Overheat alarm during idle

[birdgod]

Hi, I have a force 1989 force 85 hp outboard that I having overheated alarm problems. I have installed a telltale on the outboard have have been using it for 3 years now. Then yesterday when I brought it out for fishing after the long winter, the overheat alarm when off when the outboat is at idle for 3-4 mins. The alarm will stop if I keep put it in gear. Here is what I have notices: 1) When the alarm come on at idle, I notice that the telltale have no water coming out, it use to have water even when it is idle. 2) if I put it at fast idle or in gear ( faster engine speed) the telltale will have water coming out and alarm will stop. What should I do ? The impeller was chased two year ago. Thanks

 

[jerryjerry05]

I'd start with a new impeller.
Sometimes they last 10 years or more(not a good idea) sometimes a month.
Drop the lower and inspect.
Fresh water?

 

[gm280]

I'll absolutely second jerry's suggestion above. Time to change the water pump impellor or the entire water pump kit if it looks suspect. Your problems will be solved....only if everything else is clean and clear...

 

[birdgod]

Yes, fresh water. I will take picture and show it, thanks

 

[Jiggz]

Start with Jerry's suggestion which is the most logical. If the impeller looks to be in perfect condition, inspect the passages for scaling or clogging.

 

[Frank Acampora]

Agree with everyone else! The impeller is shot and needs to be replaced. REASON: The water pump acts like a displacement pump at low speeds. At higher speeds it acts like a centrifugal pump. SO, if one or more of the impeller vanes is broken it will not pump water at idle yet the stub vanes will move enough water centifically at high speed to cool the engine.

 

[jerryjerry05]

Guess I should have asked.
You ever start without the hose being hooked up?
Even for 10 seconds it can do some serious damage.

 

[birdgod]

Guess I should have asked.
You ever start without the hose being hooked up?
Even for 10 seconds it can do some serious damage.

yes, thinking of it, right before the problem start, I did a dry start to make sure it can run as it had been sitting there for more then a year. Once it finally started, I shut it off, the run time is less then 2 sec. I guess damage is done just not big enough to show until I idle it for too long. All talk aside I will take pictures once I got it open. Thanks

 

[birdgod]

Finally replace the impeller today. The old one look almost perfect with no more then 5% wear. I replace anyway since it was already taken apart. I will try it in the water after the rain stop the week. By the way, I inspect the water passages and it look ok. Also test the thermostat by putting it in different temperature water, work fine too.....

 

[scout-j-m]

Agree with everyone else! The impeller is shot and needs to be replaced. REASON: The water pump acts like a displacement pump at low speeds. At higher speeds it acts like a centrifugal pump. SO, if one or more of the impeller vanes is broken it will not pump water at idle yet the stub vanes will move enough water centifically at high speed to cool the engine.

Great explanation Frank.

 

[birdgod]

Thanks guys, it was the impeller. After replace the impeller the water flow from the tell tail nicely and no more alarm problem. Thank you again for all your help.