There have been quite a number of posts in this thread and elsewhere about temperature gauges on the FIRE family engines showing steady readings somewhat below the half way "normal" mark - quite often around half way between "cold" and "normal". People report that the car continues to run well and pass it's MOT test like this. Indeed our present Panda - Becky - had this problem when we bought her and, knowing there was probably nothing seriously wrong I sorted out other more pressing stuff, like the timing belt etc, before I did a thermostat and she ran absolutely fine and passed her MOT with the old thermostat in. With the new thermostat fitted I get a quicker warm up, slightly better fuel consumption, the heater is definitely somewhat hotter on cold winter days and the tick over is slightly smoother (she had a slight tendency to miss a beat now and again when idling with the old thermostat in). Mostly though, because the car does a lot of local journeys, I like the fact that the engine is now getting fully up to temp more quickly and runs hotter so is probably driving off internal condensation and evaporating any fuel that might be diluting the engine oil on cold starts. In my opinion, as long as there's no other problem - like a faulty sensor perhaps? or loose/corroded connection? - the needle should sit half way up the gauge with a hot engine.
I suppose it's possible that a very few of these may be due to other reasons, but, as long as the coolant is up to the correct level and there's not a serious air lock somewhere in the system, I can say, with some considerable certainty, that these cars most probably have a thermostat problem. Often due to the coolant leaking past the rubber seal on the disk but I've also seen the thermostat itself just opening too soon. 2 of my 3 children, now well into their 40's, learned to drive in Pandas and one now has a Punto - and we've run Pandas as second "city" cars for over 30 years. We generally keep them for many years - one we had for about 20 years - and all have suffered this temperature gauge aberration. Keep 'em long enough and they'll probably do it. Stick a new thermostat in and all is well until it does it again. Some last for ages, others for a couple of years or so, seems to be pot luck whether you get a "goodun" or not.
As mentioned by Koalar above. With the engine cold start it up and grip the top radiator hose with your hand (taking care to avoid rotating or hot engine parts - exhaust, fan belt, etc) The hose should stay cold for quite a while, maybe 5 minutes? depending on ambient temp, because the thermostat should be preventing any water from the engine going through this hose to the radiator. Then, very suddenly, as the engine water temp reaches the thermostat opening temp (not far short of 90 deg so nearly boiling) the top hose should get hot, very hot very quickly, and you'll want to take your hand off it! if it starts getting warm soon after starting it and it then gradually continues, over a period of minutes to get gradually warmer and then hotter then the thermostat is not holding the water back and needs to be renewed.
Damn, I've done something which is making this come out in italics - don't know how to stop it!
If you're not very experienced it can be difficult to know how long that top hose should stay cold or how hot it should feel. So, if you want to further verify this, and you know where the feed pipe to the heater is, - back of the cylinder head on earlier engines and coming off the thermostat housing on newer ones - then, after starting from cold hold on to both the top rad hose and heater feed hose. The thermostat doesn't stop water going through the heater so you should feel the heater hose heating up gradually as the engine heats the water but the top radiator hose should stay cold until the thermostat opens so your heater hose is going to be roasty toasty with your top rad hose cold until it very suddenly gets very hot as the thermostat opens and lets hot water from the engine go to the radiator. It's worth factoring in that the rubber of the hose itself is heat insulating so sometimes you'll get a better feel by putting your hand on the radiator header tank rather than the top hose as the header tank will often transmit the heat quicker. By the way, on modern engines the dashboard heater controls don't affect water flow so it doesn't make any difference whether they are set to hot or cold in terms of the water heating up - although if you're moving, or have the heater fan on, and you want the coolant to get up to temp as rapidly as possible you are best to set the heater controls to cold and turn the fan off which will stop cold air going through the heater matrix.
Right, I'm off to google how to switch these italics off now - Me and computers? a disaster! wish me luck.
