Mercruiser Cooling Issues

[balzeriv]

I have a 2.5L mercruiser Inboard w/ Alpha 1 lower unit. I was running it with the baffels on a while ago and after a while a lot of smoke was coming out of the exhaust. Come to find out that the engine was overheating. So I had taken off the lower unit off and come to find out the impeller had all broke apart. So I have replaced that with the housing kit, and the circular pump, and the thermostat. The thermostat is set to 140 deg. Now you would think that everything is good, wrong. I was still not getting water up to the circular pump. I was wondering if anybody has some suggestions. I am thinking that the house that connects the thermostat housing to the impeller in the lower unit might have some pieces of old impeller in it, or am I missing something larger here. I have it schedualed to go into the shop in March but they charge $75 an hour, and if there is something else I can do to try to get it fixed so I could save a lot of money please let me know. It is currently winterized but as soon as the freezing temp stops I am going to try any suggestions. Any help would be greatly appreciative.

[mikie]

I'm assuming this is all salt water cooled. First, don't run the engine for even a couple seconds without water going into the lower unit, you'll burn up your impeller. Besure you have sufficient water pressure on your muffs to supply the pump.
I'd start by taking the salt water supply hose off of the thermostat housing to see if you have water at that point. That will isolate the problem to either the stern drive end or the engine itself.
Also, before the thermostat opens, there should be sufficient water flow bypassed through the thermostat housing to cool the exhaust.

[balzeriv]

Well, I don't take the boat into salt water, just fresh, but that is all the same. I will try it, but like I had said before I have to wait till the weather stops freezing. I am just trying to get as many solutions and try them before I take it in. But when I try it I will let you know how it turns out.

[done workin]

Mikie's right. Pull the intake hose off of the thermostat housing with the tengine running, If you have water there, either the water pump in the block isn't working or maybe the thermostat is stuck. If you don't have water up that far, take everything back apart on the stern drive and make sure the impeller is working.

I replaced mine this year on an '86 stringer unit and they're a B---. The pictures in the shop manual are deceiving as to how to put the new impeller in. They're sorta backwards. Are you sure you put the impeller in the right way. Stupid question, but I almost did it. I was lucky and could look at the old one to see which side was worn, otherwise I would have had it in wrong.

Also, are you sure that you have the correct thermostat installed properly. I had issues with this also. The one listed in the catalog when I replaced it WAS NOT the correct one. It would work about half the time. Never overheated, just ran hotter than it should have. It was also of a different design. I ordered a new one with a new thermo housing from www.basicpower.com and everything performed flawlessly after.

GOOD LUCK