Puking Coolant it’s never a good day for it.

Twin 496 Mag ho’s RAYLAR 600 starboard engine is Puking coolant out of tank. Gauge and IR readings are the same. Temp rises to 180 at idle. I’m running merc 160 T-stat. It has been tested in water but that was when new before installation.
Only pukes when running at speed.
Head’s were rebuilt because of this previous problem it still occurs.
doesn’t really get over 180 maybe a few degrees. Guardian mode sets in.
New Hardin sea pump and impeller.
Had a serious impeller blockage last year at oil cooler which blew a couple of hoses because of high pressure. New hoses installed
New power steering cooler
New oil cooler
New circulating pump
New water pressure sensors

When you loosen cap tank is holding pressure. Which leads me to believe it’s not a leaking head gasket from cylinder to water jacket. Just strange that it would blow coolant out at 180 without extra pressure from cylinder.

It takes 10-12 minutes for temps to rise 180 at idle on the hose. No Puking occurs at this time only at higher rpm.

Can you BURP this engine platform? Other than leaving cap open for awhile?

Swapping caps doesn’t help.


ALL verifies temps at different location.

Have you pressure tested the Heat Exchanger?

have a radiator shop boil out the heat exchanger,sounds like it may be scaley

Do you know anyone at an automotive shop that might have a combustion gas tester ? If not they are not that expensive and it would be easy to see if it is a head gasket leaking combustion gas into the cooling system.

https://www.harborfreight.com/combus...tor-64814.html

Another alternative would be to use a radiator pressure tester but I dont know what your cap is like and if there would be an adapter available to fit.

From the symptoms you are describing it almost has to be a head gasket.

Leaking heat exchanger will allow seawater into the cooling system overfilling it and causing it to puke. Been there done that.

I don't mean to insult anyone's ability, just making a suggestion because it has happened before. Are you sure the head gaskets are on in the correct orientation? The 496 is slightly different in cooling passages from the front to rear of the engine and the gaskets can be installed backwards, causing cooling issues.


Also, how old are the Raylar heads? Early versions did have some issues with cracking.

When the heads were rebuilt, was the block surface checked for flatness?

only the coolant system has been tested but one would think that if it is holding pressure then the heat exchanger is not leaking. Is that correct?

Heat exchanger is completely clear of any debris end gaskets are new end of last season all be it our season never ends in Phoenix.

One would think so. At cruise speed you may have 25-35psi seawater pressure inside of the heat exchanger. At what pressure did you test the cooling system?