BX overheating

czenda · Post by **czenda** » 26 Dec 2004, 20:44

Hi, my BX 16 TRS begun to overheat after antifreeze change and application of Stop-a-leak (the radiator leaked after antifreeze renewal). The problem appears only during long trips. When "overheat" lamps glow, the cooling fan in front of the radiator is not on. I am unable to locate the thermoswitch for the fan - it is supposed to have three wires leading to it. There is no such part on the radiator, I only found a silver cylinder in front of the fan housing (2 blue wires) and "Valeo" part above the coolant level switch (one brown, four green wires. The part is black, about the size of a matchbox. I am unclear of its function). As the hose leading from the thermostat becomes warm after the engine is started and run on idle for about 5 mins, I do not suspect the thermostat. Any idea is appreciated, thanx.

JohnD · Post by **JohnD** » 26 Dec 2004, 21:15

If your trouble started immediately after a coolant change, I'd make sure you've got rid of any air locks in the system.

beezer · Post by **beezer** » 26 Dec 2004, 21:17

A picture may help:

alan s · Post by **alan s** » 27 Dec 2004, 02:28

Did you have the heater in the "High temperature" position when you bled the system? This is often a source of air getting trapped inside.
The fan swith I think you'll find is down one side of the radiator (RHS as you stand at the front of the car I think??) yet I don't see it on the diagram.
The fact it does it on a long trip may be a sign of something a bit more sinister though. You say you put "Stop leak" in the system? Not a real good career move with a lot of these kinds of cars as it may have put a coating over the sender switch or as sometimes happens, partially blocked the radiator core. After all, often a radiator that leaks is also partially blocked with internal corrosion and this kind of stuff will tend to stick to it and slow down the circulation.
Alan S

czenda · Post by **czenda** » 27 Dec 2004, 03:50

Any step-by-step, foolproof ideas about bleeding the system? I have seen the fluid going out only from the heating circuit while filling up the angtifreeze, being told that the rest is "self-bleeeding". The system seems to be overfilled, the level of the antifreeze is 1 cm below the cadiator cap while cold. Maybe the radiator is overfilled, as the recommendes levell is 25 - 35 cm (from the bottom of the rad or from the rim of the filling cup?). Bleeding screws I have located are 1. radiator (upper rim, screwdriver), 2. hose from carb ending by thermostat - Allen, 3. heating pipe/hose - Allen. How do I make sure there is no airlock?

alan s · Post by **alan s** » 27 Dec 2004, 04:21

I normally work on the principle of bleeding from the lowest point to the highest.
This I usually do by overfilling the cooling system and letting the level drop through the bleeding process.
Personally, I don't worry too much if it seems to be over full as it seems to usually find its own level whilst running and if it does get too high a pressure during running, that's when the cap does its job. At that stage is when the level may need a slight top up in the rare instance that too much gets out during depressurisation.
Alan S

beezer · Post by **beezer** » 27 Dec 2004, 05:35

Surely the 'temperature switch' number 6 on the diagram is the fan switch?

alan s · Post by **alan s** » 27 Dec 2004, 10:27

Could well be, but what's it doing up there?
Every one I've seen was mounted lower down, so presuming the terminology isn't in question and it is supposedly the fan switch and not the switch for a temp light, that's it.
Alan S

wonderd · Post by **wonderd** » 27 Dec 2004, 12:02

I believe that the problem of car overheating after liquid change means that you left air in the system,
the best thing before disconnecting anything is to open the bleeding bolt on the top right hand and take it all the way out while engine idle, open the radiator cap and let all the air come out, if there is a lot of air in the system you might have a lot of water coming out of there, let it all out and then fill up liquid again and you should be fine.

JohnD · Post by **JohnD** » 27 Dec 2004, 23:40

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by czenda

How do I make sure there is no airlock?
<hr height="1" noshade id="quote"></blockquote id="quote">
Did you use a header tank when you refilled the system? Use the 'search' feature to find out how to make and use one.

AndersDK · Post by **AndersDK** » 28 Dec 2004, 01:03

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by beezer

Surely the 'temperature switch' number 6 on the diagram is the fan switch?
<hr height="1" noshade id="quote"></blockquote id="quote">
YES !
Mounted low down on radiator towards engine. Has a rather large angled rubber gaiter on the connector. 3 heavy gauge wires from connector.
The switch is 3-pole, meaning it has the normal cut-in for the low speed (with a current path trough the silver cylinder - which is a power resistor).
The high temp cut-in on the switch effectively shortcircuits the resistor, thus providing full current - and high speed - on the fan.
The silver cylinder power resistor may have passed to silicon heaven - meaning it is disrupted.
You can test the fan circuit by unplugging the connector from the temperature switch :
have ignition on then :
1) Bridge any 2 of the 3 pins in the connector plug. This should bring on the fan in either high or low speed.
2) Bridge 2 pins in the other possible combination. This should bring on the other of the 2 possible fan speeds.
If you can only get on the high fan speed - then your silver can power resistor - or related wiring - is faulty.
If you can get both speeds on the fan using one or the other cobination, then the temperature switch is faulty.

czenda · Post by **czenda** » 29 Dec 2004, 23:10

Hi to all - the mystery is solved. It is a faulty thermostat. It opens only to 1 mm instead of 7,5 mm suggested by "Ole Heinie", but, as it still opens a bit, it could not be diagnosed by checking its hose for being cold. Contrary to this, the temperature switch (which is OK, I used the method suggested to check it, then removed it and checked it in the same can with the thermostat) switches sooner than it is supposed to, some 76/84 centigrades instead of 88/92. This, I believe, also explains why the system behaved as it did - the insufficient flow through the thermostat was somewhat balanced by the fan cutting in sooner.
Thanx to all for their input. It is good to know that there is a well of wisdom available for the BX puzzles...