strange 1.9 cdti 8v engine temperature goes up and down ???

[lollypop]

desperate for some advice as this is doing my head in !

iv got a facelift 1.9 cdti 8v vectra. its been fine up until (might be a coinsidence) i gave it an oil change. i used the best stuff the steelers had which was fully (super) synthetic and an oil filter.

anyway,a few day later i noticed that my dashboard terperature guage was taking longer to move up to the normal 80 mark than usual !
it probably took 10 minutes longer,and when it did get there it went uptp 87ish ? then a few seconds later it dropped to 70ish,then went to 80.....
this continues up and down between 75 and 87ish ever since.

so i went back to the steelers and ordered a replacment temperature sensor, strangly the bloke at vauxhall parts told me that he had never sold one ever ? but ordered me one anyway.

next day i fitted it but no differance !

i have checked the dashboard against the secret menu on screen temp and that does exactly what the dash does,goes up and down between 75 and 87 degrees

so my question is..... how can the water temperature fluctuate between to temperatures so quickly and keep doing it over and over again whilest driving ?

any advice or help would be a big help please

[keith1983]

could it be some of the wiring between the sensor and display?

[lollypop]

thanks for the unbelivably quick reply mate !!

i did think of that, but eliminated it when i pulled the plug of off the temperature sensor and started the car, both radiator fans came on and also the spanner light on the dashboard.... proving the wiring is working fine ?

[Avenged]

i have checked the dashboard against the secret menu on screen temp

The secret what now??
how do you do this then??

[LJ sxi-nav]

The secret what now??
how do you do this then??

On some Vx HU's (like CD70) you can press and hold the settings button for a few seconds to access test mode. Then pressing some of the buttons repeatedly takes you through various hidden settings menus. On the CD70, pressing BC gives loads of screens including basic car data like temp in deg C and speed in KM/h. Press and hold settings to return to normal mode.

thanks for the unbelivably quick reply mate !!

i did think of that, but eliminated it when i pulled the plug of off the temperature sensor and started the car, both radiator fans came on and also the spanner light on the dashboard.... proving the wiring is working fine ?

Have you checked/changed the thermostat? maybe it is opening late (when temp is up higher than normal - 87C) then staying open too long so the water temp drops low (75C) - and it yo yo's between the temps

[lollypop]

thanks for your help mate i have been reading topics all night and lots of sites/threads mention changing the thermostat... so thats the monday job i think.

cheers mate, lollypop

[lollypop]

just thought id update my own thread changed the thermostat today, what a ******* of a job that was ! vauxhall decided to bolt some sort of catalyst on the bottom bracket where the thermostat housing bolts to the engine, but didnt bother to make it removable unless you strip half the engine off first !
this is the 8v and not the 16v cdti by the way.
it took 3 hours to complete the job because of this stupid bracket that stopped the bottom bolt comming out.

anyway, got it fitted and guess what......yep ! still the same problem

temperature guage goes up and down willy nilly, and hidden menu display does the same ?

what else could cause this ?

please help.......

[trickydickySRI]

What exactly did you have to take off?

I have the prefacelift 8v CDTI and my thermostat housing is leaking.. I have a new gasket/o ring so I need to take my themostat off to change it.... I have had a look and can see 2 nuts on there and some bracket in between the nuts,,,

And I did the same trick with the thermostat electrics.. how do you get rid of the code as it still showing the error on the dash!!!

Arrrggghh!

[deg]

Take it for a steady run down the motorway at a steady speed and see what it does.

[trickydickySRI]

It runs fine as long as there is water in it...

I just cant clear the error code from the ECU after pulling the Temp sensor plug