Ok, I've been anxious for a long long time about little bubbles that I see in the filler neck. Up until 140F, the filler neck is flat, at 140F-180F I start seeing bubbles appear....tiny bubbles like dust rising to the surface. If I rev the engine to 5-6k, the bubbles increase to tons of little bubbles. Agains, the bubbles do not break on the surface and slosh coolant out, they just look like carbonation.

So I took it to Express Oil and watched the guy hook up a cylinder filled with blue fluid on top of my fill neck. The bubbles traveled into the fluid but it never changed colors. He let the engine run for about 3 mins and revved it up a few time...still no change in color meaning no hydrocarbons detected...so WTF is going on?

 

Sounds like your coolant is boiling. Without pressurizing the system, it will have a lower than normal boiling point.

Go boil a pot of water and look for the little bubbles... if that looks similar to your situation, then that is probably your answer.

 

coolant doesnt boil at 180F at atmosphere......

It looks more like the waterpump is creating bubbles if that is possible.

 

water pump cavitation, also, check your hoses. I had to track down several leaks when I bought my FD.

 

well it certainly seems like water pump cavitation, considering the bubbles increase tremendously when held at 4-5k rpm. If this is normal, then why do people consider the champagne test to assess o-ring failure...how absolutely inaccurate of a test if its normal for your water pump to stir up bubbles. Maybe my pump is worn causing more cavitation?


All of my hoses have been replaced....the only thing I can think of that could ever cause a leak would be the drain plug on my koyo radiator, its cross-threaded in. However, I haven't moved it since its cross-threaded and it has a rubber gasket sealing it....no leak at all, even under pressure.

 

maybe the system needs burping? just trying to rule other things out... I have heard that certain issues with a pulley can cause abnormal water pump cavitation which might cause these fine bubbles but I can't confirm... been a long day.

would be interested to know what you find out.

 

I've burped so many times.

Yea...a small pulley at high rpms will cause cavitation...however I have a larger WP pulley

Seriously, the coolant fizzes up when I rev and hold it at 4.5k....then when I let of the throttle, the coolant settles with a few tiny bubbles. This is pissing me off.

 

One thing I can think of that may account for your bubbles - air will dissolve in water. However, the warmer the water is, the less air it will hold. In addition, the rapid pressure decrease and turbulence of the coolant passing through the thermostat will tend to cause that dissolved air to separate into bubbles. The higher the coolant temperature and the faster the water flow, the more this will happen. So what you are seeing is not, IMO, abnormal. The champagne-bubble test is probably only valid at low RPM's.

 

iirc I dont think I have seen a champagne bubble test done other than at idle. Maybe that's one of or the main criteria for doing the test.

Honestly, I never thought of testing at higher idle, but I would imagine it would skew the results the way compression readings would show slightly higher values if the cranking rpms were done at 1,000 instead of 250... right?