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Water flow was normal. What would cause the cap to release the pressure? Or better put, cause the pressure to exceed 16PSI (assuming the cap held to that value). A head gasket would certainly pressurize the coolant side, but I would see that leak on the compression test. Maybe the cap is...

Well, I got it all back together and took it for a long cruise. The overheat issue is fixed, and I can now confirm the head gasket was the cause. It ran great at cruise RPM, good oil pressure and temps. However, it still sounds like marbles in the transmission at idle. Others have related that...

FWIW, that cylinder does have good compression. The mechanic at the marina said he thinks it is corrosion from coolant sitting in the cylinder over the winter.

Ha, it’s a good thing I have two of them!

Thank you for all of the advice! It is much appreciated. I think I will just replace the head gasket and put it back together. Hopefully it will run well enough (and not overheat), to get a few more runs in before it gets pulled out for the winter. I guess it’s time to go motor shopping.

A look at the cylinders. I am concerned about the scoring on #4. My compression numbers (except 6) are in the 100-120 range. I’m wondering if I can get some more life out of this one with just a new head gasket. I was going to get the heads redone. Maybe it’s not worth it at this point. This is...

Got the head off. Cylinder 6 is the one with low compression. It appears (to me) the gasket is blown between 6&8.

Exhaust. I believe so, but it’s hard to tell. I’ve had it apart so many times this summer. Each time I lose some. I ran out of time today, I will be back at it mid week. Hoping to pull that head and see if it has a story to tell.

I’m curious, the exhaust manifold gasket on the (boat) left side shows signs of leaking. Could a leaking exhaust manifold gasket cause an overheat? Also worth mentioning, I don’t believe these manifolds have ever been changed. I was able to remove both sides with ease. I was expecting the bolts...

I may have found the cause of my overheating. Through the process of pulling the head, I found the riser elbow inlets to be partially obstructed by gasket material. Picture below. Also, isn’t there supposed to be a flapper valve on the riser elbow? *** disregard. I think the gasket covers are...

I removed both end caps on mine and found impeller bits. I then used a long drill bit (a dowl will work)to clean out the tubes. I then flushed it with water. It didn’t fix my problem, but the heat exchanger flows well now.

I was able to do the leak down by dividing the balancer into quarters. I also removed the distributor cap, to aid in finding TDC on compression stroke. While I had the plugs out, I also did another compression test. The results surprised me, and leaves more questions. I only did the right...

Well, tried to do a leak down and I was having a difficult time finding TDC. I am a one man band and trying to rotate the fly wheel while holding a dowl in the spark plug hole isn’t possible with the manifolds in place. I pulled the rocker cover, and alligned both rockers in the up position...

I finally got around to chasing this overheat issue. The results of the compression test is not good. Especially, cylinder 6 at 65 PSI. The other results are 8=120, 6=65, 4=112, 2=94, 7=118, 5=95, 3=110,1=122. Could this be a valve, or head gasket issue? Or is it time to start looking for a new...

I didn’t even realize this existed! (Newbie). I see it in the diagram, right after the sea water pickup and before the oil cooler. I will chase that hose and try to find it. Thank you for the tip!

I replaced the circulation pump and I have the same issue. I ran it without the thermostat, and it still over heated. I also still have the air bubbles in the coolant. I’m leaning more towards this being my issue. Could these bubbles be causing the circ pump to cavitate? I did not run the motor...

I am replacing the recirculating pump this weekend. I am curious about the “$30-40” comment. The one I bought is a Quicksilver and they all run around $250. Are you just replacing the internal impeller or the whole pump? I believe the manifolds and riser elbows to be original, my elbows are...

When cracked the bleeder did you still have coolant pump out, like a small geyser? I figured the circ pump was good because of that. I also have small air bubbles that appear at the bleeder and in the heat exchanger.

I do not know much about thermostats. The guy at the boat store said I need a 140 thermostat for my motor, so I went with that. Both motors typically run at 160, not sure if that makes sense for a 140 stat? My temp gauge gradually climbs to 160, and never moves or fluctuates beyond that. I did...

I am three years into this boat. It ran fine without any issues prior. I did replace the impeller, which was fine btw, however I did find rubber in the heat exchanger from a previous failure.