1988 454 Mercruiser Over Heating when at idle

[LazyGatorBfin]

Was wondering if anyone had any advice I am looking at buying a boat everything looks great on it but the port engine is over heating. I am going out there Saturday morning to see if there is something easy to fix it. I have a feeling it must be something with the raw water flow. Where do you feel I should start. It ran Idle for about 20 min we raised the rpm's to look for leaks or noises we turned if off started it back up 10 min later let it run and it over heated. Any help would be greatly appreciated. I wouldn't normally buy something like this with problems but its someone I know and I am getting it for a steal because they are moving.

 

[HT32BSX115]

Re: 1988 454 Mercruiser Over Heating when at idle

Was wondering if anyone had any advice I am looking at buying a boat everything looks great on it but the port engine is over heating. I am going out there Saturday morning to see if there is something easy to fix it. I have a feeling it must be something with the raw water flow. Where do you feel I should start. It ran Idle for about 20 min we raised the rpm's to look for leaks or noises we turned if off started it back up 10 min later let it run and it over heated. Any help would be greatly appreciated. I wouldn't normally buy something like this with problems but its someone I know and I am getting it for a steal because they are moving.

Howdy,

Welcome aboard!

First and foremost, it's good if you post the model/serial numbers so we know what you're talking about.

If it's a sterndrive boat, most likely the raw water pump has failed. If it's a twin, plan on changing BOTH. If it's Alpha drives, you'll need to pull the lower units to do this.

Bravo's have the raw water pumps on the engines.

If you don't know anything about boats, it might be worth it to pay someone to inspect.

Cheers,


Rick

 

[LazyGatorBfin]

Re: 1988 454 Mercruiser Over Heating when at idle

Its an Inboard raw water cooled 454 I know its a 1988. When I was out there it was at night that is why I am going out Saturday Morning to work on it in the sun. Not sure if it helps but here is a picture of the motors

 

[Don S]

Re: 1988 454 Mercruiser Over Heating when at idle

Lots of things can cause an overheat at idle, or any other speed for that matter.
The first thing you look at on any marine overheat problem is the impeller. So little can destroy an impeller.
Did the elbows get hot when the engine overheated? Since the engine has fresh water cooling, you could have a defective thermostat.
Could also be plugged up elbows, plugged up heat exchanger. Remove the end caps and see if things are blocked.

 

[LazyGatorBfin]

Re: 1988 454 Mercruiser Over Heating when at idle

Thank you for the heads up some things to look for on Saturday. I will look for the S/N and more information for any future questions. With the boat not being in my hands its hard to get the information. But thanks for the help and I will let you know how it works out.

 

[HT32BSX115]

Re: 1988 454 Mercruiser Over Heating when at idle

Its an Inboard raw water cooled 454 I know its a 1988.

Most would call that a CLOSED cooled or fresh-water cooled engine because of the heat exchanger.

You also might have an oil/transmission cooler that is clogged with debris or impeller fragments. Does it have a "Sea-strainer"? That might be clogged.

If it only does it at idle, (I.E. it cools when you increase RPM) it could be the impeller. If the impeller is missing vanes, pieces went down-stream and can clog the oil cooler, heat exchanger or supply hoses etc.....