Refill / Bleed Procedure 2 of 3

Refill / Bleed Procedure 3 of 3

One further diagram. A schematic of the cooling circuit from the XM Manual.

Hi All

Thanks for the input to this one! I have learnt alot about the cooling system on a 2.5 and no doubt the saga will continue for a little longer until Noz solves it.
The comment about is the gauge reading correctly is an interesting one. We seem to naturally assume that any gauge is reading correctly without a second thought. The dismembering of the dash makes checking so difficult. I have a fuel gauge on one of the cars that reads a graduation high and only found out when I fully filled the tank. Just as well I did it that way round rather than found out when I emptied the tank. Anyone got an easy system of checking gauge accuracy?

Regards

XMexc

Hi All,

I've now had a chance to have a look at my own car in daylight and that's thrown up some unexpected things.

Firstly - despite what I said about only one cooling fan coming on to start with (information taken from the XM manual - and from previous experience with a slightly older 2.5TD) I find that both my fans come on at low speed together.

Interestingly - my own temp gauge always sits one gradation below 90 degrees and very seldom moves. My previous car always sat bang on 90 degrees. The difference however is that with my previous car I hardly ever used the aircon and with my current car it's permanantly on. I discovered that with the engine ticking over at normal temp (one gradation below 90 degrees) - the fans were operating almost constantly. If I switch the aircon off however - the fans switch off straight away and the temp rises to bang on 90 degrees with the fans cutting in only to maintain that temperature.

Based on a limited test I found that my bottom rad hose was cool (not quite stone cold) after a normal run of around 15 miles. Even after ticking over for some time it stayed this way - despite the fact that both fans were running (aircon was on). If I run the engine at around 3k revs for a while - the bottom hose gets hot. (I can't recall if this was with the aircon switched on or off).

I'll now try the same run with the aircon switched off and check the bottom hose again.

I'm slightly puzzled by all this - particularly that the fans are running without the engine apparently reaching normal operating temperature (indicated by cool bottom hose - ie 85 degrees or less). It's highlighted however that I don't really understand how the aircon works - and without this information can't really get to grips with the correct operation of the cooling circuit.

Can anyone tell me where the heat exchanger is for the aircon (presumably there is one). I imagine the fans are operating to circulate air through that and are over-cooling the radiators slightly in the process.

Like XMexc - I've learned a lot about the XM in going through this topic.

Cheers

Roy

Hi Mackay1

The aircon heat exchanger is under the centre of the dashboard in the same plastic box that holds the heater, airflow flaps and fan.

Regards

XMexc

Hi Noz and All,

I've now tried the same run in my own car with the aircon switched off. The temperature now sits just below 90 degrees and the bottom radiator hose is hot.

I tried the same run with my other XM (2.5TD VSX - without aircon) and it sits at the same temp (just below 90 degrees) and the bottom rad hose also gets hot.

I hope this info might help.

Cheers

Roy

Hi XMexc,

Thanks for that. I'm still puzzled though. I don't know much about aircon but using the principle of a domestic fridge I imagined there was a coolant circuit inside the heater matrix which went cold (cooling the interior of the car) and a corresponding coolant circuit outwith the passenger compartment that was hot (getting rid of the heat from the car interior). It was this second circuit that I thought the 2 fans were cooling (in addition to the std rads of course).

Are you saying that this second circuit is also inside the heater matrix unit? Is it then cooled by fans inside the matrix and vented outside? Or have I got this all wrong (likely)? This was what I was starting to wonder - because there's no sign of the second circuit in the engine compartment.

If this is the case - why do the 2 main fans on the engine cooling rads come on when I switch on the aircon (see earlier post)? Can anyone else confirm this is correct operation?

Cheers

Roy

Hi Mackay1

I was too quick for my own good!

I suspect that the reason that the fans run when the aircon is on is that the aircon rad sits just in front of the two water rads so the fans run for the aircon system as well as the engine cooling system. There are very few 2.5's with aircon and most of us have only experience of cars without. I would not be surprised that the climate control system got modified over the years as the production run progressed.
It is an interesting thought that as the aircon rad cools its contents it will heat the air that then tries to cool the main rads. This suggests that the fans in an aircon fitted car will be controlled to run differently (harder) than those in a non aircon car.

Regards

XMexc

Hi Roy

Only my V6 has working aircon and the two fans come on as soon as you switch the aircon on so I guess this is normal behaviour.

Regards

XMexc

Hi Roy,

Thanks for your contribution to this debate. Every bit of information helps build a clearer picture of this conundrum.

To confirm the operating principle of air conditioning:
There are 4 main components:- compressor, condenser, expansion valve (or throttle) and evaporator. The compressor is belt driven from the engine (on the same belt as the alternator in the 2.5). The hot compressed gas is routed to the condenser where it cools and condenses. The condenser looks like a radiator and is situated in front of the other two radiators. You'll need to peer through the grille to see it. The cool condensed liquid passes through the expansion valve reducing in pressure as it does. The expansion valve is so small that it might be hard to find. I don't know where it is on the 2.5. The cool, low pressure liquid then passes into the evaporator where it evaporates (at approx -10degC) absorbing heat as it does so. The evaporator looks like a heater matrix and is located inside the black plastic box which constitutes the 'heater' box between the driver's and passenger's footwell. The evaporator is bigger than the heater matrix because the difference in temperature between the refrigerant gas and the air is smaller than the difference between the hot water and the air so more surface area is required. The evaporatated gas returns to the compressor after passing through a filter to remove liquid droplets. The only real connection with the engine, apart from the drive belt, is that when the aircon is on, the ECU raises the tickover speed by 200rpm to compensate for the additional drag on the engine by the drive belt.

I'm a little confused by your description. Firstly you say that the bottom hose stays cold (cool) then you say it gets hot. Can you be a bit more specific on the conditions so that I can compare them to my own?

I've had a closer look at the wiring diagram for the cooling fans for models fitted with aircon. The two fans are operated independently by the aircon ecu. You can't see the relay logic like you can with the non-aircon so I can't tell how it works. The description in the manual probably refers to cars with aircon because it definitely doesn't match the wiring of the non-aircon models. At least 1 fan will have to operate when the aircon is on to dissipate the heat produced by the compressor. It may go off whilst the car is travelling along with the air whistling through the grille. However, it would be a tad dangerous to ride along with the bonnet open to check.

Judging by the number of downloads there are more readers of this topic than posters. Come on, don't be shy. If you have an opinion, spit it out. No-one will laugh, least of all me.

Cheers

noz

Hi Noz,

Thanks for the information on the aircon. I can't see the 3rd rad - is it between the other 2 and the fans or is it in front of the fans somewhere in the nose cone? (I'll trace the pipework when it's light tomorrow - but as you know there's little room to see on the 2.5 TD.)

OK - to clarify. I took the car out from cold this morning about 15 miles (normal driving on A & B roads). The aircon was switched on as normal the whole time. The temperature gauge went up to its normal position of about 80-82 degrees and stayed there. When I stopped the bottom rad hose was cool (but not stone cold). I left the engine running for a while (10 mins) and because the aircon was on both fans were running at low speed. The temp gauge didn't alter and the bottom rad hose remained cool. I then started to experiment with the aircon and found that switching it off stopped the fans straight away and the temp increased to 90 degrees with the fans cutting in to maintain it at that temp. (At this point I didn't check the bottom rad hose again - but from what I now know I suspect it was hot.) I then increased the engine revs to around 3k for several minutes and checked the bottom hose again - it was hot (can't recall if the aircon was on or off during the 3k revs period).

Later in the day I did the same run but this time with the aircon switched off all the time. The engine warmed up to around 88 degrees and remained there. When I stopped the bottom rad hose was hot.

I've also got a 2.5 TD VSX without aircon and I then took it on the same run from cold to get a comparison. It heated up to about 88 degrees (normal) and when I stopped the bottom rad hose was hot.

I was puzzled by the various comments about the bottom hose remaining cold and I thought I'd try for myself. I hope the comparison helps you - it certainly seems to show that the system design does work! (Both cars have done about 60k miles.)

Sorry if the extra information about the aircon has created further confusion - but I thought I should include it in case it was relevant to your situation. (I now need to establish why the car with aircon is running slightly too cool - faulty sensor perhaps. Until I discovered the bottom hose was cool I hadn't thought it was a problem - now I'm not so sure.)

Cheers & good luck

Roy

Hi Roy

Yes the aircon rads sits between the fans and the water rads. Order fron the nose cone is: Cooling fans/aircon rad/small water rad/large water rad.

Regards

XMexc

Hi all,

Here's the next thrilling installment.

I thought it was about time I fitted my new stat. I had a go but discovered a split hose into the bargain. The new stat is fitted but the water is pouring out of the split in the hose so I won't be able to tell for sure if it has made any difference until I get a new hose. If its not one thing its another.

The stat turned out easy to fix which was helpful. I poured boiling water over the sensing bulb of the stst I took out and it behaved exactly as the other one did. The boiling water manages to open the first stage disc but not the second. I heated it on the gas cooker and after a lot of persuasion it finally opened. I am now convinced that the old stats in each of my 2.5's were goosed. Having replaced one I'll order another for the one in the garage. My hopes are high for a resolution to this.

I've attached a pic so you can survey the damage.

Cheers

noz

Hi all,

I don't want to speak too soon but I think the problem may be solved. I changed the stat, replaced the split hose, backflushed the whole system and refilled. I took her out and gave her a jolly good thrashing. The gauge sits dead on 90Deg going downhill, 92Deg on the flat and 95Deg going uphill. And now for the good bit....the bottom radiator hose gets HOT, not just warm but HOT....yippee. I haven't towed the caravan yet but that will be the acid test.

Calling all 2.5 owners:
Whether you think your cooling system is working fine or not I urge you to take the main thermostat out and do a simple test. Boil a kettle of water and slowly pour the water over the sensing bulb for several minutes. The inner disc should open first and then the outer disc should open very wide(approx 8mm rise). If the second disc does not open at all or only 1-2mm then you have a faulty stat. The two stats I remmoved from my 2.5's both exhibited exactly the same symptoms - only the first disc would open. I tried the same test on the new one and both discs opened wide. The two old stats were definitely faulty, no question. I advise purchasing a new one. The cooling system on a 2.5 is stretched to the limit. The last thing it needs is a lazy stat. I could not find anyone who either stocked it or could even obtain one apart from Citroen. It is £24 which is steep for a stat. However, the stat is pressed into an aluminium housing complete with hose tail. You cannot buy the stat by itself. You have to buy the whole thing hence part of the reason for the price.

Removing the stat is fairly easy:
Remove the big hose from the intercooler heading to the inlet manifold.
Remove the small hose with three connections which joins on to the header tank.
Remove the tension band which holds the header tank in place.
Remove the header tank having first disconnected the hose on the bottom.
Remove the hose which connects to the thermostst housing/pump inlet.
Remove the three fixing bolts for the stat housing.
With a small knock with the handle of a hammer the housing will come free in your hand.
Replace the stat and follow the above in reverse order (in true H@ynes style)

I would use the opportunity with no hoses connected to flush the system out every way you can with the garden hose (unless you live in the south-east that is ).

I still don't understand how the hot water gets to the bulb on the stat to open it. But I suppose now that the system is fixed I've got a lot more time to think about it.

Any questions, please ask.

Cheers

noz