I look back on the highway and my Tohatsu 9.8 is smoking...

I used the motor all weekend with no problems. I fished in the morning and packed up and left about 2pm. It was a very hot day, around 100 degrees. I drove about 200mi, stopped to get gas and food... As I was pulling back onto the highway, I looked back and saw the motor smoking. I immediately pulled over and disconnected the battery and it slowly burnt for a little longer than stopped.

What was burning was the throttle control cables coming out of the tiller handle. They are (were) covered in plastic tubing and that plastic was what was burning. Pretty much all of the plastic burnt up, leading into the motor but I can't see that there is any damage inside. I'm not sure if it was a short or what. I also noticed the tiller handle is 'stuck' on low throttle. If I try to twist it to full throttle it moves a little but if I let go it comes right back to low.

My motor is under the Tohatsu 5yr warranty and I have an appointment at a dealer for Aug 10th.

The first dealer I called asked a ton of questions, like they were trying to find a way around the warranty. They wanted me to bring in the whole boat. This other dealer said I can just throw the motor in the back of my truck and bring it in.

Is there anything I should watch out for... to make sure I don't mention something stupid? I have a habit of saying too much in these situations.

My setup: The battery was in a box and it was connected directly to the motor, the motor was in R so it didn't bounce up (plenty of clearance), gas was connected... I'm not sure if the throttle was up or down, usually I keep it on 'start'. I'm not sure what else is relevant.

Has anyone ever heard of this before? Or have any ideas for me?

An idea...

Throttle cables are at ground potential, I would look for a short to a positive potential wire or lug, etc..

Tim

I was wondering if you ever learned what caused this?

I never found out exactly the cause, but I have a hunch.

Earl was on the right track with a short. One thing I didn't realize until I took it into a dealer was that the grounding wire on the shaft of the motor was burnt up. The dealer replaced my throttle control cables and the grounding wire and everything is working fine.

Here is what I think happened:

The starting battery was sitting in the boat without being in a battery box. It was pretty close to the aluminum hull, and the motor was still connected while I was towing the boat. I think the terminals of the battery connected together somehow, maybe it was through the aluminum hull or some other way, and it created a short that did the damage.

The boat has 3 separate circuits (1 for TM, 1 for accessories, 1 for motor) so I'm sure there are other things that could've happened. Although I checked all the wires and could not find any open wiring or anything that could cause a short.

Hopefully it didn't take this long to get fixed...
Glad it's working

Sent from my SM-T350 using Tapatalk

So, your findings indicate an unsecured battery caused the short. That will do it. I had my pickup truck do that due to a loose battery. I was noticing that sometimes the engine would die for a split second while driving down the road. It would stay running due to it being a standard transmission in it. It kept happening more often. I would open the hood and could not find any problems with it. Then early one morning on my way to work while crossing a bridge with a pronounced bump I saw a lot of sparks come out from under the hood. I pulled over and found the battery hold downs were loose and when I would hit a bump in the road the battery would jump up and the top terminal would short out on the hood killing the engine for a split second.

Lesson learned? Secure the battery.