85 VT500C overheat, blows out coolant - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 11 (permalink) Old 08-02-2010, 08:29 PM Thread Starter
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85 VT500C overheat, blows out coolant

My VT500C always seems to have run a little hot, even though it's got new coolant. It likes to sit in the bottom part of the red on the temp gauge, which I understand isn't actually unusual or dangerous for these bikes. But it does concern me.

A few days ago I let it idle for about 30 minutes before my ride. It spat out all its coolant onto the ground - I believe through the overflow hose because the engine didn't appear to be wet.

I refilled with water and let it idle for a few more minutes while I watched it... it kept it in. After riding for about 10 minutes though, it creeped back up into the red.

I had a friend suggest that my radiator may be blocked or corroded, and that I should have it piped (scrubbed out). If it's got a blockage, he thinks the backpressure may cause the coolant leak I saw.

Thoughts? I looked up a radiator on bikebandits and it was something like $430, so I don't want to go that route on a $1500 bike.
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post #2 of 11 (permalink) Old 08-02-2010, 09:05 PM Thread Starter
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You'll have to forgive me, I'm brand new with bikes (hence why my bike is old and cheap!)

Talked to the local shop around here and they say that 30 minutes is way too long to idle the bike - although it's cold natured and has to have 5-10 to warm up. And they suggested I check the fan and its fuse. Seems like a good place to start. I'll do that, and I'm open to other suggestions as well.
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post #3 of 11 (permalink) Old 08-02-2010, 09:20 PM
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my bike puked antifreeze after i messed around with it. reason why? I didn't have the cap on all the way, which made the pressure come out of there and made it puke out the overflow tank.. well after it pukes enough there isn't any in there and it over heats.

So maybe check your cap first to see if its tight and maybe see if the rubber is all crappy and cracked.

You might also want to take your thermostat apart and test that. hang it in a pot of boiling water and see if it opens. if not then your thermo isn't working and not letting coolant into the engine. (overheating)

and yes check to see if your radiator is clogged up with crap or blocked.

1984 VT700
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post #4 of 11 (permalink) Old 08-03-2010, 12:27 AM Thread Starter
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Thanks for the suggestion. I'll try that.

(making this post so I can subscribe to thread)
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post #5 of 11 (permalink) Old 08-03-2010, 11:47 PM Thread Starter
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I watched it carefully today. I let it idle for awhile. The temp slowly creeped up until it touched red, then it started belching coolant from the overflow hose. The fan never came on.

I checked the fan fuse - it's good. So I guess the thermostat is next. Now the fun part - figuring out where the thermo is on this thing
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post #6 of 11 (permalink) Old 08-04-2010, 12:37 AM
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OK first things first... get yourself a manual from here


Then test to make sure your fan is working by jumping a test wire from battery to fan.

Post your findings here.

Good Luck!
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post #7 of 11 (permalink) Old 08-04-2010, 11:54 PM
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The fan switch on my vlx is in the bottom of the radiator. Mine was just one wire. The fan has power to it all the time, grounding the wire at the switch will turn on the fan if it is working. BTW check for rocks and sticks keeping the fan from turning. I put a togge switch in the line to turn it on till I had time to change the switch.
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post #8 of 11 (permalink) Old 08-05-2010, 02:20 AM
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The over flow hose goes to a coolant recovery tank where it stores the hot coolant untill it cools off and is sucked back into the radiator, the hose from the Rad to the tank MUST be air tight or it won't work, as the coolant gets hot it expands and when the pressure exceeds the cap pound rating it shoved to the recovery tank and don't use water to cool the engine, it must be a 50/50 mix with a NON SILICATE coolant.

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post #9 of 11 (permalink) Old 08-05-2010, 02:58 PM
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Use Preston 50% Premixed antifreeze.

My Shadow had similar problem; it was a bad radiator cap.

Honda wants a lot of $ for a new one. I heard that you can buy from an
auto parts store, if you can get them to look up the part number.

Ride safely,

1983 Nighthawk 650
1989 VTR250
1985 Sabre 700 - - Sold
1983 Shadow 500 - - Sold
2006 Ninja 500- - - - Sold
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post #10 of 11 (permalink) Old 08-05-2010, 04:06 PM
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I just resolved my problem, Same symptoms,it was the cap. I pulled thermostat and tested, it opened, but slightly out of spec. Not wanting to order the oem part, I took it to autozone and the guy there found me one same size and heat rating for 10$. They also had a cap tester and so I tested it right there. It was holding 9 psi. Slightly out of spec and I thought," it can't be that easy?!" so I bought the thermostat instead and put it in, same symptoms again. So now I'm freaking out thinking it's he water pump or something major and I'm screwed, but I went back to autozone and asked if he had any caps that were similar to mine. He found one that he said was for an older Honda civic. We put it onthe tester and it was the same size and held 11psi, which was in spec, so I figure what the hell, bought for 6 bucks. The only difference is tha cap has ears on it, not round. So I topped off coolant at radiator and burped it. I also got some clear tubing from home depot and used it like a diptsick on my recovery tank, cause it was too yellowed to see anything in there. I saw coolant so I didn't add anymore. I crossed my fingers and went for a short ride. This time the temp gauge never got above halfway and went I stopped, I heard no boiling at all. I did see about 20 drips, but I mean drips, and not boiling fluid spewing out. I think my recovery tank was a bit full before riding though. My fan has not come on since I've had the bike, about two months. I shorted it and it kicked on so I know it works, but I'm not spending $100 on a new thermo switch, I'm probably going to wire a manual switch like some of the guys herehave done. Hope that helps...
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