mk3 temp gauge not staying on 90'c when warm ?

[spudboy6]

ive only noticed this since its been getting colder

i hop in the car its stone dead cold , start it up i always let it idle for a couple of mins before setting off .

the car takes ages to get up to temp if i have heaters on . so i stick them on cold up on the screen and it takes about 3-4miles to reach temp of sensible driving .

but when you stick it on warm the temp drops down to 80'c and if you run the heater on warm from cold it wont ever make 90'c unless you sitting at lights after a few miles .

so it drops down to 80 so i stick the heater back on cold and it goes back to 90'c . and eventualy after about 8miles or so it will stay at 90 unless you give it the full beans on hot .

what do you guys think ? ive changed the coolant since ive had it and bled the system this was before summer so a while ago no problems in summer really but only noticed it recently . i changed the cracked plastic housing on the front of the engine at the same time . no coolant system leaks and changed the sensor in that housing .

its a 1.8 8v ADZ engine ....

[supergeeman]

sticky thermostat?

[VW BUSH]

 

[spudboy6]

what i thought just read some posts on here and seems to point to the peoblem .

thanks guys 
i best order one and get it done dont fancy any funny buissness on a cold night

[VW BUSH]

Its just a slow thermostat, change it for the sake of a fiver but the temp fluctuation you are seeing is quite normal.
The heater in your car is an extension of the radiator, by opening up the valve you increase the cooling of the engine causing it to drop in temperature, closing it makes it go up...
The wax/bi metal in the thermostat takes time to switch causing the fluctuation.
On a cold day with the heating on from start up you are increasing the cooling making it hard for the engine to heat up...
A good trick for limping an overheating engine home is to run it on full heat with full fan, b!tch if its July

My GTI runs just above 1/4 on the gauge on the motorway with the heating on at 70

[DCmk3]

Sticky/slow or no thermostat is your problem.