Low coolant mimicked failed thermostat

[BC Rider]

Just a post in case it helps anyone else.

It has been getting colder out here and my bike refused to warm up to the customary 3 bars, unless idling at a standstill.

I figured it could be the dreaded failed thermostat, but topped up the coolant before the next days commute (at even colder ambient temperatures).

Problem solved. Got the three bars back.

 

[curmudgeon]

Somehow that seems backwards. Anybody have an explanation how low coolant could cause the temp to run lower?

Phil

 

[Mellow]

Could an air bubble over the sensor cause a false reading?

even then.. wouldn't that 'air' get hotter than the coolant?

That's strange.

 

[Mellow]

Good point.. beats me...

 

[curmudgeon]

On ST1100's when the radiator was low the temperature indication showed hotter. I have to agree with Joe.

Phil

 

[BC Rider]

Sure, the air would get hot, but would that sensor work correctly in air?
I think a thermometer meant to function in liquid would NOT pick up correctly in an air pocket.
Just my guess.

I believe the coolant temperature sensor is located in the thermostat housing, which is pretty close to the top of the system. I agree with you that the heat transfer to the temperature sensor from air will be substantially lower than from the liquid coolant.

Perhaps a low coolant level (combined with cold outside air whistling past the thermostat housing) can result in the problem I had which showed the temperature dropping as I sped up.

I've also read that the sticking thermostat can be an intermittent problem. So my "solution" could be temporary. If it is, I will post a follow-up on this thread. At this point I'm crossing my fingers and hoping it lasts. :

 

[Larry Ramel]

You are correct, sensors will not read correctly, if at all in most systems if not immersed in coolant. If it was low enough not to cover the sensor that could have caused the problem. Time will tell, keep us posted.

 

[Killtimer]

The problem can be intermittent at first with the 'stat only sticking once in a while. I'd keep an eye on it (and a spare 'stat and o-ring in my spares drawer).

 

[dduelin]

The problem can be intermittent at first with the 'stat only sticking once in a while. I'd keep an eye on it (and a spare 'stat and o-ring in my spares drawer).

+1

Isn't the usual failure mode is for the thermostat to stick intermittedly for period of time? Mine took about 8 or 10,000 miles between first symptoms and stuck for good.

I can't see how topping off the overflow tank increases coolant temp. The temp sensor is located well below the top of the cooling jacket so it seems to me that there is little likelihood of an air bubble being created and sustained within the thermostat housing where the sensor is located.

 

[Blrfl]

I can't see how topping off the overflow tank increases coolant temp. The temp sensor is located well below the top of the cooling jacket so it seems to me that there is little likelihood of an air bubble being created and sustained within the thermostat housing where the sensor is located.

:chicken: It doesn't increast the coolant temperature, but it does get coolant to the ECT sensor. The sensor screws into the back of the thermostat housing, which is at the very top of the cooling system. (See item 22 on the Water Pipe page of the parts catalog.)

:chicken: I've got some experience with this since my ST leaks when it's full. The sensor is probably fully-imersed during warm-up while the system is in bypass, but as soon as the thermostat opens, the level in the housing drops, exposing the ECT to air. The ECU starts getting bogus information about the actual engine temperature and feeds it to the temperature gauge and makes fueling decisions based on it. I suspect that this may be one of the factors behind my poor fuel economy.

--Mark

 

[larryensley]

I would be more concerned with where the lost coolant went than anything else. How low was the coolant. You should have pulled coolant from the reserve tank long before the radiator got low enough to cause an issue with the guage. Was the reserve tank empty? The proper way to bleed the system is to fill the reserve tank to fill mark,fill radiator to top of cap neck, start bike and let it idle not touching the throttle for 3 or 4 minutes with the cap off. when bike is warm blip the throttle several times which will force any traped air out of the system. Refill the radiator, install the cap, check the reserve tank, fill to full mark.

 

[05ST1300ABS]

Just a post in case it helps anyone else.

It has been getting colder out here and my bike refused to warm up to the customary 3 bars, unless idling at a standstill.

Just wondering..what year is the bike, how many miles on this bike, and has the coolant ever been changed prior to this.?

 

[dduelin]

:chicken: It doesn't increast the coolant temperature, but it does get coolant to the ECT sensor. The sensor screws into the back of the thermostat housing, which is at the very top of the cooling system. (See item 22 on the Water Pipe page of the parts catalog.)

:chicken: I've got some experience with this since my ST leaks when it's full. The sensor is probably fully-imersed during warm-up while the system is in bypass, but as soon as the thermostat opens, the level in the housing drops, exposing the ECT to air. The ECU starts getting bogus information about the actual engine temperature and feeds it to the temperature gauge and makes fueling decisions based on it. I suspect that this may be one of the factors behind my poor fuel economy.

--Mark

The ECT sensor isn't the highest location in the system. The outlet side of the coolant system runs uphill from the thermostat housing into the radiator plus the hoses that connect the SE thermal valve and the input/output hoses above the oil cooler are all volume at or above the water temp sensor. I believe there is some water jacket volume in the cylinder heads above the thermostat as well. The highest place is the radiator fill.

I suppose the system could be really low and cause your problem but would simple topping up of the tank to the full line be enough volume to replace all of the above?

 

[Blrfl]

The ECT sensor isn't the highest location in the system...

Good points. No more posting after :chicken:! (Where are the smileys for stuffing and green bean casserole?)

BC, does yours leak after you've topped it off?

--Mark

 

[BC Rider]

05ST1300ABS>> Just wondering..what year is the bike, how many miles on this bike, and has the coolant ever been changed prior to this.?



2003, around 20,000 km, changed out the coolant last year.

Blrfl>> BC, does yours leak after you've topped it off?

Mark - never seen coolant on the ground. I don't believe I have a leak as the amount I've added over the years has been negligible. Never seen evidence of leakage around any of the hose junctions.

Larry - I added about a cup or 250 ml....so given the capacity of 3 quarts or so, I'm guessing I was about 10% low.


Anyway - today -2C and 3 bars. So far so good.

 

[BC Rider]

Just a follow-up as promised.


Looks like my thermostat failure was intermittent as reported by some others here. My theory of low coolant causing the problem has over the last two weeks been thoroughly discredited :

For instance, this morning on the drive to work at 1C, my bars dropped to no bars when moving, but then ramped up to as high as 3 bars when idling in traffic.

Looks like a new TurboTom thermostat is in my future.

Thanks for all the comments and discussion here.

 

[mageerc]

I would think that whether or not the sensor read correctly in an air bubble would be much less important than why the coolant is low in the first place. Obviously you have a coolant leak that needs to be addressed.

 

[Highway Troll]

Not really bike related but honda related. My SO's 2002 odyssey developed a very irregular idle sometime ago. Cause low coolant level!!
took it to mother honda,tech topped up coolant and voila its fixed. Air on sensor he stated.
Now my question- anybody had these symptoms with the coolant leak??

BTW coolant was about 1 litre low.

 

[RibsST1300]

I Rode My 06 ST about 300 miles yesterday in 45 air degree temps, I never got over 1 bar until the end of the trip, the air temp rose to almost 50, and I got 2 bars for a while, but then down to one bar as temp dropped again. I guess I will check my coolant level. The bike came back from the Dealer recently, and has only been run 500 miles since June.....(now has 10,800)

 

[curmudgeon]

I'm just glad my instinct was right about low coolant not causing temp to run cool. I still don't see how that could happen, and as it turns out it didn't.

Phil