1988 mercury 45hp 2 stroke overheat

[Votabledog]

I recently bought a 1988 bass tracker with a 45hp mercury 2 stroke. The motor runs well but when it gets around 5500 rpm I get a continuous beep indicating a overheat after about 5-10 seconds and when I let off the throttle the alarm stops. The motor has a solid stream from the tell tail the entire time. I’m not sure if it’s a false alarm or not and what the fix would be if one is needed. Any help would be much appreciated, thanks.

 

[QBhoy]

Although you may have a good visible stream of water…it’s perhaps not a true indication of sufficient cooling, enough to prevent an overheat at full throttle perhaps. Might be just on the edge of falling short of being enough.
The other thing that could be going on, is perhaps the set up of the engine or your level of trim perhaps. You could be losing some flow if the intake is perhaps taking some air in too.
You may also have some restriction or build up of salt deposits in the cooling passage ways perhaps.

 

[saltchuckmatt]

Although you may have a good visible stream of water…it’s perhaps not a true indication of sufficient cooling, enough to prevent an overheat at full throttle perhaps. Might be just on the edge of falling short of being enough.
The other thing that could be going on, is perhaps the set up of the engine or your level of trim perhaps. You could be losing some flow if the intake is perhaps taking some air in too.
You may also have some restriction or build up of salt deposits in the cooling passage ways perhaps.

Or maybe thermostat needs attention.

 

[Votabledog]

Would you suggest starting with a lower unit rebuild? As far as I’m aware the engine is where it was installed at the factory(no jack plate) and I run it with the trim all the way down. The water pressure gauge on the console does jump up and down a little when I’m running at the rpm I’m getting the alarm at but I’m not sure if the gauge is accurate or not.

 

[Votabledog]

Or maybe thermostat needs attention.

Is there a way to test if it is a bad thermostat?

 

[QBhoy]

Would you suggest starting with a lower unit rebuild? As far as I’m aware the engine is where it was installed at the factory(no jack plate) and I run it with the trim all the way down. The water pressure gauge on the console does jump up and down a little when I’m running at the rpm I’m getting the alarm at but I’m not sure if the gauge is accurate or not.

Mmm. Likely not common for an engine like that to have or need a water pressure gauge on the dash. Usually only a thing on high performance set ups or when there is a risk of losing pick up, as a result of it’s set up on the transom. Any pics ?

 

[saltchuckmatt]

Is there a way to test if it is a bad thermostat?

Remove it see what it looks like. If clean drop it in some boiling water with a temp gauge.

 

[racerone]

There may not be a thermostat in the 4 cylinder " classic " motors.-----Pictures or serial # of this motor ?

 

[Votabledog]

There may not be a thermostat in the 4 cylinder " classic " motors.-----Pictures or serial # of this motor ?

#0B284736

 

[Votabledog]

Mmm. Likely not common for an engine like that to have or need a water pressure gauge on the dash. Usually only a thing on high performance set ups or when there is a risk of losing pick up, as a result of it’s set up on the transom. Any pics ?

It’s on a 1988 bass tracker tournament tx17.

 

[QBhoy]

It’s on a 1988 bass tracker tournament tx17.

Ok so…just looking at that picture there. Hard to tell. Engine bracket doesn’t look high mounted, but lower unit looks like it might be high when down. Unless that hull has a slight tunnel or a hull that suits the set up. Can’t tell from that picture really.

 

[Votabledog]

Ok so…just looking at that picture there. Hard to tell. Engine bracket doesn’t look high mounted, but lower unit looks like it might be high when down. Unless that hull has a slight tunnel or a hull that suits the set up. Can’t tell from that picture really.

The water inlets appear to be under the bottom edge of the hull. I don’t see any tunnel down the center of the hull

 

[QBhoy]

Yeah. Sure does

The water inlets appear to be under the bottom edge of the hull. I don’t see any tunnel down the center of the hull

yeah. Sure looks that way. Wonder if there is a restriction somewhere in the cooling passages. Have you tried a hand held thermometer gun with the cover off to see what’s happening? Felt the head for heat etc ?

 

[Votabledog]

Yeah. Sure does

yeah. Sure looks that way. Wonder if there is a restriction somewhere in the cooling passages. Have you tried a hand held thermometer gun with the cover off to see what’s happening? Felt the head for heat etc ?

I just did. I didn’t get it up to the high rpm the alarm sounds at due to my water muffs not being the greatest(tons of water spill out of them and the tell tail stream is not as strong as when in the water) but I ran it at about 3500-4000 rpm for about 5-7 minutes and never got the alarm my temp gun read around 180-190f. I could put my hand on it for about 5 seconds before it got to hot, I’m not sure what the normal temp range is and if this is normal or running hot.