Somewhat erratic coolant temperature readings

Hawat

New Member
Hello,

I just bought a used 2009 FZ6-S and rode it home for about 300km.

It was a very hot day (about 36 degrees C ambient) and I noticed that the coolant temperature reading kept creeping higher, slowly but steadily regardless of rpms and speed. It increased to 114 C and I heard the fan kicking in (fan works), but didn't really cool the temp down.
Even when I was coasting in 6th gear, low RPM the temp kept creeping higher until it reached 120 C and the overheat warning came on.

I stopped immediately and let it cool down. However there was no indication that the bike was really all that hot .. no bubbling in the overflow tank, no steam or coolant coming out etc.

After about 20 mins I opened (very carefully !) the radiator cap and the coolant was full and only luke warm, although the temp reading still showed 72 C. I verified the pump working and the coolant is very nice and not contaminated.

So I kept on going and soon the temperature went up to 115 degrees again. So I decided to pull in the clutch and let it coast down a hill to let it cool in idle, and the temp jumped almost immediately to 124 C and the overheat
warning came back on. I couldn't really pull over, so I let go of the clutch in 6th gear and the rpm went back to about 4500 rpm and the temperature reading changed almost instantly to 102 C ! Like within 2 seconds. And the overheat
warning disappeared.

I then stopped for fuel and for the rest of the trip the temperature never exceeded 102 C - but then the sun was down and it was much cooler ambient temp.

I contacted the former owner and he states he never had any problems with it.

Now what do you guys think ? I dont think the coolant temp could change from 124 C to 102 C within seconds ? Faulty coolant temperature sensor ? Corroded wiring / contact issues ? Or is the 124 degree reading correct and there is another coolant problem (i.e. thermostat ?)

Thanks.
 

Motogiro

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:welcome: to this great forum! :) Oh yeah, your summer, our winter.
Could be a faulty sensor but I would certainly check the thermostat to see that it it is opening when it is supposed to. The boiling point of coolant is much higher than water so the system might not show those signs as soon if the coolant is pretty new.
 

TownsendsFJR1300

2007 FZ6
Site Supporter
I would feel the upper, larger hose for how hard it is and also get an idea how hot it gets at normal operation temps (feel right after warming up)

If you have access to a lazer temp gun, that'd help..

If the gauge is jumping that much, that quick, I'd be looking at the temp sensors...

As the bike is new to you, I would also change out the coolant just cause-rule the basic's out...


*As I was out riding today, about 60'F, the temp gauge showed it's normal 171F running... Once in heavy traffic / stopped, it went up to about 195F (gradually). Once moving again, the temp gradually dropped back down to 171.

You shouldn't have major temp "jumps/spikes"..

.
 

Hawat

New Member
Thanks guys for the replies. Yeah the behavior of the temp display was weird. It went from 124C to 102C in like 2 seconds. I assume that 102 C is actually the correct temperature (which would be expected) while the 124 was glitching ?
Yesterday I've started the bike and let it idle for a while. The temp went up to 100, then the fan kicked in and brought it back down to 94, when the fan stopped. So thats totally expected behavior. I am not sure why the temp would creep up to 115+, but then this happens when
the engine is under load (i.e. up a steep hill), so maybe that reading is correct ?
The only other thing I've noticed is that I had 95 Octane fuel in it when it happend. Since I've topped up with 98 Octane premium it didn't happen again. Would that make any difference ?
The coolant looks almost brand new. I actually suspect that somebody changed it recently because they had issues there. But I will change it again. Its easy and as you said just to eliminate one of the variables.
How easy would it be to test the Thermostat without actually removing it ? I have the service manual and to get to the Thermostat you need to remove Tank, and the Throttle Body. That scares me a bit and is probably beyond my mechanical talent.
I guess I need to ride it a bit more and see if this problem appears frequently and in which context. Right now its just to hot here to ride (38 C +)
 

TownsendsFJR1300

2007 FZ6
Site Supporter
One member removed the t-stat W/O pulling all the manual calls for. It was tight but do-able.

I'd replace the t-stat as it is a PIA to get to. Obviously, still check it in hot water to determine it's condition..

You shouldn't have to run anything else but regular fuel (as called for). For any load, going up a steep hill, un-less at a very low RPM (say under 4,000), there shouldn't be any knocking.

Might want to check the radiator cap as well too. That wouldn't explain the jumping in temp #'s, but it does sound like the bike isn't cooling as it should.
 

Hawat

New Member
Thank you. I've ordered a new radiator cap. I checked the old one and it looked o.k but its worth a try I guess. And I will flush the coolant, just in case. Does the bike just use normal 50/50 pre-mix Green Coolant ? Somebody has a link to a youtube video on how to do this ?
It looks like the water pump is relatively easy to replace ? I might do this next and see if this fixes it before I dive in and remove the tank and throttle body to replace the thermostat and coolant temperature sensor. Yes I will for sure replace them both when I am in there, dont
want to do this twice. Thanks for all your help guys. Nice to be here.
 

Motogiro

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Thank you. I've ordered a new radiator cap. I checked the old one and it looked o.k but its worth a try I guess. And I will flush the coolant, just in case. Does the bike just use normal 50/50 pre-mix Green Coolant ? Somebody has a link to a youtube video on how to do this ?
It looks like the water pump is relatively easy to replace ? I might do this next and see if this fixes it before I dive in and remove the tank and throttle body to replace the thermostat and coolant temperature sensor. Yes I will for sure replace them both when I am in there, dont
want to do this twice. Thanks for all your help guys. Nice to be here.
I would not just throw parts at this. You don't want to damage the bike because of overheating if that's what is occurring. If the cap is bad you will see signs of cracking on the rubber seal as well as poor spring tension. The coolant temperature sensor could be the problem as Scott (TownsendsFJR1300) mentioned. The wire colors are green w/white tracer and black w/blue tracer. These, as most sensors do, are read by the ECU and it the puts out all the data to a CPU in the instrument cluster that distributes the proper data at the readout.

If you can pull the coolant temperature sensor you can put a thermometer in the water with the sensor and heat the water above the test temperature. As the water cools test the lead of the temp sensor and with the meter on x100 range in ohms you should see 0.29 - 0.35 k ohms at 80 deg. C. At 0 deg C you should see 5.21 - 6.37 k ohms.

Also , I don't have the FZ6 anymore but is there a possibility you're reading the temp in F?
 

Hawat

New Member
Hello fellow riders:

Just to give you an update whats happening: I have done a really good coolant flush and ran some commercial radiator cleaner / flush solution, then flushed it again with distilled water. Also emptied the overflow bottle and then refilled it all
with pretty expensive Engine Ice (not that readily available here). I also replaced the radiator cap with a brand new one, just in case.

I also did an engine oil + filter change (10W50 semi-synthetic 4 stroke motorcycle oil for wet sumps).

Unfortunately all of this didn't fix it. The bike still runs too hot. Reaching 100 C after about 15km of moderate open road riding. Fan kicks in and keeps it somewhat in check but it reached 117 C after about 30 km and the overheat
light came on and I had to pull over to let it cool down. And yes the temp is in Degrees Celsius, not Fahrenheit :).

So, bummer.

Now I ordered a new Thermostat and a new Waterpump, both genuine Yamaha parts. After looking at some youtube videos etc. I kinda start to doubt that they cause this issue, though. They are
engineered in a way that there is not really all that much what can go wrong with them. If anything, the waterpump would start leaking if a seal goes out, but there is really no scenario
where the pump would not pump water or not enough water. The impeller is made out of metal and its driven by a shaft which is directly run via gears from the engine. So my guess would be
that if the pump breaks it would not pump at all which would cause the bike to overheat much more quickly and severely.

Its also interesting that if I just let the bike sit idle it doesn't overheat. The fan kicks in at about 100 C, then cools it down to about 94 and switches off. It seems to get hot more quickly
if the engine works harder, i.e. up steep hills etc.

I wait for the parts to arrive and put them in, then update here. Any thoughts ?
 

Motogiro

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There's a good chance the water pump impeller may have detached and when the engine is at idle the impeller can turn enough for coolant recirculation. Once the engine works harder the impeller can not spin enought because of the detached condition, hence the quick overheat. As Scott mentioned earlier it probably would not hurt to check temps with an infrared tester to see temperature at the radiator tank to confirm this isn't a sensor malfunction.
 

Hawat

New Member
OK Thanks. Good advise. I didn't know the impeller can detach from its shaft. From the diagrams (https://www.yamahapartshouse.com/oemparts/a/yam/500460e1f8700209bc7952bd/water-pump) it looks like its all one part. But I haven't taken the pump apart yet and probably will not until I have installed the new one.

I have a friend with a infrared thermometer. I will ask him if I can borrow it to confirm the temperature readings.

I kinda hope that you are right. If the new pump would fix it I am happy. Otherwise the only other possibility would be :

- A blocked radiator (expensive !)
- Some blocked passages in the engine block itself (even much much more expensive and potentially fatal !)

After all I only paid $ 1900.- for the bike, so a new / replacement engine wouldn't be justified.
 

Motogiro

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I'm not sure about the impeller as I haven't seen the FZ6 water pump but I have seen it happen on other types.
I once had a member that had a Daytona 675 with an overheat problem and it was because someone got the radiator fins loaded with motor oil and the radiator loaded up really quick after a couple of rides. We live in arid climate and dry dust did it's thing. I used a good dish washing liquid and flushed it clean. Worked great! Check your fins are not clogged. :)
 

Hawat

New Member
Hello,
thanks for asking. No updates yet. Still waiting for the parts to arrive - they come from the U.K. (same part in Australia cost about 4 times as much !) and it takes a while to get here. Cheers, thanks for all your help and merry Christmas.
 

Hawat

New Member
Hello Everybody:
Here is an update. I've replaced the thermostat (yes - it can be done without removing the airbox and the throttle body !) and the waterpump. New seals etc. I flushed the coolant and replaced it with
high quality motorcycle coolant 50/50 mix.

The result: Nada :-( The bike still overheats the same way as it did before. Bummer.

Pretty frustrating. I noticed _a_lot_ of calcium buildup inside the water pump. I've checked inside the engine block as good as I could - removing the thermostat and the cooling hose which connects
the pump to the oil cooler and the engine block. The block itself didn't had any buildup - at least not at the ports. Wouldn't be able to tell how it looks inside without an inspection camera.
The cooling hose had a little bit, but I was able to flush that out with a water hose.

So now I've ordered a new radiator. Doesn't look to hard to replace. I

I hope the new radiator fixes the issues, otherwise I am running out of ideas :-(
 

TownsendsFJR1300

2007 FZ6
Site Supporter
Bummer but finding build up in the radiator sounds like you found the issue.

Might try some Rydlem which is used in the marine world for cleaning corroded blocks (from salt water):



I'm not sure how you would circulate thru the engine (not running), you'll have to rig up something...
 

Hawat

New Member
Thanks for the tip. I haven't found build-up in the radiator (yet), but in the old water pump which I have removed. I think there is a chance that there is some build-up in the radiator (well,
I actually hope that's the case). This would be obviously fixed when I replace the radiator with a brand new one.

I am afraid that there might be buildup in the engine block itself, which could prevent the coolant to circulate as it should. By the looks of it this bike might have been run for a while with either just ordinary water as coolant, or the wrong coolant. The descaler could probably help with dissolving this. I think it should be possible to
rig up some external 12 v pump which circulates the descale thru for a while.

I saw a youtube video where a guy uses a 50/50 water/vinegar mix to clean out the cooling system. Vinegar dissolves the calcium - so I guess I could fill the system with this mixture and let it run for a while, then drain it out.
It probably would be important to flush it with something to get rid of the acid, as this could damage the rubber seals. Not sure if this works, but probably worth a try.
 

TownsendsFJR1300

2007 FZ6
Site Supporter
The Rydlem is made specifically for this issue.

It's not terribly expensive and as you noted, setting up a pump would be the way to go.

A couple of hours pumping should show very good results. I'd use / do this before doing the vinegar procedure. Better results and no potential damage to the engine..
 
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