Excessive steam

[Marshall1]

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.

[Jango]

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.

[Marshall1]

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

[Jango]

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.