Cooling System BX D/TD

The cooling system on the diesel models has to be in tip top condition, these engines are not thermally efficient
and there is rapid heat build up from the cylinder head area.

Heres my check list for diesel models:

1) New rad cap (costs around £4.50). Many unexplained coolant drops are caused by an old caps inability to hold pressure.

2) Check for soft hoses! The bottom hose from the rad to the water pump can get very soft as the result of exterior contamination. If the pipe is soft
it can expand or collapse under system pressure, causing pressurisation problems (often mistaken for head gasket problems!)

3) Change the thermostat! So many BX engines have been lost because the thermostat is jambed shut (due to lack to temperature gauge on the diesels
it's invariably the illumiantion of the "Yellow warning lamp of death" that tells you this is the case, by which time the head is usually cooked!) A good BX
will run at around 80 degrees during normal driving if the thermostat and radiator are sound.

4) Check that the fan(s) work by removing connector from rad fan switch and bridging the terminals. If fans operate, I'd then fit a new rad fan switch, they
are just a few pounds. Go for the lower temperature switch 83/88 which is FAE 3780 to bring the fans in earlier. Looks of people also fit this switch to the 16v models which otherwise bring in the fans very late.

5) Its worth draining off the coolant (remove bottom hose from rad) after having added some Cooling system flush first (the Forte brand is expensive but
removes a load of crud). Refit hose and add new coolant (Citroen Procur 3000 antigel is expensive but excellent) ensuring that the system is bled well (see below).

6) Check/change the water pump. This is one part that never seems to get checked, unless of course you're changing the timing belt. Many pumps slowly leak away unseen. Worth checking or changing.

7) Check your radiator. With the engine hot and the thermostat open, the rad should be hot all over. A rad where the bottom 2 inches is cold is full of silt and must either be changed or removed from the car and flushed.

8) Get a pressure test done. A garage may do this for you for a small charge, or there are some DIY pressure testers available quite cheaply. the rad cap is removed and the pressure tester is then fitted, pressure is then pumped into the cooling system. A sound cooling system should hold around 12psi without any drops. Any drop in pressure is the sign of a problem! Quite often you'll see water gush out from some water housing or hose that has been gradually seeping away unnoticed!
If the pressure drops and there are no signs of external leaks, then it could be a cracked/warped head or failed gasket...............ouch.

9) Bleeding obvious...yes, bleeding the cooling system correctly. So many BX's have been condemmed due to the fact the heater is cold, theres water chucking out under the bonnet, it could just be that they have not been bled correctly. Late BX TD's which only have one bleed point are notorious for problems of this sort. All BX's need to be bled correctly either way due to the myriad of water pipes and a matrix which can hold air. Everyone has their own methods, buts heres some basics:

The heater control MUST be turned fully to hot or the matrix will not fill with water.
Initial filling of the system should be done with the engine off. Ensure bleed furthest from filling point is open, pour in coolant until it escapes from this bleed, replace then move on and repeat at next bleed point. Finally, replace all bleed valves, check water level and start engine (ensuring rad cap is left OFF).
With engine running, open bleeds one by one so that water escapes (leave open until bubble free water flows) then replace bleed valves. Top up coolant as required.
Leave engine running with rad cap off. As engine gets hotter the thermostat should open, and the top hose, then the rad should get warm. At this point, you may have to put a little more coolant in. Leave engine running. If all is well the fans will kick in and no water should overflow from the header tank. Replace rad cap.
When engine is cool, check the water level again, and top up if required