1978 Mercrusier 470 2 bbl. carb. OVERHEATING--PLEASE HELP!!!

[pacmanII]

We have replaced the thermostst,4" Heatexchanger,gauage,sending unit,
impellor and housing in lower unit,plugs,checked compression [All cyclinders 150+],engine has salt water cooling system--it has been flushed in both directions,fresh water cooling system has been flushed in both directions,took hose off fresh water side and antifreeze side--water
pumps both pumping good,took off Heat Riser and checked--not stopped up---Need some help BAD--Don't know what to do next!!!!
ANY SUGGESTIONS--PLEASE

 

[Fun Times]

We have replaced the thermostst,4" Heatexchanger,gauage,sending unit,
impellor and housing in lower unit,plugs,checked compression [All cyclinders 150+],engine has salt water cooling system--it has been flushed in both directions,fresh water cooling system has been flushed in both directions,took hose off fresh water side and antifreeze side--water
pumps both pumping good,took off Heat Riser and checked--not stopped up---Need some help BAD--Don't know what to do next!!!!
ANY SUGGESTIONS--PLEASE

Is it over heating on the garden hose or in the lake? And is a warning horn going off? And how hot is it getting up to before the warning horn will sound if you have one? I found some one eles say this about there Merc 470 operating temp This is just a FYI only.
my 470 runs at the thermostat 159. but my sender says 130 But i used an infared gun on it to check it out just to make sure the gauge is reading right. I did have to cut the wire to the temp sending unit in the manifold to remove it, it is respliced to rehook up the temp sending unit,I've had to pull that manifold at least 5 time since i owned the boat.
__________________
1977 proline 24 i/o cuddy mercuiser 470

 

[pacmanII]

Mercrusier 470 overheating

Overheats on hose or in water. I shut it down at 240. No horn has every
sounded. I am going to pressurize the antifreeze side of cooling system
next,to see if it holds pressure. My thinking--Possible blown Head gasket
on exhaust side????
Any other thoughts-Thanks for the reply!!!

 

[Fun Times]

Overheats on hose or in water. I shut it down at 240. No horn has every
sounded. I am going to pressurize the antifreeze side of cooling system
next,to see if it holds pressure. My thinking--Possible blown Head gasket
on exhaust side????
Any other thoughts-Thanks for the reply!!!

You also could do a cylinder leak down test. http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=94190.Or if needed you could uses your compression testers hose for a leakdown. you connect the air compressure hose to the compression tester hose also make sure the schrader valve needel end is out of the hose. then pump air into a cylinder that is on the compression stroke [TDC]. then look for air bubbles in the coolent bottle and also see if you hear any air coming out the carb with it at [WOT] or out the exhaust system or the oil fill or the other spark plug holes 'ECT'. If you do pull the head off look at the head gasket look for cracks and breaks on both sides. also use a straight edge to make sure the deck of the block is not warped and also the head.Here is alink to some cheaper tools if needed.http://www.harborfreight.com/cpi/ctaf/Category.taf?CategoryID=455 Are you using a infared gun to check the engine temp also to to make sure it is getting that hot? Do you have some water coming out the exhaust when on the hose?

 

[dave]

mine wa doing the same thing,stripped it down and found the head was cracked. i could not find a new one so i sent it to montreal and had it recast, works fine now.

 

[Fun Times]

mine wa doing the same thing,stripped it down and found the head was cracked. i could not find a new one so i sent it to montreal and had it recast, works fine now.

Thank you for the info, If you get a chance maybe you could post a link to the place that fixed you head Just in case he needs it. Andto Endless boating fourms

 

[dave]

I'm not sure where the place is excatly because I got the guy where I bought the parts to send it out. It cost around $450.00 to have it recast and had no problems in the last 2 years. The guy to talk to would be Mark at nova auotmotive and machine shop in dartmouth, nova scotia. I got the head back in 4 days and that included shipping time.

 

[Chris]

Welcome to the forums pacman - nice to have you with us.

Let us know how things ultimately turn out.

-Chris

 

[pacmanII]

Thanks for the info--but FYI--this head came from a 460 ford engine --the block was designed for mercrusier by a Ford engineer--Same head as a 460 Ford truck or car engine.

 

[Fun Times]

Thanks for the info--but FYI--this head came from a 460 ford engine --the block was designed for mercrusier by a Ford engineer--Same head as a 460 Ford truck or car engine.

Well good luck on your next step with it, Let us know how it goes.

 

[pacmanII]

We done a pressure test oon the anti-freeze side of cooling system today--Pumped it up to 15 Lbs. and it held for 4 hours. Does anyone have good explosives ==cheap==
I'm about to that point --Thanks everyone for the suggestions you have given me so far.

 

[pacmanII]

I was told by a mercruiser dealer that the head on this engine is the same head that is on a 460 Ford car or truck engine. By the way, we done a pressure test on the antifreeze side of the cooling system--pumped it up to 15 Lbs.--it held for 4 hours.
Any other suggestions and thanks for the other one. A friend told me yesterday that
"owning a boat is like owning a hole in the ocean" Thanks again!!!!

 

[Fun Times]

I was told by a mercruiser dealer that the head on this engine is the same head that is on a 460 Ford car or truck engine. By the way, we done a pressure test on the antifreeze side of the cooling system--pumped it up to 15 Lbs.--it held for 4 hours.
Any other suggestions and thanks for the other one. A friend told me yesterday that
"owning a boat is like owning a hole in the ocean" Thanks again!!!!

It sounds like you do have a service manual to that engine, and it seems like you are running out of pages to try. I was just curious,Have you tryd or thinking about trying the idea I came up with In post #4 ?

 

[dave]

usually when these heads crack it is between the valves and the problem won't arise unless the engine is hot. try starting the engine with the rad cap off and watch down inside the manifold as the engine warms up. if you start to notice air bubbles entering the coolant and the smell of exhaust the you are putting combustion into the cooling system and that is why it is overheating.