RC51 Cooling System Issues
First & Foremost the whole issue that RC51's run hot is a bit overblown. Yes if you are in stop and go traffic they run on the hotter side of 225°, but that is tolerable and if the cooling system is properly maintained then it will be just fine. Below I will outline everything I have learned or at least remember in over two decades of building, owning and maintaining these bikes. I am not going to delve into ethylene glycol versus propylene glycol as it is irrelevant in the scope of this article. Let's start with the SP1. This is in my opinion what started the rumors about insufficient cooling on the RC51. The SP1 only came with 1 fan so yea by the time it kicks on as the engine temp climbs to about 218° it works pretty hard to maintain that temp especially in stop & go traffic in Summer heat conditions. I have on many bikes over the years installed a manual switch so I can turn on the cooling fans long before they would be triggered by the thermostat switch or the ECU which drastically aids in keeping temps down even in heavy traffic. The real root of the problem is simply these bikes are just not designed for commuting in traffic. Sure they can do it, but as a homologated racebike that is not their purpose. It is evident in every facet of the bike from the cramped ergonomics to the flat seat to the dismal fuel mileage etc. To alleviate the issue on a more widespread scale Honda simply added another fan to the other side mounted radiator on the SP2 model. Now this helps to keep the bike cooler in heavy traffic and high ambient heat conditions at slow speeds, but it also hinders the airflow across the radiators at freeway speeds and race pace because the fans are now blocking a large part of the airflow that should be freely moving over the radiator core. Some RC51 owners have opted to install SPAL fans or reverse the fan direction etc and this probably works for their personal needs and that is great, but at the end of the day if the bike is in good operational condition probably all their expense and effort is unnecessary. Again though I don't care what people spend their money on.... On proper race bikes we do not run any fans on the radiators. Yes this requires that we monitor engine temps if they hold us on the grid for too long etc, but with no fans at all we get maximum cooling efficiency by allowing the greatest possible unimpeded air flow over the radiators while in motion. Obviously not a good idea for a streetbike stuck in traffic, but excellent for track only bikes in motion. This brings us to Engine Coolant. If you are in an area where freezing temps are possible you obviously need to run a glycol based coolant that resists freezing (aka Anti-Freeze). There are a myriad of these products on the market and as long as they are made specifically for motorcycles you will likely not be able to quantify any difference in performance between any of them. The reason they need to be motorcycle specific is because unlike automotive anti-freeze motorcycles need to be silicate-free which will protect delicate seals in the motorcycle cooling system. Sure there is always somebody somewhere spouting off that they use Automotive Anti-Freeze in their bikes with no issues, but just use the right shit... There
are also premixed motorcycle specific Coolants like
Engine Ice & Liquid Performance etc that offer some
level of freeze protection that are adequate for riders
in climates where freezing conditions are rare or the
bikes are always in a warm garage or inside the home etc.
I have used most of the brands on the market at one time
or another. I can discern no real differences between
them. They are convenient, but a little more pricey and
as always commonsense needs to be applied as you do not
want to risk cracking your engine block because you
gambled on having enough anti-freeze protection. I have
seen this happen just from one night of freezing temps
inside the trailer at a trackday... Lastly NOTHING cools better than just plain old water. MotoAmerica Race bikes are only allowed to run water period. If it works for them it will work for you. If you go this route use only DISTILLED WATER for both flushing and filling the cooling system. You do not want the minerals or chemicals in tap water causing deposits or corrosion inside your bike. Water Wetter Additive is also a good product and while MotoAmerica does not allow it I can attest it does work exactly as they claim. We verified this decades ago during stringent dyno testing. Just make sure you follow the directions as it is only about a capful of additive per quart of coolant and overdoing it is not helpful at all. Trouble Shooting the Cooling System I have ran built motors on several RC51 over the years with side mounted radiators and experienced zero issue with overheating. If you cannot keep your bike cool with the OEM side mounted radiators then you may have an issue with any of the following: 1. Not having burped the air of the cooling system properly. This happens way more often than it should as people do not realize that trapped air in the side mounted radiators has reduced physical coolant capacity. I actually get a buddy over and lean the bike left and right with the radiator cap off a couple of times to make sure all the air leaves the system. It seems archaic and makes a little mess, but the process works. Make sure to remove the radiator cap prior and then start the bike and let it run long enough to allow the thermostat to completely open to insure the system is flowing properly first. 2. An obstruction or kink in the hoses, bent radiator or a stuck or partially stuck thermostat can all cause overheating issues. 3. Blown Head Gasket... If you do manage to get the engine temp up to about 245° you are putting the aluminum heads into warpage territory and blown head gaskets are common after that. If the head gasket blows and allows coolant into the oil the milky residue makes it very apparent and easy to identify. If the head gasket breaks between the coolant jackets and the Exhaust then it can be much harder to detect as the coolant goes right out the tailpipe as vapor and as the coolant level drops the engine continues to run hotter and hotter. When you are burping the air out of the system as outlined above you can check for this condition by revving the bike a bit. If water spews out of the uncapped radiator when you rev it that is many times indicative of exhaust gasses entering the cooling system and forcing that coolant out. 4. Aftermarket radiators in my experience have always proven inferior in terms of cooling capacity than OEM radiators this applies not just for RC51 side mounted radiators, but others I have seen for GSXR's and R1's etc... Sometimes you do get what ya pay for.. Now while I do not believe Front Mounted Radiator Kits are neccessary as none of us have a Factory RC51 superbike or anything even close to what the Factory Teams used for racing, I do admit they look cool and if you want that aesthetic and have the coin for it then far be it from me to say anything about how you spend your money, but be advised I have actually seen some of these kits have less cooling capability than the OEM side mounted radiators.. Samco Hose Kits: These do not add any cooling efficiency to the bike. They look great and are an EXCELLENT replacement for worn OEM hoses, but nothing more. Moriwaki Cooling Fins: We tested these quite a bit way way back when they first came out and while they look cool they don't make any appreciable difference whatsoever for street riding or bikes with the OEM fans still installed. On the dyno with a bike that has the fans removed from the radiators, Yes we could verify a reduction in temps, but we were also using forced air that was likely outside of the range that would be applied through normal riding. On the track as much as I tried I could verify no real difference with the fins versus without them. I will add more to this page as needed or when I remember something I forgot initially which happens regularly now at my age... |