1982 Starcraft Questar 191 (Volvo Penta AQ140) - Battery voltage drops to 8V when starting, cables get hot

Hi everyone,

I'm hoping someone can point me in the right direction.

I have a 1982 Starcraft Questar 191 with a Volvo Penta AQ140. Recently I've been having an issue where the engine won't restart after running for a while.

I took the boat to a marine repair shop for diagnosis. They went through the electrical system and found that some of the cables become extremely hot after the engine has been running. They disconnected the alternator and the gauge/instrument wiring during testing but were unable to isolate the problem.

The only consistent issue they found was that the battery voltage drops from about 12.7V down to around 8V (or even lower) when attempting to start the engine.

Unfortunately, the shop eventually gave up and couldn't determine the cause.

Has anyone experienced something similar with an AQ140 or older Volvo Penta setup? Could this be a bad starter motor, a ground issue, high resistance in the battery cables, a faulty solenoid, or something else entirely?

Where would you start troubleshooting?

Any advice is greatly appreciated. Thanks!

No experience with your particular engine, but based in normal engine troubleshooting.....I would start with a battery test, showing 12.7 v does not mean battery can handle a load. Then have the starter tested, then be sure all connections and clean and tight. This is where I would start and see what you find.

Grounds and/ or a faulty starter will cause that issue as well as a bad battery. Take everything apart and clean up all your terminal connections

"some of the cables become extremely hot after the engine has been running." I agree with the above suggestions but what cables got hot? Look at the insulation to see if you can see if any of it got hot and started to melt. How old are the batteries, have they been load tested?

Are the cables the proper size ? Loose connections ? Alternator over charging ? Lots of could be's....

Clean all the battery cable connections with a wire brush or 150 grit sandpaper until the connections are clean enough your wife would eat off them

If your cables are crunchy, replace them

Heat in cable is because of bad connection or corrosion

I took the boat to a marine repair shop for diagnosis. They went through the electrical system and found that some of the cables become extremely hot after the engine has been running. They disconnected the alternator and the gauge/instrument wiring during testing but were unable to isolate the problem.

Ooof.... That does not say a lot about your shop's capabilities. Especially on such an old and (no offense) very basic engine with a very basic electrical system.

Here is your problem. Resistance to electromotive force creates heat. All electrical circuits are resistive to electromotive force. Certain and specific amount of heat are customarily expected and completely normal. Excessive amounts of heat are not normal. If the heat in the circuit is excessive, that is because the resistance in the circuit is excessive.

Voltage drop testing will find all the issues, and there is likely more than one issue. If the shop can do that, they can narrow it down to the specific cables and connection points. If they cannot, what you really need is a more qualified shop. Otherwise, just replace every cable that his hot, and cleant the end connections along the way.