Excessive steam

Following was also posted to Design Forum.....
I have been reading this website for some time and found a great deal of useful information. Maybe someone can help me with a problem I am fighting. Let me start with a little background. I have a Mercruiser 260 (350 ci) that is 1982-1985 vintage. I have owned it for 5 years. I have had a nagging issue with excessive steam coming from the exhaust since I owned it. I have replaced the lower unit impeller, inspected the risers, pulled the circulating pump, thermostat replaced....all looks good. This moring I connected a garden hose direct to the waterline to the motor and put water to the lower unit via the muffs. I am still gettinig excessive steam even though I know I am pumping plenty of water to the engine.
Using a infrared heat gun, I noticed the the left side of the engine is runnig 50 deg hotter at 1000 rpm. When checked the following temp were detected:

Top of Riser: Left 174 deg Right 127
Top of Exhaust Manifoild: Left 180 deg Right 137 deg
Side of Exhaust Manifold: Left 185 deg Right 135 deg

I suspect there is blockage of some type on the left side that might be causing the steam to develope. I am also getting steam from the center of the impeller hub.

Compression check passed with compression readings 130-150 psi.


Your wisdom is appreciated.

 

Sounds like water passages in your left Exhaust manifold are rusting shut. This is a common problem and one or both manifolds may need to be replaced. Check for excessive rust plugging water passages between riser and manifold first.

 

Thanks for the reply. I pull the manifold off and pumped plenty of water through it. Got a little bit of rust scale but not much.

I put on two clear hoses goint to each manifold and ther is a noticabely lower volume of water going to the left side (the hotter side).

I am going to pump additional water to each manifold to see if the steam reduces. I know I am getting plenty of water to the circulating pump because I bypassed the lower unit (but still had water going to it. to protect the pump).

Still searching for the answer

 

If there is less water going To The Left Manifold, then your problem may be in the thermostat Housing (where the hoses originate). Check for blockages.