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Post subject: RZ350 Overheating
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GirlOnRZ350  Sunday Rider Joined: 15 Jul 2008 Total posts: 36 Location: Vancouver, Canada |
Hello, I was just wondering if other people find that their RZ overheats. I was told from the guy who I bought it from that it is just like that and to try and avoid traffic. He installed two computer fans on the rad for extra cooling which make a difference in traffic. However the other day I was talking to a yammy dealer who seems to think that there is no reason for my bike to run hot and that my bike has cooling issue if it does. I checked the rad for leaks when i flushed it but since I'm a noob I didn't really know what else to check for. The other day when I was in traffic, the temp gauge was just over 1/2 and the coolant reservoir exploded and some coolant spewed out (I assumed I over filled it). I turned the extra computer fans on and it stopped. Has anyone experienced the same problem?
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Posted: Tue Jul 15, 2008 10:01 pm
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Post subject: Re: RZ350 Overheating
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| p51bombay Joined: 23 Jan 2004 Total posts: 9597 |
| GirlOnRZ350 wrote: |
| Hello, I was just wondering if other people find that their RZ overheats. I was told from the guy who I bought it from that it is just like that and to try and avoid traffic. He installed two computer fans on the rad for extra cooling which make a difference in traffic. However the other day I was talking to a yammy dealer who seems to think that there is no reason for my bike to run hot and that my bike has cooling issue if it does. I checked the rad for leaks when i flushed it but since I'm a noob I didn't really know what else to check for. The other day when I was in traffic, the temp gauge was just over 1/2 and the coolant reservoir exploded and some coolant spewed out (I assumed I over filled it). I turned the extra computer fans on and it stopped. Has anyone experienced the same problem? |
Welcome, some say that its just how they are but I don't think so. The RZ500's tended to run a bit warm in traffic but the 350's really shouldn't. Couple of potential issues here, one is there could be air in the system which needs to be bled out - to do start with the engine cold and let it idle with the radiator cap off, watch the filler neck and if there is air in the system you will see bubbles rising to the surface. (some fluid may run over too) Once the bubbles stop rising you should be done, add fluid as needed, cap the radiator and fill the overflow tank to the hot full level and recheck it when it cools completely - adjust the level as needed.
Another possibility is the thermostat has failed and usually they fail closed which causes overheating. Its localed in that tapered housing on top of the head with three bolts holding it down. You can check it by putting it in a pan of water with a thermometer and watching to see what temperature it opens at as the water warms - of IF it opens at all. Or you can just stick a new one in, they don't cost a lot.
Sometimes the gauge or the sender can be at fault, the sender is the brass plug on the cylinder head with a single wire attached to it, if you unscrew that and heat it in the same pan of water you can then measure the resistance with an ohm meter to check if its working correctly. Sorry I don't have the correct specs for a YPVS but I'm sure someone will post them if you need to check that.
Then there's the water pump, its located under that small half cover (the plastic one) on the front of the right hand crankcase cover, under that the water pump will be under the metal cover on top. The problem here is the pump is driven by a plastic gear which can sometimes fail. With the engine running (not hot please) squeeze the lower output side radiator hose, that's the on running between the carbs to the head.........if you feel pressure when you squeeze it then the pump should be working as it should.
Lastly there is the issue of a failed head gasket, and I mean failed internally so you may not actually see the leak. From the symptoms you described I think this is your problem. When it fails internally it pressurizes the cooling system and causes the overflow condition you described. This is quite common and often times is caused from the use of aftermarket brand head gaskets so if you replace it make sure to use an OEM Yamaha Gasket.
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Posted: Tue Jul 15, 2008 10:30 pm
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Post subject: Re: RZ350 Overheating
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KX3 Powerband Master Joined: 02 Oct 2006 Total posts: 988 Location: Québec |
| GirlOnRZ350 wrote: |
| Hello, I was just wondering if other people find that their RZ overheats. I was told from the guy who I bought it from that it is just like that and to try and avoid traffic. He installed two computer fans on the rad for extra cooling which make a difference in traffic. However the other day I was talking to a yammy dealer who seems to think that there is no reason for my bike to run hot and that my bike has cooling issue if it does. I checked the rad for leaks when i flushed it but since I'm a noob I didn't really know what else to check for. The other day when I was in traffic, the temp gauge was just over 1/2 and the coolant reservoir exploded and some coolant spewed out (I assumed I over filled it). I turned the extra computer fans on and it stopped. Has anyone experienced the same problem? |
I had the same problem... both thermo and head gasket were
blown 
thermo was stuck half-open.
A good way to verify if head gasket is blown is to run the bike steadily at 7000rpm (a few 10 sec runs) if it's blown, water will spill out the overflow tank instantally even at correct temp
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Posted: Wed Jul 16, 2008 1:03 am
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1982RD350LC Daily Burner Joined: 31 May 2008 Total posts: 230 Location: Vancouver, Canada |
| Quote: |
| the coolant reservoir exploded and some coolant spewed out (I assumed I over filled it). |
http://i8.photobucket.com/albums/a3/ron629/2008July15002.jpg
The exploded coolant might be related to this item in the picture (which I've seperated here). I had the same thing happen with my coolant reservoir cap exploding off. Since it was brand spanking new I had a closer look at it and realised that there was no breathing hole in the rubber part to allow preassure to escape. I hacked the top of the rubber part off but that was dumb because the only exit hole in the plastic cap is that little one visible in the picture. I finally settled on throwing the rubber part out and just using the plastic part for my coolant reseroir cap. I hope somebody else chimes in and tells us what they know about this. Surely there must be a breather hole in the reservoir.
ron
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Posted: Wed Jul 16, 2008 1:33 am
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| p51bombay Joined: 23 Jan 2004 Total posts: 9597 |
The overflow tank isn't pressurized - or shouldn't be, it only needs a vent to allow the coolant to flow in/out. All it does is let the radiator (pressure part of the system) expand as the bike warms and hold the coolant so it can go back to the radiator as it cools again, what stays in there is so the system doesn't suck air in.
This must be a Canuck only thread. 
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Posted: Wed Jul 16, 2008 1:47 am
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| p51bombay Joined: 23 Jan 2004 Total posts: 9597 |
BTW - that cap you took apart.................No Longer Available. 
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Posted: Wed Jul 16, 2008 1:48 am
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twostrokeshop Suburban Commuter Joined: 13 Feb 2008 Total posts: 77 Location: Cairns, Tropical North Queensland, Australia |
Especially in warm climes/slow speed running, the rad on the RD/RZ350 YPVS is very marginal. It was originally designed for the RD/RZ250 YPVS version - there was no upgrade in size/capacity for the 350.
I have had designed and built a double-capacity radiator to fit the RZ/RD 250/350, that has 29 cooling rows compared to the stock unit's 23 rows, and it bolts and plumbs straight in: http://www.twostrokeshop.com/RZ350_high_capacity_radiator.htm
This unit is designed to cope with the extra duty required for big-bore 500cc+ top end kits such as Cub and Cheetah kits. As such, it is more than up to the job of cooling the RZ350 engine.
Cheers,
Steve
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Posted: Wed Jul 16, 2008 4:23 am
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1982RD350LCDaily Burner Joined: 31 May 2008 Total posts: 230 Location: Vancouver, Canada |
P51 wrote:
| Quote: |
This must be a Canuck only thread.
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I'm thinking that the reason for this is that Yamaha-Canada had thought that this was an exceptible replacement for the reservoir cap and thus created a localized problem. Out of curiosity I know our bikes are different in that the RZ has a thermostat but I find that my bike will quite regularly warms up as high as the second notch on the temperature gauge which is at 3/4 of the temp meter (which is normal in stop and go traffic on a hot day) and I tend to head down the shoulder of the highway at this point for wind flow. I had a friend pulled over by a police for doing so but was let go when he explained that it was for the safety of the other traffic because if his bike was to overheat and spill it's contents on the road then others could be in danger because of the oil/fluid spill. I don't think that the argument would hold true for a bike equiped with a radiator fan though. IMO
ron
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Posted: Wed Jul 16, 2008 1:44 pm
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Post subject: thanks
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GirlOnRZ350Sunday Rider Joined: 15 Jul 2008 Total posts: 36 Location: Vancouver, Canada |
Thanks so much for all the response. I'm new to this and I'm not sure where to start. I guess I'll start by looking at the cap because that is easy to do and rev it up to 7k, also easy. The other things sound much more complex so I'll prob ask a friend to help me. This forum is great! Everyone (I've heard from thus far) is great. 
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Posted: Wed Jul 16, 2008 3:27 pm
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 627 Location: Austin, Texas |
As the guys say, the cooling system on the YPVS is marginal for hot climates. MY YPVS would overheat and I eventually traced it to a blown head gasket. However after replacing the head gasket, the temperature gauge runs very close to the red line in hot temperatures..
I haven't found any real ways to cool it down other than replacing the radiator with a larger one.
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Posted: Wed Jul 16, 2008 4:02 pm
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KX3Powerband Master Joined: 02 Oct 2006 Total posts: 988 Location: Québec |
To do the tests, I fitted a very long clear tube between the rad and the expansion tank. This way, you don't have to wait for spilled water;
as soon as you see bubbles in the tube you know you have a blown gasket
(you have to make sure there is no air lock first).
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Posted: Wed Jul 16, 2008 4:05 pm
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jante350 RD/RZ Jedi Master Joined: 05 Aug 2003 Total posts: 5130 Location: Bergen, Norway |
Ive been stuck in a traffic jam outside Venice with my F2, and the temp gauge only went upto just under the redline (there was foooking hot).
The cooling should be more than adequate if everything is stock and in good nick all around.., atleast in traffic/slow running. The engine produces a certain amount of heat that must travel away from it, and when the temperature rises in the water, the difference between the air temp and the water temp rises, and so does the heat exhange.. on very hot days (40'C) and stillstand or very slow go the temp would go up to just under the redline (Atleast on my bike). The RD500 seems to get hot quicker, but that has a electric fan to cope with it.. and it doesnt kick in before its in the red..
Remember, the red field on the F2 isnt 100'c and boiling, I think its 90 or something... its not dangerous to ride with it abit up there...
And if youre stuck in a traffic jam, just pass the wankers on the in or outside..
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Posted: Thu Jul 17, 2008 12:38 pm
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