix. Its a good early warning system that the coolant want's topping up.

Peter

[mrtee]

Thanks Peter, how often were you topping yours up when you ran for 3 years with the cap loose? how loose did you have the cap? Did it eventually blow the gasket?

[Peter.N.]

Once or twice a year I suppose, probably no more than I would have normally - but that's the only one I have had like that, most failures have resulted in the loss of all coolant on going up a steep hill. I had one that ejected all the coolant through the filler as soon as you started it, that was a cracked head.

Peter

[mrtee]

I've now drilled a hole in the top of the expansion cap to relieve the pressure as it was still pressurizing with the cap on a few turns. Didnt want to have it completely loose in case it fell off so hopefully this will work!

Will need to see if it still loses its coolant after a long journey.....

[Raul]

I have a question about bleeding the coolant system of hdi xantia. I changed coolant yesterday and it was hard to get the air out of the system. I made a header tank from plastic bottle to make things easier. Opened both bleeding screws- one on the top of the thermostat and the other on the heater matrix hoses- and got coolant out of them but after starting the engine and letting it to idle the temperature reading did not move. So I started to rise rpm to get the air out of the system and finally I got the air out as I noticed the temprerature reading started to rise and then it fluctuated to ca 100 degrees then droped quickly back to normal again. I had to top up the coolant as well. It seemed that I got an air lock near the thermostat and temperature sender and only rising rpm helped to get that airlock out. As much as I understand the bleeding screw on the top of the thermostat housing does not help to get the air out from the bottom side of the thermostat but there is a coolant hose from the bottom of the thermostat housing that lead to expansion bottle so it seems that the bottom side of the thermostatshould self bleed itself. I want next time to make it right.

[citronut]

if it were the head gasket failing it can only get worse!!!!,

the easiest way to bleed the system is

remove the bung on the right hand top corner of the radiator ( if it has one some have a bypass hose attached at some point ) if it has a bypass hose disconnect one end,
fill the header tank/radiator till coolant comes out of the bung/bypass hose and stops sinking,
replace the bung/bypass hose,
open any other bleed valves/caps you can find ( this varies from model to model ) some have one on/at/near the thermostat housing, and sometimes also on one of the heater hose's,

continue filling the header tank/radiator till coolant comes out of any bleed valves/caps you have found/opened,
if it does not come out of these by filling, start the engine, and sometimes you might need to bring the revs up a little to get coolant to flow,

once you have coolant at the bleed valves/caps close/refit these whilst coolant is flowing,

now continue to run the engine at a fast idle ( topping up the coolant as and when required )till the rad fan/s cut in, if they dont cut in make sure the coolant level is ok and refit the header/rad cap and continue running the engine at fast idle till the fan/s do cut in then out, now carefully open the header tank/rad cap,
on first go it might erupt !!!!, if it does just start at the beginging again and run through the hole process a second time,

if it still erupts on the second run through i would suspect gasket failure

[Peter.N.]

It will let you know when its had enough, you will lose the water so quickly it will become undrivable. A secondhand head might be the way forward.

Peter