GPz900r Over-heating

Hiya all, FWIW I'm trying to start collating my accumulated info on the bike into one site.

I'm not trying to undermine the value of forums (more the merrier in fact), however I'm trying to be really specific on JUST this bike and concentrate on owner-sourced data rather than general motorcycle expertise - it's all about trying to assist other owners keeping these gems running.

I've been sorting out my over-heating experiences so if there are other owners out there please feel free to peruse and comment where necessary - I definitely do not know everything and what I do know is probably wrong anyway!

Of course if anyone would like to add their bike to the database please send me a note

https://gpz900r.motoshoot.com.au/overheating/

Great article! Timely too as my 900 is running hotter than usual at the moment.
A few things to add:
Repco sells a 1.1 cap for around $14 or so. RC57-110 is the model IIRC. Had one on my bike for years and replaced recently. It is my go to motorcycle cap and I have had on many bikes.
https://www.repco.com.au/en/parts-servi ... p/A9326581
I too am suspicious of the side shrouds around the rad. My bike has only had part fairing installation up until recently after a paintjob. WIth the exception of the black panels behind the gauges mine has everything on. I reckon it has run cooler in the past- I have an article from the 80s that says the GPZ runs 10 degrees cooler without the lower fairing on it. (Might be fahrenheit- American article?)
I have swapped both relays over with I guess working ones and am suspicious of 110 degree sensor. Need to test it. My wire falls off this sensor a bit. Could simply be this. I use this connector to wire my fan switch in with.
There is a white/blue wire that comes into the back of the fusebox that can corrode and cause cooling fan issues too. UK people seem to suffer from this fault a lot.
Lastly the first year GPZ had a pessimistic temp gauge and Kawasaki supplied an inline resistor to 'fix' it. Later ones had slightly different gauges. My temp gauge is off an 85 750 which I assume is also a pessimist and could be contributing to my gauge running high too.
I notice that you are in Adelaide. Got rellies in Henley Beach. My GPZ has been there twice. 1950km from me. Rode it once, Back of ute second time. ZRX last time on a bike.

A few observations from a non-owner, take it with a grain of salt:

Thermostat
The webike article linked to shows the pic of a thermostat with 82deg on it and then contradict
themselves by stating "The valve opening temperature is imprinted on the main body of the
thermostat, and the case of this thermostat, it becomes fully open at 82degC".
I guess something was lost in the translation.


Water flow direction into the block
I notice the GPz900R appears to feed the cooled water into the front of the engine.
My GPX750R (a later design than the GPz900R) feeds the cooled water into the rear of the engine.
Does this make a difference? Is it only a packaging consideration? I'm not sure.

Coolant temperature
Something to keep in mind is that the coolant coming out of the engine is a mix of coolants coming from
different parts of the engine with different temperatures, so your gauge sensor is giving you a sort of average of the temperatures of the coolant inside the engine.
There is coolant that has passed around the hot exhaust ports, over the top of the hot combustion chamber, around the cooler intake ports and some coming around the cylinder walls.
"110degC" coming out of the engine could be a mix of maybe 90-95degC from around the cylinder liners and 120degC
from around the exhaust ports and combustion chamber.

Coolant
Type B inhibitor is just that, corrosion inhibitor.
Type A coolant contains glycol and inhibitors.

Glycol has does not have the same "specific heat" as water such that it does not transfer heat as good as water. However, glycol does raise the boiling point.

This provides a decisison for the bike owner to make. Do you use a non-glycol type B coolant which transfers heat better than a type A coolant, or do you use a type A coolant that has a higher boiling point?

The Penrite inhibitor you mention may contain a "wetting" agent (although Penrite does not specifically mention it), perhaps emulating a product from Red-Line called "Water Wetter" which changes the surface tension of the water. Either way, wetting agent is not a bad thing.

Before anyone mentions them, there are the so-called "waterless" coolants like Evans which do not use ethylene glycol but instead use (I think) propylene glycol. The idea of a waterless coolant sounds good, but we would want to check on the specific heat of propylene glycol before trying it out.

The 110degC fan switch
There is probably a fan switch rated at 100degC or 105degC fitted to some other bike and fits straight in.
The trick is to find it. The FSM for the KLR600 of that era does not even tell me at what temp the fan switch (located in
the radiator inlet) is supposed to cut in.
This assumes the stock fan is capable of cooling enough to stop the temp getting any higher.
Ideally we want the fan to cycle on and off. If the fan just runs on and on until you get moving and get some extra airflow over the radiator then the cooling system is really at its limit in the prevailing conditions.

A bigger fan could help as long as the wiring and electrical system is up to it since a bigger fan of equal efficiency will pull more current. Pulling more current at idle or low revs may require a more powerful alternator.

A few observations from a non-owner, take it with a grain of salt:

As long as it's a logical technical discussion all thoughts welcome!

Thermostat
The webike article linked to shows the pic of a thermostat with 82deg on it and then contradict
themselves by stating "The valve opening temperature is imprinted on the main body of the
thermostat, and the case of this thermostat, it becomes fully open at 82degC".
I guess something was lost in the translation.

Yeah there is a few translation glitches but I really just used it because it was a nice demonstration of where it is on the GPz! And whilst I'm certainly not questioning the failures of a thermostat, I'm not sure it really affects the city over-heating issue common with the bikes.

Water flow direction into the block
I notice the GPz900R appears to feed the cooled water into the front of the engine.
My GPX750R (a later design than the GPz900R) feeds the cooled water into the rear of the engine.
Does this make a difference? Is it only a packaging consideration? I'm not sure.

Interesting, no idea why. I think the thermostat position on later bikes is different, closer to the radiator (and easier to access) so perhaps that has something to do with it.

Coolant temperature
Something to keep in mind is that the coolant coming out of the engine is a mix of coolants coming from
different parts of the engine with different temperatures, so your gauge sensor is giving you a sort of average of the temperatures of the coolant inside the engine.
There is coolant that has passed around the hot exhaust ports, over the top of the hot combustion chamber, around the cooler intake ports and some coming around the cylinder walls.
"110degC" coming out of the engine could be a mix of maybe 90-95degC from around the cylinder liners and 120degC
from around the exhaust ports and combustion chamber.

Yup - all the temp sender is doing is reading the coolant at the thermostat housing. I'll clarify that's what the 110 is measuring. I know my fancy new Honda boat engine runs at 80, maybe that's why I found 110 surprisingly high. I suspect the Honda is reading multiple sensors but it's still a lot lower. Given that the temp sensor is almost at the top of the coolant 'tank' I'm guessing there is a risk of air pockets messing with the reading, so you would always also want the 97 switch working. Hmm - writing this has just illuminated me to the reality that manual fan activation has the same potential issue!

On a previous car I had the hose after the thermostat (with sensor) fail so I only got a clue that something was wrong when there was basically no coolant left in the system at all.....

Coolant
Type B inhibitor is just that, corrosion inhibitor.
Type A coolant contains glycol and inhibitors.

Glycol has does not have the same "specific heat" as water such that it does not transfer heat as good as water. However, glycol does raise the boiling point.

This provides a decisison for the bike owner to make. Do you use a non-glycol type B coolant which transfers heat better than a type A coolant, or do you use a type A coolant that has a higher boiling point?

The Penrite inhibitor you mention may contain a "wetting" agent (although Penrite does not specifically mention it), perhaps emulating a product from Red-Line called "Water Wetter" which changes the surface tension of the water. Either way, wetting agent is not a bad thing.

Before anyone mentions them, there are the so-called "waterless" coolants like Evans which do not use ethylene glycol but instead use (I think) propylene glycol. The idea of a waterless coolant sounds good, but we would want to check on the specific heat of propylene glycol before trying it out.

Yup. I think (maybe that's hope) that the Penrite has 'superior' coolant properties because it doesn't have glycol. I have always used glocol-based previously, but when I was down at the shop this stuff was similar priced and looked worth a go. Obviously here in Oz we need coolant with a higher boiling point and the best heat transfer as possible. I agree waterless coolant sounds interesting, but considering once you have mixed a good water-based coolant it isn't that cheap anyway - so I wonder what this stuff would cost.

The 110degC fan switch
There is probably a fan switch rated at 100degC or 105degC fitted to some other bike and fits straight in.
The trick is to find it. The FSM for the KLR600 of that era does not even tell me at what temp the fan switch (located in
the radiator inlet) is supposed to cut in.
This assumes the stock fan is capable of cooling enough to stop the temp getting any higher.
Ideally we want the fan to cycle on and off. If the fan just runs on and on until you get moving and get some extra airflow over the radiator then the cooling system is really at its limit in the prevailing conditions.
A bigger fan could help as long as the wiring and electrical system is up to it since a bigger fan of equal efficiency will pull more current. Pulling more current at idle or low revs may require a more powerful alternator.

I don't have an issue with the 110 switch - I've enough faith in the Kawasaki engineers to leave this at the temp they specified. I'm just beginning to think the airflow produced by the stock fan isn't quite strong enough. This could be addressed in several ways.

As I described the stock fan isn't that big the GPZ1000RX is much bigger. And I'll check (if I can find it) the amp spec of the fan used on the GPZ1000RX and when I pull the bike apart the GPz900r. If it draws more current then it would pop the fuse so I'll have to wire in some more circuits. Experienced wiring commercial boats so comfortable with this stuff.

I would always want to keep the main fairings, but removing the 'side-fill' panels might help air flow.

I'm still not clear as to why the top part of the fan is shrouded. Shrouds redirect but never help air flow.

Maybe using a modern after-market fan (or fans) is another option. Or motors. This isn't such a silly idea, modern electric motors are far more efficient.

I've read somewhere else that increasing the size/efficiency of the oil cooler helps with coolant overheating issues. Normally I'd be inclined to agree that this is beneficial except I am really trying to address over-heating when the bike is stationary, with no airflow (except a fan) over either the coolant or oil radiators.

At the end of the day the idea of this discussion is to try and get some options! Appreciate your input.

Great article! Timely too as my 900 is running hotter than usual at the moment.
A few things to add:
Repco sells a 1.1 cap for around $14 or so. RC57-110 is the model IIRC. Had one on my bike for years and replaced recently. It is my go to motorcycle cap and I have had on many bikes.

https://www.repco.com.au/en/parts-servi ... p/A9326581

Cheers mate. That Repco cap is so much cheaper, I'd definitely add it to my parts list.

I too am suspicious of the side shrouds around the rad. My bike has only had part fairing installation up until recently after a paintjob. WIth the exception of the black panels behind the gauges mine has everything on. I reckon it has run cooler in the past- I have an article from the 80s that says the GPZ runs 10 degrees cooler without the lower fairing on it. (Might be fahrenheit- American article?)

I'm probably going to move the fan switch and remove those 'side-fill' panels anyway. I'm a form-follows-function kinda guy, and IMHO these are purely visual but are basically unseen so IMHO just excess weight (lol!). I am considering the possibility that these (and the fan shroud) are there to direct hot air away from your legs - but that's not going to worry me.

Yea I expect naked bikes to run cooler, but even 10F (~5.5C?) is quite a lot. Can you send me a copy of the article (or web link) I'd like to post that info. I wonder if a naked bike might actually run too cool when on the move?

I have swapped both relays over with I guess working ones and am suspicious of 110 degree sensor. Need to test it. My wire falls off this sensor a bit. Could simply be this. I use this connector to wire my fan switch in with.
There is a white/blue wire that comes into the back of the fusebox that can corrode and cause cooling fan issues too. UK people seem to suffer from this fault a lot.
Lastly the first year GPZ had a pessimistic temp gauge and Kawasaki supplied an inline resistor to 'fix' it. Later ones had slightly different gauges. My temp gauge is off an 85 750 which I assume is also a pessimist and could be contributing to my gauge running high too.

Yes my recent experience (corroded terminal affecting resistance) has made me kinda cautious about the 'natural' temp gauge position! In some ways I really prefer the VDO sensor and gauge option - because it actually tells you the coolant temp. I just wish the sensor length was the same. The more I ponder it the more I'm thinking of getting the whole OEM sensor/fan set-up working again and then wiring in a complete circuit to manually bypass/override. I'll probably do this when I replace the radiator.

I notice that you are in Adelaide. Got rellies in Henley Beach. My GPZ has been there twice. 1950km from me. Rode it once, Back of ute second time. ZRX last time on a bike.

My lad plays footy against the Henley Sharks - Adelaide is a small town! I've ridden mine to Phillip Island & back - don't mind it on the highway now and then but there's plenty of bikes (or cars) much better for chewing up serious miles.

My 89 CBR1000F is a much better mile eater than the GPZ900R but it is BORING comparatively even though it has a lot more go. Really boring. GPZ heaps better bike despite bike mags of the period saying the CBR was the best big sport bike then. Bullshit...

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Still suspicious of 110 degree switch I swapped it out with one that I had tested working. My second complete bike had a broken one. Turns out that my original one tests ok too.
Let the bike get 'hot' on the drive while running. Just been riding through traffic and gauge was high but not high as pictured. This is the point where the bike switches the fan on- 110 degrees, verified by infra red temp gun. This is still some way from boiling so maybe the gauge is ok.

Now have a 88, 89 and 91 GPZ900R. Will be interesting to compare new model once I have it running/riding. I rode one 23 years ago a bit.

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You need to remember that.... The further on the edge, The hotter the intensity



I have learnt to live with my GPZ900R heat temperaments. All is good until you are stuck in the city at 30 deg and more. Then the temperature will start to climb regardless of the fan being on all the time.

I think it's just that the technology had not caught on. Notice how small the radiator is compared to its POWER

Few things I did to somewhat "slow down" the temp climb:
- Disconnect oil temperature sensor plug under the bike (will kickstart the fan earlier)
- Ensure that coolant pipe near mufflers are away. It used to almost touch (1-2mm ) so I messaged it and got about 5mm now. Avoid it from radiant heat

I have one that I have fitted a ZZR1100 radiator, fan and oil cooler to.
This bikes controls it temperature really well but can't run the middle or lower fairing.

I had a stock one that used to get hot when your stuck in traffic but was fine on the open road.
I had to replace the switch on the lower left side of the radiator once as it stopped the fan coming on.