CBR 600F 1987 - 1990 CBR 600F Forum

Temp gauge going all over the place....vapor lock?

Old 08-06-2017, 11:15 PM
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Default Temp gauge going all over the place....vapor lock?

Got a new issue with the bike.

On Friday, my bike was having battery issues (turned out to be loose terminals) but as I was idling the bike to check for a charge, after revving a couple of times, a bunch of coolant puked out from the reserve tank.

I topped it back up the next day with the bike not running, then rode around for about 10 minutes. On the highway under load, I began to see the temperature gauge jump up, and then down, then back up again.

Before I wanted to jump to conclusions of a borked thermostat or water pump, i called the previous owner of the bike, and he said he had this problem before, stating it to be vapor lock. He said it was a matter of running the bike without the radiator cap on, and blipping the throttle a few times.

​​​​​I did this, and had to top the reservoir back up as well, and gave the bike a few blips while doing so. Looks like it hasn't changed.

Perhaps I need to run it a bit longer and do it a few more times? Maybe I need to flush the coolant out and start over? Anyone have a similar experience?
Old 08-07-2017, 08:55 AM
heresolong's Avatar
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Location: Blaine, WA
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Don't know that flushing the coolant will have any effect but if it is vapor lock, then you have an air bubble in the system. This probably means that you have an air leak in the system also, either due to a faulty radiator cap or a leaking hose. I would do what he suggests as far as running the bike without the radiator cap as this is the standard procedure for getting rid of air bubbles when you fill a coolant system but I'd also check the radiator cap to see if it is any good.
Old 08-07-2017, 08:56 AM
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PS Seems like you could also check the gauge electrically to see if it responds properly to varying voltage but maybe someone else will chime in here.
Old 08-07-2017, 01:22 PM
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Check every hose to be sure the clamps are tight even the ones that go into the head on either side. Look for weeping...actual wetness or white powder around the hoses. Vapor lock on these engines is quite rare.

Check the radiator for weeping or leaks.

Then if you don't find anything get a water pump gasket kit (I think it's just an Oring). The pump can push air or mix with oil if the seals go.

After that if it doesn't stop you likely have a blown head gasket. Tell tale sign of blown head gasket is small bubbles coming through the overflow pipe into the overflow bottle when there is liquid in there.
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