Cooling issue - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 13 (permalink) Old 05-22-2019, 07:28 AM Thread Starter
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Model: VT700c
Year: 1984
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Cooling issue

Hey guys been a long time since I've been on here. Here is the issue, bike is a 84 VT700c. My coolant is flowing into the overflow to the point of overflowing the overflow. I checked the system and verified it is not cracked or leaking, it is filling the overflow and flowing out the vent tube of the overflow. This implies its not being drawn back into the system like its designed to do. I checked the radiator cap and it has good rubber seals, the smaller plunger has good movement and is tight at rest. The larger plunger is loose, i can move it about 1/8" or more up and down with the spring not touching it. Just want to confirm if thats normal movement or am i right its got a worn spring and could be causing my issue. Thanks in advance for your opinions

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post #2 of 13 (permalink) Old 05-22-2019, 08:17 AM
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Is your fan working? Thatís a sign of overheating


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post #3 of 13 (permalink) Old 05-22-2019, 08:28 AM Thread Starter
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Is your fan working? Thatís a sign of overheating


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Yes the fan is kicking on normally. The bike is staying in safe temp ranges. Im just not getting coolant back into the system once it goes to the overflow, its flowing out the overflow vent once the overflow is full. My thought is the radiator cap is basically a check valve its not opening up to allow the system to pull coolant back to the radiator like its design to.

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post #4 of 13 (permalink) Old 05-22-2019, 08:29 AM
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Thatís a possibility. I think there is a Honda Civic radiator cap you can pick up at an auto parts store that would work.


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post #5 of 13 (permalink) Old 05-22-2019, 08:36 AM Thread Starter
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Awsome. Ill check into that as a back up plan. First there is a local shop here that quit often has the oem part i need. Its usually a used part but a good part and they stand behind it.

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post #6 of 13 (permalink) Old 05-22-2019, 10:15 AM
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Quote:
Originally Posted by bigolepit View Post
Hey guys been a long time since I've been on here. Here is the issue, bike is a 84 VT700c. My coolant is flowing into the overflow to the point of overflowing the overflow. I checked the system and verified it is not cracked or leaking, it is filling the overflow and flowing out the vent tube of the overflow. This implies its not being drawn back into the system like its designed to do. I checked the radiator cap and it has good rubber seals, the smaller plunger has good movement and is tight at rest. The larger plunger is loose, i can move it about 1/8" or more up and down with the spring not touching it. Just want to confirm if thats normal movement or am i right its got a worn spring and could be causing my issue. Thanks in advance for your opinions

A sure sign that someone put too much coolant into the system.
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post #7 of 13 (permalink) Old 05-22-2019, 10:24 AM
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Check the entire length of the overflow hose for cracks and check that the connections are tight. Any leaks will allow air to enter the system and prevent coolant in the overflow reservoir from returning to the radiator. This is a somewhat common issue.


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post #8 of 13 (permalink) Old 05-22-2019, 10:54 AM Thread Starter
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A sure sign that someone put too much coolant into the system.
No coolant was not overfilled. The overflow started empty. I always fill the radiator then run it once with a empty overflow then top off the radiator once it cools.

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post #9 of 13 (permalink) Old 05-22-2019, 11:14 AM
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Three tips from my experience...
1) Pull the plastic shroud off the front of your radiator and inspect the radiator fins. If you ride on gravel roads at all like the previous owner of my '85 VT700C did, the front fender does not extend down far enough to protect the radiator from stone damage. Mine was beat to a pulp. Though not leaking, the fins were damaged beyond repair, clogged with dirt, and shutting off the air flow.
2) Pull your radiator cap off with the engine cooled down and make sure it's full. Pull your plug wires off to prevent firing, and crank your engine. If you hear huffing air coming out the radiator fill, you have a blown head gasket. A blown head gasket near an exhaust valve will force cylinder air into the cooling system, over-pressurizing the system and blowing your coolant out. You can confirm it with a compression test..should have 150psi + on each cylinder.
3) Look for a coolant drip underneath the left side of your bike when it is parked. On mine, the rubber nipple that connects the overflow tube from the radiator to the reservoir was cracked from age. Over time you can lose enough coolant from "normal" radiator overflow to cause overheating and filling the reservoir. You can inspect the nipple by removing the left fairing "Shadow" cover and then swing-out the plate with the stator wiring and looking at the coolant reservoir entry nipple. Wiggle the overflow hose to see if the rubber grommet on the nipple is cracked.

If it jams, force it. If it breaks it needed replacing anyway.
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post #10 of 13 (permalink) Old 05-22-2019, 12:54 PM
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The 1/8th inch movement of the main spring plate is not good. They are usually snug against the spring. The small plate is the return valve and should snap back when lifted with a finger nail.

Maybe try a new cap first.

And make sure of the pressure. If it says .9 (.9 BAR) on the top it is about 13 pounds. Many newer cars go up to 16 + pound caps and that would be too high.


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