| Author | Message | ||
     Lemonchili_x1 |
Ok, I'm sure it's been discussed before, but I couldn't find it after searching, so... What is the logic behind running the fans with the ignition off on the 1125's, and what advantages does it offer? Without the water pump running is there really much flow due to thermo-syphon effect? Is it safe to assume there must be some flow as the temperature sensor is in the head not in the radiators, and there would have to be some flow to make running the fans of any use? I understand the control logic is that with the ignition off the fans turn on above a certain setpoint (higher than normal turn on setpoint) and the fans turn off below a certain setpoint (also higher than the normal turn off setpoint). Is there a time function as well, or just temperature? cheers, chili | ||
| Cycledoc59 |
.With all engine and cooling system designs, when you shut off the engine, you also shut off the water pump. Coolant trapped in the heads can boil as it absorbs the heat in the metal engine parts with no way of transporting this heat to the radiator. Running the fan for a few minutes can prevent this from turning into a boil-over and coolant loss.. If a temperature gauge still operates when the ignition is switched off, as it does on some cars, you will see the needle rises after the engine has stopped. That is because it is measuring coolant temperature, not engine temperature. The engine is still much hotter than the coolant. Air-cooled Buells use the fan to prevent oil breakdown/carbonization in the rear cylinder after shutdown for the above reason | ||
| Brumbear |
heat soak | ||
| Geforce |
All of my modern vehicles operate electric fans for a while after shut down on hot days. That includes my 1987 Buick Grand National which is the oldest in the line up. | ||
| Lemonchili_x1 |
Air-cooled Buells use the fan to prevent oil breakdown/carbonization in the rear cylinder after shutdown for the above reason I can see the logic with an XB, the fan will move coolant (air) over the head/cylinder to remove heat. If a temperature gauge still operates when the ignition is switched off, as it does on some cars, you will see the needle rises after the engine has stopped. That is because it is measuring coolant temperature, not engine temperature. The engine is still much hotter than the coolant. Yep, understood. I'd never checked the temps on my 1125 after shutdown until this morning. I got to work with the bike at 82°C (180°F). I switched off and let the fans run until they switched off and then turned the bike on to check the temp again - 90°C (194°F). So I guess the fans are either running on a timer or until battery level gets below a certain point. All of my modern vehicles operate electric fans for a while after shut down on hot days. My cars are old, though the Valiant now has an electric fan  . I seen cars/bikes that will run the fan with the engine stopped/ignition on, but I can't remember riding/driving something where the fans run with the ignition off. | ||
| Two_seasons |
Fans run for 60 seconds after shutdown, even in the hottest conditions. Cycle is repeated if you cycle ignition switch power. (Message edited by two_seasons on November 22, 2011) | ||
| Sprintst |
Lemon - I understand your questions and wonder the same. I don't think anyone has actually answered it If you are blowing a fan onto a radiator that doesn't have coolant flowing through it, how does that cool the heads? | ||
| Jules |
I see your point - I suspect the answer is thermal transfer, water (as you know) is a great conductor, so the heat from the engine will heat up the localised water, but as that's connected to a larger pool, the overall temperature would rise too - with the fan cooling the radiator that'd make the overall temperature lower (countering the localised heat).. Itg's like sticking a hot iron in a bucket, it'll warm the water up, if you add more cold, it cools the iron faster... | ||
| S21125r |
A radiator that is cooling off and a head that is warming up will create a bit of a convection cycle that will continue until the temps equalize. So the fan probably help jump start the convection cycle. | ||
| Azxb9r |
What cycledoc said  | ||
| Cycledoc59 |
Sprintst has a logical question:"If you are blowing a fan onto a radiator that doesn't have coolant flowing through it, how does that cool the heads?" Conduction cooling of the heads by the fan reducing coolant temps may be a factor, but not likely much of the reason the fan runs on. Modern engines are being made with increasingly thinner engine castings, that transfer heat into coolant quickly. That, and high pressure efficient cooling systems, have resulted in low amounts of coolant. (a 1950 Ford V-8 held 5 gallons of coolant..and was rated at 100hp, while an 1125 holds .8gal, including the expansion tank) If an engine has been run hard in hot weather, then shut down, it's possible the hot engine could raise coolant temps enough to result in coolant loss. Today's radiators have no expansion space at all, since excess coolant is pushed into the remote expansion tank. That tank has limited capacity. If residual heat causes coolant to expand too much, the tank could overflow. The running fan reduces coolant temp in the rad, so there's less liquid expansion... | ||
| Syonyk |
*mutters annoyedly* I was told that I was nuts when I reported that particular issue. With the stock ECU, in the summer, even not riding hard, I'd have coolant temps up in the 220F range. I live in Albuquerque, 5000', so the boiling point in the summer is lower (water boils around 200). If I saw 225 or so on the coolant gauge in the 15 minutes before shutting down, I was going to leave a puddle. I tried a variety of things, but there was just enough heat that it would blow coolant into the overflow tank, which would then proceed to boil vigorously, and overflow. Even with the overflow tank at the correct level. Race ECU fixed all of this, btw.  I'd guess there's actually a pretty good convection set up between the hot engine & the cooling radiators. | ||
| Two_seasons |
Point taken on the puddle after a hard ride. Experienced that myself when one fan wasn't working. | ||
| Lemonchili_x1 |
Ok, thank you all for your info, I can see the reasoning now. I'm running an E-B-R ECU so I haven't had any temp issues, but the fan running does give the battery a pretty hard time. Funny thing - while looking for info I found a thread on a Triumph forum with a guy trying to figure out a way to make his Speed Triple's fans turn on when he switched off the ignition. |
