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Discussion Starter #1
So, as I mentioned in the "Lots to sort out" thread, the bike has generally been behaving well. One exception has cropped up, however, and that is with the cooling system.

The bike seems to run at normal (for this bike) temps. During long idles, the fans turn on at 220 and, temp immediately begins to come down and fans shut off about 208. While cruising, the temp is anywhere from 180 - 205. My problem is with coolant recovery. The overflow tank fills itself up, but does not draw the overflow back in to the radiator and ultimately pisses some coolant overboard. In fact, The system seems to stay pressurized LONG after the engine has cooled down (I'm talking after DAYS of not running). Literally a week after the big ride to Tellico, I popped the radiator cap and it blew off positive pressure! Meanwhile, the overflow tank is completely full and levels in the radiators and definitely down.

My first instinct was that the cap was either malfunctioning or perhaps the wrong one, but if the system doesn't generate a vacuum as the engine cools, then of course there's nothing to draw the coolant back in to the system, regardless of the cap. Anyone have any ideas on what might cause this? Maybe I should try a new cap anyway? Kinda stumped...
 

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I'd say first try a new radiator cap.
It's supposed to open when expansion or excessive pressure occurs and vent to the recovery tank, then allow the system to pull from the recovery tank when the system cools off.
Sounds like it's not doing it's job and acting like a one-way check valve.
 

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One item worth mentioning is to remove the recovery bottle and clean it out.

I usually pull the bottle and fill it with hot water and a few drops of Dawn dish washing detergent. Let that sit over night and then take a soft bottle brush and scrub out the inside.

Make sure to clean the nipple where the return hose attaches to the bottle, it has been discovered these have become clogged over time. Replace that line attached there if it clogged, just for cheap insurance.

This all sounds like a PIA but it is worth doing.:nerd:
 

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I second the cap :D
 

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Discussion Starter #6
New cap installed, took it for a short ride and allowed to heat up to fan temp twice so now we'll see if it pulls the excess back in after a cool down. I'll post what I find tomorrow.
 

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New cap installed, took it for a short ride and allowed to heat up to fan temp twice so now we'll see if it pulls the excess back in after a cool down. I'll post what I find tomorrow.
Good time to place our bets then?



;)
 

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Discussion Starter #9
OK so the coolant level was down this morning by perhaps 3/4 cup (in the radiator). Overflow tank slightly higher than yesterday but nowhere near full. There seemed to be a bit of positive pressure on the radiator when I removed the cap this morning.

I replenished the coolant and will see if it keeps filling the overflow with subsequent running. I don't understand how the system is not generating a vacuum as it cools down though. It has been off since about 6PM yesterday evening.
 

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Discussion Starter #10
Well I just returned for a great trip to western NC on the RC this weekend. Bike behaved well and my riding confidence on it continues to improve.

Unfortunately, the cooling system is still blowing coolant into the overflow tank and not recovering it in spite of a new cap. Yesterday, after a cool down during lunch, I looked in the radiator and it was down over 2 inches from the top. I replenished the coolant and of course, the bike did fine on the remainder of yesterday and on the ride home today. The temperature seems to vary quite a bit with riding conditions, but any time it gets to about 220, the fans kick on and it immediately begins decreasing. This is pretty much the same behavior I've observed on the VFR with a very similar cooling system.

The bike now needs a front tire and I'm considering taking it to a local shop to have a cylinder leakage test performed along with the tire. I have no problems with how it runs and I have not observed or smelled any coolant/steam from the exhaust but I'm beginning to run out of ideas here. If it turns out to need a head gasket, I may just shoot it! (JKJK!)

I suppose a thermostat could be tried as well, but since the temperature seems to behave appropriately, I kind of think changing it would be pointless. I'm open to any other ideas or suggestions.

Thanks in advance guys.
 

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I would have thought the radiator cap was the fix from the problem description.
Got me why the cooling system still maintains pressure even overnight.
It might just be a crazy thermostat problem.
 

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Grasping at straws here. Are you certain the system has been properly burped - no air bubbles trapped in cooling system? Probably not that anyway - from your description.

Is it possible you got a defective radiator cap? It's rated for 1.1 bar, right? I'd be inclined to try another new cap just to double check.

May be time for a cylinder leakdown test...
 

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Discussion Starter #13
Yes, it's a 1.1 cap purchased from Honda. Not sure about the burping but I may review the manual and see if that is worth a try. About the only things I see possible at this point are thermostat (which seems unlikely to me, frankly) or a bad head gasket, which the leakage test would discover. I'll keep you posted.
 

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Do you smell any exhaust in the cooling system?

I found the rad caps are available at the major auto parts stores for about $10 if you want to try another cap.

I'm trying to wrap my mind around how the thermostat could cause pressure to remain in the system once cooled...

Not to second guess you, but you're sure it's pressure on the (cooled) rad cap, and not vacuum?
 

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Discussion Starter #15
I agree about the thermostat.... Totally whacky Longshot.

It sure feels like positive pressure when I remove the cap but that may be something to double check also. I've not smelled the radiator so I guess I'll try that.

I just wondering if maybe the hose connecting the radiator top to the tank might have some kind of internal defect that is causing it to behave like a 1 way valve and preventing coolant from flowing back into the radiator. I've heard of old brake hoses doing this and causing calipers to not release. May try replacing that hose just for giggles.
 

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When was the last time you performed a drain/refill of the coolant system?

If it's due for one you can ensure that the system has been properly bled/burped of any air while refilling it...
 

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Discussion Starter #17
Only owned the bike since February but I'll review the burping procedure and verify no air pockets. Are these bikes known for this being a problem?
 

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Discussion Starter #18
Well I looked over the burping procedure and there's really nothing special. Top off radiator while bike is on side stand, start engine with cap off and allow it to reach full temp, blip throttle a few times and if coolant falls below full, re-top. I haven't followed this procedure to the letter so it's worth a try, but since it doesn't involve cracking special bleed valves or some oddball loosening of hoses I'm skeptical that this is the problem. Certainly worth a try though.

The shop I spoke of that I was hoping would do a cylinder leakage test apparently doesn't have the equipment to do the test so I'll have to try another shop for that. In the meantime I'll try the burp procedure, test the hose between the radiator and the expansion tank and possibly try another cap.
 
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