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Bad Thermostat?

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43K views 95 replies 31 participants last post by  jsp1990  
#1 ·
I've been riding the bike on some really cold mornings, between 28 and 40 degrees and I've noticed that the coolant temp never gets anywhere near normal operating temp like it should.

I like to see at least 160 degrees and most modern engines have a 180 to 190 degree thermostat. When it is 28 degrees out the coolant temp stays at or below 130 degrees, no matter how long I ride it. This is at highway speeds. As air temp warms up, so does the coolant temp.

Has anyone else seen this on their bike, it can't be normal and it's really bad for an engine to never reach high enough temperature to cook out the water and acids produced by combustion.

I'm going to pull the thermostat and test it this week. I will post up my findings.
 
#3 ·
That sounds the same as what mine is doing. Thanks for that info. Maybe some kind of design flaw in the cooling system. I haven't looked closely at how the system works, it's set up a bit differently from other bikes. Every other liquid cooled bike or car/truck I've had keeps temps steady even in extreme cold.
 
#6 ·
160F, my FZ6R was the same in cold temps. I can see the thermostat open at 160 then the water temp go down a bit when it open and climb up again. I agree 160 is a bit cold. The 09 in general run a bit cold compare to my 6R who was in the 190 to 200 all the time. Could always use rad blocker to limit the cooling effect.

Sent from my SAMSUNG-SGH-I337 using Tapatalk
 
#9 ·
Funny thing is with a digital readout everyone is looking at numbers.
If it was a segmented or dial gauge no big deal but now everone is seeing a number thus all the speculation.
Reminds me of the 1985 GPZ 900,when it came out everyone was complaining that it was running hot because the gauge would
run in the 60% range.
Guess what Kawaski did to fix that; they ran an inline resistor so it would read lower and presto no more complaints. :D
 
#12 ·
on my way home from the dealer it was 85 degrees and I am on the freeway stop and go. The temp on the gage went to 223. It was too noisy to hear if the fan was on but I think it was. It cooled down once I got up to 20mph. Hard not to worry about it but it only had 45 miles on it then. We get hot summers like 105 and I ride to about 95 or so and I am hoping this will not be a hot running bike. I like the fact it actually has a water cooled oil cooler sitting next to the oil filter.
 
#14 ·
If anyone makes a change so it comes on sooner will get my money. Might have to put a manual switch on it with an led to show when it is on.
 
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#19 ·
yup mine does the same thing. On cold mornings it was around 140-150 at higher speeds, but it was more like 50 degrees out for me. I can see it showing even lower when its 30. (brr!) Then sitting in traffic it hits 220 pretty quickly and the fan kicks on. hopefully this has no adverse break-in effects when you punch it with 140 (or less) coolant temp.
 
#20 ·
I took a look and took apart my cooling system today(don't tell the warranty police). I drained the coolant and pulled the thermostat housing off. It's the black plastic thing behind the header pipes. I pulled the exhaust to make it easier. What I found was a big disappointment.

The thermostat and housing are a sealed unit, no easy way to test the thermostat. But much worse yet, the thermostat is just rattling around loose in there and not even remotely sealed to the housing. Thermostats always have a rubber or other seal around them, otherwise they can't work. This means that coolant can bypass the thermostat when it needs to be stopped by it. I ran some water into it with my hose and a lot gets by, even without a water pump trying to push it through.

This seems like a serious design or manufacturing defect to me, and I can't think of any way to fix the situation, not being able to open the housing. Not only the coolant but also the oil temperature will be too cold, this is really bad, and can cause a lot of extra wear to the engine. I ride even when it's cold out so I'm not too happy Yamaha screwed this up. I hope after they get enough people noticing this and complaining they will come up with an updated part.

Also, the only temp sensor I can see is right in the head, so it is sensing actual engine/coolant temp.
 
#25 ·
I like to see at least 160 degrees and most modern engines have a 180 to 190 degree thermostat. When it is 28 degrees out the coolant temp stays at or below 130 degrees, no matter how long I ride it. This is at highway speeds. As air temp warms up, so does the coolant temp.
tell your dealer about this. if you've got a bad thermostat, it should be an easy warranty fix.
 
#33 ·
Is the design wrong or the manufacturing? Hard to believe Yamaha would get something this important and basic wrong.
I'm assuming the design is wrong since there is nothing in there to seal the thermostat to the housing, or space for anything to fit. Maybe they never rode the bike in cold temps or figured most people don't ride in the cold. Or maybe they weren't worried about it because the extra wear on the engine will take a fair amount of time and miles to be noticeable.
 
#29 ·
You remind me of....me. I had the reverse problem on my pickup truck. Tried three T-stats, and it was running too hot. I took the last one and drilled a hole in it to create my own "2-stage" thermostat. This way a small amount of coolant gets through even when the thing is closed. No more overheats.

I'm sure this isn't a Chilton's or Haynes approved repair method, but it worked. I like the saying if it ain't broke don't fix it. But by the same token, if it's ef'd up, you have to get creative sometimes. Well played.
 
#31 ·
You are making me wonder if there's an issue, but I don't think it's out of the ordinary. All the liquid cooled bikes I've had responded to cold temps the same way. At 5 degrees C the FZ is stuck at 55 C on the highway, and my 500 Ninja is pegged just below the warm range.
 
#34 ·
I don't ride in the cold as much as some riders, and I don't know as much about thermostats and running a engine on the cold side, but I want my engine to last etc. I'd like it to be investigated further and if there is an issue have a good company develop a replacement for it. Seems like Graves would be the best people for the job, I'll post about this on that thread. Thanks Corey.



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