i have a peugeot 806 with xu9tde 1.9td engine i have had it for about 6months its had a new head when i got it. the problem i have is a full tank aprox 70ltr only returns aprox 400 miles. im not sure but i think i should be getting more than this. my temp gauge only gets to 71 then the fan cuts in and brings it down to 70 so my guess is im using so much fuel as my engine is always cold. ive changed all three sensors by the thermostate but still the same.
does anyone have some kind words of wisdom
fan won't let engine warm up above 71
Moderator: RichardW
Are they OE sensors?
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yes i got them direct from peugeot as i said the compleate head has been replaced inc buckets and valves. the RAC have tested the expansion tank for gasses so the head gaskit is fine. the only other thing i can tell you the engine stop light used to flash at 72 then the fan would cut in and the light would go out. but that stoped when i changed the sensors. the car has done 180k and i bought it from a cabbie and was'nt that well looked after.its costing me a fortune and the great fuel robbery isnt making my life any easier. 
The 806 is a large heavy car, and would need a heavy foot to be reponsive in daily use with 19TD engine.
but still I'd expect something like 600miles on 70liters at least.
It is of outmost importance that the engine is running at correct working temperature, to achieve best mileage.
If your 806 is fitted with aircon - it makes it even worse, as the aircon consumes some 5Bhp from your engine, besides commanding the fans running all times.
IF then your standard thermostat - build into the waterways of the engine - is defective and wont hold back the coolant flow, THEN you have the worst scenario of bad combinations.
I suggest :
1) make sure the cooling system is fully topped up and bled for any air locks. Its got to be checked once every day over a week to ensure its settled correctly. Any excess coolant will automatically be expelled.
2) drive around with the a/c completely turned off - if fitted of course - and note the mileage return next couple of weeks.
3) have the ACTUAL TRUE engine working temp checked with an external precise temp gauge. The temp sensor element of such a gauge should be tie/tape wrapped solid on to the radiator top hose, and then wrapped over with a layer of insulation foam to ensure no external temp losses disturbs the correct temp reading.
4) depending on this reading (over a couple of days) : replace the coolant thermostat if true engine temp readings continue to never reach more than some 70-75deg. The true reading must be very close to approx 87-90degrees in normal conditions.
The coolant thermostat resides inside the thermostat housing, which is where the large radiator top hose comes from on the engine.
A new thermostat is some £5-10 aftermarket places. Ensure you get a new seal with the thermostat (may not be included).
but still I'd expect something like 600miles on 70liters at least.
It is of outmost importance that the engine is running at correct working temperature, to achieve best mileage.
If your 806 is fitted with aircon - it makes it even worse, as the aircon consumes some 5Bhp from your engine, besides commanding the fans running all times.
IF then your standard thermostat - build into the waterways of the engine - is defective and wont hold back the coolant flow, THEN you have the worst scenario of bad combinations.
I suggest :
1) make sure the cooling system is fully topped up and bled for any air locks. Its got to be checked once every day over a week to ensure its settled correctly. Any excess coolant will automatically be expelled.
2) drive around with the a/c completely turned off - if fitted of course - and note the mileage return next couple of weeks.
3) have the ACTUAL TRUE engine working temp checked with an external precise temp gauge. The temp sensor element of such a gauge should be tie/tape wrapped solid on to the radiator top hose, and then wrapped over with a layer of insulation foam to ensure no external temp losses disturbs the correct temp reading.
4) depending on this reading (over a couple of days) : replace the coolant thermostat if true engine temp readings continue to never reach more than some 70-75deg. The true reading must be very close to approx 87-90degrees in normal conditions.
The coolant thermostat resides inside the thermostat housing, which is where the large radiator top hose comes from on the engine.
A new thermostat is some £5-10 aftermarket places. Ensure you get a new seal with the thermostat (may not be included).
Anders (DK) - '90 BX16Image
fitting a new themostat makes a lot of sence i dont know why but thats probably the only part of the engine bay that has not been of the car. so i will change that today. it might not even have one in there after being owned by a mini cab driver.
yes it is does have air con and both fans apeer to be on all the time the ignition is on and i thought that might be the problem.
the stop light has failed to come on after i changed the sensors and although i dont know what the problem was i should just be contempt the problem has gone.
just gutted now at all that money i have wasted over the last 6months throwing over taxed fuel into the tank.
yes it is does have air con and both fans apeer to be on all the time the ignition is on and i thought that might be the problem.
the stop light has failed to come on after i changed the sensors and although i dont know what the problem was i should just be contempt the problem has gone.
just gutted now at all that money i have wasted over the last 6months throwing over taxed fuel into the tank.
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If the fans are running all the time the ignition is on, there is a problem. They should be off all the time the aircon is off unless the engine temperature rises significantly. With the aircon on, the fans should run continuously at half speed.
Are they running at full speed all the time the ignition is on but with the aircon off? If they are, you have a problem with the Bitron sensor and/or control unit. Basically, if you disconnect the Bitron (brown) sensor on the thermostat housing the fans should run full speed. This is a fail-safe to prevent overheating in case of Bitron failure.
The sensor itself or its associated control unit may be the suspects. The unit itself is rarely faulty but the connections to it can suffer due to it being in an exposed position, often under a headlight.
Do a search on on Bitron and you'll find lots and lots of helpful posts covering this and similar problems.
Are they running at full speed all the time the ignition is on but with the aircon off? If they are, you have a problem with the Bitron sensor and/or control unit. Basically, if you disconnect the Bitron (brown) sensor on the thermostat housing the fans should run full speed. This is a fail-safe to prevent overheating in case of Bitron failure.
The sensor itself or its associated control unit may be the suspects. The unit itself is rarely faulty but the connections to it can suffer due to it being in an exposed position, often under a headlight.
Do a search on on Bitron and you'll find lots and lots of helpful posts covering this and similar problems.
Jim
Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
Never seen an 806, put its later vintage relatives have a function where if the air flow slider is set to demist, it will automatically turn on the air conditioning, and send both fans to the low speed for all the time that the demist position keeps the aircon running.
The stop light coming on to indicate overheat at low engine temperature is caused by a dodgy connection from the brown temperature sensor to the Bitron input.
My Xantia’s had that, caused by a faulty crimp connection in the socket that goes into the inner guard near the battery.
It was measuring 3 Ohms … highly suspicious.
Was too much trouble
getting behind the socket inside the guard, so soldered 2 wires outside to bypass the plug/socket.
If there’s no thermostat, the top radiator hose will start warming up soon after the engine is turned on from totally cold.
A good thermostat will keep the warming water in the engine for several minutes, then release it into the radiator when it’s reached its opening temperature.
The stop light coming on to indicate overheat at low engine temperature is caused by a dodgy connection from the brown temperature sensor to the Bitron input.
My Xantia’s had that, caused by a faulty crimp connection in the socket that goes into the inner guard near the battery.
It was measuring 3 Ohms … highly suspicious.
Was too much trouble
getting behind the socket inside the guard, so soldered 2 wires outside to bypass the plug/socket.If there’s no thermostat, the top radiator hose will start warming up soon after the engine is turned on from totally cold.
A good thermostat will keep the warming water in the engine for several minutes, then release it into the radiator when it’s reached its opening temperature.
2002 C5 2.0i AL4 230,000 km 76372389
. why why why?
after i replaced the head the stop warning light kept coming on, so in fear i called the rac they checked the engine temp. he put a digital reader inside the expansion tank and that read 69. i was told my gauge was 2degres out. thats when i changed the blue,brown and green sensor that sit around the thermostat.
Thats not really, REALLY, the true engine temp 
But fair enough.
It seems you have the wrong type of fan controlling thermistor (= thermostatic electric switch) in the radiator - or it is defective then cutting in at too low temperature.
This is the radiator sidetank mounted 3-pin device controlling the fan relays.
Should be a rather lumpy device with a large diameter thread.
But fair enough.
It seems you have the wrong type of fan controlling thermistor (= thermostatic electric switch) in the radiator - or it is defective then cutting in at too low temperature.
This is the radiator sidetank mounted 3-pin device controlling the fan relays.
Should be a rather lumpy device with a large diameter thread.
Anders (DK) - '90 BX16Image
i went to my local motor factors and they sold me a fan switch that looks as you describe. my rad is plastic and i have followed the water pipes from block to water pump and cant find were it goes. any ideas? i thought i was mis-sold it and one of the three sensors i have already changed must already do the job. i have worked on all my cars for the past 10yr and everyone has had a fan switch on the rad.
No more talks on that thermoswitch then, as I'm confident you know whats worth knowing on that lump.
To me it seems you have just exactly missed the location of this switch. Its got to be there - on the sidetank - near the radiator bottom hose leading to the water pump.
Because the sensor is working off the chilled coolant just leaving the radiator, and then decides if the fans needs be on work to further cool down the coolant.
Does the 806 have the same engine bay layout as most other PSA's from the same era with the same engine types ?
As then its GOT to be in the car's RHS on the radiator you should find it.
To me it seems you have just exactly missed the location of this switch. Its got to be there - on the sidetank - near the radiator bottom hose leading to the water pump.
Because the sensor is working off the chilled coolant just leaving the radiator, and then decides if the fans needs be on work to further cool down the coolant.
Does the 806 have the same engine bay layout as most other PSA's from the same era with the same engine types ?
As then its GOT to be in the car's RHS on the radiator you should find it.
Anders (DK) - '90 BX16Image
suspect bitron unit
i have given up looking for the thurmostat it must be faceing the bumper out of sight. the main fan sticks every now and again and that is putting the STOP light on. pop the bonnet turn the fan by hand and all is ok for a while, i will get round to changing it. the speedo now has stoped working when i turn the key it moves to 0 mph then no further after resurching on here it seams to be only one of three problems.a dry joint on the dash, but the neddle moves so i dont think its that. a broken cable is possable. or the bitron unit, and with the temp problem i still have could be my best bet. the car is a t reg 806 1.9td engine type xu9tde. does anyone know where the unit can be located on this car?