Johnson Over Heating Problem

[ironhaven]

Hello
I have a 1997 Johnson 9.9 two stroke motor.
I have changed my thermostat and I have a good flow of water coming from the pee hole. But when I idle the motor overheats and the warring sound and light comes on. when I give it throttle it will stop. Is there a sensor or something that might be going bad. I don't think it is the impeller cause I get a good flow of water??? is there something else I can check?

 

[BaitThrower]

Re: Johnson Over Heating Problem

Could be a sensor, because usually, when you throttle up a bit, you get more water flow and hence the temperature should lower a bit than when just running idle. Get yourself one of those infrared thermometer guns. Can get them cheap these days. That will tell you the temp of the motor and probably determine whether it is a faulty sensor, of if indeed the motor is running hot!

 

[Vic.S]

Re: Johnson Over Heating Problem

Change water pump impeller if its not been changed recently.

I sounds as though it is only just pumping well enough to maintain the pee stream at idle

 

[nguoi_viet41]

Re: Johnson Over Heating Problem

Hello
I have a 1997 Johnson 9.9 two stroke motor.
I have changed my thermostat and I have a good flow of water coming from the pee hole. But when I idle the motor overheats and the warring sound and light comes on. when I give it throttle it will stop. Is there a sensor or something that might be going bad. I don't think it is the impeller cause I get a good flow of water??? is there something else I can check?

try iwombat post rerouting the outlet line over the block see it may help I idle the motor overheats
http://forums.iboats.com/showthread.php?t=222677


rerouting the outlet line over the block

 

[Vic.S]

Re: Johnson Over Heating Problem

In the engine in question, a 1997 model, the telltale connection is near the top of the exhaust cover. The re-routing suggestion is for (older) engines where the telltale connection is from a low point.

#58 is the telltale hose in THIS DIAGRAM of a 1997 9.9.

 

[ironhaven]

Re: Johnson Over Heating Problem

Could be a sensor, because usually, when you throttle up a bit, you get more water flow and hence the temperature should lower a bit than when just running idle. Get yourself one of those infrared thermometer guns. Can get them cheap these days. That will tell you the temp of the motor and probably determine whether it is a faulty sensor, of if indeed the motor is running hot!

What is a normal temp?

 

[BaitThrower]

Re: Johnson Over Heating Problem

What is a normal temp?

Depends on your thermostat I guess. My older model 15hp has a 143 degree F thermostat, so operating temperature is usually around 145-155 degree F, sometimes around 160 if idling for a while.

 

[ironhaven]

Re: Johnson Over Heating Problem

Thank you all for your help.
I'm not sure if I want to tackle the job of replacing the impeller and it is around 100 dollars or more to have a mechanic do the job. I might just re-look it over the weekend. Is there a good article on replacing the impeller?
I did buy a manual last year but of course I cant find it when I need it.

 

[Vic.S]

Re: Johnson Over Heating Problem

I'm not sure if I want to tackle the job of replacing the impeller and it is around 100 dollars or more to have a mechanic do the job

Something that has to be done every few years though.

Basically just drop off the gearcase and there's the pump on the top.

If it is a long shaft take the extension off with it, clean up the drive shaft then remove the extension.

Top and bottom sections of the shift rod have to be separted. I think on that one the joint is accessible when the gearcase has been lowered a little.


Find that manual!

 

[ironhaven]

Re: Johnson Over Heating Problem

Yes, it is a long shaft and I did watch it done just for a few minutes the last time and he did unscrew the shift rod when the gear case was lowered a little.
That was all I seen I didn't see anything else. It would be nice if I could see a video on it like you tube or something. Well we were hoping we could use it for the holiday this weekend. Would it hurt it if I just kept it using it but just don't idle for long to let it overheat? It on a 24ft Pontoon and only a 9.9hp so when we are going it is always at full throttle.

One last question also. What is the right prop for my motor. I have a 9.25x10 and I just ordered a 9.25x8. when I use the 10 I get only around 3500 to 3900 rpm where I think it should be up around 5000 to 5500? I'm hopping the 8 will give me more RPM's.

Thanks

 

[Vic.S]

Re: Johnson Over Heating Problem

I'd use it . Just don't let it idle too long.

Nice of you to offer to Video the impeller job!

The smaller pitch prop will increase the revs at any given boat speed. The increase in revs will mean its producing more power so that will enable the boat to go faster so the revs will be able to go a bit higher still
With luck you'll end up close to max revs for the motor (5500 ? )

 

[HighTrim]

Re: Johnson Over Heating Problem

Here is some available help.

http://www.sschapterpsa.com/ramblings/Lower_unit.htm

http://www.sschapterpsa.com/ramblings/water_circulation.htm

finally a video that you requested, not for the 9.9, but same idea none the less

http://www.meegsonline.com/tmd/waterpump.wmv

www.themarinedoctor.com/videos/removecase.wmv

www.themarinedoctor.com/waterpump.wmv

 

[ironhaven]

Re: Johnson Over Heating Problem

I just wanted to give you a follow up just in case this will help someone else out with the same problem. BTW thank you all for the help and the video's.

I did change the impeller over the weekend and it only took around an hour to complete. I looked at my impeller and it seemed fine no bent fins or cracks and the housing looked good too. I went to the boat store down the road and they looked at it too and the only thing we came up with was the new impeller seemed more stiffer (Dense). We think the person that changed it last year maybe used a cheap aftermarket brand cause if was much softer than the new one (OEM). Well I bought a new impeller and put it all back together and it seems to be working fine. Good stream of water and no warring alarm.

 

[ironhaven]

Re: Johnson Over Heating Problem

The smaller pitch prop will increase the revs at any given boat speed. The increase in revs will mean its producing more power so that will enable the boat to go faster so the revs will be able to go a bit higher still
With luck you'll end up close to max revs for the motor (5500 ? )

Hey Vic
When I changed the Prop I did gain about 10,000 RPM's I went from 3,700 to around 4,700 and thats good but, is there anything else I can do to get it up to around 5,000 or 5500?

 

[wbeaton]

Re: Johnson Over Heating Problem

10,000 rpms and you want MORE? lol

What is your boat set up? Are you reaching plane? Do you have an exceptionally heavy boat? RPM's that low sounds like a problem. I assume you are using a tach.

 

[ironhaven]

Re: Johnson Over Heating Problem

Sorry, I didn't mean to say 10,000 RPM's I just went from 3700 to 4700.

And yes all I have is a tach.

 

[Vic.S]

Re: Johnson Over Heating Problem

is there anything else I can do

It was fairly predictable that the change from a 10" to an 8" prop would give you that increase in rpm but I though it might just lead to a sufficient increase in power to push the boat a little faster and hence a further small increase in rpm. I assume you are still moving at the same speed but doing so at higher rpm! Basically the change has achieved nothing apart a bit more noise and a higher fuel consumption

A further reduction in pitch, would increase the rpm but if it does so with little or no increase in speed there is nothing to gain.

For non planing boats the object is to match boat hull, engine power and prop size so that you achieve max hull speed at maximum engine revs. Multihulls and presumably pontoons have totally different characteristics to monohulls. Planing boats a different kettle of fish again.

I know nothing about the characteristics of pontoon boats, a totally alien concept in the UK I think, and am not qualified to offer anything more.

Put a question on the The "Props questions" forum perhaps, giving details of the boat, the engine, and the props you have tried.

Maybe also a question on the "Pontoons" forum but not exactly the same question as that would be breaking the rules. Perhaps more aimed at the power of the engine than the choice of prop.

Good to hear that the new impeller has sorted the cooling problems.