My Citroen XM 3.0 PR-Vestige

[Dean]

The melted looking connector is the oil level sensor, that has always worked fine but under the black wrap there was no insulation for a good 10" of cable, how it worked I will never know, that section of the loom runs over the bell housing of the gearbox along the side of the block and round the back of the engine, all the insulation has just turned to dust. I have re built the whole injection loom during the re furb as it was in a similar state and runs under the intake manifold against the block across the front of the engine, this is a smaller separate loom that looked OK until the fan and starting fault appeared this week.

Pleased to report with a little digging in the shed and some soldering and wrapping I have a brand new loom made up and back on the car, its running at the moment while I get a brew, seems to be perfect now .

Interestingly although all the wires for the starter solonoid, oil level, two temp sensors, oil pressure, air con clutch engine ECU power and alternator where without insulation and bound together I could not get the fault to show itself the other night, came out this morning turned the ignition on and the fans went full bore with overheat warnings to be fair though I was wiggling the wrong bit of loom, I thought it was the plug but it was everything but the plugs!

[White Exec]

Would understand wiring round the back of the engine, maybe near the exhaust manifold, to have a bit of a hard time.....but all the other stuff just shouldn't get in that kind of state.

Is this a common problem on S1 of that year? Do wonder whether the cooling fans have been under-working for some time, since they do reduce under-bonnet temperatures when on. Might be worth dangling a digital thermometer in the engine compartment to see what sort of temperatures are developing there. I don't know what might be considered normal, though.*

Insulation just should not bake, whichever way you look at it......unless it was defective, in which case others will have had this too.

* Edit:
Have just googled and found this...
http://www.mvfri.org/Contracts/Final%20 ... es%201.pdf
which looks at underhood temperatures, under various conditions.
Includes a figure of 500degC for a 2 litre petrol engine, driven at steady 70mph. Climbs to 550C when engine is switched off.
This report by a Fire authority.
Would be interesting to compare these temperatures with the working temp spec for cable insulation.

If a general problem (the insulation, that is) others will have had it too.
Usual first problem with hot petrol engine compartments used to be vapour lock, caused by pumps and lines overheating, leading to poor re-starting or cutting out.

Wonder whether the presence (or not) of an engine under-mat would alter u/b temps?

[Dean]

After 23 years I will let it off, its an air con model so two fans and they have always run fine, just one of those things, island life may not have done it many favours, under bonnet temps rocket after a journey when its turned off, all it does is lots of short trips so lots of cooking time after engine shut down over its life, its why I wanted a run on feature for the fans.

D

[White Exec]

Sorry, Dean, but this just SHOULD NOT HAPPEN, even after 23 years.
There has to be a reason for this.

I have never seem such damage on a vehicle, even one twice that age with a petrol auto V8 with twin-Aga's (for that read Rover V8 with twin cast-iron manifolds) and electric fans (which by design provide intermittent cooling).

Perhaps there might be an argument for having the fans run on low-low speed whenever the engine is on, IF the problem cannot be identified.

[Dieselman]

The insulation is made from PVC, which does suffer heat degradation. Ideally the new wiring should use PTFE insulation, to ensure this doesn't happen again.

[Dean]

Chris

My voltmeter has a temp prob on a lead, I saw your edit, I think their cars may have been on fire
Since I was doing a trans fluid change again I decided to have a little play....
Driving with undertray removed v having it fitted made no difference
Stationary with fans running the undertray keeps engine bay temps lower
Stationary without fans running the undertray increases engine bay temps
After engine shutdown engine bay temps spike higher with undertray

On the fly with the thermostat open it was about 60c with stat closed near ambient,

Max temp spiked at 160c 3 minutes after engine shutdown, ignition on then brings the fans on and within 30sec or so they are down to near ambient temps.

The findings? My god I need to get out more, I may also look into cooling fan run on.

D

[White Exec]

Well done, you, for making all those test temperature measurements! Think you could probably put it in the class of "getting out more", and must be worth at least two brownie points - although maybe not in the kitchen!

I also have one of those DVM (a Uni-T) temperature probes, but have never used it. Must give it a whirl.

Interesting to read your exact comments about the fans keeping u/b temps down, and the temp spike after shut-down, made higher by undertray being in place. All makes sense, as undertray will decrease airflow by convection.

160C isn't too bad, I would think, and mercifully a long way short of the 500C recorded in the study above. (Being American, I did go back and check it wasn't Fahrenheit....but no, decent scientific Centigrade.) The temps reported in that study were recorded during normal driving and parking up, and peaked at 550C u/b in some cases. These were not cars on fire (!) or which had burned, but normal vehicles. The FD's concern was that such temperatures are hundreds of degrees more than the flash/ignition point of most of the fluids on the vehicle - even the antifreeze! Given these conditions for vapourisation, it might only take small spark (relay, ign...) to ignite. The motorways here are littered with patches of scorched tarmac, where vehicles have gone up. Seems mainly to involve newish vehicles, many of which have incredibly tiny u/b spaces.

If you take the likelihood of extensive vapourisation (as per to the report), and add into that possible damage to electrical insulation, then electrically triggered u/b fires might not be totally unexpected.

I wouldn't have thought your 160C should spell widespread death for all that plastic insulation. Why are others not reporting this too? Must be something else too. Perhaps corner-cutting on cable quality????

If low-low running fans are a possibility, operating whenever the engine is, then these items wired in series should do the job:

- a +12v IGN supply (probably from an existing fan fuse)
- a dash switch/indicator (to allow on/off)
- a heavy-duty diode (to prevent supply feeding back into the ECU)
- a heavy duty ceramic power resistor (to give low-low fan speed), placed in the fan airflow (a la Citroen)
- all fed to the Slow speed input to the set of 3 fan relays.

Shouldn't affect normal fan operation.

Just a few thoughts.

C.

[ekjdm14]

Sorry to hear about the wiring troubles, keeps you out of bother though I guess! Just wanted to chime in Re aircon, I've run propane in a Nissan Largo aircon system last year, filled myself using adaptor/gauge from ebay. Filling from the low pressure side with aircon switch on, slowly slowly is the key so as not to "slug" the compressor with liquid propane, you can go a bit quicker once the pressure has built up enough for the compressor to kick in again. It was highly effective in my experience and I'd do it again for sure.

[Dean]

Thanks for that, was it the duracool kit you used? Prices are pretty reasonable and I may consider trying a gas myself as its not dealing with dodgy gasses and materials, my local shop was happy to do it but the price was eye watering, they will charge £15 just to VAC it though so that could be the way fgorward, my system hasn't dropped any pressure at all so I'm sure its sealed up really well now but after being open and pumped up with compressed air a few times it could do with a damn good flush out and VAC.
Not seen a Largo for a while, always loved them, camping kit in the back, electric curtains, split air con. A wonderful old bus.

Thanks Chris I'm thinking of putting some sort of over run power supply to the whole system but other things to do first.

D

[ekjdm14]

I can't remember the seller's name now but it was just cheap knockoff valve adaptor and pressure gauge, hooked up to a big 47kg calor propane tank/reg from my mates yard, formerly used to run a space heater or something like. Filling with the tank sideways to draw liquid is quickest but you have to be careful not to damage the compressor. Safer but slower to keep the bottle upright and charge with just gas.

Probably "safer" and more sensible to use a dedicated kit if the price is right, but as long as you know what you're doing pressure & leak wise theres no reason a homebuilt rig won't charge it just fine. IIRC I paid about a tenner all in for the fill valve and gauge, made up pipework at the yard from flexible gas hose.