Sticky Thermostat?

[Dj Brady]

I'm thinking my thermostat is sticking closed from cold start because twice now it's behaved a little erratically. Cold start, now bars for a few minutes and then it jumps up pretty quickly. Once on the road, it kicked up to 6 bars and then dropped back down to far and this morning while letting it shake off the winter blahs in the shed, no bars for about 4 minutes and then it rose pretty quickly (15 seconds or so) to 4 bars and leveled off.

Does that scream anything besides sticky thermostat? Can I find a stat swap write up at fjrtech?

Thanks y'all.

 

[scubatech]

I'm thinking my thermostat is sticking closed from cold start because twice now it's behaved a little erratically. Cold start, now bars for a few minutes and then it jumps up pretty quickly. Once on the road, it kicked up to 6 bars and then dropped back down to far and this morning while letting it shake off the winter blahs in the shed, no bars for about 4 minutes and then it rose pretty quickly (15 seconds or so) to 4 bars and leveled off.

Does that scream anything besides sticky thermostat? Can I find a stat swap write up at fjrtech?

Thanks y'all.

Dj,

Could be coolant temperature sensore?

 

[Dj Brady]

possibly but symptoms don't match... all the symptoms point to a thermostat sticking closed and then popping open allowing the backed up hot water to run past the temp sending unit in one rush and bring the temp up on the display... that's my thinking anyway.

 

[Geezer]

Your coolant level where it should be?

Maybe there's an air bubble in the system from a recent coolant change.

 

[Dj Brady]

judging by my reservoir, yeah, coolant level is fine.

No coolant tech work done since last spring, before I purchased the bike so I don't think there's any bubbles... plenty of miles put on since then.

 

[RaYzerman19]

Possible thermostat issue, but before going there, is it repetitive in a "normal" environment, meaning not too cold ambient temperature, and with some airflow (riding). If it jumps to 6 bars on a GenII that is not too awful, although it shouldn't jump unless the sensor is getting real hot for some other reason. Another thing to check is the rad cap. Bottom line, see how it goes on some road tests before you decide to strike out on a LD trip.... if it's repeating, then yes change the stat.

 

[jcyuhn]

Feels like a thermostat on the way out to me. I vote change it out. It's normal for the coolant temperature to overshoot a little bit then settle down to steady state normal on a cold engine. I can see this on my cars with an analog non-idiot temperature guage. On the FJR I would not expect enough overshoot to light up one or two additional coolant bars - that would worry me.

 

[Dj Brady]

of the two times I've seen it, it only overshot once by 2 bars when I started it and hit the road. Both times it stayed "cold" (zero bars) for a few minutes and then quickly rose to warm temp, increasing bar by bar in a matter of about 5 seconds.. so it wasn't a "digital" jump or glitch, but one that signaled the temp sensor got a rush of hot water and was rapidly increasing in temperature to reflect that.... which leads me to believe the t-stat was stuck closed until it 'freed'....

out of curiosity, does anyone have a cooling system schematic that shows where the temp sending unit is in relation to the thermostat in terms of water flow?

Do these bikes have one or two temp sensors? On my car, I have 2. One for the computer and one for the dash.

 

[scubatech]

of the two times I've seen it, it only overshot once by 2 bars when I started it and hit the road. Both times it stayed "cold" (zero bars) for a few minutes and then quickly rose to warm temp, increasing bar by bar in a matter of about 5 seconds.. so it wasn't a "digital" jump or glitch, but one that signaled the temp sensor got a rush of hot water and was rapidly increasing in temperature to reflect that.... which leads me to believe the t-stat was stuck closed until it 'freed'....

out of curiosity, does anyone have a cooling system schematic that shows where the temp sending unit is in relation to the thermostat in terms of water flow?

Do these bikes have one or two temp sensors? On my car, I have 2. One for the computer and one for the dash.

You could be right. The newer thermostats I have seen fail usually stick open as a fail safe mode. Any way good luck on it.

 

[escapefjrtist]

I would change the thermostat as cheap insurance against future problems. On GEN II's it's an easy job, the stat is located just behind the *glove box* on the outside of the frame. Access by removing the left lower fairing piece, a couple hose clamps, a screw and the housing is on the bench.

Mine will be changed in the next couple months too. The thermostat has been acting up...or I should say, not acting what I consider normal or how it behaved in the previous 40K miles.

Good luck!

--G

 

[Constant Mesh]

There's always a small coolant flow circulating through the engine past the temperature sensor even with the thermostat in its closed position. The flow splits off from the coolant header pipe above the engine and goes to the high idle wax motor at the throttle body assembly. The flow passes through the wax motor and goes to the radiator. This flow is just a small percentage of the total flow when the thermostat is fully open.

 

[RaYzerman19]

The coolant sensor is on the upper water pipe above the valve cover, right side. The thermostat has a bleed hole, which should be positioned at 12:00 o'clock.