Cooling / overheating problem?

[Richi]

Hey guys I have a 1989 zxr400 have only had it a few months, and after taking it on its first lonng ride, the temp went well over half on the guage. Now when i stopped to see what was wrong fluid was spraying out, i just ambled it home.

Now after taking it for a half hour to hour ride it will overheat, and only when i stop, the radiator overflow bottle will boil up and drip out the tube to the road.

I have Refilled the radiator with water at this stage.

Does anyone know what may cause the water in the radiator to get passed boiling point? I can take a few lame guesses like maybe it needs proper coolant to keep the bike cool enough, or blocked radiator, bung waterpump etc.

Is the an easy way to address this or is it just a trial and error thing?

Sorry for the long post but any help would me much appreciated!!!

[FJRider]

It should have a cooling fan behind the radiator, they run off a thermostat near (I think/usually) or on the radiator. This may jam partially shut. OR. cooling fan FUSE may have blown.Check this first. A wire direct to cooling fan should prove if it works.Check second. Where radiator hose connects with engine is USUALLY where thermostat is housed. Look up bike model parts online/internet and see for yourself. OR ASK AT A BIKE SHOP. (find a workshop manual)...good luck...

[karbonblack]

Having coolant will definitely keep it cooler but a healthy cooling system will run fine on pure water so I don't think that is your problem. But... if it has been running without coolant for a long time you are going to have some serious corrosion which COULD be the source of your problem.

Hopefully not though, let's hope it is either blocked with something that can be flushed or is something simple like a blocked thermostat. It could of course be a stuffed water pump. Personally, I would take it to a bike shop but if you want to avoid that unless absolutely necessary, you may like to try and flush it clean yourself. I would start the engine so that water is circulating and loosen off the lowest hose where it goes into your engine. Put your garden hose into the top of the radiator. This of course assumes that you have no coolant and that you only have water pouring out (coolant being toxic). Stage 2 is to get a product from Repco/Butlers etc. to flush the radiator while you ride.

[Richi]

Hey cheers for the quick replies, the fan did seem a bit funny yesterday it ony started when i stopped and went for about 2/3 mins then turned off. If this runs off the thermostat then i think it might be that. I hope it is easy enough to get off lol.


But... if it has been running without coolant for a long time you are going to have some serious corrosion which COULD be the source of your problem.

I am pretty sure the first time it leaked it had coolant coming out...thats long gone now haha. Will be sure to get some more when the problem is remedied.

Also do all bikes have thermostats?

Cheers for the info guys!

[racefactory]

Hi there,

As far as i'm aware- cooling probs normally indicate 4 things:

Number 1 being air trapped in the system- i know from personal experience this sends temps soaring. If you've ever topped the water up yourself you may have put air into the system. If you put the water in slowly it reduces the amount of air that gets trapped. Have the bike idle with the radiator cap off until it reaches running temperature... air bubbles should start to come up and appear at the top of the water. Squeeze your hoses from the bottom up- this also gets air out. Also, once the bike is nearing running temp, blip the throttle as this will also send more air out to the top. bolt up that cap again and it may well be all fixed. In my experience anyway... that has solved it before.

Fucked radiator cap- can't keep it pressurized.

Stuffed thermostat.

Fucked water pump- self explanatory. Check it to see if it's all corroded, broken, jammed etc.

Probably not useful, but maybe a reminder at least.

Good luck man.

[Richi]

Cheers for that. when i put water into it it fills up ok but when its full and running sometime the water surges out of the cap then back again. so i put more in and it surges again! probably lose 300-500 mls each surge. sounds dodgy as, hope its not a headgasket ... :no:

[racefactory]

if it was a head gasket you'd know about it surely, right?- wouldnt the motor be running like mouldy poon?

what do you mean by ''and then back again?''

maybe a rooted rad cap here?? is the water actually boiling when it comes out of rad? if it is not boiling and spewing out of rad cap then that suggests a fucked rad cap- anyone agree?

[racefactory]

and maybe it is getting worse each time you put water into the radiator as you might be trapping more air in there?

[FJRider]

Check the OIL. if it is WHITE... you have problems...water in the oil (head gasket... or worse)

[awayatc]

You have either got a seized thermostat or a stuffed waterpump...as has been correctly mentioned
And if you keep running the engine without sorting that out real soon you will stuff up your headgasket and or head......

[CB ARGH]

My bike appears to have the same problem, or similar. It heats up a lot, anough that the radiator pipe leading into the engine felt like it was boiling. The fan never came on again even after checking the fuse and checking the fan works by itself (connecting it to the battery directly). The temp never gets super high, but I'd rather the fan was on to keep it a bit cooler. Any ideas?

[honda929]

Back in 1986 i had a gpz900r which was prone to over heating when in slow traffic.The fan only came on when the temp showed hot,so i fitted a switch so i could turn it on before it got hot when in traffic.

[Wannabiker]

OK....
1 Radiator cap. This is the first place to look. For evey pound of pressure, the boiling point goes up 4 degC. Modern vehicles are designed to run hot, so a leaking cap could cause boiling of coolant by not holding enough pressure.

2. Coolant expands....so every time you fill up radiator cold, then heat the bike, coolant will expand into the coolant tank, and should draw back if a sealed system, or will just natrually find its own level. The type of radiator cap will determine this, as some have a small diaphram in the centre allowing it to draw back. If it does not have this type of cap, there will be a small air=space in the radiatior after the bike has got warm. If you continue to fill the rediator, then run it till it is hot, the coolant overflow tank will natrually overflow in time.

3. Fan runs for 2-3 mins. Sounds about normal. Fan controlled by thermostat. (not the thermostat, but a thermal cut-out switch)

4. Coolant surges up and down in the radiator. This can be normal. The safest way to ensure that there are no air traps in the engine is to do this, and this applies to most motor vehicles when the radiator/block has been drained. Fill up cooling sysyem slowly until rad full. ( you should have an idea of the capacity of the sysyem, so will have a rough idea of how much to put in) Start engine and let warm up without radiator cap on. The coolant will expand and overflow a bit as it heats up. Run the engine until the thermostat opens and the hot water circulates. (you may notice the water level surging as you rev the engine...this is the water-pump pressurising the water in the block). Once the water is hot, top up and then place the radiator cap on.

5. Temperature guage hot, but engine not boiling. Possibly a faulty connection in the guage system. (or faulty guage or sender unit)

6. Guage hot, engine overheating. Possible causes:
a. Faulty thermostat
b. Leak in the system
c. Blocked radiator (unlikely)
d. Water-pump not working or worn.
e. head gasket
f. worst outcome, cracked head or bore.:bye:

[awayatc]

My bike appears to have the same problem, or similar. It heats up a lot, anough that the radiator pipe leading into the engine felt like it was boiling. The fan never came on again even after checking the fuse and checking the fan works by itself (connecting it to the battery directly). The temp never gets super high, but I'd rather the fan was on to keep it a bit cooler. Any ideas?


there is a thermal switch in yur cooling system......(bottom radiator?) with 2 wires, one going to the electric fan.
This switch is supposed to make contact at about 80 or 90 degrees or so....
which turn the fan on.
If that switch is faulty your fan won't turn on.
Either replace it, or make a manual/override switch ....

[FJRider]

You have either got a seized thermostat or a stuffed waterpump...as has been correctly mentioned
And if you keep running the engine without sorting that out real soon you will stuff up your headgasket and or head......

if he hasn't already...surging water. Have you any way (ie. know how or know who can) pressure test the cooling system. If it holds pressure, it should hold water.

[FJRider]

Shorter version...Have you checked the radiator cap is the CORRECT one for YOUR bike ??? It may have been on it when you got it...BUT...You said after your FIRST long ride. Have you not had this bike long.
If the cap was fitted by someone who didn't know differently... ie. if it fits on it, is not meaning,it is ALWAYS the correct one.CHECK !!!

[awayatc]

if he hasn't already...surging water. Have you any way (ie. know how or know who can) pressure test the cooling system. If it holds pressure, it should hold water.

Regarding surging water....the other day had something similar with a car i was fixing.....turned out impellor of waterpump was broken off.
Water in engine heated, did not get circulated...and steam forced its way out through bottom hose/radiator.....

I would take out thermostat and see if pump circulates water.....

[FJRider]

The old story...start at the beginning. Its always the LAST thing you check... so do that first...

[CB ARGH]

there is a thermal switch in yur cooling system......(bottom radiator?) with 2 wires, one going to the electric fan.
This switch is supposed to make contact at about 80 or 90 degrees or so....
which turn the fan on.
If that switch is faulty your fan won't turn on.
Either replace it, or make a manual/override switch ....

Thanks mate, yeah I'll give that idea a go. I don't want to risk it overheating, plus it's only five or so bucks and ten mins of my sad life to make an on/off mechanism haha.

[awayatc]

You got a bike ,so how can your life be sad.....?
Good luck

:scooter:

[Max Preload]

Having coolant will definitely keep it cooler...

Actually, coolant has a lower specific heat than water.

Richi, start with your radiator cap. Check the spring isn't broken and the seal is intact. Check the operation of the valve which allows coolant to be drawn back into the cooling system from the reservoir as the engine cools after it's stopped.

If all is well there, get the cooling system pressure tested. If you're losing coolant, the bike will overheat. If the system loses pressure and there is no external leak, the news is all bad. You're looking at a head gasket leak (combustion chamber to cooling system or oil gallery to cooling system) or corroded or maybe even a cracked head. You should not just nurse a bike home that dumps it's coolant - you should immediately stop and trailer it if the leak is not roadside repairable.

The fan shouldn't normally operate off the thermo switch in anything other than slow, heavy city traffic. The fan should come on automatically before the temperature reaches 3/4 on the gauge. If it's a 2 wire fan switch, just short the wires together to check there is power and the fan motor itself is operational. If a single wire system, ground it to do the same test. If the fan operates, the thermo switch is faulty. If the fan doesn't operate when you perform the shorting or grounding check for power with a test light or better still a multimeter. If there's no power, check the fuse. No problem with the fuse, power the fan manually with a direct 12V and ground connection to the fan plug (not the thermo switch plug - the one that you'd disconnect to remove the radiator). If it doesn't run with a direct connection the fan motor is dead. If it does run with a direct connection there's a wiring fault.

If you're going to fit a manual switch (I have one as a precaution now after my thermo fan switch died last year) for gods sakes do it properly. You'll be hard pressed to get a discreet waterproof switch that will carry the current required, so get a smaller rated waterproof switch and run a relay.

[racefactory]

hve you checked if your rad cap is ok?

have you checked if there is air in the system?

[awayatc]

If you're going to fit a manual switch (I have one as a precaution now after my thermo fan switch died last year) for gods sakes do it properly. You'll be hard pressed to get a discreet waterproof switch that will carry the current required, so get a smaller rated waterproof switch and run a relay.

You make it sound harder then it is....even on a 2 wire thermo switch both wires are neutrals and dont carry current.
All the switch does is make contact at a certain temperature, so that the circuit closes....
Any sort of switch will allow you to do this safely, it is just an earth wire....like a horn.