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Discussion Starter #1
Hello everyone :)
Just about a week ago, I bought my very first car - Alfa GT 1.9 jtdm 150hp. Its a great car and I really like it. I did complete maintenance, fixed whatever had to be fixed and removed the swirl flaps and EGR. The car runs pretty sweet from what I can tell. One problem I have noticed tho is that the engine rarely reaches 90 degrees if it reaches them at all. Even on the freeway with a 140km/h constant speed and no AC running, the gauge barely reaches 80 and more often sits at about 75 (the outside temp was between 16 and 19 degrees). This was during 370km drive. Even on a shorter and slower drive - about 30km with speeds between 60-90km/h it never reached over 70-75.

What is wierd tho is that at the garage where I had the maintenance and everything, they checked the thermostat and said it was fine and did not need replacement. Should I be concerned about this issue, are there any other effects besides the engine being a bit more fuel hungry? Any ideas regarding the possible reason (I will get the car to a mechanic this monday but still wondering)?
 

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As you describe it, it sounds 100% like a failed thermostat.

You could plug in a laptop with a copy of MES to check the coolant temperature being registered by the ECU, but gauge not getting to 90 is likely the thermo.
 

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Discussion Starter #4
My fuel consumption seems pretty high too so I think there should be something not quite right. 7-7.5l/100km does not seem right to me.
 

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+1 thermostat.

These thermostats are unusual, they fail open. Which is confusing to garages who may be more used to thermostats that fail closed and cause overheating. They'll look at the thermostat and think 'it's open, it's fine'.
 

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I have the same problem with my 156 1.8 ts, so I plug it in diagnostics and checked the temp on the computer if it is the same as on the gauge....sadly it was so my thermostat is gone.

Try to pull out the hose from thermostat, see if it leaks. After changing the radiator, putting new water in the system, I noticed that is leaking so mine rearly reaches 90.

But also could be broken gauge, the resistor in the gauge has failed.
 

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+1 thermostat.

These thermostats are unusual, they fail open. Which is confusing to garages who may be more used to thermostats that fail closed and cause overheating. They'll look at the thermostat and think 'it's open, it's fine'.
I know fail-closed thermostats exist, but I don't understand why you'd use that option when you're designing a cooling system.
For that reason I assumed that the fail-closed ones are rather rare...
 

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Cost and simplicity I think. The Alfa is the first car I've owned that doesn't have a bog standard fail-closed thermostat cartridge like this https://en.wikipedia.org/wiki/Wax_thermostatic_element
I had Fiat Brava 1.6 16v 1996, the same type of thermostat that went wrong all the time! I replace it, two months later cannot reach the "normal" temperature or I froze to death in the cabin :D My advice is to see if it leaks, pull out the hose that goes from thermostat to main radiator and put water in the expansion tank on the right side of the car and see if it leaks, you should see water coming out.
 

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Cost and simplicity I think. The Alfa is the first car I've owned that doesn't have a bog standard fail-closed thermostat cartridge like this https://en.wikipedia.org/wiki/Wax_thermostatic_element
I'm not sure where you get this "failed open" idea from. The Alfa JTDM thermostat does in fact use the same bog standard thermostat cartridge shown above. It's just built into an alloy housing to make it more expensive to change than it needs to be. In fact it uses the "Double valve engine thermostat" shown in that Wiki page to also control (reduce) the flow through the heater matrix as the thermostat opens. Alfa could have made the bog standard wax stat element replaceable if they'd tried harder. Pretty wasteful having to chuck away the whole assembly just because the £5 wax stat part has failed.

Whether it fails open or closed just depends on the failure mechanism. Rupture of the wax stat part and it fails closed because there's no wax to expand to push it open. Weakening of the return spring/seizing of the sliding mechanism and it fails open. They normally fail open because failure of the wax stat part is rarer than the thing seizing in the open position. There's no intentional design here one way or the other.
 

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Uh, OK. I've never come across a thermostat failure that didn't cause overheating, and if my wife's driving, a cylinder head gasket failure (2x car, 1x motorcycle to date).

When these AR thermostats fail they seem to allow coolant to circulate the entire system and run under temperature, rather than the more conventional outcome where the cooling system is isolated by closure of the top hose by a shut thermostat, and overheating is the outcome of the coolant circuit being restricted to the bypass. I thought that must be ingenious design rather than AR thermostats just breaking in a different way to the majority.
 

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Discussion Starter #13
Thanks alot for the replies everyone.
I was at the garage today and the gauge at the dashboard actually shows higher temp than the ECU. At neutral we managed to reach 83 degrees (read from the diagnostics computer) and the gauge was showing 90. It took quite a bit of time - at least 20minutes to reach that temp. After reaching this temp, I drove a bit to see if it will drop or remain constant. The temperature dropped to 70 on the dashboard gauge, thats without even turning the AC on.

So a new thermostat has been ordered, and will be changed tomorrow. I hope this will resolve the issue. Is there need to change any of the car liquids (coolant or something else) when changing the thermostat?
 

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So a new thermostat has been ordered, and will be changed tomorrow. I hope this will resolve the issue. Is there need to change any of the car liquids (coolant or something else) when changing the thermostat?
Makes sense.. Idling in the garage there's no airflow to cool the radiator so you get some temp built up.. As soon as you're on the road the airflow cools the radiator and your temp drops.

Don't need to fully replace the coolant, but make sure you've got some to top back up as you'll definitely spill some.

Get the right stuff too - red/pink OAT coolant, not bog standard blue/green.
 

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The gauge on these cars is designed to show a fixed 90C whenever the coolant temperature is in the range 80 - 100C. Hence the discrepancy you saw.
 

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If you change the sender as well you may see a difference in where the gauge sits .. I did on my TS, It was slightly more accurate with a new sender.

Having owned a few cars with fail-closed thermostats, I can safely say we are in a much better position with it failing open. OK it might use a bit more fuel when it goes but you don't end up at the side of the road with steam pouring out of the bonnet and possible heat damage the engine. Ali engines are more susceptible to warping due to over-heating which is why I think they are fitted .. plus you can at least get home under your own steam (excuse the pun!)
 

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You could always squeeze a Renault 5 thermostat in the top hose for considerably less money. Bit slap dash I know but if your car is a banger and you're on a budget it saves a few quid.
 

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Discussion Starter #18
Today I got the thermostat changed with a brand new Behr one for about 65 pounds and the car runs perfectly. Even with the AC turned on and driving with high speed the temp goes up and stays at 90.
Thanks for the help everyone.
 
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