Overheating (New Owner) - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 11 (permalink) Old 09-03-2018, 12:38 AM Thread Starter
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Post Overheating (New Owner)

Hello all,
I am a new 2002 RC owner. I purchased the bike about a week ago after having a few friends that have them and doing my usual OCD research on them. I have fallen in love with the twin, performance, and timeless bike that it is. It's a 2002 with 13,8xxx miles, slip on ladybird exhaust. I am however having an issue with overheating and was hoping anyone here could help point me in the right direction. I have approached temperatures of 250+ cruising on the local streets and pull off to cool the bike off. While I am at a light at idle the fans do the work and cool the bike down. While I am on the freeway the temperatures stay relatively cool. Around 230 or so ( I know still no ideal ). I do want it to be known that I am in Arizona and the temp does tend to get hot. I have changed the oil with amsoil, had a coolant flush performed with engine ice, changed out the spark plugs, remapped the bike on the powercommander v. Still hitting those horrible temps though. Before I got to the shop for the coolant change I informed them it was overheating and to look into it. They told me they would. They said they let it idle for around 10+ minutes and it cooled great. The problem isn't at idle, but at cruising speeds. I checked the coolant reserve tank tonight after they performed the coolant flush and it is above the "Upper" line on the tank when it wasn't before. After scouring the web all day, am I looking at a blown head gasket? ( I don't notice white smoke or anything), bad water pump, exhaust leak due to the previous owner putting the slip on lady bird? I'm really just at a loss and am looking for some guidance or a push in the right direction. Thank you for ya'll's time and I hope you are having a great labor day weekend!
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post #2 of 11 (permalink) Old 09-03-2018, 09:20 AM
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So there are a few things you can do to help keep the temperatures down on the RC. The DHC air scoops do make a difference while riding. They mount inboard of the radiators and channel air directly through both radiators while moving. You can reverse the polarity of your fans so then push air through the radiators instead of pulling (makes a little difference in slow traffic as it works with the forward movement of the bike instead of against it). You can install a manual fan switch enabling you to turn the fan on before the bike gets hotter. This wont do much when riding but helps a bit in stop and go traffic. 230 degrees while riding is a bit too high even on hot days. I'm in central California and see consistent 100+ temps for most of the summer. 190 degrees it typically what I see while riding on the freeway. In traffic is a bit different story though.

I might check the thermostat to see if it's operating properly first though. It may not be opening all the way.
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post #3 of 11 (permalink) Old 09-03-2018, 12:36 PM
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Thermostat should be changed and make sure nothing is blocking the coolant flow. I had a brand new YZ125 years ago, it ran great for a month, then overhead so i started looking into it, drained the coolant pulled hoses and found a bunch of o ring chunks blocking the lower radiator. Your bike has much more time on it but you never know who did any previous work and how they did it.
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post #4 of 11 (permalink) Old 09-04-2018, 01:02 PM
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In light of your story, I'd burp the cooling system, maybe you have an air bubble.
Bike on it's sidestand and completely cold, remove rad cap (and inspect).
Leave the rad cap off and start the engine, let it warm up.
If your thermostat is opening when it should, somewhere around 167F degrees, the coolant will start to move in the rad. By 172, it should be moving rapidly through the rad. At that point, if you have air bubbles, they should begin to expel while you roll the throttle.
When no more air bubbles come out, 1-replace the cap, 2-then turn off the bike.

After the bike cools completely, check coolant level in rad, and fill the overflow container just at 1/3 to 1/2 full.

Did you try smelling the coolant in the rad for exhaust fumes? Keep a close eye on your oil.
Is the rad cap a good healthy one? Overflow line clear?

John, 2000 RC51 #000100

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post #5 of 11 (permalink) Old 09-10-2018, 03:39 PM
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The problem can be caused by doing the coolant replacement (I had this happen once). Because you fill the coolant from one side of the bike (radiator cap), and it has to make its way across to the other and into the coolant tank, it is very easy to get air locks. So it looks like you have a full system, but in fact you don't! The factory service manual gives very good advice on how to fill with fresh coolant to avoid this. However, given your situation, what I did was to open the radiator cap and the coolant reserve bottle and let the bike idle, and blip the throttle to try and get any trapped air to move. Beware of hot coolant! Worst case, drain it all out and start again, and measure how much you drain to check with the tech. spec. amount (i.e. that will tell you if you have emptied it all out and/or if it wasn't full in the first place). Good luck - you just need to persevere :-)

(UK-spec. SP2, 2002 owned from new, 45k miles)
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post #6 of 11 (permalink) Old 09-10-2018, 03:48 PM Thread Starter
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Thanks everyone. Swapped out thermostat which helped a lot. Have great cruising temperatures on the freeway now. Swapped out with engine ice as well.
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post #7 of 11 (permalink) Old 09-10-2018, 05:54 PM
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I've never had any bleeding problems after changing my coolant at all.
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post #8 of 11 (permalink) Old 09-11-2018, 01:49 PM
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Also look for coolant residue from loose hoses or pin-hole leaks, and fan motor bearings.
I was having heating problems years ago, and found two issues:

1) The hose clamps were a bit loose due to the hose rubber taking a set from age.

2) I had shifted over to Engine-Ice and noticed purple coolant residue on the left cowl.
After investigating further, I found the left upper radiator tank had a hole in it the prior owner had patched with JB-Weld, which does't work with radiators, due to the expansion and contraction of the metal.
After having the hole welded and pressure tested, I ceased having cooling issues.
On a hot summer day at idle in traffic, it would not exceed 218, which the fans quickly dropped down to 208. Once moving, the temp dropped even lower.
And in the spring, with temps in the 80s, I saw temps below 180 degrees while on the move.

3) For either SP1 or SP2, check condition of the fan motor(s).
With the engine off and cool, try to spin fan(s) by hand. They should easily and freely spin.
When I was refurbishing my SP2 (due to prior owner), I noticed left fan motor bearing was squeaking when rotated by hand and would immediately stop rotating, plus indication of fan blades rubbing against the radiator fins.
I corrected the fan to radiator clearance issue, and replaced both fan motors.
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post #9 of 11 (permalink) Old 09-26-2018, 12:28 PM
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I don't have near the expertise or experience with the SP as 99% of the members here to offer much, but in the 7 years I've had mine, I can honestly say they are one of the more difficult bikes to replace the coolant on. My first go around with it was a real exercise in temperament. Got more than one moderately warm (LOL) glycol bath in the first go around. I was better prepared when I switched to Engine Ice (our track rules won't allow glycol based coolants) but it was still a painfully slow process. Patience is a virtue.

Duct tape can't fix stupid...but it sure helps muffle the sound
'03 SP2, '09 GL1800
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post #10 of 11 (permalink) Old 09-26-2018, 12:39 PM
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I pull the hose off of the water pump , let it drain and then suck out the rest with a wet vac. By the way , Redline Supercool works better than Engine Ice.
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