phantom overheat on a new to me 140 crossflow

[big boat little motor]

I finally got my new motor hung on the boat. Conducted the following tests to make sure that I was not going to have any problems:

1. Ran at idle on muffs for 10 minutes to get engine up to operating temp no hot light.
2. Took boat and motor to the ramp and backed in to test in gear since I don't like to run the motors in gear on muffs this test ran for about 15 minutes no hot alarm.
3. Launched and took the boat out for a cruise. after about 5 minutes in a no wake zone and the "hot" alarm came on.

Not knowing where to go with this I immediately killed the motor and trolled back to the launch. Before we pulled out I tried again and again within 5 minutes the hot alarm came on.

We promptly loaded out and assumed it was a valid overheat situation. After getting home I pulled the thermostats and replaced them as well as inspected the poppet valves. The water pump is projecting a solid tell tale. So after isolating the 2 major components of the cooling system i started it again on muffs and again I got the "hot" alarm within 5 minutes. At this point I as able to put my hands on the heads and they were solidly warm but not to a temperature that would require me to remove my hands from the head.

I pulled a 1989 88 spl and replaced it with a 1984 140 bubbleback the harnesses connections seemed to directly connect.

So the question that I am having is this a real overheat or a tack/alarm that is heading south or an incompatible wiring harness?

Thanks
Jason

 

[jonesg]

Re: phantom overheat on a new to me 140 crossflow

How do you know its an overheat alarm?

couldn't it be a fuel restriction alarm?

What yr is your engine.

 

[big boat little motor]

Re: phantom overheat on a new to me 140 crossflow

new (to me) motor is a 1984 bubble back. My tach is an OMC type that has the 4 idiot lights on them. The hot indicator light is the one that kicks on when the alarm sounds. That is how I came to the conclusion it was an overheat alarm. again the motor that was replaced was a 1989 88 and was told that these harnesses were compatable and plugged together as expected.

 

[emdsapmgr]

Re: phantom overheat on a new to me 140 crossflow

A constant horn indicates an overheat. The overheat warning goes off at 212 degrees. There are two temp switches (one in each head) that will sound the horn of one/both heads overheat. The telltale indicates the water pump is good and is a good sign. However, you can have a water restriction at the thermostat housing which will prevent cooling water from leaving the block-causing an overheat. I'd run the engine on the muffs, then pull the hoses off at the thermostat housing one at a time. Check them for water flow. I'd also borrow/rent a laser temp gun and check the head temps when warmed up. Should be between 143 and 150, normally. I'd also check the thermostat valve body. It has (depending on year) either one or two small holes in it to pass water. If one/both get plugged up, you will get an overheat at idle.

 

[big boat little motor]

Re: phantom overheat on a new to me 140 crossflow

we ran the motor for a full day today and after taking a temp reading every 15 minutes or so we never got a reading above 140 on the heads. Given that it has to be an electrical issue somewhere in the tach or the senders

 

[jonesg]

Re: phantom overheat on a new to me 140 crossflow

we ran the motor for a full day today and after taking a temp reading every 15 minutes or so we never got a reading above 140 on the heads. Given that it has to be an electrical issue somewhere in the tach or the senders

But did you get an alarm?

Disconnect the temp sensor and ground it to the block with ignition key on, it should sound.
Look for an intermittent ground of the temp circuit wires.

I suspect its not the temp circuit at all.

 

[DJ]

Re: phantom overheat on a new to me 140 crossflow

I think you have a mixture of parts that are not playing nice together.

The tach. sounds like it is from a later model "System Check" engine. It might not be 100% compatible. At least in the warning systems.

Was either engine an oil injected model? If so, you have to make sure that system is 100% functional (electrically/alarms) or 100% disconnected.