1974 25 Johnson dying

[brycebell]

Hello, I ran my motor yesterday and the water coming out was hotter than I thought it should be. Could hold my hand under it for a few seconds but was definitely warm. Once the motor ran for a while I went down to a slow idle where the motor eventually died. After this I was not able to start it again for another hour or so where then it did start fine. Any opinions on what my problem would be. My first thought would be to take the water pump apart and make sure it has no clogs or anything and is pushing enough water out. Is there anything else I should be looking for. Any advice would be much appreciated. Thanks in advance.

 

[Howard Sterndrive]

Re: 1974 25 Johnson dying

where does water come out on a 74 25HP?

start with compression test
then spark test.

if in doubt - change the impeller

 

[kbait]

Re: 1974 25 Johnson dying

The water out of the exhaust on your motor should be warm once the thermostat opens. If you can touch the head near the spark plug bases for a few seconds when running, you're good to go. If water will boil off the head, you have a cooling issue. Do the touch test at slow idle.. that's when a worn impeller will show it's failing. Good luck!

 

[brycebell]

Re: 1974 25 Johnson dying

Okay that's kind of what I figured. I think i could touch it for a few seconds but it was pretty hot. Would there be a reason it was dying and not able to start tho other than overheating from a cooling problem?

 

[Howard Sterndrive]

Re: 1974 25 Johnson dying

there isn't "a" reason...

there are at least 100 possible reasons an outboard can die and not restart.

compression test
spark test
make sure it's getting all the fuel it needs

 

[brycebell]

Re: 1974 25 Johnson dying

I know it can be a lot of different things. But it was running for a solid 10 minutes before it eventually died. The motor was really hot that's why I was just assuming it was something to do with the cooling system. I did a compression test before I took it out and it had 100 in both cylinders.

 

[OptsyEagle]

Re: 1974 25 Johnson dying

Well obviously the compression was OK before you took it out or you would not have been able to take it out. If you can, you should take a compression reading now. If you had an overheat condition it will most likely show up in those readings. By the way, my 1976 15 HP motor (same basic design) has some very hot water that shoots out the exhaust hole. I wouldn't want to take a shower in it, but it is normal for the exit water on that motor, especially since the cooling water going in is probably a little hotter these days. It is the middle of July.

 

[brycebell]

Re: 1974 25 Johnson dying

Okay thanks I will make sure I do that. I think I was getting enough fuel but I will check out that too. Is there anything else to check?

 

[Howard Sterndrive]

Re: 1974 25 Johnson dying

one way to eliminate a fuel issue, is to fill a spray bottle with 50:1 mixed gas and mist it into the carb throat. If that makes it go, you might have a carb that needs rebuilding, or a bad fuel pump... or a clog in the fuel system

it is odd that it restarted an hour later and can see why you would jump to overheat conclusion, but still start with the basics
if it seized - it would be hard to pull over (if rope start)

any ignition or fuel problem can show up on a long run - didn't necessarily overheat, but compression test will verify
have a look at the spark plugs too -

if the heat range in there was chosen for trolling, maybe the electrodes are going white hot on a long run.... there's some good threads here on iboats about plug choice in these 22 cid 18/20/25's
J4C's are the fast cruise plug - J6C better for trolling

and hey - change the impeller - it's a $20 thing - not worth analyzing - just throw one in.

 

[brycebell]

Re: 1974 25 Johnson dying

Okay I will try all of those. Thanks a lot