Observations of a stuck open thermostat

[Gug]

I have had a stuck open thermostat for going on a year now. To give you a little history, I have called Honda several times only to fall on deaf ears. They would do nothing. When it was brought in in February for the 16K service I asked them to change it out under warranty or even at my expense being it would be torn down anyway and they said there was nothing wrong with it. Again they commented that the manual calls for the bike to run between 1 bar and the hot end of the guage. (They also did not have a thermostat in stock) Well the purpose of this is to show what I have seen as a result of the thermostat being stuck open.

I have seen no significant reduction in milage to speak of. This makes perfect sense though in that the only time it runs under 3 bars is in the colder weather. At temps in the upper 30 to low 40 range I notice maybe a 2-3 mpg difference but that is a several fold reason. I'll list them.

More windshield (all the way up) being used.
My Hondaline Topbox stays on the bike fulltime. (The installation of this reduced my mileage about 1.5 mpg)
More viscous fluids due to cold weather.
Higher idle speed.
Longer warm up times in general.

My lowest mileage I have seen is 39 mpg. That was a one time deal all the riding was in the upper 30's with alot of stops (more warmups). Otherwise in the colder temps I get about 41- 43 mpg in the 30's. Now that is driving slab at 70-75 speedo indicated. In the 30 temps I stay at 1 bar in temp the entire time.

When I get into the 40's, (temp again) My mileage may improve by 1 mpg or so.

Yesterday I drove about 250 miles on the slab in low 50's with full windshield and it got 45.993 mpg gas/mileage calculation. I never got over 2 bars on the slab. When I got in town it went to 3 bars.

Above 60 degrees I run consistently at 3 bars. Again the best mileage I have seen running 70-75 mph on the speedo is 47mpg.

I want to note that when you are driving slab and come into a city within the time of a red light to pass the bike will jump one bar in temp, of course unless it is already at 3 bars. It never goes above that.

So with what I have seen in variation of temps and the temp guage indicator I don't think there is a very wide spread in engine coolant temp between 1-3 bars in general. As noted above sitting for the duration of a red light will bring it up a bar in the 40's and below.


In conclusion, is the bikes fuel mileage compromised? I am certain it is by maybe 1-2mpg being the bikes computer is likely having it run a bit richer when it is reading the coolant temp and it running at less than 3 bars on the guage. But for me that is insignificant. I am still getting 45+MPG on superslab and even in the city 43-44 is normal. It makes no performance difference that is even remotely perceptable to me (allthough I don't ride it hard). As far as doing the repair myself, it's not worth the effort of 3-4 hours labor to fix something that has become negligable to me (I am not mechanically challenged, just mechanically impatient). The only tools I carry outside the Honda toolkit are a credit card, tow service and a cellphone.

I am not saying to follow this observation if this occurs to you. You may have something completely different and could potentially damage something. For me this has worked for about 10K in miles.

 

[wjbertrand]

Beyond that one day, which I posted about separately here, my temp gauge has returned to normal function. It was a cool morning (40s) and I was running 75 mph when I noticed only one bar showing. On the way home that night, after work, I could only reach two bars. This was followed by a few days where the bike took a longer than normal amount of time to reach 3 bars but it always did and stayed there once achieved. Lately (after I acquired, but have not yet installed, the replacement T-stat) the bike has returned to it's normal behavior. Warms quickly to 3 bars and stays there under all circumstances. Obviously the fix is to buy a new thermostat and place it on your work bench! Go figure.

 

[SteveST1300]

I have been fighting this same problem. I took the bike to my local dealer and they checked it out. Now here is what they told me. The thermostat is fine, they said the coolant was a bit low and this is what was causing the problem. I then proceeded to argue ( I mean discuss ) the issue further. I said I had never heard of an engine running cooler because of low coolant. Their mechanic says that the thermistor that transmits the coolant temp to the guage is in the side of the radiator near the top and when the coolant level fell below this level and the air was cold it gave a false reading:bsflag: I said. But none the less they weren't going to replace it. I couldn't take it anymore and had to leave probably never to return! I haven't had time to try another dealer yet but as mentioned above I haven't nseen any negative impact yet. I will probably replace it myself in the near future just for peace of mind.

 

[CrashTestDanny]

Eastbound toward Moonshine I was getting low 30s - windshield all the way up and pushing a 20-30 knot (guesstimated) headwind. Coming back, I got low 40s. In the past I've observed that the windshield all the way up will drop my mileage to low-to-mid 30s.

 

[nm6r]

I have had a stuck open thermostat for going on a year now. To give you a little history, I have called Honda several times only to fall on deaf ears. They would do nothing. When it was brought in in February for the 16K service I asked them to change it out under warranty or even at my expense being it would be torn down anyway and they said there was nothing wrong with it. Again they commented that the manual calls for the bike to run between 1 bar and the hot end of the guage. (They also did not have a thermostat in stock) Well the purpose of this is to show what I have seen as a result of the thermostat being stuck open.

Wow! Dealer incompetence before they even touch the bike.

I noticed a several mpg decrease in mileage when my thermostat failed. The fuel economy would return when the ambient temperature warmed up allowing the engine to approach normal operating temperature.

I would say the manual is being misinterpreted. Normal operation would be to let it warm up to 1 bar before riding. To continue, normal operation would be for the gauge to read 3 bars when at proper operating temperature. Something is wrong if it doesn't reach normal operating temperature (ie. stuck thermostat). I would insist on the dealer replacing it. Once they have the old one out, it will be obvious it is stuck open and be covered under warranty.

BTW, I replaced mine myself to eliminate dealer incompetence.

Ray

 

[Gug]

Wow! Dealer incompetence before they even touch the bike.

I noticed a several mpg decrease in mileage when my thermostat failed. The fuel economy would return when the ambient temperature warmed up allowing the engine to approach normal operating temperature.

I would say the manual is being misinterpreted. Normal operation would be to let it warm up to 1 bar before riding. To continue, normal operation would be for the gauge to read 3 bars when at proper operating temperature. Something is wrong if it doesn't reach normal operating temperature (ie. stuck thermostat). I would insist on the dealer replacing it. Once they have the old one out, it will be obvious it is stuck open and be covered under warranty.

BTW, I replaced mine myself to eliminate dealer incompetence.

Ray

The manual is not being misinterpreted, at least not according to Honda customer service. It's very specific. I went round with these folks twice. Documented the conversation very accordingly. That is what they stick with.

 

[Killtimer]

St-N's down again or I'd just post the link, so from memory. This same discussion took place over at St-N last week. The poster who had a stuck 'stat had been round and round with his dealer a few times. He finally changed it out himself and found that his thermostat had indeed stuck...... but he went a step further. He put some major heat to the unit and ran it through a few hot to cold water cycles. It started closing again. He then really put the heat to it and forced it to open well past it's normal opening, toward the max. Once the total length of the actuation rod was exposed he discovered a ring of crusted green residue that he surmised may have been stopping the unit from closing. After cleaning up the crud, his thermostat worked normally through a bunch of hot cold cycles. His theory is that it's a coolant related problem. Again, I'm posting this from memory so I may be a bit off on the procedure he used, but his green grunge findings I'm sure of.

Anyone else pushed their stuck stat? Any comments on the theory? I know that my dealer has done at least 3 warranty (including one on my '03) replacements so Honda has to be aware of the "issue" I wonder what would happen if someone were to hint that a stuck 'stat "might" affect your emissions. In this day and age that just might get someone's attention. An exhaust gas measurement should show up a problem you would think. I'm just waiting for the tell tale signs on my '05.....not.

Good luck in whatever you decide to do.

 

[nm6r]

Gug, Honda customer service also won't admit to a problem so they are trying to mask it with symantics. We know how the bike is suppose to operate properly. Don't worry about it if you are happy with a stuck thermostat.

I attribute the stuck thermostats to paint flakes in the radiator hose fittings after cleaning a bunch of crap and residue out of the overflow bottle. That would explain the green crusty stuff.

Ray

 

[BigBadblue]

Cold oil does not lubricate nearly as well as properly warmed oil and the sooner you get it to temp the better. You will accelerate engine wear with cold oil. I was the green grunge guy. BTW the paint in the radiator is black, not green like the coolant.
https://www.st-owners.com/forums/showpost.php?p=113691&postcount=27
IMHO I think there is a problem with the coolant solidifying on the t-stat actuator shaft and preventing it from closing, as to why this is happening, I don't know.

 

[msev111]

Bought my bike in October 04 and drove it thru the winter of 04-05 as much as I could. Don't remember any issues where it didn't come all the way up to temp, regardless of ambient temperature. But this winter I have seen the symptoms you guys are describing alot, almost from the onset of cold weather. It frequently doesn't get up to 3 bars and if it's really cold I have seen it warm up, then go back down to 1 bar.

How do you know if you T Stat is stuck open? Is there any way to test without pulling it out? I too asked my dealer about it at the beginning of the winter, he said it was normal, etc.

 

[Gug]

Cold oil does not lubricate nearly as well as properly warmed oil and the sooner you get it to temp the better. You will accelerate engine wear with cold oil. I was the green grunge guy. BTW the paint in the radiator is black, not green like the coolant.
https://www.st-owners.com/forums/showpost.php?p=113691&postcount=27
IMHO I think there is a problem with the coolant solidifying on the t-stat actuator shaft and preventing it from closing, as to why this is happening, I don't know.

Well the question would be how much difference in temperature is the motor at 1,2 or 3 bars? Anyone have this? Being The bike comes up to temp in most cases during the duration of a red light, I would guess it would be no more than 10-20 degrees maximum. Most or all engines can run comfortably on varied temp thermostats anyway. Maybe that's why I have never noticed a heat issue??? In the same breath with oil changes at the 5K interval on synthetic there is no measuable oil consumption. If there is it's only CC's that I can't measure.

Don't get me wrong folks, I know the thermostat is stuck open without a doubt. But I have seen nothing to be alarmed about. If the motor is hypothetically running say at 180 degrees vs 200 degrees (don't know it's temp range) that will make no difference in the performance or wear that I can see. It is still an air/water cooled motor. Not designed to be water cooled exclusively. I'll keep you all posted of any changes that may occur.

 

[nm6r]

I was the green grunge guy. BTW the paint in the radiator is black, not green like the coolant.

This is true. Black paint flakes can be removed from the radiator hose connections. Some with your finger. The rest will require the use of some scotchbrite. My theory is the paint flakes coming off on their own break down to very small pieces and give the appearance of the green grunge due to the color of the antifreeze.

Ray

 

[BigBadblue]

Bought my bike in October 04 and drove it thru the winter of 04-05 as much as I could. Don't remember any issues where it didn't come all the way up to temp, regardless of ambient temperature. But this winter I have seen the symptoms you guys are describing alot, almost from the onset of cold weather. It frequently doesn't get up to 3 bars and if it's really cold I have seen it warm up, then go back down to 1 bar.

How do you know if you T Stat is stuck open? Is there any way to test without pulling it out? I too asked my dealer about it at the beginning of the winter, he said it was normal, etc.

It should aways go to 3 bars fairly quickly and stay there no matter what the ambient temp is. Your t-stat is stuck open, your symptoms are EXACTLY like mine was. No test that I know of, I would bet a bunch that yours is stuck too.
Here is a drawing depicting what I found.

 

[Gug]

It should aways go to 3 bars fairly quickly and stay there no matter what the ambient temp is. Your t-stat is stuck open, your symptoms are EXACTLY like mine was. No test that I know of, I would bet a bunch that yours is stuck too.
Here is a drawing depicting what I found.

Thanks for the feedback. I know it's stuck open. But it makes no difference to me. It runs fine. Today was 73F here. It was at 3 bars the entire time I drove home from work. I just got back from a ride in 55F temps and it ran at 2-3 bars. When I stopped at a red light it came up to 3 bars. I have had this for about a year now with no ill effects. I've come to a conclusion that if it can come up a bar at a red light all in less than a minute, it can't be a dramatic coolant temperature change taking place. So it's running as far as I am concerned in a relatively safe temp range. I feel comfortable enough with it to leave for California tonight. I'll keep an eye on it and if it acts up I'll bring it in for repair. Otherwise I'll just ride it. In calling Honda they said it was fine. I just documented and recorded the conversations I had with them after having listened to others on this board. I'm done calling them.

 

[BigBadblue]

Thanks for the feedback. I know it's stuck open. But it makes no difference to me. It runs fine. Today was 73F here. It was at 3 bars the entire time I drove home from work. I just got back from a ride in 55F temps and it ran at 2-3 bars. When I stopped at a red light it came up to 3 bars. I have had this for about a year now with no ill effects. I've come to a conclusion that if it can come up a bar at a red light all in less than a minute, it can't be a dramatic coolant temperature change taking place. So it's running as far as I am concerned in a relatively safe temp range. I feel comfortable enough with it to leave for California tonight. I'll keep an eye on it and if it acts up I'll bring it in for repair. Otherwise I'll just ride it. In calling Honda they said it was fine. I just documented and recorded the conversations I had with them after having listened to others on this board. I'm done calling them.

I would think that just short intermittent trips would be the most harmful because the oil would not get up to operating temp quickly at all before it was turned off, where as a long ride like the one you have planned would not have this problem.

 

[Gug]

I would think that just short intermittent trips would be the most harmful because the oil would not get up to operating temp quickly at all before it was turned off, where as a long ride like the one you have planned would not have this problem.

I agree there also. If you leave to early it can fall right off the guage in the mid to low 30's. But I just let it warm up longer and generally hit 3 bars. It will drop back to 1 bar but runs fine. That is where the reduction in mileage occurs though, from the longer warmups. Down the road when the opportunity presents itself, I will eventually have it taken out and replaced. Ironically on my 16K service I had them change out the coolant and had asked them to change the thermostat, descibing the issues. They changed out the fluid and said the thermostat was operating properly. I am sure they changed out the fluid and started the bike and let it idle for 10-15 minutes, it came up to 3 bars and did not overheat. It satisfied them as not being a problem. Unfortunately I am sure they did not take it for a ride like I had asked in January when I had dropped it off. They would have seen what occurs, although they said again that it was not uncommon to run as low as one bar and that's what Honda tech and he manula told them as well. Unfortunately this is a unique problem that if handled properly likely won't be a problem. In the same breath I am tired of the revolving door of symantics I have gotten at 2 dealers and Honda itself. Their customer service sucks!

 

[wjbertrand]

Don't get me wrong folks, I know the thermostat is stuck open without a doubt. But I have seen nothing to be alarmed about. If the motor is hypothetically running say at 180 degrees vs 200 degrees (don't know it's temp range) that will make no difference in the performance or wear that I can see. It is still an air/water cooled motor. Not designed to be water cooled exclusively. I'll keep you all posted of any changes that may occur.

It's probably running cooler than 180F. The ST's T-Stat is marked 82C or 179.6F.

 

[04ST1300a]

Anyone else pushed their stuck stat? Any comments on the theory?

I tried that last night by running on the centerstand with a towel on the radiator to block airflow. The temp guage went to 4 bars which is 230 deg. measured using a IR temp guage on the radiator endcap, then to 5 bars/240 deg.
This morning it was 50 deg oat, it still wouldnt get past 2 bars in town or 1 bar on the hiway. So that didnt help.....

 

[NormanPCN]

It's probably running cooler than 180F. The ST's T-Stat is marked 82C or 179.6F.

Interesting info. The service manual only gives the full open temp, 203F as I remember.

 

[Gug]

Interesting info. The service manual only gives the full open temp, 203F as I remember.

Your right on the mark Norman. It begins to open from 176-183F and 203F fully open it is!

I don't know this motor that well, but having just looked this up in the manual is it sound to assume that 1 bar the thermostat is beginning to open and 3 bars is fully open? The fan then kicks on when coolant temp exceeds fully open position?