Changing the Thermostat

SparrowHawkxx · Aug 11, 2019

Surprisingly I could not find anything threads already started about actually changing out the thermostat. I wanted to check to see if there was anything I should know besides what was in the service manual.

The change out procedure in my service manual (page 6-4 and 6-5) just shows the thermostat orientation and torque values for the 3 housing bolts. It looks like the only thing I need to order is a new thermostat, no gasket is shown. The parts diagram (Radiator Hose diagram) shows the same thing.

So when I get my parts and take the thermostat out there is a rubber gasket around the edge of the thermostat but there is also a silicone RTV sealant between the cover and the thermostat. So I am wondering do I just stick the new thermostat in and put it back together or wait and get some RTV to install it.

I figured I better wait and get some RTV. I ordered a tube of Water Pump and Thermostat RTV – link

I believe the RTV was put in at the factory but I am not 100% sure about that. I bought my 2013 Tenere new and have done most of the maintenance but have had some work done where they could have had the thermostat cover off and put it back on with the RTV. Either way I don’t think it hurts to install the new thermostat with the RTV.

Does anyone have any experience or input on this?

Don in Lodi · Aug 11, 2019

Looks like the thermostat has a rubber gasket around the edge, it's an 'assembly'. Many auto makers use this method. I have never seen a t-stat housing sealed with silicone. Why do you need a thermostat change?

RonH · Aug 12, 2019

Yea, I think no prior threads on the change because far as I can tell no one has ever changed the thermostat. Also it shouldn't matter it doesn't seem like, but sometimes the thermostat should be turned to a specific position. My Ford diesel is this way. Probably not an important detail, but put the new one in exactly same orientation as the old one.

SparrowHawkxx · Aug 12, 2019

Don in Lodi said:
Looks like the thermostat has a rubber gasket around the edge, it's an 'assembly'. Many auto makers use this method. I have never seen a t-stat housing sealed with silicone. Why do you need a thermostat change?

Thanks Don for the quick reply. Your short reply helped me a lot.
Yes, the thermostat has the rubber gasket around the edge so I was surprised to find there was RTV on top of it. As soon as I read your reply it dawned on me what I think happened. When I had the bike in being worked on a couple years ago I was just told they spilled some coolant is why there was some on the bike. I now think that is when the RTV was put on. I will go ahead and put it back together now and not put any RTV on the thermostat. I think that solves that dilemma. Thanks for your help.

Now to answer your question why I need a thermostat change.
I think the thermostat was starting to stick.

I normally keep the engine coolant temperature on the top display and just occasionally monitor it. The best I can remember, when I am just cruising down the highway at 65 mph. the temp stays right at 170. When going slow or stopped, especially in hotter temperatures, the engine temp climbs and the fan cycles as normal between about 222 and 212F.

I was on a trip a 2 weeks ago and started noticing the temp staying about 178F, not a big deal just thought it was odd that it was running hotter than normal so I started watching it closer. On the way home it started out staying at 170 then after riding a while it would sometimes get up to about 204 then creep back down to about 182. The outside temp got up to about 95 but I don’t ever remember it doing this before under the same conditions.

Checked it out at home. Nothing blocking the intake to the radiator. Shining a light behind the radiator I could see the fins looked perfectly clean. Coolant looked like new and filled to the top. Reservoir was full to the top line. No leaks from the water pump or anywhere else. I thought the thermostat may be sticking or possibly the temp sensor may be drifting some but I am not so sure a sensor would fail like that. The thermostat and sensor are right there together on the bike so I figured if I was going to have to take everything off including the throttle bodies to get there I would order both the thermostat and sensor and probably just replace the sensor anyway whether it was bad or not.

2013 Tenere, bought it new and have had it 6 ½ years and 89,500 miles.
Coolant was changed once, 2 years ago with 48,000 miles.

SparrowHawkxx · Aug 12, 2019

RonH said:
Yea, I think no prior threads on the change because far as I can tell no one has ever changed the thermostat. Also it shouldn't matter it doesn't seem like, but sometimes the thermostat should be turned to a specific position. My Ford diesel is this way. Probably not an important detail, but put the new one in exactly same orientation as the old one.

Yes, you are correct on the thermostat position. As I mentioned above the service manual does show the thermostat orientation. Page 6-5 in my manual.

However, the only instruction is just "Install: Thermostat:
Below that they have a diagram and a tip.
TIP: Install the thermostat with the breather hole "a" facing forward.

Thanks for your reply.

Don in Lodi · Aug 12, 2019

Exactly, some breathers have a little brass dingle in them, sometimes you need a really bright light from the back side to see the notch in the rim. I've drilled a1/16" vent hole in some if the system orientation seems like an airlock might be a problem. The Tenere is very vertical, a very nice system to fill. The vent needs to be in the most 'up' orientation available. The bulb and spring always go towards the engine heat.

Fortech · Aug 12, 2019

SparrowHawkxx said:
Thanks Don for the quick reply. Your short reply helped me a lot.
Yes, the thermostat has the rubber gasket around the edge so I was surprised to find there was RTV on top of it. As soon as I read your reply it dawned on me what I think happened. When I had the bike in being worked on a couple years ago I was just told they spilled some coolant is why there was some on the bike. I now think that is when the RTV was put on. I will go ahead and put it back together now and not put any RTV on the thermostat. I think that solves that dilemma. Thanks for your help.

Now to answer your question why I need a thermostat change.
I think the thermostat was starting to stick.

I normally keep the engine coolant temperature on the top display and just occasionally monitor it. The best I can remember, when I am just cruising down the highway at 65 mph. the temp stays right at 170. When going slow or stopped, especially in hotter temperatures, the engine temp climbs and the fan cycles as normal between about 222 and 212F.

I was on a trip a 2 weeks ago and started noticing the temp staying about 178F, not a big deal just thought it was odd that it was running hotter than normal so I started watching it closer. On the way home it started out staying at 170 then after riding a while it would sometimes get up to about 204 then creep back down to about 182. The outside temp got up to about 95 but I don’t ever remember it doing this before under the same conditions.

Checked it out at home. Nothing blocking the intake to the radiator. Shining a light behind the radiator I could see the fins looked perfectly clean. Coolant looked like new and filled to the top. Reservoir was full to the top line. No leaks from the water pump or anywhere else. I thought the thermostat may be sticking or possibly the temp sensor may be drifting some but I am not so sure a sensor would fail like that. The thermostat and sensor are right there together on the bike so I figured if I was going to have to take everything off including the throttle bodies to get there I would order both the thermostat and sensor and probably just replace the sensor anyway whether it was bad or not.

2013 Tenere, bought it new and have had it 6 ½ years and 89,500 miles.
Coolant was changed once, 2 years ago with 48,000 miles.

I’ve noticed my temps staying higher than usual for the past two seasons. I bought a new OEM thermostat this past spring but have been busy at work and this had little time to ride of wrench. I’m nearing the first valve check so am hoping to install a new thermostat at the same time - hopefully later this fall.

My temps climb and fall quite erratically sometimes despite ambient air temp. My thought is the thermostat is sticking and thus influencing the fluctuations...

Tenman · Aug 14, 2019

My gen 1 cycles at 207 to 217 since new

SparrowHawkxx · Aug 18, 2019

Notes on changing the thermostat:
Parts ordered: new thermostat, coolant temperature sensor and washer, and coolant drain bolt washer.
You will also need 1.83 L (1.93 US qt) of coolant to fill the radiator and 0.26 L (0.27 US qt) to fill the coolant reservoir.

The FSM procedure for Removing the Thermostat is on page 6-4.

To drain the coolant it refers you to Changing the Coolant – FSM page 3-28

To remove the throttle bodies it refers you to Removing the throttle bodies – FSM page 7-5

The FSM says to remove the coolant reservoir to drain it. I did not remove it. I sucked the coolant out using a cooking baster and put a piece of vinyl tubing on the tip so it would reach the bottom of the reservoir. This worked OK but was a bit messy, the coolant dribbled out of the baster.
A large syringe would work better. A 300 ml syringe would hold all the coolant, 0.26 L (260 ml), but I think I will order a 150 ml syringe to use next time. A smaller one takes up less space for storage and using it 2 times would get all the coolant out.

The FSM says to remove the throttle bodies. I did not completely remove it. I removed all the electrical connectors and loosened the clamp screws. I did not remove the 2 throttle cables or the throttle body joints. I lifted it off and used some heavy cord to hang it off to the side from the fill neck on the radiator.

The FSM says to remove the coolant temperature sensor. I see no need to remove it unless you are replacing it or testing it. I was replacing it and it came out easy with a 19 mm deep socket.

The FSM says to remove the radiator inlet hose that is attached to the thermostat cover. I did not remove the hose, just removed the cover from the engine and pulled out the old thermostat.

Installing the Thermostat – FSM page 6-5
The FSM just says “Install: Thermostat” and gives a TIP to install the thermostat with the breather hole facing forward.
There is also a bolt hole for the cover at his position, so the breather hole would line up right behind that bolt hole.

Or worded more like Don described it in his reply above, the hole should be oriented so that it is in the highest position, which makes more since, it is a breather hole. Either way, both descriptions would be correct.
The thermostat breather hole is easy to see, it’s a 3 mm (about 1/8”) diameter hole.

The spring end of the thermostat goes in to the engine side as Don mentioned above and as shown in the diagram in the FSM. The cover is such a tight fit that I don't think you could install it backwards anyway.

SparrowHawkxx · Aug 18, 2019

I got the thermostat and coolant temperature sensor installed on Monday. This appears to have fixed the problem.
I don’t really think anything was wrong with the temperature sensor but I ordered one so I put it in. I would not want to take everything apart again if something was wrong with it.

We had a hot day Monday, then a cold front moved in overnight and Tuesday was about 25 F degrees cooler so I had two good days to test it out under different conditions. I would take routes where I could keep my speed up mostly at highway speed (around 65 mph). I would monitor the coolant temperature on the bike display and the air temperature on my KOSO thermometer mounted on the bike.

The only thing I really needed to test for was that the coolant temperatures stayed consistent at highway speed and did not drift too high like it was doing before. That is; at highway speed and air temperatures in the 70s and 80s, it would vary between about 178 F and sometimes up to 200 F. At 98 F air temp, it did get up to 204 then drifted back to about 188 F.

Monday
I got the installation done, then took a 2 hour test ride. The temperature was 100-102 F. There was not a lot of wind but I still noticed that it was running cooler going into the wind and hotter with the reduced air flow when riding with the wind.

At 100-102 F it was running at 176 to 181 F. The temperature did get up to 186 F for a while. After sections where I had to slow down, after getting back up to speed it would take 3-4 miles for the temperature to cool back down and stabilize again.

At 98-95 F - The last 15 minutes of the ride the air temperature cooled down and it was running at 172 to 174 F.

Everything looked good. The coolant temperatures were stable (not drifting too high) and even though the air temperatures were hotter than when I was having the problem the coolant temperatures were cooler, more like what I remember they were before I had the problem.

Tuesday
The cold front made the temperatures much nicer and had some light rain today. I took my wife on a 200 mile ride. The temperature was mostly 75 but got up to 80 F at the end. The bike was running at about 167-171 F.

It seems to me if the temperature is below about 95 F, the bike will normally run around the 170 range (+/- about 4 F).

SparrowHawkxx · Aug 18, 2019

A few more threads related to this topic.

SparrowHawkxx · Aug 18, 2019

Tenman said:
My gen 1 cycles at 207 to 217 since new

I do not see it in the owner or service manuals anywhere but from what I've seen posted on here, I think most people say the radiator fan cycles on at 221 F (105 C) and turns back off at 212 F (100 C). That is unless those points were changed with an ECU flash.
Was your ECU flashed?

Lux · Sep 7, 2019

This happened to me today, exactly the same scenario. Off to the stealership for some parts.......great job on the write up, very helpful!

Tenman · Sep 8, 2019

SparrowHawkxx said:
I do not see it in the owner or service manuals anywhere but from what I've seen posted on here, I think most people say the radiator fan cycles on at 221 F (105 C) and turns back off at 212 F (100 C). That is unless those points were changed with an ECU flash.
Was your ECU flashed?

yes

MidlifeMotor · Apr 9, 2023

I pulled up this thread from 2019 at my 2012 S10 has been experiencing the same symptoms as the OP's bike. Every indication is the thermostat is stuck. Ordering parts tonight including the radiator hose that goes to the thermostat cover. Out of an abundance of caution and to save having to do this again, I'm gonna replace the temp sensor and radiator cap based on the recommendation of a mechanic friend.

I checked the partzilla diagram and the Factory Service Manual diagram for a gasket and could not find one. Searching other threads leads me to believe there will be a gasket attached to the thermostat cover when I remove it. Can anyone confirm?

I will post results when done. At this time temps stay cool when bike is moving, but seem to be higher than I remember. When riding the other day on the freeway the air temp was 72F but engine was running at 194ish. When stopped, temps quickly climb over 221, fan kicks on but temps climb as high as 230. As soon as I start moving temps drop very quickly, sometimes as much as 15 degrees in seconds which leads me to believe temp sensor might also be part of problem.

Any thoughts?

SparrowHawkxx · Apr 10, 2023

MidlifeMotor said:
I pulled up this thread from 2019 at my 2012 S10 has been experiencing the same symptoms as the OP's bike. Every indication is the thermostat is stuck. Ordering parts tonight including the radiator hose that goes to the thermostat cover. Out of an abundance of caution and to save having to do this again, I'm gonna replace the temp sensor and radiator cap based on the recommendation of a mechanic friend.

I checked the partzilla diagram and the Factory Service Manual diagram for a gasket and could not find one. Searching other threads leads me to believe there will be a gasket attached to the thermostat cover when I remove it. Can anyone confirm?

I will post results when done. At this time temps stay cool when bike is moving, but seem to be higher than I remember. When riding the other day on the freeway the air temp was 72F but engine was running at 194ish. When stopped, temps quickly climb over 221, fan kicks on but temps climb as high as 230. As soon as I start moving temps drop very quickly, sometimes as much as 15 degrees in seconds which leads me to believe temp sensor might also be part of problem.

Any thoughts?

The parts diagram (Radiator Hose diagram) shows item #1 is: THERMOSTAT ASSY.
This is an assembly that includes the thermostat and the rubber gasket around the edge. (See the discussion above)

No gasket attached to the thermostat cover.

MidlifeMotor · Apr 10, 2023

Thanks for the quick reply. Hopefully I can get my hands on a thermostat assembly soon.

sandro1973 · Apr 10, 2023

RonH said:
Yea, I think no prior threads on the change because far as I can tell no one has ever changed the thermostat. Also it shouldn't matter it doesn't seem like, but sometimes the thermostat should be turned to a specific position. My Ford diesel is this way. Probably not an important detail, but put the new one in exactly same orientation as the old one.

I changed mine, it stopped working properly, opening too late and taking too long to close...tested it myself after replacing with a new one. These things can go bad...nothing is forever.

Mr. BR · Apr 10, 2023

And here's a generic pic of a Super T thermostat with rubber gasket.... no other gakset needed. Just ensure the sealing surfaces on the head and cover are clean.
Regards,
Mr. BR

MidlifeMotor · Apr 10, 2023

Thanks guys.

Having a hard time finding anyone with one in stock i.e. local dealers, partzilla, babbits etc. Looks like there's a back order from Yamaha. ETA mid-May! Yikes, gotta get scrounging to find one.

Changing the Thermostat

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