87 supra 351 Windsor overheating

I have an 87 supra that just recently started overheating. Replaced raw water pump impeller, replaced main engine water pump. still overheating. I verified sea strainer was not clogged and that water lines were not clogged into raw water inlet. Lines are not clogged into thermostat housing, I have no thermostat installed and have ran it this way for years with no problems. I am not sure if water is exiting rear before anyone asks because but is still currently in the water. what could possibly be stopping the water flow or what is another possible problem. Once I get it out of the water I intend on checking for flow by hooking up a hose at the raw water inlet as I always do to run it on land. I hook hose directly to cooling line before sea strainer/cooler. Possibly traps at back of boat exhaust, block blockage? all thoughts and ideas appreciated.

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Originally Posted by gunner81

I have an 87 supra that just recently started overheating. Replaced raw water pump impeller, replaced main engine water pump. still overheating. I verified sea strainer was not clogged and that water lines were not clogged into raw water inlet. Lines are not clogged into thermostat housing, I have no thermostat installed and have ran it this way for years with no problems. I am not sure if water is exiting rear before anyone asks because but is still currently in the water. what could possibly be stopping the water flow or what is another possible problem. Once I get it out of the water I intend on checking for flow by hooking up a hose at the raw water inlet as I always do to run it on land. I hook hose directly to cooling line before sea strainer/cooler. Possibly traps at back of boat exhaust, block blockage? all thoughts and ideas appreciated.

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Have you checked for head gasket leaks? Compression test and a check of the oil would help isolate that as an issue.

First did you install the raw water pump correctly ? It can be installed upside down. The two 1'' hoses should face the engine block . Second did you install a genuine Sherwood impeller ? There are a lot of cheap knock offs out there that look the same but will cause a overheat . I learned this the hard way . Go to Home Depot and get a piece of 1'' braided clear hose install it between the raw water pump and the thermostat housing . It should start flowing water while you are cranking and have a steady stream of water without bubbles when running.