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Hey everyone, just bought myself a 2003 ST4S. Took it around the neighborhood today, noticed that the temps quickly shot up to 248 F :frown2:

Ambient temps were 75F, was only cruising in 1st/2nd gear at around 20-30 mph for around 5-10 minutes.

So where should I start in diagnosing/fixing the issue? Obviously checking the coolant will be the first step, gonna pull the RH fairings later to check it out. Any particulars that I should be looking for on this? I've got the service manual.

I'm a competent auto mechanic but rather new to wrenching on bikes. Completely new to Ducatis- always been a dream.
 

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Welcome to the forum.

If you haven’t added you location info to your user profile, please do so. It’s also good to have your bike details in your signature line.

The ST4 has two temperature sensors, one for the ECU and one for the temp display. You can try swapping leads to see if a sensor is bad. They are readily available At the local auto parts store (see sticky above for alternative parts). Check for coolant level and circulation.




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if it has had the coolant replaced and the front not raised when bleeding they can get air pockets in them that can make them overheat. also check the rh side of the radiator is hot. i've seen the plate in the lh tank fail and had them overheating while the rh side tank is cold to touch

also the sensors can be reading rubbish - i've seen a few where the dash and ecu are saying quite different things. was this moving or stationary? the ecu turns the fan on. did the fan come on?
 

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Hey everyone, just bought myself a 2003 ST4S. Took it around the neighborhood today, noticed that the temps quickly shot up to 248 F :frown2:

Ambient temps were 75F, was only cruising in 1st/2nd gear at around 20-30 mph for around 5-10 minutes.

So where should I start in diagnosing/fixing the issue? Obviously checking the coolant will be the first step, gonna pull the RH fairings later to check it out. Any particulars that I should be looking for on this? I've got the service manual.

I'm a competent auto mechanic but rather new to wrenching on bikes. Completely new to Ducatis- always been a dream.
Been there done that. I've tried every trick on this forum to eliminate the hot nature of this beast to no avail. I've cleaned and flushed the system several times with both over the counter products and self prescribed concoctions. Removed the water pump to inspect the integrity of the impeller, filled the system with different formulas of water(distilled and not) anti-freeze and water wetter, replaced the hoses, replaced both temp sensors with Bosch sensors, checked the accuracy of the temp when the fan comes on. Each of these perhaps made a slight improvement but over all this is one hot machine.

All of the fairing severely restricts the air flow so much that even when the fan is on you can hardly feel any air coming out the duct work. The machine does run much cooler if you leave the fairing off so I believe it's not a mechanical problem.

I installed a separate switch to turn on the fan as soon as I come into traffic to get a head start but it just delays the inevitable. Sometimes I have to lane split or turn around to get moving to keep from melting. I just learned to live with it and watch the temp gauge.

If I have missed anything new to prevent this please post it here so maybe I can be a cool Ducati rider.

Ride On(cooler?)
Dave
 

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My ST4 doesn't overheat even when stuck in traffic on a 30+ degree Celsius day. I do have the upgraded aluminium fan and a manual switch which lets me turn it on a bit earlier.
If it's still overheating and the fan is working it would be worth checking the thermostat and getting the radiator profesionally cleaned. Different brands of coolant can react and form hard crystal deposits which are very difficult to budge. Also old coolant can turn to jelly also blocking up the radiator.
 

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If ur coolant is ok, and you probably should remove the rad. cap to ensure that it has fluid in it -- some folks report that the coolant reservoir can clog at bottom and not pass fluid to/from radiator.

Then, it's probably the coolant senders. The front one on the horizontal cyl does the read-out. The vert. cyl. one does the ECU (and ECU controls the fans).
They are French made, Jaeger brand, and they are CRAP. Buy the Napa or Bosch equiv. and be done with that. The 248 F reading on my ST2 was a result of a faulty intermittent sender. I originally thought it was the connector. Boy was I wrong. They not only go intermittent, they also scew the reading. Like sending a lower (temperature) signal to the ECU than reality. Buy a cheap optical pyrometer at Harbor Freight and aim it at/near these senders to confirm accuracy to the read-out. After I put my Bosch ones in, the readings agreed by about 1 or 2 degrees F.

And normally, it's ok to see temps up to about 215, maybe 220F, but the fan should be on, and it should not rise above these figures. 220 F is OK, because UR running a pressurized system. Oh, that too -- make sure that upper hose is firm when hot. I also had a problem rad. cap that would not hold pressure. Turned out that it's tiny valves needed cleaning (it was sludgy).
And, if you want to get crazy, a 220 Ohm resistor inserted in place of the sender, will give you a readout of 207F. I tried this on my ST2 when troubleshooting a stumbling issue. I fed the 220 Ohm resistor into the ECU, adn the bike ran perfect, instead of seeing intermittent values from the crapola French senders,
 

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Also note, if when you flush and re-fill, do the re-fill on the side stand. It makes the rad. cap the highest point. There are also bleeders built into the fittings that bolt onto the side of the jugs (or heads). It's an "extra" bolt that does nothing else.
 
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