Merc 260 stalling and overheating

[kumi]

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OK I have a 5.7 Mercruiser 260hp it is overheating and after about 5-10 minuets it will sputter and die. I checked the thermostat it is ok I am getting water to the exhaust so I assume the water pump in the out drive is good. I do not have water in the oil and the oil level is consistent. I have ran clean fuel from a separate tank and it still does the same thing runs sputters dies it is not a fast kill in the engine that would lead me to think it is not spark. The engine starts to cough choke and backfire then it dies. If it sits for a half hour I can restart it and it will do it again. Note: it is rough to restart. Could this be a bad gasket head or exhaust manifold causing water to mix with the fuel???

Thank you,

Kumi

Also I have removed the circulatory pump it is working fine.

 

[sarantis]

Re: Merc 260 stalling and overheating

If your engine overheats and you keep runing above fast idle for 5-10 minutes i'm afraid you may have seized it.Have you replace your impeller recently? Does the water input hose that goes to the thermostat housing brings enough water in? Take it out only for some seconds and check the water flow .Replace the hoses from manifolds to the thermostat housing with clear ones and rev it up.If you see any bubbles in them look for any leakings.If you don't find anything start dissasemling and check thermostat housing ,hoses ,circulator,thermostat,risers,manifolds and head gasket-heads-cylinders.

 

[kumi]

Re: Merc 260 stalling and overheating

Never ran it past the point of 185?. Circulatory pump seems to be good I took it off and filled it up then spun the pulley and the water shot right out, bearings on it seem solid. I am getting water to the exhaust (plenty of water shooting out the exhaust) so I would say the outdrive pump is good. I was thinking bad head gasket or exhaust manifold but people tell me if it's the head gasket I would have water in my oil and I don't have water in my oil. And the way the engine stalls with popping and hesitation I was thinking water isn't circulating in the block because I have a leak that is affecting the fuel. Would water leaking thru the exhaust manifold or the header gasket cause this kind of problem?

Oh and engine is not siezed it cranks fine just doesn't want to start after it stalls like water in fuel maybe even a hydro lock

 

[sarantis]

Re: Merc 260 stalling and overheating

Who told you that if you don't have water in oil the head gasket is good???!!!!
At my previous engine i had many hydrolocks and never had a drop of water in the oil.I started dissasembling the block when after replacing the manifold hoses with clear ones and reved it up i found out that the exhaust gases were getting the cooling system.So go on and do some simple tests.