overheating??

88 merc 3.7 alpha 1 just bought the boat . got her running with new points,then found out trim lines were installed wrong!! started it up let her run about 15min no signs of leaks,temp gage rose above 180* notice what looked like steam comming out of exhaust .. i did have the muffs hooked to it. todays temps here was in the 50`s.i didnt want to blow her up so i shut it down.thermostat?? or is that normal? coolant level good .engine ran solid. no blow back in resivor. thanks for any help.

Re: overheating??

When was the impeller in the drive replaced last? The impeller is the first thing to check in any overheat problem.

Re: overheating??

Don S said:

When was the impeller in the drive replaced last? The impeller is the first thing to check in any overheat problem.

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not sure Don is that a big job to do??

Re: overheating??

You need to spend some time in the stickies of this forum. It includes info on the impeller in item #10.

http://forums.iboats.com/mercruiser...have-technical-information-diyers-342393.html

You may want to update your other post.

Re: overheating??

Don is right on, the first maintenance thing you are going to want to do is replace the impeller, however before you do that you need to know that your engine is a 470 Mercruiser and they have a couple of issues, like a tendency to blow head gaskets, and leaky engine water pump seals. While you have it running on muffs, you should warm it up and do a compression check and a cooling system pressure check. You can borrow the tools from Autozone. While you are at it look at the lower starboard side of the engine water pump to locate the weep hole, make sure it is open and look to see if any antifreeze is leaking out of it when the engine is running. That will give you a good idea of the overall engine and cooling system health. 180 is OK for the 470, it is fresh water cooled (has antifreeze in the block) so it is OK to run a little warmer, at least for the tests. A lot of folks that have a overheat problem think thermostat, while in truth it is probably the last thing to suspect in a 470, especially since it runs antifreeze in the block. The most likely cause of your overheat is poor raw water flow through the heat exchanger, either a bad impeller (by far the most likely) or a restriction in the heat exchanger or in the exhaust elbow where the raw water exits into the exhaust. This is the manual that you will want: Boatinfo - Mercruiser Service Manual nr. 8 - 1985-1989 - Mercury Marine 4 Cylinder Engines BTW welcome to the 470 club :facepalm:

Re: overheating??

gfk71jr said:

88 merc 3.7 alpha 1 just bought the boat . ....then found out trim lines were installed wrong!! ....

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Would have been nice if you had posted that in the thread you started on the subject!!!...

Re: overheating??

Hampstead,Kentucky,Maryland,Florida,New Mexico???
Profile,location??
You might be close to someone who can help.
I'm one of the very few who like the 4cyl Merc.470.
I had one in a Thompson21 and it was/is a great runner.
Some steam in the exhaust is ok.If you have water/steam comming out of the drive then your pump is probably ok.
Just watch the temp guage and make sure it doesn't go over the 180 mark.
Make sure the resivoir is full.
To test the impeller without removing the lower,follow the water line from the back to the thermostat housing.
Get it running and undo the hose.
It should be pumping a lot of water.
This motor had a few problems but it's almost 25 years old and they probably have been fixed by now.
The seal around the end of the camshaft/waterpump would go bad and antifreeze would leak.
The gasket under the resivoir would go bad and again leak antifreeze.
But like I said they probably have been fixed a long time ago.

Re: overheating??

yea the other post about trim i solved lines were hooked up incorrectly,thanks

Re: overheating??

it was closed

achris said:

Would have been nice if you had posted that in the thread you started on the subject!!!...

Click to expand...

Re: overheating??

hampstead n.c will check for water flow today thanks

Re: overheating??

thanks captain for service manual will be put to good use thanks don,and jj

Re: overheating??

removed caps from exchanger one in rear leaking. started motor ,put hand over end of exchanger noticed maybe small amount of exhaust leaking out is that normal???

Re: overheating??

Nope, that is not normal. No water. You need to check your raw water pump impeller in the drive.

From the stickies. http://forums.iboats.com/mercruiser...cellaneous-mercruiser-information-329915.html Look at the second section on impeller replacement.

Re: overheating??

yea had a little water but i fixed the leak and ran it some more temp started creeping above 180 so i shut her down i guess i ll pull lower unit and instll new impellor