overheating - still - merc 888 302 ford CRACKED BLOCK?

seafever

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Dec 7, 2013
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Stilll fighting the same battle - the question is Is The Block cracked?? (We get 40 below zero here)
boat is 1974 Silverline Antigua 18T, engine is mercruiser 888 (302 ford)
Problem: Overheating at higher RPM not WOT
SO FAR have replaced impeller pump and seals in lower unit, pulled heads, magnafluxed and planed, replace both exhaust bellows, replaced water pump, no evidence of water in oil. no obvious coolant leaks. replaced all coolant lines and checked for blockage. have run with water muffs and drive in a tank, also did a river run
I installed a 1" clear plastic section in the cooling water inlet hose. When engine is started and idling, coolant flows to and from engine. At higher rpm temp starts to climb and water goes backwards through intake line against impeller pump. Then air in intake line (Exhaust??)
My theory= block is cracked internally allowing exhaust pressure from a cracked cylinder into the water jacket???

Where else could that kind of pressure build up? How can I check this without pulling the engine? Dye check the cylinders?
Thanks, I been 2 years on this problem, right now it is minus 28 degrees so lotsa time for more research before spring, and no shop to work in... lol
BTW the hull serial number is 001 is this the first Antigua out of the mold??
 

alldodge

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Stilll fighting the same battle - the question is Is The Block cracked?? (We get 40 below zero here)
boat is 1974 Silverline Antigua 18T, engine is mercruiser 888 (302 ford)
Problem: Overheating at higher RPM not WOT
SO FAR have replaced impeller pump and seals in lower unit, pulled heads, magnafluxed and planed, replace both exhaust bellows, replaced water pump, no evidence of water in oil. no obvious coolant leaks. replaced all coolant lines and checked for blockage. have run with water muffs and drive in a tank, also did a river run
I installed a 1" clear plastic section in the cooling water inlet hose. When engine is started and idling, coolant flows to and from engine. At higher rpm temp starts to climb and water goes backwards through intake line against impeller pump. Then air in intake line (Exhaust??)
My theory= block is cracked internally allowing exhaust pressure from a cracked cylinder into the water jacket???

Where else could that kind of pressure build up? How can I check this without pulling the engine? Dye check the cylinders?
Thanks, I been 2 years on this problem, right now it is minus 28 degrees so lotsa time for more research before spring, and no shop to work in... lol
BTW the hull serial number is 001 is this the first Antigua out of the mold??


:welcome: to iboats

I'm thinking there is a hose routing setup that is incorrect. For the water to flow back toward the inlet after it warms up leans me to the thermostat, housing and hose routing. Can you supply some pics of your engine setup?
 

Boatdoc58

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Dec 12, 2013
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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Check for blocked manifolds and/or risers. The only way for the hot water to get out is through them. If they are clogged, the heated water cannot get out and eventually builds enough pressure to force the water back out the way it came in.
 

Fun Times

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Overheating at higher RPM not WOT. Have run with water muffs and drive in a tank, also did a river run. I installed a 1" clear plastic section in the cooling water inlet hose. At higher rpm temp starts to climb and water goes backwards through intake line against impeller pump. Then air in intake line (Exhaust??)
Hi there, You may want to try separating the drive system from the engine system as a test by removing the drive and inserting a garden hose into the water inlet hole at the bell housing and re-run the clear plastic hoes test to see if it's still doing the same.

This should help tell you if it's an engine problem or a stern drive problem as it could easily be either or at this point.
 

tpenfield

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Could be a combination of things . . . like head gasket and clogged manifolds.

Check out this video, where the cooling system becomes saturated with air (exhaust) bubbles at higher RPM.

 

seafever

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

:welcome: to iboats

I'm thinking there is a hose routing setup that is incorrect. For the water to flow back toward the inlet after it warms up leans me to the thermostat, housing and hose routing. Can you supply some pics of your engine setup?

It is 33 below zero this morning - sorry no pics for a while lol :embarassed:
However this engine has only one water intake from the outdrive to the engine, it has been flow checked. with the engine idling there is plenty of water from the exhaust. manifolds were checked and bellows changed. I have had this boat to two merc dealers. One near parker AZ. and one here in Canada. No one agrees with my cracked block theory but then no one else can figure out why the cooling system is pressurizing causing backward flow.
I have the original Merc 888 manual and it clearly shows the routing of the hoses from thermostat housing.
thanks & merry Christmas :cold:
 

tpenfield

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Bad head gasket ( or cracked cylinder head) could pressurize the cooling system as shown in the video I posted.
 
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seafever

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Bad head gasket ( or cracked cylinder head) could pressurize the cooling system as shown in the video I posted.

Both heads pulled and magnafluxed then resurfaced, (planed) not the heads
 

bonzoscott

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Messages
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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Something may have went wrong with the head work or gasket/s. Leak down test is in order. I think if it were a crack somewhere, you'd get the back pressure almost immediately.
 

alldodge

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Maybe try more clear hose to other locations to see if it points to another location
 

NHGuy

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

You can also pressurize the block by line clamping the cooling hoses to the exhaust manifolds. Pump in about 15 psi then listen for air at the intake, spark plug holes and exhaust.
 

Boatdoc58

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Here are the hose connections for an 888.
hose.jpg
 

seafever

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Well thanks Gentlemen, The leak down test is a very good plan, don't know why I didnt think of it, I used to do that on aircraft engines years ago. I think I still have a home-brew tester.
The hose diagram for the thermostat housing is interesting, doesnt look familiar somehow, but I will check that out.
Menawhile this is a time of research since it is 27 degrees below zero and there is 18 inches of snow on the boat.
Great forum and a good bunch of skippers, glad to be aboard.
SF
 

bspeth

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Good thing its not cold.
 

seafever

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Crazy day to think about boats - it is minus 38 C ( -36F) windchill is minus 49C (-56F) and 2 feet of snow on the boat.
anyway there are 2 hoses going to the rear of the manifold one says to exhaust, the other says to rear end cap???? what is the function or flow of the rear end cap? Is it not also to the exhaust? These two lines may be turned over but not exactly boat work weather. I dont understand how this cooling system works. There are 8 lines. To the water pump I can see, the water pickup from the lower unit ok. The front cap connection I thought was to cool the manifold with water from the engine, is the rear cap hose returning water to the engine???
Somehow doesnt make sense to return hot water from the manifold to the thermostat housing????
Um yup! I need some schooling on this and the book doesnt explain it.
Thanks, and happy new year - only 5 months to soft water... lol
 

Bondo

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Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Crazy day to think about boats - it is minus 38 C ( -36F) windchill is minus 49C (-56F) and 2 feet of snow on the boat.
anyway there are 2 hoses going to the rear of the manifold one says to exhaust, the other says to rear end cap???? what is the function or flow of the rear end cap? Is it not also to the exhaust? These two lines may be turned over but not exactly boat work weather. I dont understand how this cooling system works. There are 8 lines. To the water pump I can see, the water pickup from the lower unit ok. The front cap connection I thought was to cool the manifold with water from the engine, is the rear cap hose returning water to the engine???
Somehow doesnt make sense to return hot water from the manifold to the thermostat housing????

Um yup! I need some schooling on this and the book doesnt explain it.
Thanks, and happy new year - only 5 months to soft water... lol

Ayuh,.... How 'bout some Pictures,..?? We can't see what yer seein',...
 

haulnazz15

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3,720
Re: overheating - still - merc 888 302 ford CRACKED BLOCK?

Check the Merc #2 Service manual for a diagram of the cooling system on the 888/233 Ford. The flow actually goes from the thermostat housing to the rear of the exhaust manifold and then exits through the front of the manifold back to the thermostat housing. From there it goes to the exhaust riser and out through the exhaust.
 
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