470 Overheat

[dan4836]

I used Mercruiser parts.

On the muffs, I can't get the temp gauge over 120.

In the water, temp gauge will stay at 120 at idle.

At 2800 RPMs, I can run all day around 170 degrees.

As soon as I bump the throttle to 3200, the temp will slowly rise to 200.

If I open it up, it will quickly jump past 200 and boil.

My recovery tank makes all kinds of noise...I am not sure if it's air or boiling coolant?

If it's air, then I know it's the head gasket.

My research tells me you can't find a small leak with a compression test because it's not enough pressure at low RPM's to find. Also, a leak down test may not work either.

I don't want to pull the head and find it's something else.

I do notice the riser gets hot as well as the heat exchanger. This still points to seawater not flowing fast enough?