bad fuel economy, thermostat problem?!?!

kiklop123

Member
Hello everybody,
had experienced high fuel consumption (from 5,9 to 7,7 L/100KM) in this cold days.
Looking at temperature sensor, i noticed it takes a very long time to warm the car on working temperature, and even than never reach 90deg. It will mostly stop on 80deg. This indicates me, that thermostat is on its end, therefore car is mixing more fuel to run, what explains high fuel consumption.
My car is 2000 1,4 petrol AUA.
Can anybody confirm my suspicions, and tell me how to change the thermostat. I read in TDI threads with same problem how to do it, but not sure is the same with petrol engines.
Thank you all, and sorry for my bad english.
Andrej
 
Part 5 here:

It sits above the gearbox. Looks ok to change I think.
Your English just fine.
All the best,
Matt


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It may indeed be the thermostat, or it may be a failing sensor. Changing the sensor is discussed here:
 
just to be on the safe side...
so i need to change a part no.5 as from 7zap picture (uploaded by BiggDogg) + O ring (no. 7) correct.
Can anyone tell me the spare part number.
Thanks in advancxe
Andrej
 
If you scroll down the webpage a little, it tells you part numbers, but there are 2 options for the thermostat (coolant regulator), so it’s best to have it confirmed by the supplier, based on the VIN.


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All right now. WIll go to the nearest dealer and get the part. Any instructions on how to replace the thermostat. I read that belt tensioner has to be removed, or is it just for diesel engines.
 
That’s just for diesels. I’m pretty sure your thermostat housing is bolted to the side of the cylinder head, so higher up and above the bell housing and gearbox. My son’s car is a Polo with the BBY engine and I went to look on that. It is in the same place. I would change part 8 and 11 at the same time-these are the ones Steve refers to. Get some fresh coolant too, it may need mixing with de-ionised water to the correct strength.
I’ve not done this exact job on an AUA, but I would:
Start with cold engine. Drain some coolant first, which means removing the engine undertray and unclipping the lowest radiator hose, catching the coolant in a large clean bowl. Put some rag under the thermostat housing and remove the 2 bolts, swap the thermostat and o-ring, replace bolts. Pull out the clip on the temperature sensor (item 9) then remove 8 and 11, replace with the new ones, put everything back except for the undertray, refill the coolant. Check for leaks. Start the engine with the coolant filler cap removed and let it come up to temperature, topping up as needed - it will burp the air out. If you feel the radiator hoses you will know when the thermostat opens, just mind your fingers and clothing in the belts and radiator fan . It may take 30 minutes to do this if the weather is cold. Keep the heater in the car set to hot but the fan off.
I like to use VCDS to look at the engine temperature and watch it go up and down as the radiator fan cuts in and out before declaring the job done, screwing the coolant filler cap on and refitting the undertray after again checking for leaks.


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BiggDogg, thank you so much for your instructions. You are very, very kind. If ever in Slovenia, contact me to take you out for a beer. With the right car, of course.
My phone no is 00386 31 686 277. Anytime, mate....
 
Not at all, you’re welcome. It’s a while since I was last in Slovenia, beautiful country. I was visiting a motor manufacturer in Železniki.
I hope it goes well. I forgot: the connector for the sensor is like all the others: to release it, push it in first, press the small lock clip while still pushing, then switch from pushing to pulling while holding the clip. The secret is to push first (compress the rubber seal, then you shouldn’t break the clip).
Good luck.


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I thought I would ask about thermostats. I am running a 1.4tdi and have also had the temperature gauge refusing to move. I have changed the thermostat twice. The last time the temperature did rise after a motorway run, but then it struck me that the sensor is beyond the thermostat in the cooling system and with the opening thermostat temperature of 87.5 and the cabin heater blowing, it struck me that the engine may be up to temperature even though the radiator is stone cold.
 
Thanx Rod. The problem is that the low temperature is causing higher fuel consumption as the engine is injecting more fuel.
But i heard same as what you are saying, that with cabin heater blowing on full temperature can decrease from optimal for couple of degrees.
A
 
Problem solved. I didnt dare to change the termostat by may self, my friend mechanic did it. It was abt 2 hours of work, including coolant to cool down. I paid 50EUR together with the termostat and cooling liquid. Car's fuel consumption is back to normal. Thanx you all to help me with this problem, especially BiggDogg with his instructions and prompt replies.
 
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