1988 Johnson V120 overheat problem

[crabby_bob]

My brother and I were scooting across Buzzard's bay a few weeks ago and we hit a wave pretty hard. We took quite a bath over the bow and after that the motor started to overheat. The first time it overheated we limped into a harbor and let it cool for about 20 minutes. We headed back out to the bay and didn't get far before it overheated again. We were able to get the heat down by throttling the motor back to less than 2000 RPMs, and rode it back into the harbor where we pulled it out trailered it home.

We don't know where to start troubleshooting. My brother suspects the pickup tube that goes from the pump to the head might have been dis-logged. We replaced the water pump last year to fix an overheating problem and noticed that the upper part of the tube was pretty corroded, so I'm planning to drop the lower unit in the next few days to check it out. But we're still getting water out the check valve so I would think the tube is still connected.

What other things can I look at? Would it be worth taking the pump apart? Is it possible the impeller was damaged? We hit a few waves where the motor would rev up pretty high, much higher than the 3500 or so RPMs we were running at.

 

[imported]

Re: 1988 Johnson V120 overheat problem

how hot did it get?

 

[crabby_bob]

Re: 1988 Johnson V120 overheat problem

I'm not sure of the exact temperature. The needle was almost pegged on the high side. We were able to keep it in the middle of the temp range by limping home at the lowest RPM possible while still keeping it in gear. The overtemp alarm never went off and it worked the last time we tested it.

Is there a way to test the water pump without taking it out? We were getting water out the checkport but I know that doesn't mean much.

Thanks,

 

[imported]

Re: 1988 Johnson V120 overheat problem

Did you notice if the tell tale got any weaker after the wave? Also did you test the thermostats?

 

[crabby_bob]

Re: 1988 Johnson V120 overheat problem

Unfortunately I didn't have chance to look at the check port. We weren't able to get much power out of the motor, so controlling the boat was difficult. I was worried we might take a large wave over the transom, so I focused on watching out for waves and other boaters. Some of the boats that went past us created a pretty big wake. My brother is the one who noticed that water was still coming out the port. I'll ask him about the stream.

We haven't checked the thermostats yet. We have a manual, and I assume the process is in the book, so we'll be able to do it this weekend. We're also going to test the alarm system again. We tested it last year while troubleshooting a S.L.O.W. mode problem and found a faulty sensor and horn. We replaced them and the system checked out OK. I guess we should have done it again before putting the boat in the water. I did notice that the connection on the temperature sensor has a lot of corrosion on it, but I don't believe that could be the problem.

 

[billboard_ne]

Re: 1988 Johnson V120 overheat problem

Are you sure the motor is over heating? Is the gage going up the only symptom?

Could be an electrical problem with the gage or gage wiring.

 

[crabby_bob]

Re: 1988 Johnson V120 overheat problem

Are you sure the motor is over heating? Is the gage going up the only symptom?

Could be an electrical problem with the gage or gage wiring.

That would explain the alarm not going off, but it seems like S.L.O.W. mode kicked in which sounds like it was actually overheated. We'll retest the alarm system, clean up the connections, and look for things that might have come loose by pounding into the wave.
Well also test the thermostats.

Thanks.

 

[crabby_bob]

Re: 1988 Johnson V120 overheat problem

Well, we changed the thermostats and that seems to have fixed the problem. We took it for a test run and it ran perfectly at high and low RPMs. The only anomaly was at around 2200 RPM. The motor runs a little on the hot side when we run it in that range but we're not very concerned about it. We figure it might have something to do with redirecting the water flow through the power head.

On a side note we're pretty sure the power pack has a problem with the S.L.O.W. mode alarm system. We were talking to someone at a marina and she said we should hear the alarm every time we turn the ignition on. We don't hear the beep, and the wiring that's external to the power pack checks out OK, so our conclusion is that the reason we didn't hear the alarm last weekend was because there's some sort of solid state relay built into the power pack that has been blown.