1994 Mariner overheating

[Wavemaster]

I have a 1994 2.0 liter 150 hp V6 Mercury Mariner. Everything worked when I winterized it. When I cranked it up in a barrel of water for the first trip of the spring, no water came out of the telltale. It normally takes a minute or so for the t stats to open. When the overheat light came on, I shut it down. The heat guage never moved, so either it or the sensor has gone bad since I winterized it as well. I pulled the lower unit and the waterpump was shot. Melted impeller breached cover. I replaced the waterpump and t stats. I blew air up the water pipe and it freely flows out of t stat housings. Hoses from t stats to water return and telltale are clear. Water now flows from the telltale, however engine runs hot. The overheat light is variable intensity and is on enough to see on the lake, but not nearly as bright as when the water pump was failed. The light does not come on when t stats are removed. But both old and new t stats cause light to come on. I have not bought an infrared thermometer to determine if the overheat sensor is also bad. My thoughts are the sensor or obstructed flow from impeller debris in water path somewhere, which will be beyond my skill level. Any other possibilities I could check first?

 

[sullmate]

Re: 1994 Mariner overheating

could it be the poppet valve? I have a mariner 135 hp, 1997. I had problems with an overheat condition at low speeds. When I replaced the P. V. the problem cleared up.

 

[Wavemaster]

Re: 1994 Mariner overheating

Thanks for replying. I researched that and from what I read if that we're stuck, the engine may overheat at low speeds or at high speeds, but not both. This light comes on after the engine warms, and remains on at any speed.