Hi everyone

I've already started a thread related to this and had some advice. However it's got a bit long now and I thought it would be clearer to start afresh. i hope that's ok?

The issue is that my Fabia 1.4 MPi 8v 2000 ref is only returning about 25 mpg and I really need it sorting before driving 300 miles on friday.

I have a incling that the problem is the thermostat/temp sender related. The temp sender was replaced in April however - so perhaps this narrows it down to the thermostat.

Anyway - this is a day in the life of my fabia's temperature gauge:

9am. Cold outside, frost all over car. I drove 20 mins at approx 30mph witha little bit of stopping in traffic, and then 20 mins up M1 at average 60 mph, fairly clear run. Temperature gauge did not lift off the bottom all the way.

4.40pm. Not quite so cold outside. Drove 20 mins down M1, average of 50 mph, with 5 mins in traffic moving approx 10 mph. Arrived to pick wife up from work. Gauge had not lifted all the way. Then, immediately...

5.00pm start car up almost immediately again and set off driving through Wakefield city centre. Notice that the temperature gauge needle rises to what it usual half-way mark up the gauge. it stays like this for the 25 minute drive to the supermarket. In supermarket 15 minutes. Back in car, start it up and needle goes straight back up to half way mark. Drive home - needle stays at half way mark.

7.15pm. Drive 10 minutes across town, approx 3 miles. I try to keep the revs up around 2500 mark. As I arrive at my destination I notice that the needle has just about started to lift off the bottom mark

10.00 pm. Drive 10 minutes across town again, about 3 miles again. Half way through journey notice the needle has not lifted. For last 1.5 miles of journey I keep the revs up about 28-2900 to try and generate some heat. Needle does start to lift off the bottom mark just by the end of the journey.

Now then... Perhaps all this might be a normally operating thermostat. Perhaps it just needs the connections testing and a bit of WD40. Perhaps I need a new thermostat part. Perhaps I need a whole new thermostate body and temperature sender.

What do you all think? Does something seem to be wrong to you? The morning run that took 40 mins, where the temp gauge did not lift at all is what makes me think something is wrong with the 'stat - but then again it was very cold outside, and I didn't really get stuck in much traffic, it was a fairly clear run apart from 10 mins in centre of town.

ANY advice very welcome. I have the whole thermostat body unit on order from Skoda. I can pick it up tomorrow morning and fit it myself - but it's £40 and if there is nothing wrong it it then I'd rather not waste the time and the money!

Cheers, Ian

You're probably hoping to hear from someone other than me, but I reckon your course of action is:

1. Check connections to sensor.

2. If that doesn't work, go ahead and get 'stat body pack. You need only replace the 'top' half of the 'stat body if you want, but you're not really saving yourself any work by not doing the whole thing. What's important is that you replace the top bit of the body AND the sensor - the 'bottom' half of the thermostat body is your call.

3. There are three reasons I'm suggesting this:

a. Any other diagnosis will require a fault code scan, which, in the absence of a local, available Briskodian with VAG-COM will cost considerably more than GBP40 (worth asking about, perhaps???);

b. There really isn't that much that can go wrong with the cooling system in terms of controlling temperature. The thermostat opens and closes (ca. 85degC) to allow coolant to pass through the radiator as required, and the temperature sensor measures that temperature, sending a signal to the gauge on the dash as well as the various other things that need a signal from it, like the fuel injectors (which do a similar job to the choke on a carburettor-ed car, and is probably why your fuel economy is so bad - it's like driving with the choke out all the time!);

c. The thermostat body is a bit of a timebomb, being a plastic part holding coolant containing organic chemicals ( ) so if you don't do it now, chances are you'll have to do it later. At least but replacing it now. you oughtn't to have to do it again for six or seven years...

HTH

After a long drive is the radiator hot?

If the radiator is cold then change the stat as your engine is never getting up to temperature.

If the radiator is hot then it's a gauge or sensor or wiring issue.

This is a good point cheezemonkhai - I'll look in to it

Our Fabia 1.4 mpi 8v W reg (2000) has had a problem similar to this. It just took too long to heat up to normal temperature. The gauge sat at the bottom for ages and only began to move towards the middle when sitting in traffic. Back on an open stretch of road as the cold air flowed into the front of the car you could see it get lower again until it reached the rock bottom. It was temporarily helped by placing a bit of plastic over the grill restricting the airflow which allowed it to get to operating temp. That was winter last year.

This year the plastic has not helped and it rarely moves from the bottom.

I have sorted it by replacing the whole thermostat housing which included the temp sensor. The part was around £33 from VW TPS (trade parts services). I think im lucky to have one of these near me.

Pretty easy diy job, and believe me im not one who is able to do much on my car. It has sorted out the problem and the car warms up great and stays in the centre all the time.

I've changed the thermostat now, and have just given it a good long run (250 miles from Leeds to Southampton). I've just worked out the fuel economy, and we did approx 35 mpg. Which isn't great on a long motorway run, but better than the 25 mpg I was getting before I changed it! thanks for all the advice, especially ap0gee

cheezemonkhai — If the motor isn't getting warm, it's because the thermostat is stuck open. In that case, the radiator will be luke warm after a run. If the thermostat is stuck shut, the rad will be cold and the engine will be decidedly warm.

Maintaining high revs does not warm up the engine unless the lubricating system is failing. Quite the reverse: with a light load on the engine (maintaining a moderate steady speed) the increased engine speed will result in a greater rate of coolant flow, which will keep the engine temperature down. If you want to warm the engine up quickly, you need to increase the thermal load: keep the revs moderate (there's no need for more than 2500 or so) but put your foot down hard. Accelerate firmly but briefly. The combustion chambers will get nice and hot and the coolant will warm up.

Unless the thermostat is stuck open...