[gnarly]

hi guys,

My 749 has been overheating pretty bad. I've seen some articles where people have experienced this and included that when they turned the bike off, they saw a lot of coolant leaking.
Had the issue 2 times at 200 to 220 deg F*

I want to troubleshoot the coolant temperature sensor but it says I need a DDS tester. I can take it to the shop that I've been going to for a long time but I kind of want to do it at home. But how can I do this without the DDS tester?

Here's the SCRIBD 749 workshop manual comments attached as a word doc. Can also be located on the scribd page for Ducati 749 workshop manual on page 599.

 

[mrnelectro]

You don't necessarily need to plug in DDS to test the coolant temp sensor.
The coolant temp sensor housing incorporates thermistor ( a sensor that changes it's resistance depending on temperature).

If you have multimeter, set it to 20 kOhm range and probe either pins or pin & casing. You should get 3k-1k around ambient temperature. Resistance decreases with hotter coolant, i.e. you get around 0.4 kOhm when +100C

The chart is here for both air and coolant temp sensors:
http://www.ducati.ms/forums/attachm...mp-sensor-resistance-readings-916-img032a.jpg

I hope this helps.

 

[mrnelectro]

BTW,

thermistor failure syndroms:

1. no resistance at all (open circuit)
2. stuck resistance (temperature does not change resistance)
3. excessive resistance drift (thermistor got good range when 0-40C, then after getting hotter than 40C it quickly drops to almost 0 ohms (thus can show real 50C as 150C)

sorry, shitty english.

 

[mrnelectro]

I have 749 and overheating in my case was caused by 2 things:

leaky radiator cap: When my bike reached 102C and more in trafic, it has started to puke coolant from radiator cap. Solution: I have replaced cap with compatible 1.1Bar radiator cap (used on many bikes, I bought http://www.uscoolsports.com/v/vspfiles/photos/CAP-3000318-2.jpg

I had dirty air filters. There was crap beyond belief, suspected fueling issues.

 

[gnarly]

cool. Thx Electro.
I don't really have to take the coolant temp sensor off right?
I can just let the bike warm up and then pull the plug off of it and then touch the terminals with the leads from the multi-meter?

 

[gnarly]

ok Electro. Here's what I did, let me know if I did it right.
I set the multimeter to 20k Ohm
I probed the pins on the temp sensor and got a reading of 3.51
I then probed the terminals that (multimeter at 20k Ohm) plug into the temp sensor and got a reading of 2.82

Looks good then, yes?

I'll probably be off to buy one of them radiator caps.
I had a BMW E30 a long time ago where I replaced the radiator cap and my overheating problems went away.

Sounds like a replacement cap needs to be changed every 8 years? Is that about right?
They just don't hold pressure after that time?

Thanks Electro. Appreciate the advise.

 

[mrnelectro]

"I don't really have to take the coolant temp sensor off right?" No need to take it out, you can test it in place. It does not make any difference.

"I probed the pins on the temp sensor and got a reading of 3.51" You have measured 3.51 kOhm, that's good. You should see that value drop as you heat the engine during idle.

I am quite sure your cap is old and not sealing and therefore puking coolant once it is heated above +90C (200 fahrenheit?)

I would clean the area where cap goes, replace the cap with new one (buy those 1.1 bar for around 4$, they are universal and used also on Honda CRF250). Don't buy used OEM ducati ones.
Then top up your radiator/overflow tank with coolant fluid.

The reason why your radiator pukes coolant is that once the liquid is heated it expands and reaches the throat of radiator cap. Since it no longer seals under pressure, it pukes some of it through the rubber seal underneath the cap. Some of the coolant flows to overflow tank, some of it gets splashed all over your bike.

They are known to fail. Mine failed too.

You said overheating: If you are experiencing 104C (220fahernheit) in still traffic, that's normal.
My bike runs (in celsius degrees):
70mph on motorway : 68-75 degrees.
30-40mph in town : 80-90 degrees
Sitting in traffic : 101-104, but never more than 105.

this range is normal, confirmed by 2 other people owning 749

I think that once you replace the cap you will fix this. I hope this helps.

 

[Craighjr]

ok Electro. Here's what I did, let me know if I did it right.
I set the multimeter to 20k Ohm
I probed the pins on the temp sensor and got a reading of 3.51
I then probed the terminals that (multimeter at 20k Ohm) plug into the temp sensor and got a reading of 2.82

Looks good then, yes?

No; probing the sensor part your ok. Probing the wires that go to the ecu does nothing. You haven't proved the sensor works, but if the dash was changing the display temp it was probably fine. Replace your rad cap thermastat and top off the coolant.

 

[mrnelectro]

No; probing the sensor part your ok. Probing the wires that go to the ecu does nothing. You haven't proved the sensor works, but if the dash was changing the display temp it was probably fine. Replace your rad cap thermastat and top off the coolant.

Yes; Actually it does.

Probing the wires that goes to the ecu is a good practice in this case. This proves that the thermistor inside coolant sensor will be loaded with current from ECU and it also proves that wiring from the connector of coolant sensor to ECU is good. He is in fact measuring some resistance from circuit on PCB inside ECU (most likely open collector with boostrap resistors or operational amplifier combo with bootstrap resistors). It does not matter what value he measures in there, only the fact "something" is there and NOT a open circuit or short (which would then explain internal fault in ECU pcb for coolant sensor input or problem with wiring that goes to ECU)

Anyway ,the real proper way to measure the coolant sensor would be to measure it at 0C, 25C and 100C and see if the values match up with thermistor temp/resistance value table (which is available online for 5k/10k resistance series)

He tested it at some temperature (either at 25C or 50C depending on type of thermistor in sensor). That value matches the temp/resistance for 5K or 10K thermistor inside coolant sensor. So I can say 99% it is OK.

As said, I suspect old/weak/worn radiator cap.

 

[gnarly]

cool, thanks gents. will keep ya updated.

 

[gnarly]

Got the 16psi (1.1bar) cap and refilled the coolant (removed bubbles).
I noticed some tiny black particles when I was letting it run w/o the cap.
I ran it for about 10 min / 190*F +/-.
Not sure if I ran it long enough. Some folks say to run it until the fans turn on.

Rode the bike over the hill yesterday (temp at the valley was 80*F). The bike's temp was 180*F.
I opened the throttle to 100mph...I hear a pop.
Next thing you know, the bike jumped to 200*F. Didn't understand it at the time coz my leg was feeling a breeze. I looked down on my knee and it was filled with coolant.
Pulled over to surface streets and removed the fairing (I carry a 4mm allen wrench nowadays).

Right side of the bike had lots of coolant.
Rez tank was empty.
hoses were fine, did not find a hose that was either detached or crack.
waited 1.5 hours and rode back home over the hill to the coast.
the temp reached 200*F (I guess it doesn't matter).

I squeezed the hoses connecting the water pump to the vert head and the hose connected to the thermostat / thermostat housing.
Did not feel any coolant squashing around.

Could it be the:

a) thermostat
b) water pump

I'm gonna change the oil right now and see what the engine has to tell me.

 

[gnarly]

damn! The biggest fear has come true.
drained the used oil in an empty can and saw lots of green dots.
Yep, you guessed it. A blown head gasket.
I wonder if I can make more in parting this thing off than selling it for $3k to adjust for the cost of an overhaul?
what do you guys think?

 

[Tuned]

Didn't you replace the head gaskets recently? Did you torque the head properly?

 

[gnarly]

Yep, I did. I got new ones and did the torque as advised by local shops.
Not sure how the head gaskets blew. Maybe they got loosened up?

Maybe I can sell this motor and get a new one off of eBay?
I like this bike a lot. It flicks like no other bike I've ever ridden. Not a lot of power but still pretty awesome.

 

[gnarly]

I mean the head nuts loosened.

 

[mrnelectro]

"I noticed some tiny black particles when I was letting it run w/o the cap.
I ran it for about 10 min / 190*F +/-.
Not sure if I ran it long enough. Some folks say to run it until the fans turn on."

The cooling system is meant to run pressurized.
Nowhere in manual is mentioned that you supposed to run it with cap off. The manual says to run it for a while (with cap on) and then top up if necessary and/or lean bike side to side to get rid of any potential air in cooling system.

 

[gnarly]

just gonna part it off

Anyone want any parts? Probably need to post a new thread for the parts I have, but if you have anything in mind, let me know and we can work out a deal and shipping or just get the whole bike for what...3k? Is that a douche move?
I figured I could get up to $5k on parts but would take longer but 3k for the whole bike and someone can use parts?
Anyone have a 749 for a track bike could probably use 'em.