Engine overheating problem ... help

[Scubaseas]

"When I start the engine up and have the pressure cap off the fresh water rises a bit, and bubbles out and floods out the cap. I assume that this is just trapped air bubbles finding their way through the system?..."

This is typical of a post overheat head gasket issue just starting. Even if you are properly bleeding all the air out of the cooling system it sounds like you are pumping small amounts of air into the cooling jacket due to a head gasket or head not sealing the pressure differential of about 1200 PSI when the cylinder fires to the 0 to 12PSI of the water jacket. Couple of ways you can verify this. One is to use a pressure tester to observe if the pressure constantly builds up. You can expect a slight movement of the coolant when starting the engine escpecially if you took the thermostat out but if you continually build pressure from zero to ?? you have either a cracked head or a blown head gasket. Any presssure gauge would work if you can't get your hands on one that fits the fill reservoir. Just tee into a coolant hose. Watch that you do not over pressure the system. If using the coolant cap/radiator tester type you have then removed the cap which is the pressure relief valve for the cooling system.
It's normal for the pressure to rise a bit as the engine warms up but if you have a head gasket issue the pressure will creep up within about 1 to 3 minutes. And continually do so after venting the pressure off.

Another way is to test any gas build up out of the cooling reservoir for hydrocarbons. This is what a test kit for cracked block or blown head gasket does. Or use your $10K emmissions tester left over from vehicle State Inspections to check for elevated hydrocarbons.

Another way is to eyeball the cooling reservoir with the engine running. You may or not see bubbles on a fairly regular basis but not always. Depends on where the reservoir is in relation to the head and hoses.

I doubt if it's an issue but did you happen to check the impeller of the old and new to this motor pump for direction? They are probably the same but stranger things have happened. I also assume you checked for good flow on the fresh water side/ engine coolant side of the system by removing one of the hoses to the water heater and started the engine. You should have a decent stream even at idle. Say at least 4gpm at 800rpm.

The above symptoms you noted and kudos to you for precise and detailed observations, could also be caused by an air bubble in the system. Pour your coolant in, loosen the hoses to the water heater and the upper engine hose to "burp" out any water. Or rig up a vacuum fill system.

[ebs001]

You have an air lock on the coolant side. Keep burping.

[c.K.]

Originally Posted by clakiep

Would not be good news, but what if there is some leakage of the cylinderhead gasket, putting bubbles and creating vaporlocks in the cooling system ?

Capt. Claus - ocean tramp of the eighties

Hey I would agree with you, head gasket, maybe even due to previous overheating

[sinnerman]

Originally Posted by Scubaseas

"When I start the engine up and have the pressure cap off the fresh water rises a bit, and bubbles out and floods out the cap. I assume that this is just trapped air bubbles finding their way through the system?..."

This is typical of a post overheat head gasket issue just starting. Even if you are properly bleeding all the air out of the cooling system it sounds like you are pumping small amounts of air into the cooling jacket due to a head gasket or head not sealing the pressure differential of about 1200 PSI when the cylinder fires to the 0 to 12PSI of the water jacket. Couple of ways you can verify this. One is to use a pressure tester to observe if the pressure constantly builds up. You can expect a slight movement of the coolant when starting the engine escpecially if you took the thermostat out but if you continually build pressure from zero to ?? you have either a cracked head or a blown head gasket. Any presssure gauge would work if you can't get your hands on one that fits the fill reservoir. Just tee into a coolant hose. Watch that you do not over pressure the system. If using the coolant cap/radiator tester type you have then removed the cap which is the pressure relief valve for the cooling system.
It's normal for the pressure to rise a bit as the engine warms up but if you have a head gasket issue the pressure will creep up within about 1 to 3 minutes. And continually do so after venting the pressure off.

Another way is to test any gas build up out of the cooling reservoir for hydrocarbons. This is what a test kit for cracked block or blown head gasket does. Or use your $10K emmissions tester left over from vehicle State Inspections to check for elevated hydrocarbons.

Another way is to eyeball the cooling reservoir with the engine running. You may or not see bubbles on a fairly regular basis but not always. Depends on where the reservoir is in relation to the head and hoses.

I doubt if it's an issue but did you happen to check the impeller of the old and new to this motor pump for direction? They are probably the same but stranger things have happened. I also assume you checked for good flow on the fresh water side/ engine coolant side of the system by removing one of the hoses to the water heater and started the engine. You should have a decent stream even at idle. Say at least 4gpm at 800rpm.

The above symptoms you noted and kudos to you for precise and detailed observations, could also be caused by an air bubble in the system. Pour your coolant in, loosen the hoses to the water heater and the upper engine hose to "burp" out any water. Or rig up a vacuum fill system.

Good info above. My first thought like above was a head gasket leaking after the first overheat.

Then like above, are you sure the salvaged water pump is actually working? Sometimes the impeller will be loose and the shaft will rotate without the impeller spinning . (Didn't even think of the reverse direction impeller.)

Stuck thermostat & air in system would be then next items. If there is air in the system, the water pump may not be able to prime itself.

cheers

[sharutika30]

The fast and easy way to check for headgasket leak. First remove coolant fresh water pump drive belt, then remove filler cap and top up antifreeze right to the top. Then start the engine and look for any bubbles right away. Even one or two bubbles is a bad head gasket. If the antifreeze rises or pushes out it is a very bad gasket leak.
Cheers
Dan
Retired mechanic

[RSB333]

I had a similar problem with my Universal M-25. It has a bleeder at the top of the thermostat chamber and once I let the air out and a squirt of coolant, the overheating stopped.

[Manateeman]

We like the sharutika suggestion and several other posts. Air being sucked in ?
Thermostat don’t respond to air. Pieces of impeller can block a lot of flow.
Make a list from the above suggestions. Follow the flow of both the raw water and antifreeze side ...step by step. You can begin with the engine because if you have an issue within the engine, all the sea water in the world isn’t going to cool it.
Don’t get discouraged. Every time you add a new part...think it’s a rebuild. Yes. This is good. Happy engine.
Every time you skin a knuckle ...think ...I’m a better sailor.
Lots of great advice already given.
Happy trails to you.
The manatee crew.

[Mike Banks]

Blown head gasket would be my first guess--you get five more--

[Madehn]

I really think you have air in the system probably at your thermostat. That is the simplest explanation. If you hear hoof beats think horse not zebra.

[Msea]

My thinking is air trapped. Loosen hose at highest point in system until coolant leaks out. As others pointed out burp the system.

[garison]

[QUOTE=edhuckle;3583962]Hello all:
so i had a similar problem with the water rising and bubles after i replaced my thermostst which did not have a vent hole in it, this prevented all the air from clearing out of the system so that the thermostst sat in an air buble as it was the high point and did not open and caused overheating and alarm, i overcame this by continually topping up as the engine was running till all air leaked out , that fixed it untill I got new thermostat, your problem may be a blocked or no vent hole in thermostat

[sailorboy1]

before going crazy

are you sure engine is overheating and there isn't a problem with the temperature sensor

[edhuckle]

Hey, thanks for the response. yes, it was exactly what you said.

[edhuckle]

Originally Posted by Cheechako

I had a problem like that once when I had reassembled the engine. I previously had the head worked on .
What was going on was the thermostat was surrounded by air and thus heat wouldn't transfer to it and it stayed shut. I solved it by filling the engine with hot boiling water, closing the thermostat housing quickly and starting the engine.

However you say you took the T stat out, so that's not it.
I was going to suggest a bad freshwater pump, but you changed that also.

So sea water is flowing through readily. That means something is not circulating the fresh water in the engine.
Do you have a transmission cooler the engine water goes through? Maybe that is clogged.
Are you sure the used fresh water pump was good? (impellor not spinning on the shaft or...?)

yes, I had an airllock and i burped it alot and it totally fixed the problem. thanks, Ed

[Lepke]

Some engines collect air under the thermostat causing the thermostat to remain closed until very high heat is reached.
The solution is drill a small hole in the thermostat plate, about 1/16" or more and air passes thru.