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Whenever I ride through town my bike over-heats, often boiling. This can even happen in mid winter! It`s done it ever since I`ve owned the bike (3years) and is really p***ing me off!<br>I`ve rebuilt the top end so am sure it`s not a head gasket fault, flushed the rad, wich was clean anyway, chacked the pump- clean as well. Put a new fan switch in, no improvement. Took out the thermostat, still the same.<br>On the open road, all is fine, as soon as I hit traffic, the gauge rises and rises, if the road clears, the needle falls within a mile.<br>It`s getting to the stage where I try to avoid posing down my local high street( gutted!!)<br>It seems as if there is a restriction or kink in a hose somewhere but I`ve checked and re-checked and all looks good.<br>My next step is to give the rad to a specialist and get it double cored. <br>Am I alone or is this a common fault? <p></p><i></i>

Question 1 - is it a stock head gasket? If not, replace it with the stock head gasket. <br><br>Question 2 - Did you scrape the gasket surface when it was apart? If you did, and you had a stock gasket, You probably put a small scratch in the head. Its very sensitive to scratches. You'll need to get it resurfaced.<br><br>Qestion 3 - during the assembly, did you keep your hands clean and grease free? the gasket is sensitive to oil films, lint and debris. <br><br>I've had this problem before, licked it, removed the head to do some work and have it now. My problem this time, is the non stock gasket. I'm going to replace the cometic crapsket with a genuine Yamaha gasket. Beware, they have two types and neither work. Because of molecular size, and a high pressure differential, combustion gases have an easier time getting into the cooling system vs. the other way around. They pressurize the cooling system, forcing coolant to blow through the cap and into the tank. You will lose fluid until it reaches the point where the combustion gases can percolate through the remaining coolant, collect in the filler neck, and vent continuously through your cap. A tell tale way of determining this is if you remove your cap, cold of course, and start your bike. If you see bubbles that never cease, they are combustion gases. <p></p><i></i>

It was doing it before I pulled it apart and after the re-build, although it isn`t any worse, it`s no better!<br>I initially thouhgt it was the head gasket but when I looked at both the head and block I could see no signs of blow-through.<br>I fitted a new genuine head gasket, cleaned both surfaces to a nice shine, I sanded them down with a block and 1500 grit paper. Home skim job!! I`m pretty confident the surfaces were scratch free and uncontaminated.<br>I agree it is still possible that gasses are forcing into the coolant, this weekend I`ll get an anti-freeze check to see if CO2 is present, if thats ok, Im gonna go with re-coreing the rad, not sure I can be bothered to remove the head again!!<br>On a lighter note, I cured it`s oil consumption- it doesnt use a drop!!!! <p></p><i></i>

I wonder if you have a case of a crack or porosity in magnesium castings or maybe in the iron liner. Have you had a cooling system pressure test done? They pump it up and check over time for a pressure decay. I would hold off on the double core radiator. You might be throwing good money at the wrong solution. Remember that when it was new, it was designed to run in traffic without boiling over. <p></p><i></i>

is it running lean down low??? mine does that when my jetting is off in that direction.<br><br>zoid <p></p><i></i>

Good points guys!<br>As it`s done it ever since I`ve owned it, I would guess it`s not a jetting problem. I think I will definitely get a pressure leakage test done.<br>Cheers, I`ll keep you updated! <p></p><i></i>

Just signed on and read this - probably too late.<br>Have had FZR1000RU for ~4yrs am on 2nd engine - last one dropped a valve at around 80K miles. It ran within temp limits (just) within town. Changed engine ~1.5k miles ago (6weeks) it ran hot and would 'boil over' if stationary for any time even though the temp guage was not in the red. Checked & cleaned radiator - all ok. No gases in rad whilst running implying no head gasket problems. Timing was fine so problem pointed to radiator cap. Like the ones for many cars it has a spring to seal the rad from the overflow tank, the spring presses on a washer which has a rubber seal next to it. The seal presses on the neck of the radiator filler. Once pressure exceeds 15-20lb/sqin, pressure lifts the spring, and removes the rubber seal from the top of the rad allowing the coolant to exit along the overflow pipe. If too much exits (it always does) then the tank overflows. With age/use the rubber seal on the cap degrades. A new rad cap costs £30. Standard Jap bike over-pricing. I Bought an O ring seal that filts into the top of the rad so now the seal on the cap mates against it rather than straight onto the metal of the radiator filler. It cost £0.15 and works a treat. <p></p><i></i>

cheers for that, whyml, but I have changed the cap for a new one already, so I`m guessing thats not the fault. My bike seems to boil when the gauge reaches the red, I`m still worrying that the head may be porous but I havent done a gas or pressure test as yet. <p></p><i></i>

Mine used to badly overheat in traffic until I fitted two rad fans. It still gets hot but not enough to cause concern. I got a second fan from a bike breakers and used this with the original to "upgrade" the cooling system. You need a mig welder to fix it all together but it is a cheap effective mod.<br>Mark <p></p><i></i>

Hi all<br>my '93 exupru gets well hot in town but as i live in a small town i have never seen the temp gauge go into the red, yet. i feel that radiator efficiency is degraded by the crap that flies on to it. as this is a fairly delicate lump of metal, i wonder if anyone has a good idea of the best method to clean it?<br><br>shiney side up everyone. <p></p><i></i>

Yup, I`ve cleaned my rad! I took it off, then blasted it with the garden hose from behind to clear all the crud. I also flushed it through in the same way. I`m pretty confident the rad isn`t blocked and the fins are all clear. <p></p><i></i>

Just joined and read your post, only about a year late but maybe I can help someone else with the same prob.<br>Once you've checked all the obvious things rad cap,thermo etc and made sure your not pressurising the rad and blowing water straight out, have a think about this!!<br>Your fan is operated by a thermo switch which connects the power supply at a pre-determined temp which in turn starts your fan.Is your fan working? can you hear it going when your bike starts to get hot?If everything is working and your bike still overheats then maybe your fan is not coming on early enough at least thats what I thought when my 87 FZR 1000 over heated every time I spent more than 5 minutes sitting at a set of lights.So I brought a workshop service manual and went through all the electrics and tested everything.That didn't help at all, then I noticed the operating temp figures given in the manual they are:<br>THERMO SWITCH<br>HEATING UP<br>BELOW 98DEG C NO CONTINUITY<br>ABOVE 105 +/-3DEG C CONTINUITY<br>COOLING DOWN<br>105 -98DEG C CONTINUITY<br>BELOW 98DEG C NO CONTINUITY<br> <br>In other words your fan is not supposed to start until the water temp is at least 105deg c and it will turn off as soon as the temp drops below 98deg c! Thats bloody hot, I've been a automotive mechanic for 15 years and factory specs or not there is no way any cooling system should be allowed to get that hot.I live in New Zealand and during the summer we regulary get temps that exceed 30deg c, at that you will cook your bike very quickly.It's not just FZR's that have that problem here brand new TL 1000's, FZ1's,VTR 1000's all had overheating probs at slow stop start speeds.The cure?<br>Two ways -fit thermo switches with lower temp ratings which can mean going through a lot of parts manuals trying to find the right thread,pitch etc,or put a manual override switch on by that I mean a simple 12v switch wired onto each wire going into your thermo switch when your gauge gets to 3/4 just hit the switch and your fan will start, I wired mine up to a small light mounted on the instrument cluster so I could see when it was going and remember to turn it off.Either solution works a charm as long as you have made sure the rest of the cooling system is ok.<br>Hope that helps someone<br>fzrnut<!--EZCODE EMOTICON START :hat --><img src=http://www.ezboard.com/images/emoticons/pimp.gif ALT=":hat"><!--EZCODE EMOTICON END--> <p></p><i></i>

just a little note from me too. <br><br>My yzf 750/1000 was overheating badly last summer and i thought that since my fans are not working .. (it boiled in 100deg) ... they must be broken. <br>When i heard that they are supposed to first work at 103deg .. I started to wonder about this .. and<br><br>some half witted mechanic had put the two little rubber hoses that come to the high right on the radar in wrong places.<br><br>this caused the water that should be gone to the radiator from the waterpump to get under the radiator-cap! .. and all the water in the radiator to get to the "collector".. (i dont know what this part is in english) .. when 100deg.. <br><br>i shure did curse the poor bastard for not thinking straight. <p></p><i></i>

I should add that I have noticed that the temp build up is very sensitive to the idle mixture. Leaning the mixture out to where the idle runs rough and drops by 200 rpm is so lean that there is no problem with heat (runs very cool, actually). Adjusting the mixture to the rich side doesn't cause heat either. adjusting the mixture slightly lean of optimum causes heat to build up fairly quickly and would run the fan continuously while sitting still at idle. Both other conditions caused the fan to cycle on and off, drawing the temp down quickly. Just one more thing to check if you still suffer from the problem. <p></p><i></i>

fzrnut,<br><br>"...I mean a simple 12v switch wired onto each wire going into your thermo switch ..." just wondering how exactly the 2-wire switch is being hooked up. Did you just tape into the existing 2 wires from the sensor and hooked that up to the manual electrical switch? <p></p><i></i>

hkwan <br>check your inbox sent you info regarding wiring up aux fan switch.<br>cheers<br>fzrnut<!--EZCODE EMOTICON START :hat --><img src=http://www.ezboard.com/images/emoticons/pimp.gif ALT=":hat"><!--EZCODE EMOTICON END--> <p></p><i></i>

my bike also heated in town til a mechanic told me that my after market exhaust would make it do that unless i rejetted my main carb jets atleast 2 sizes bigger if yours has aftermarket exhaust maybe this will help <p></p><i></i>

Just installed the switch, the 2-wire method. Seems easy enough, besides the fact that I got to take the gastank and airbox out to access the wires.<br><br>Bike has not ran hot enough to the need of the switch yet. <p></p><i></i>

I know this not a timely reply, Did you get the overheat fixed? Iv'e seen rad hoses come apart inside, forming a 'bubble' or 'flapper' on the inside wall of the hose due to seperation of ply bonding in the hose it's self. I'ts very hard to catch, but it is a flow restriction, and will cause an overheat. Maybe try Shooting temps with a raytech infared thermometer with the fairings off and the bike up to temp, you would see a obvious temp difference midway along a restricted hose if that's the problem. Good luck. <p></p><i></i>

Boy I’m starting to feel guilty already,<!--EZCODE EMOTICON START :o --><img src=http://www.ezboard.com/images/emoticons/embarassed.gif ALT=":o"><!--EZCODE EMOTICON END--> I’ve just posted about how I’ve taken my fans off my YZF as they weigh ¾ kilo each & it never gets hot enough to use them. But I don’t use it in town so. . . <p></p><i></i>