1989 Mercruiser 5.7 Alpha Overheat

[TedCT]

After reading many threads, I see this overheating is not uncommon! I have a new pump on engine, pump on outdrive 1 season old, new thermostat. I undid the drains on the risers, took a couple hoses off and ran water through. Got a bit of rust, not much. Flowing good and clean I think. The engine only overheats above 1/2 throttle. Below that, fine around 150. Any ideas? I did retard my timing a little at the beginning of the season. Could it be leaning out? I know these are all possibilities, anyone have a similiar problem?

 

[anesthes]

Re: 1989 Mercruiser 5.7 Alpha Overheat

How much water are you pulling in above 1/2 throttle?

 

[Bondo]

Re: 1989 Mercruiser 5.7 Alpha Overheat

Just How Hot are you running ?????

 

[TedCT]

Re: 1989 Mercruiser 5.7 Alpha Overheat

I'm not sure how much water she is pulling above 1/2 throttle. How can I check this? The temp. really begins to spike, up to 180-200 and climbing at which point I immediately back off and resume below 1/2 throttle at 150 degrees. <br /><br />I tried pulling the port riser yesterday to do a good inspection. One of the bolts was frozen, so I'm in the penetrating oil process so I don't snap the head off. I'm good at doing that.<br /><br />I read a lot about a rubber/plastic flap somewhere in there that gets stuck. Before I pull the boat to inspect/replace the lower unit pump/impeller, I want to eliminate the rest of the variables.<br /><br />I do appreciate the response!

 

[akriverrat]

Re: 1989 Mercruiser 5.7 Alpha Overheat

rule of thumb--overheat at idle...pump, at speed...restriction. most likely rust clogged manifolds/elbows.

 

[TedCT]

Re: 1989 Mercruiser 5.7 Alpha Overheat

Thanks for the advice. I'm planning on taking the risers off thiss afternoon and checking that out. Actually, I ordered new ones (risers). If the manifolds look ok, I'm going to try to get the rest of the season out of them and replace them at the end of the season. Do you necessarily have to change the risers and manifolds at the same time? I opened the drain on the riser and started the engine. Some rust came out, not a lot, but enough. I'll have to wait to see what the manifolds look like when I separate them.

 

[flashback]

Re: 1989 Mercruiser 5.7 Alpha Overheat

change out the thermostat, its easy and cheap to do and will be one more thing off the list.............good luck............