Merc 170 Overheated and now it won't start

tnorthern

Recruit
Joined
Sep 1, 2003
Messages
3
Okay as the subject sugests my 86 Merc 170 overheated this weekend and now it won't start. It turns over fine but when I pull the coil wire and try to get it to jump a spark I get nothing. It has an electronic ignition conversion so maybe the problem lies there? Swapped coils, still nothing. Cap, rotor, and electronic ig. look fine. Put old points and condenser back in still nothing. Read the volts from positive on bat. to coil pos. shows 12.5, however when the key is on it drops to about 6.5! (burned wire maybe?I can't see one!) I will try to jump from pos. on bat. to pos. on coil tonight unless anyone has a better idea?? Also checked cylinders no water, plugs and wires look fine. Major water leak at the water pump, (the cause of the overheating problem) but it is dripping down into the bilge not onto anything important. I think I tried just about everything I can and I read lots of posts so maybe some of you more seasoned veterans have seen this before. Thanks in advance.
 

beckerdg

Petty Officer 2nd Class
Joined
Sep 9, 2002
Messages
147
Re: Merc 170 Overheated and now it won't start

Try disconnecting the shift interupter switch. It is over around the exhaust manifold. The overheat may have damaged it or the the shift cables causing it to ground out the ignition.
 

Northern Eclipse

Senior Chief Petty Officer
Joined
Jun 24, 2003
Messages
665
Re: Merc 170 Overheated and now it won't start

If this is a 470 170hp you may have cooked the voltage regulator,they are water cooled..How bad did motor overheat?
 

tnorthern

Recruit
Joined
Sep 1, 2003
Messages
3
Re: Merc 170 Overheated and now it won't start

Got it running. After some tinkering and general trickery I discovered that the lead from the coil to the starter solenoid was cooked on the back of the block. I was blown away by the routing of the wires. Right against the block and around the exhaust. Thanks for the help.
 

merc 140 pontoon

Petty Officer 2nd Class
Joined
Aug 23, 2003
Messages
129
Re: Merc 170 Overheated and now it won't start

When you say "electronic ignition conversion", do you mean a Pertronix Ignitor? That's what I have, and the mechanic who installed it INCORRECTLY ran the Pertronix red lead to the coil positive post. My Merc 140 has a resistance cable in the harness (some have ballast resistor(s) on the transom). The Pertronix positive lead needs to attach to a switchable 12V source BEFORE the resistance cable. I tied mine into my harness prior to the resistance cable, and my ignition problems have gone away. My resistance cable had deteriorated, and like you I was seeing less than 7.5V while cranking--so the Pertronix was shutting down. I also ended up eliminating the resistance cable (and the ballast resistor I tried), and going to an internally resisted (3 ohm) coil. Much happier now, although I am also still fighting an overheating problem. I recommend you check where your electronic ignition power source is tied into, so you have no risk of it shutting down on you. It's best to have the full 12V. Good luck.<br /><br />Steve
 

tnorthern

Recruit
Joined
Sep 1, 2003
Messages
3
Re: Merc 170 Overheated and now it won't start

Thanks Steve. I had no problem with the ignition before this incident so my only think was that in the confussion of my boat overheating the key was left on. It turns out that my waterleak is actually very common. They even have a page on sterndrives.com dedicated to fixing this problem. I am currently in the process of getting everything fixed so if you have a waterleak you may consider looking at the front cover on the engine. There is a bypass there to allow water to leak out instead of into the motor.
 
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