Coolant Temperature Sensor Mystery

[atomsplitter]

Good info- thanks. At this point not intermittent, just a one time occurrence. We'll see over time if that changes....

Glad to help.

 

[zenbiker]

Has anyone had a coolant temperature sensor go bad on the 2.5s? I was about 10 miles from home when my engine check light came on and a temperature warning. It brought up the temperature gauge and it was pegged all the way to the top (solid red)! I pulled over immediately.

The bike didn't seem overly hot. I checked the coolant level and it was somewhat below the low mark, but not enough, I would think, to cause a problem. There was definitely coolant in the tank. I pulled the seat and checked the fuse for the fan and it was good. I prepared to hitch-hike back home to get my trailer, but thought I'd fire her up again just to see and the temp gauge read normal- too soon to have cooled that quickly.

I rode home and, although the engine light stayed on (normal after throwing a code), the coolant temperature stayed in the normal range. Once there I topped off the coolant and hooked up TuneEcu. It showed P0117 (coolant temperature sensor) and P0704 (clutch switch 1) codes. I cleared both and have since ridden the bike over 100 miles without issue- runs great and not hot.

From what I'm reading about the coolant sensor code- it usually indicates a bad sensor. I'm also wondering, given just how much that POS clutch switch affects seemingly unrelated things (like your gas gauge, for example) if that might not have been the cause. I tinkered with the "tang" on it for the umpteenth time and it's no longer throwing a code. Or, best case scenario, if the coolant being slightly low (maybe a pint or less) was it- but I don't think the bike was ever really overheated.

Now, I'm just a bit paranoid that I'll take a long trip and it will act up again.

p.s. the sensor is located behind the radiator in the thermostat housing (fun to get to). Related information is on pages 876-877, 656-659, and 600 in the manual

 

[zenbiker]

I think it's intermittent though like yours. It's running fine now. You mean even so- might show an issue? I'll give it a go.

Hoping to do a 4 - 5 day trip next week (to be determined). I just changed the oil and put on a new rear tire. What else does she want?

I think it's great that you were notified of a below optimal coolant level! You should feel great about this!

 

[Journeyman]

I think it's great that you were notified of a below optimal coolant level! You should feel great about this!

I haven't had another incident, so assuming it was the low coolant level only.

 

[Journeyman]

Update- Two more events. I thought I reported the first incident here, but looks like I actually posted on @Nashvegas post here...

Help, please! Engine overheating 🥵

No, and I feel extremely confident that has nothing to do with it. I've been running Zerex G05 for over 20,000 miles. This first happened many many miles ago (10-15K) and just came up again for the first time since then. Update- TuneEcu shows the P0117 Coolant Temperature Sensor code. I cleared...

www.r3owners.net

Two months ago... Was riding (not stopped) about 5 miles from home and looked down to see the temp gauge on red. Pulled over and checked- It didn't seem overly hot (no ticking, etc.). A few attempts after waiting and restarting and it kept indicating hot. Wish I had remembered @atomsplitter 's advice to check for puking into overflow container. Caught a ride home to get my trailer and later at home once cooled it was fine on startup and long idle and many, many, rides since. TuneEcu showed the P0117 Coolant Temperature Sensor codeMy theory at the time was maybe it had air in system from previous radiator service and bouncing around in the trailer on the way home burped it out.

So, all is well until a couple of days ago riding The Snake. Bike was fine until on the way home it started running hot on the scale, but never hit all the way red. This, again, is while moving.

Next day I opened the radiator and ran it until warm. I did see fairly large air bubbles surfacing and then, what I would guess would be normal without the cap, boiling (very small bubbles). It puked a little from the radiator cap opening, so I killed the bike and filled to top. Capped it and started bike and it ran normally at idle and the fans both soon kicked on. Took it riding and it was fine. Took it today for five hours of spirited riding on twisties and temp remained completely normal.

Does it sound like I just had some trapped air that never got purged until now, or something else going on that will likely rear its head again- probably at the most inconvenient moment? Mentioned earlier in this post, or the other one, are failing pump or thermostat and in addition to temperature sensor and PWM controller. Hoping the trapped air theory wins by a majority though

 

[atomsplitter]

What is the level in the overflow tank? That tank provides a loop seal to the system. The coolant is 50% water and if the overflow tank is empty or too low to quench the steam from the radiator overflow you lose water volume over time, but the antifreeze (a very poor coolant) remains behind.

Background: The radiator and cooling system are engineered to operate at a given temperature to maintain engine material expansion and contraction limits. System design of the cooling requires an upper limit of coolant temperature. The water pump, radiator, thermostat and overflow tank are all sized to maintain the engine within the design parameters under a very very wide range of conditions. So, overheating can be a result of low coolant flow from the pump, inadequate flow thru the radiator (air flow thru the rad to remove the heat of clogged water passages). To ensure the radiator isn't the problem flushing the external cooling fins with water to ensure air flow isn't impeded is the first step, then flushing the cooling water channels to ensure no corrosion product buildup is the next. Once the radiator is verified as no longer the source of overheating, move on to the water pump. If the pump is working as it should, i.e. water is being moved around the system then cavitation can only occur 2 ways, steam ingestion or air ingestion. In the case of steam ingestion that occurs when the coolant is at saturation temperature for the fluid and at the suction eye of the impellor the drop in pressure flashes the coolant to steam. The water pump cannot efficiently move steam, so system flow drops off and temperature rises. Air ingestion requires an air source into the suction eye, usually when there is inadequate coolant in the system at start up (no coolant visible in the radiator).

I'm going to make a side note here. Antifreeze (that 50% of the coolant) is a very poor coolant because of its low specific heat capacity. The actual coolant is the water (the other 50%) because it has a very high specific heat capacity. It takes on average about 1190 BTU's to turn one pound mass of water into one pound mass of steam at a saturation temperature of 212 degrees Fahrenheit (atmospheric pressure). The cooling system operates above atmospheric pressure, so the coolant saturation temperature is also raised. The lift pressure of the radiator cap (relief valve) sets the maximum system pressure and thus limits the saturation temperature of the coolant to the set system pressure. You can find those values on any steam table (you can use AI to find the temperature=pressure relationship. For example: At 14 psig (≈ 28.7 psia, ≈ 2 bar absolute), the saturation temperature of water is about 120 °C (≈ 248 °F).). This is all predicated on a sealed system where-in the coolant is a fixed volume (water solid) and all components are operating as designed.

The coolant mass changes from cold to hot because water expands as it heats. This expansion removes coolant mass from the system while the system volume remains constant. When the system cools down the contraction of the coolant creates a vacuum in the system that draws coolant from the overflow tank back into the system to maintain total system volume this a constant volume system. That's why the overflow tube from the rad cap to the coolant tank goes to a cap with a straw to the bottom of the overflow tank. So, the hot liquid from the radiator is quenched in the overflow tank preserving the water (less evaporation) and has a suction path of coolant in the tank back to the radiator to maintain the system full.

 

[Journeyman]

What is the level in the overflow tank? That tank provides a loop seal to the system. The coolant is 50% water and if the overflow tank is empty or too low to quench the steam from the radiator overflow you lose water volume over time, but the antifreeze (a very poor coolant) remains behind.

Background: The radiator and cooling system are engineered to operate at a given temperature to maintain engine material expansion and contraction limits. System design of the cooling requires an upper limit of coolant temperature. The water pump, radiator, thermostat and overflow tank are all sized to maintain the engine within the design parameters under a very very wide range of conditions. So, overheating can be a result of low coolant flow from the pump, inadequate flow thru the radiator (air flow thru the rad to remove the heat of clogged water passages). To ensure the radiator isn't the problem flushing the external cooling fins with water to ensure air flow isn't impeded is the first step, then flushing the cooling water channels to ensure no corrosion product buildup is the next. Once the radiator is verified as no longer the source of overheating, move on to the water pump. If the pump is working as it should, i.e. water is being moved around the system then cavitation can only occur 2 ways, steam ingestion or air ingestion. In the case of steam ingestion that occurs when the coolant is at saturation temperature for the fluid and at the suction eye of the impellor the drop in pressure flashes the coolant to steam. The water pump cannot efficiently move steam, so system flow drops off and temperature rises. Air ingestion requires an air source into the suction eye, usually when there is inadequate coolant in the system at start up (no coolant visible in the radiator).

I'm going to make a side note here. Antifreeze (that 50% of the coolant) is a very poor coolant because of its low specific heat capacity. The actual coolant is the water (the other 50%) because it has a very high specific heat capacity. It takes on average about 1190 BTU's to turn one pound mass of water into one pound mass of steam at a saturation temperature of 212 degrees Fahrenheit (atmospheric pressure). The cooling system operates above atmospheric pressure, so the coolant saturation temperature is also raised. The lift pressure of the radiator cap (relief valve) sets the maximum system pressure and thus limits the saturation temperature of the coolant to the set system pressure. You can find those values on any steam table (you can use AI to find the temperature=pressure relationship. For example: At 14 psig (≈ 28.7 psia, ≈ 2 bar absolute), the saturation temperature of water is about 120 °C (≈ 248 °F).). This is all predicated on a sealed system where-in the coolant is a fixed volume (water solid) and all components are operating as designed.

The coolant mass changes from cold to hot because water expands as it heats. This expansion removes coolant mass from the system while the system volume remains constant. When the system cools down the contraction of the coolant creates a vacuum in the system that draws coolant from the overflow tank back into the system to maintain total system volume this a constant volume system. That's why the overflow tube from the rad cap to the coolant tank goes to a cap with a straw to the bottom of the overflow tank. So, the hot liquid from the radiator is quenched in the overflow tank preserving the water (less evaporation) and has a suction path of coolant in the tank back to the radiator to maintain the system full.

I really do appreciate the time you put into that. You definitely know your stuff and, although I understand most of what you're explaining, I may still have some questions (even though the answers are probably already in there.)

I'm going to need to be more vigilant about paying attention to what exactly is happening and what steps I'm taking to address it. I've just topped up the bottle cold to the upper level mark so I can keep better track. Just reading over the manual again and I see that should be done with the bike level, so I'll adjust as necessary.

So, I'll be watching this closely and just hoping it's a case of trapped air, but life is never that easy.

Wondering if based on some of my observations what your guess might be as to what's going on. The last time it went full red on the dial I noticed the radiator cap was not hot, which makes me wonder if it's a sensor issue. I got down to check the bike and it was hot (of course), but since I usually avoid getting close to the pipes and engine when hot I couldn't say it was overly hot. There was no ticking noise.

The second observation to ask about was when I got back from the last incident and it just ran hot (not in red) and I opened the cap, topped it just a little and let it warm up leaving the cap off. Once to a certain temp some fair sized bubbles came up, then it just had very small bubbles (like a slow boiling kettle). Is this normal without the cap on? Giving it some throttle caused it to puke, which seems right- is it? I killed it and refilled everything and have done more than several hundred miles with normal temps on the gauge since then.

Does any of this suggest a problem in and off itself, or do I just need to see what happens next, look for puking into the overflow bottle and see if my overall levels change?

Again, thanks for your insights....

 

[atomsplitter]

There are a couple things you can do to test what's happening with your cooling system. The easiest thing is make sure the rad is full and the overflow tank is above the MIN mark cold. Then start the bike and let it idle and watch the overflow tank for a level/temperature increase. The rad fan will kick on when it senses the coolant is getting too hot. When that happens the level in the overflow tank should be rising as the coolant expands in the cooling system. Keep the bike idling and monitor the tank level, it should stabilize as air being drawn across the rad will stabilize the engine temps. If the level continues to rise and the fan is working, there isn't enough air being drawn across the rad cooling fins suggesting the rad fins are possibly blocked and need backflushed to free up air flow. If the fins are clean, then the problem is total coolant flow through the system, i.e. water isn't flowing through the rad fast enough to carry off the heat. If the level stabilizes with the cooling fan running over a period of time, then two possibilities occur. Either the thermostat is not fully opening, or the water pump output flow is too low. The easiest (and cheapest) to start is replace the thermostat. The thermostat setting can be tested using a string and hot water, but if you're going to that trouble, it's just easier to stuff a new thermostat in there and call it a day. If a new thermostat doesn't fix the problem that means the water pump isn't pumping enough water through the system to cool the heat load and that usually entails a new impellor, which on these Rockets is probably not a consumable item, i.e. you gotta replace the pump.

The dash temperature sensor would appear to be working fine as it is telling you the coolant is overheating, so idling the bike until the rad fan kicks on will demonstrate that sensor is working as well. It seems to me that the problem you describe is that under load the system isn't getting adequate cooling. Test the system as described above and let me know what happens. Also, when in doubt you always have the option of taking it to your local dealer for diagnosis and repair.

 

[Journeyman]

There are a couple things you can do to test what's happening with your cooling system. The easiest thing is make sure the rad is full and the overflow tank is above the MIN mark cold. Then start the bike and let it idle and watch the overflow tank for a level/temperature increase. The rad fan will kick on when it senses the coolant is getting too hot. When that happens the level in the overflow tank should be rising as the coolant expands in the cooling system. Keep the bike idling and monitor the tank level, it should stabilize as air being drawn across the rad will stabilize the engine temps. If the level continues to rise and the fan is working, there isn't enough air being drawn across the rad cooling fins suggesting the rad fins are possibly blocked and need backflushed to free up air flow. If the fins are clean, then the problem is total coolant flow through the system, i.e. water isn't flowing through the rad fast enough to carry off the heat. If the level stabilizes with the cooling fan running over a period of time, then two possibilities occur. Either the thermostat is not fully opening, or the water pump output flow is too low. The easiest (and cheapest) to start is replace the thermostat. The thermostat setting can be tested using a string and hot water, but if you're going to that trouble, it's just easier to stuff a new thermostat in there and call it a day. If a new thermostat doesn't fix the problem that means the water pump isn't pumping enough water through the system to cool the heat load and that usually entails a new impellor, which on these Rockets is probably not a consumable item, i.e. you gotta replace the pump.

The dash temperature sensor would appear to be working fine as it is telling you the coolant is overheating, so idling the bike until the rad fan kicks on will demonstrate that sensor is working as well. It seems to me that the problem you describe is that under load the system isn't getting adequate cooling. Test the system as described above and let me know what happens. Also, when in doubt you always have the option of taking it to your local dealer for diagnosis and repair.

All good - thanks! Let me add a couple of things. It's very intermittent, as in months go by with no elevation on the gauge, but this gives me something to look for when it happens and I'll also just watch to see what the overflow tank does next time at idle until fans come on.
This thing is a super PIA to get to the thermostat. As you said, once there I'd go ahead and replace it and, depending on the cost of that pump, probably it as well.
This is my third Rocket for a total of about 100k miles and I've never taken it to a dealer, preferring to do my own work- often with the advice from folks like you- thanks!

 

[atomsplitter]

No problem. To expand a bit on cooling systems, consider your radiator is the heat sink or heat exchanger where engine heat is dumped to atmosphere. The second law of thermodynamics says that heat can only go from a high source to a low source and never in the reverse. The physics behind any heat exchanger is heat flow is based on the mass flow rate of the hot fluid and differential temperature of the heat sink (measured in either degrees Fahrenheit or enthalpy). The equation is Q-dot (heat rate) = m-dot (mass flow rate) times delta T (temperature (or h, enthalpy). Q = m ΔT or Q = m Δh The dot above the Q and m (when used) are flow rates, i.e. mass flow and heat flow.

That's why diagnosing symptoms of heat exchange that's not right can be limited to just a few components. The coolant has a constant specific heat capacity that doesn't change unless you add or subtract water to the coolant mix. If you want maximum cooling replace the antifreeze with water so the system is 100% water and you have the maximum cooling available. The more antifreeze you add the lower the specific heat capacity or put another way the fewer BTU's per pound mass the coolant will carry. Therefore, cooling is a function of specific heat capacity of the coolant (BTU's/lbm) flow rate of the coolant and the differential temperature of the coolant to heat sink (atmosphere). The size of the radiator affects the total volumetric flow rate that can be achieved thru the system (i.e. limiting factor). The Rocket's radiator is sized to handle the severest conditions, so unless the radiator is blocked on the air side or liquid side heat exchange should be constant. That's why I recommend looking at the rad first, it's the heart of the process.