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Post subject: Overheating RZ
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Thrasherg  Powerband Master Joined: 18 May 2007 Total posts: 721 Location: Austin, Texas |
Okay guys, I really need you to put on your thinking caps.
I have 2 RZ350's that both overheat after riding 3 or 4 miles. I thought the thermostat was bad, so I fitted a new one. It made no difference. I then removed the thermostat and the bikes still overheated. Thermostat ruled out.
I thought the radiator might be blocked. I took it to a radiator repair shop and they flushed it out with some kind of acid/alkaline. They said nothing was wrong with the radiator. I refited it and the bikes still overheat. I am running antifreeze, so I changed it for regular water. They still overheat. The only things I can think of now are:-
1) bad water pump
2) blockage inside engine cooling system
Both bikes are 31K models. Is it possible to fit the head gasket incorrectly and block/restrict the water flow? How would you check the water pump? I have removed the metal plate over the water pump and confirmed that it is turning when the engine runs. Apart from the impellor there are no moving parts and the impellor looks fine on both engines. I am at a loss as to what could cause this overheating.. I am going to try some engine ice, but I think that is just a band aid as the colling system should work without any special cooling fluids..
Any thoughts?
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Posted: Tue Apr 15, 2008 2:48 am
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Bigmaxy Suburban Commuter Joined: 10 Apr 2007 Total posts: 53 |
Some of this is less likely since you are having the same problem on two different bikes which throws a spanner into the works.
1. Are you really running hot? Is the gauge lying? Is the sender working correctly?
2. Is the radiator cap sealing effectively, if you don't have pressure in the system the boiling point is lower
3. Lean Condition. running lean will cause higher temps
4. With RZ's I don't think you can put the head gasket on incorrectly so that it is restricted.
Should not need special cooling fluids.
Is the ambient temp over there bulk hot at the moment?
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Posted: Tue Apr 15, 2008 3:15 am
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 721 Location: Austin, Texas |
The gauge is not lying as the engine does spit out coolant when the needle goes in the red zone, so it's definately getting very hot..
The ambient temperature is around 20C so not very hot, certainly not hot enough to cause this kind of overheating.
The engine could be running lean, but the plugs look okay. The engine has a stage 2 tune, spec 2 exhausts and is running the standard inlet and air filter. I have 190 mains (they are power jet carbs, so full throttle should be equal to 240), anyone have any idea if this jetting sounds reasonable?
Thanks for the suggestions.
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Posted: Tue Apr 15, 2008 3:22 am
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Post subject: Re: Overheating RZ
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KX3 Mmm, Fully Synthetic! Joined: 02 Oct 2006 Total posts: 1188 Location: Québec |
| Thrasherg wrote: |
Okay guys, I really need you to put on your thinking caps.
I have 2 RZ350's that both overheat after riding 3 or 4 miles. I thought the thermostat was bad, so I fitted a new one. It made no difference. I then removed the thermostat and the bikes still overheated. Thermostat ruled out.
I thought the radiator might be blocked. I took it to a radiator repair shop and they flushed it out with some kind of acid/alkaline. They said nothing was wrong with the radiator. I refited it and the bikes still overheat. I am running antifreeze, so I changed it for regular water. They still overheat. The only things I can think of now are:-
1) bad water pump
2) blockage inside engine cooling system
Both bikes are 31K models. Is it possible to fit the head gasket incorrectly and block/restrict the water flow? How would you check the water pump? I have removed the metal plate over the water pump and confirmed that it is turning when the engine runs. Apart from the impellor there are no moving parts and the impellor looks fine on both engines. I am at a loss as to what could cause this overheating.. I am going to try some engine ice, but I think that is just a band aid as the colling system should work without any special cooling fluids..
Any thoughts? |
Can you try an LC rad?
Also, Cairnsy on here offers replacement rad.
EDIT:
what pipes are you running?
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Posted: Tue Apr 15, 2008 3:24 am
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nokturnalPowerband Master Joined: 22 Jan 2004 Total posts: 810 Location: Toronto, Canada |
that jetting does not sound reasonable. PJ carbs are stock at 185. You have chambers AND stage 2 porting, and think that one jet size increase is sufficient? I am no expert, but that's crazy talk to me. dump some more gas in there man! 
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Posted: Tue Apr 15, 2008 4:18 am
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BigmaxySuburban Commuter Joined: 10 Apr 2007 Total posts: 53 |
Other possibility is a faulty head gasket. This can pressurise the cooling system causing the spitting described.
Have you run it with the rad cap off while cold, check for bubbles etc.
Also steam from exhaust although harder to see in a 2 stroke.
Weird to happen on 2 different bikes though.
Jetting.
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Posted: Tue Apr 15, 2008 4:20 am
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 721 Location: Austin, Texas |
Thanks guys,
I ran with no radiator cap, and could not see any bubles in the water.
When I originally rebuilt the engine I was told that power jet carbs ran with 140 mains so 190 seemed a reasonable start. I will try dropping in something larger (240's and see what that does). The spark plug looks a nice tan colour, but I am not really thrashing it for the moment as it's overheating!! Will change the jets tonight and see what happens.
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Posted: Tue Apr 15, 2008 2:23 pm
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nokturnalPowerband Master Joined: 22 Jan 2004 Total posts: 810 Location: Toronto, Canada |
stock jetting on 86+ pj carbs is 27.5 pilot, 185 main.
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Posted: Tue Apr 15, 2008 4:47 pm
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jante350 RD/RZ Jedi Master Joined: 05 Aug 2003 Total posts: 5220 Location: Bergen, Norway |
Jetting could be off, but should only affect significantly when the engine is trashed... but with stock airfilters and inlet it just might be right, cause filters does the biggest difference...
Impeller could spin on axle, or be broken, check that out. You should see the indicator stream coming into the top of the filler cap when its on idle.. sometimes this looks good, and the impeller spins under load... are the radiator very hot when it spits out the fluid?
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Posted: Tue Apr 15, 2008 9:12 pm
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 721 Location: Austin, Texas |
Thanks Jante, I will try taking a look. I hadn't checked the temperature of the radiator when it boiled over, I will check next time. I have tried turning the impellor by hand and couldn't so I doubt it is spinning, but I will try looking in the radiator to see if I can see a stream of water coming back into the radiator, I wasn't sure if the water came out the bottom of the radiator and returned to the top or visa versa!!
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Posted: Tue Apr 15, 2008 9:18 pm
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jante350RD/RZ Jedi Master Joined: 05 Aug 2003 Total posts: 5220 Location: Bergen, Norway |
It returns to the top. Also check if the hoses are hot aswell.. I have on a few occasions had this on my F2 after rebuild, it did boil over a few times, than sorted it self out. Im guessing airlocks in the system... getting out all of them can sometimes be a real bitch!
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Posted: Tue Apr 15, 2008 9:43 pm
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nokturnalPowerband Master Joined: 22 Jan 2004 Total posts: 810 Location: Toronto, Canada |
but this is happening on 2 bikes? what are the chances both impellers are cooked?
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Posted: Tue Apr 15, 2008 11:43 pm
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