470 MerCruiser head gasket diagnosis

[Big Guy]

Hi gentlemen, I'm on vacation and I'm depressed. My 1987,165 hp,470 is having issues. 4 years ago this motor was rebuilt after a crankshaft bearing went bad. It runs great and i watch it closely knowing its quirks.
Over time I have fixed the cam issue. I have swapped out the points and condenser to electronic ignition and installed an alternator from Breezeworks. I think I have solved or managed most of the problems on this motor. This week it ran great and then all of the sudden it started to behave differently. When I shift it into forward or reverse will stall at idle after a few seconds. It will start up but when I shift it it stalls. Once I coax it to increase the RPMs the boat runs phenomenal. I have never rebuilt the carburetor, but I only run non-ethanol. I just replaced the water separator filter and checked the filter at the carb and everything is clear. I am inclined to rebuild the carburetor. So here are the symptoms that I recognize as I lay awake all night on my vacation thinking about the issues.
I'm getting a strong scent of burning antifreeze under the engine cover.
My daughter said after wakeboarding that she could smell antifreeze.
It sounds like there's lifter knocking that wasn't there a few days ago.
When I pulled the carburetor off last night I noticed a significant amount of chocolate colored cream coming built up in the carb throat from the valve cover vent hose to the flame arrestor on the top of the carb.
It won't low idle for long and sometimes it is hard to restart.
Since I have owned this boat I have always consumed some antifreeze now and then. This year the antifreeze level has held steady until this week and I've noticed the level has dropped quickly.
I've checked the dipstick and I don't see any creamy oil in the crankcase oil. It seems to be isolated to the valve cover. I am traveling for the next 3 weeks so meanwhile I'm going to have the carb rebuilt to eliminate that potential issue. I have to admit after laying here all night thinking about it it probably is the head gasket.​
Knowing what you know about this motor does this sound indicative of a head gasket issue?

 

[Oshkosh1]

It's either the HG is toast or the head itself is cracked. IF it's cracked on top near one of the valve guides it will allow AF to mix with oil in the valve cover and created the chocolate milkshake while not making it to the sump.

 

[AnthraxBird]

How does the oil look?

 

[Scott Danforth]

first, please use punctuation and spaces

scent of burning antifreeze is pretty much a give away of glycol in the combustion chamber. that tied with moisture in the oil is generally a head gasket.

pressure test the water jacket of the motor. with a heat exchanger, this is easy as you use a radiator pressure tester. drain the coolant, pressurize to 15psi.... if it doesnt hold, listen for the leaks. that helps pinpoint the issue. however depending on the head gasket or crack, it sounds like you will have leaking into a combustion chamber and the oil sump either way....so the head is coming off one way or another.

if your head is cracked, the head is a Ford "FE" head (427 and 460) with a hole drilled in it for the right angle fitting. buy an aluminum head as this helps prevent loss of head gaskets. not to mention the aluminum head is about #40 lighter

your oil in the dipstick tube will always show good oil until the milkshake pressure gets high enough to push the good oil out of the dipstick. change oil is the only way to verify

ethanol only fuel helps with carb issues, however doesn't prevent them

 

[stonyloam]

Do a compression check. Check the color of the spark plug insulators to see if any of them are Snow White, a sign that AF is getting into the cylinder ( especially #4).

 

[Big Guy]

All good information. I believe the head is probably bad. I am traveling for work and I think I am done boating for the summer. Bummer!

Before I pull the thing out of the water in a few weeks I'll check the plugs and compression first. If that's not it, I'll do a coolant system pressure check. I will look into an aluminum head if I have to replace it. That is a heavy motor. Anything I can do to decrease the weight would be good.

Thank you all for your input and sharing your experience.