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
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.
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.
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
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.
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.
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.
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.
Thanks @swifty2014. The local old school shop didnt have a cap to my suprise, they usually have what i need. I did go ahead and get a new thermostat and tossed that in and toped off the radiator just for good measure. That did help. Got the temp just below the red and only got about 4-6 oz of coolant bubble out of the overflow vent. Did this in my garage on the center stand so only the bikes cooling system was controlling the temp.
Hey tc862011, I am having the same issue with my 1984 VT700C. The only difference is I am unsure if the fan is turning on or not. If the fan doesn’t turn on does that mean the coolant doesn’t flow ?
Coolant flow is directed by the water pump. A fan that doesn't come on when it should is either a faulty fan, or the thermoswitch that measures the water temperature in the radiator and turns on the fan when the temp reaches a certain point, and shuts it off when the temperature drops.
The water pump would be the last thing that would be a problem . It could have no impeller blades because the coolant was never changed or people only put in water but not a very common thing.
Check the fan first, by grounding the black wire at the temp sensor on the bottom of the radiator. It should turn on the fan with the key on. If it does the sensor may be bad.
But mine doesn't come on til very near the red zone on a hot day.
You can see what he water pump is doing by taking off the rad cap when it is cool and start up and rev the engine. It should raise the level in the filler neck. Not blast out but raise it.
The ⅛ inch play on the large valve will be tight when you push down and rotate the radiator cap to tighten it. The valve seats snug on a circular ridge inside the radiator throat. The two rubber gaskets make a double seal on the radiator throat so inspect the larger rubber gasket on the under side of the radiator cap, too. If the tabs (X) are bent down too much than the cap won't rotate tight as it should. Rare, though. Leave the cap on or loose while you blip the throttle to get rid of trapped air. It ain't going anywhere.
Anytime the engine is running the water pump should be turning, and cause at least a possible little circulation movement in the coolant even with the thermostat closed. If no movement at all take the thermostat housing cover off and thermostat out and watch for movement. If still no good the pump impeller may be ruined.
I actually saw that one time working on an old Toyota Corolla that was overheating. I heard about that test and took the thermo out and the coolant did not move. The car was from HOT Arizona and they never put any antifreeze in and the water was rusty and the impeller blades were all rusted off. No circulation at all. Rare other wise.
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