The Infamous open Thermostat 2.0TS - Alfa Romeo Forum
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The Infamous open Thermostat 2.0TS

I have recently asked a non-franchise workshop to replace my broken/open thermostat on a phase 1 2.0TS Spider. I complained afterwards that the temperature gauge was still reading too low to my liking. The mechanic then showed me a photograph showing that the brand new, OE thermostat was slightly open at room temperature. He thought it may be within specs, in order to assist in bleeding the system. As a lay person, I believe it should be completely closed at room temperature. Please confirm whether a slightly open thermostat (at room temperature) is normal, or not. (I try to attach the photograph.) Thanks.
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Originally Posted by Andricus View Post
I have recently asked a non-franchise workshop to replace my broken/open thermostat on a phase 1 2.0TS Spider. I complained afterwards that the temperature gauge was still reading too low to my liking. The mechanic then showed me a photograph showing that the brand new, OE thermostat was slightly open at room temperature. He thought it may be within specs, in order to assist in bleeding the system. As a lay person, I believe it should be completely closed at room temperature. Please confirm whether a slightly open thermostat (at room temperature) is normal, or not. (I try to attach the photograph.) Thanks.
Actually, the one in the photo looks OK, got a new with me and it looks the same.
I tried blowing through the large opening that you attach the hose going to radiator, and it's blocked. If I'm not mistaken they should start to open as the temperature increases over 80 degrees.

Last edited by antonius; 18-08-16 at 22:19.
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That thermostat in the picture is neither new, nor closed. It should be absolutely closed.

Why I say it's not new is because it is all rusty inside. I am going to give pointers on how to properly care for your thermostat in order to ensure that it works correctly:
1. Always inspect before fitting, and test it. It should be fully closed when at room temperature and once placed in boiling water it should be fully open. As the water cools to below 80 degrees it should start cooling again, being fully closed at around 50 degrees.
2. Always, always, always drain your coolant when replacing your stat. The rust and scale affects the operation leading to premature failure.
3. Replace coolant and add rust inhibitor to your coolant. Use at least 50/50 coolant mix. Even if you are in a temperate climate. It contains additives to protect your water pump, thermostat, rad hoses and prevent rust.
4. An open stat will eventually fail closed and cost you your engine.
5. An open stat will eventually fail closed and cost you your engine.
6. Revert to point 4 and point 5 above.

Please also note that the coolant should be replaced every 2 years, at which time it also makes sense to replace the thermostat. Even if longlife coolant is used, the thermostat will only last 2 to 3 years anyway.

A correctly functioning thermostat heats the engine up to 90 degrees within 7 minutes. The temperature should stay absolutely still at 90 degrees in town driving, only moving one needle width at most. If it ever moves more, for example to 95 degrees, then replace the stat. See points 4 and 5 above.

At freeway speeds the engine will cool to a minimum of 70 degrees (the line between 50 and 90). If the engine ever cools below 70 degrees then replace the stat. See points 4 and 5 above.
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Originally Posted by Ian Lusso View Post
A correctly functioning thermostat heats the engine up to 90 degrees within 7 minutes. The temperature should stay absolutely still at 90 degrees in town driving, only moving one needle width at most. If it ever moves more, for example to 95 degrees, then replace the stat. See points 4 and 5 above.

At freeway speeds the engine will cool to a minimum of 70 degrees (the line between 50 and 90). If the engine ever cools below 70 degrees then replace the stat. See points 4 and 5 above.
I second this.

Moving a needle width at town driving speeds is correct, with the fans kicking in when it moves a needle width above the 90 line.

At speed, if it cools below the 70 line, it's a dud and has failed open.
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Agree with Ian and Giorget 2. One other point is what condition is the radiator in? Chances are if it's never been replaced it's probably full of crud and muck. The system does not have bleed points, refill with new coolant and top up as necessary once the thermostat has opened.
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Great clarification on what to you do when replacing a thermostat. I am going to change mine soon and will definitely be following your advice. Thanks guys.
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Thank you for all the information. It seems then that Antonius is also sitting with what should have been a factory reject thermostat. Off back to the workshop with my car then...
One would have thought that Alfa Romeo should by now have identified the thermostats as problematic - it is after all 20 years since my car left the factory! Or can it really be that so few people complain when their vehicles are running below optimum temperatures?
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That thermostat in the picture is neither new, nor closed. It should be absolutely closed.
It's obvious that it's not new looking at the photo, I have a new one, and looking at the valve it's in a similar position to the one in the photo, although if it were open by a mm or two, there's no way of telling without testing it. I can't blow through my new one, which means it's closed at room temperature. I'll be fitting it over the weekend, new rad as well, so will soon find out if it will work as it should.

I've had to replace thermostats on my last two Alfas, TS 2.0 then a V6, both new thermostats worked fine, and by fine I mean that they get up to temperature, 3-4 minutes for a TS, V6 5-6 min, at remain around the optimum operating temperature, going by gauge.
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If in doubt you can always test the stat by putting it in a pan of boiling water. Some of these stats could have been in the warehouse for some time and therefore look a bit rusty. If it doesn't open or close properly send it back.
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Alfa thermostats are pretty rubbish.

They fail with a regulariity that I have never experienced with any other brand (although Fiat are bad as well)

I have owned 15 Alfa's and I would guess that I have replaced 12 Thermostats.
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Originally Posted by Ian Lusso View Post
4. An open stat will eventually fail closed and cost you your engine.

At freeway speeds the engine will cool to a minimum of 70 degrees (the line between 50 and 90). If the engine ever cools below 70 degrees then replace the stat. See points 4 and 5 above.
I've only ever known Alfa thermostats to fail open, it seems to be the default failure mode.

The temperature gauges are not very accurate at the best of times. The unmarked lines just indicates normal temperature ranges but the scale isn't linear - I'm pretty sure the lower one is higher than 70 degrees but I agree, if it can't hold the temperature above this mark change the stat as it is starting to fail open. The needle bobbing up and down within the "normal" range is quite common and nothing to be concerned about.
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The needle bobbing up and down within the "normal" range is quite common and nothing to be concerned about.
Yes, I actually like the fact that the signal is not made "clean" electronically, like in most new cars today. Any VW product, the indicator never budges from the middle indication, unless there really is a big problem. The analog signal in the Alfas enable you to notice anything strange right away, not only after some damage has already been done.
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I've only ever known Alfa thermostats to fail open, it seems to be the default failure mode.
Yes. Initially they fail open. The thermostat doesn't fail dead. It just has a much smaller range of movement. Eventually the thermostat will tend to the closed position with a few hundred cycles and it will cost you an engine. This has happened to me.
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I think I have the same problem with my 98 TS Spider. It won't warm up on the open roads at night.
I am going to change the thermostat but I can only find the entire housing. Is this correct, or should I be able to just replace the thermostat itself?

regards

Robert
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I think I have the same problem with my 98 TS Spider. It won't warm up on the open roads at night.
I am going to change the thermostat but I can only find the entire housing. Is this correct, or should I be able to just replace the thermostat itself?

regards

Robert
I know on the V6 you get the quality Behr/Mahle unit which comes in the housing as well as the cheaper unit which comes without the housing. The cheaper unit doesn't last though.
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I know on the V6 you get the quality Behr/Mahle unit which comes in the housing as well as the cheaper unit which comes without the housing. The cheaper unit doesn't last though.
thanks for the reply, I'll get the housing too.

Robert
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