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Thread: Gen 4: 2011-2015 OVERHEATING! Help to diagnose 2011 ABS
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post #4 of Old 11-01-2015, 04:11 PM Thread Starter
GP Rider
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Originally Posted by SkyDork View Post
I just fixed the same issue with my ZX-7R. First things first, start with the easy stuff and go from there.

What's happening is you're boiling the coolant. Water boils at 212 degrees under ideal conditions. Anti-freeze doesn't change this, it keeps the water from freezing and makes it a lubricant for the pump and anti-corrosive. What keeps the water from boiling is the pressure. Remember from science class in high school that you can make water boil at room temp if you drop the pressure low enough? Well, the opposite is true is you increase the pressure. This is how pressure cookers work. Increase the pressure and water won't boil until it's much higher than 212 deg. So, you're not maintaining the pressure in your bike.

First thing to replace is the radiator cap. The whole purpose of this piece is to keep the pressure at 14-18psi to keep the coolant from boiling. But as the water gets hot and expands, it goes out into the reservoir tank and as it cools and contracts the water gets pulled back from the reservoir into the engine. There should be no air in the system of the pressure balance goes out to whack and you boil it out into the reservoir. The radiator caps job it to keep the pressure up, yet allow the coolant to move in and out of the engine as it expands and contracts. Cheap and easy as they can fail.

Problems get more complex from there. If the radiator cap doesn't fix the issue, it's likely you have a leak somewhere else which is causing air to get into the system. The second most likely place with will happen is a faulty head gasket. This is what it turned out to be on my ZX-7R.

I replaced the radiator cap, thermostat, thermostat housing, fan switch, cleaned the radiator, checked the water pump, pressure tested the block, and in the end it was a bad head gasket. Combustion pressure was overwhelming the gasket at high RPM and blowing air into the cooling system. Air in the system = no pressure = boiling coolant = over heating.

Do not ride the bike any longer until you get this sorted out. Since you're boiling the coolant and getting air in the system, the reading your seeing on the gauges is not accurate. The sensor only works well when submersed in water. Since you have air in the system, the temps are likely higher than what you're seeing. And severe engine damage can occur at 230-240 degrees. In 80 degree outside air, cruising down the street, the bike should be running consistent temps in the 180 degree range. Fan comes on at 212 degrees and the shutdown "HOT" warning at 239 degrees. I hope it's just the cap in your case.
thank you for reply. wouldn't you think that if its the head gasket then i would be boiling coolant consistently? because since i topped it off with 50/50 mix, i haven't seen any bubbles. the temps are better but not stable now. i will definitely replace the cap. I'm trying to reason what would happen if the head gasket was letting exhaust into coolant system.
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