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Discussion Starter · #1 ·
Before I push the button, if I ride the bike on a cold day, say 40f and it does not warm up past 150 or so, I need a new $66.00 thermostat correct?
 

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The main reason a thermostat is incorporated into the cooling system is to divert coolant flow away from the radiator during engine warm-up in order to help temperatures get above 150°F as quickly as possible. Its secondary function is to help keep the engine operating temperature within a reasonable range, but not necessarily the optimal range for performance.

The cooling system is designed so that the maximum flow of coolant to the radiator occurs when the thermostat is heated to about 180°F, the minimum (but not zero) flow occurs when the bike coolant is at ambient temperature, 70°F or so. Different thermostat ratings indicate what the fully open temperature will be.

The radiator, water pump flow rate and hose diameters are all sized by the Ducati coolant system engineers to achieve an engine coolant temperature of 180°F, when moving at a constant highway speed with 85°F air flowing through the radiator.

So, when you ride on a cold day, the stock thermostat never opens fully and you get less coolant flowing through the radiator. The coolant temperature then stabilizes, but doesn't get up to the design temperature of 180°f because the radiator is too big and the coolant pump capacity too large for the incoming low temperature cooling air. On cooler days, you should expect to see lower coolant temperatures.

Unfortunately if you run too cool, the bike isn't operating at its best efficiency. In this case, the most practical solution is to cover a portion of the radiator to reduce cooling air flow and raise the coolant temperature. How much radiator area you cover depends on how low an ambient air temperature you expect. You'll make your best power at 185°F. Trucks in arctic climates, for example, will run with 90% of the radiator covered.
 

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Discussion Starter · #3 ·
OK one yes and one no. This is an odd cooling system. If it were on my big Honda I would say it ran too hot, and ran too cold. But on a Ducati it's normal.
You would think the thermostat could keep it up to 180 on a 40f day. I guess 150 is OK. Runs fine. I wonder what the computer thinks.
 

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I guess 150 is OK. Runs fine. I wonder what the computer thinks.
On Ducatis, the computer uses the engine coolant temperature sensor to supply additional fuel while the engine is warming up. Engines need more fuel when for a cold start as there is no heat in the ports and chambers to keep the fuel atomized as vapor, so it condenses. Fuel as a liquid burns very badly in the combustion chamber, so throwing more at it ensures enough stays as vapor for some sort of combustion. Injected engines get a very nice fuel spray from the injectors and this is why injected engines behave better when cold.

The computer will add fuel to the base map for cooler outside temperatures until the engine coolant reaches 150ºF, after which it slowly leans out fueling. It used to go to 185°F before about 1995.

So you're OK to run at these lower temperatures.
 

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I have the same issue with my ST4 in winter and it doesn't even get that cold here, around 0 deg Celcius.
I believe the problem is twofold, the thermostat opens to early (66 deg C) and the thermostat is in the wrong place (the bottom hose).
I am aware btw that there should be approx 15 to 20 deg C difference between the top and bottom hoses but the thermostat is sensing the heat from the bypass hose which is in the top for when to open so it will begin to open at 66 deg.
Unfortunately there are no alternative thermostats available with a hotter opening temp so have to resort to blocking the radiator.
 

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Discussion Starter · #7 ·
Hmm..someone changed their mind.
Thanks for the info and link. I did search but didn't find that.
I am calling my thermostat good, and operating as designed. I just disagree with how it's designed. No amount of changing it will change that.
I wonder if the thermostat actually stays closed till 150 OR, it stays closed to 180 or so but the oil cooler and cooling fins cool the engine so much that it does not get up to temperature under way.
I remember last summer disagreeing with the cooling system design, and now here I am in the winter disagreeing with the warming design.
Well my air cooled BMW runs ice cold in the winter and hot as hell in traffic on a hot day and IT'S still alive. I guess the Ducati is much better regulated then no regulation.

Thanks guys.
 

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Yep I don't think it's the best design either but as you say it does work albeit not as well as I/we would like.
Interestingly, later water cooled ducati's seem to have changed the design running the thermostat in the top hose like it should.
 

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If either of you have the OEM temp senders, I would highly recommend Bosch or NAPA replacements. Both senders on my ST2 went loopy years back. It's one of the first "upgrades" that I did to my newer ST4s.

Basically, they were so far skewed, that by the fan turned on, the engine was overheating (boiling the coolant that was under pressure!).

You could verify with an optical pyrometer (point it at the area where the sender is).
 

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I just stick a piece of cardboard in front of the radiator that covers about half of it. That and a red traffic light and my AT-4s is plenty warmed up.
 

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Discussion Starter · #11 ·
If either of you have the OEM temp senders, I would highly recommend Bosch or NAPA replacements. Both senders on my ST2 went loopy years back. It's one of the first "upgrades" that I did to my newer ST4s.

Basically, they were so far skewed, that by the fan turned on, the engine was overheating (boiling the coolant that was under pressure!).

You could verify with an optical pyrometer (point it at the area where the sender is).
I replaced mine last summer.
 

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Yeah I have replaced both sender's with Bosch ones.
The problem is more to do with the physical location of the thermostat and the bypass hose.
 
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