1979 Johnson 100hp

[Kymc3000@gmail.com]

I have a 1979 Johnson javelin 100hp on my bass boat and the issue I’m having is at an idle the engine will stop peeing. If I rev it up it starts peeing and cools right down but if I leave it at an idle the over temp alarm goes off and I shut it down. I replaced the impeller and still same results. I suspected thermostats so I ordered new ones but tried removing them and the tried running it again with same issue. I did notice that when I rev it up water comes out the pee hole strong and out the 2 holes above the lower unit. Compression is 134-135 on all 4 cylinders. Any ideas greatly appreciated!
thanks

 

[boobie]

Is the water pump put together correctly ??

 

[oldboat1]

Maybe your idle speed is too low. The standard is typically 650-700 rpm at idle in gear.

You cannot test the cooling system running on muffs, btw.

 

[Kymc3000@gmail.com]

I believe the water pump is installed correctly with new sleeve and plate.

Ya with muffs it doesn’t have an issue, I have it in a cut off barrel for testing.

 

[oldboat1]

Water level about 6 inches (3-6 inches) above the impeller (i.e., above the l.u.). More rather than less.

 

[Kymc3000@gmail.com]

The water level is right where the lower unit mounts to engine, maybe it’s too low for accurate testing.

 

[oldboat1]

Yeah, that's where the impeller is. The water should be maintained 3-6 inches above that (let the hose keep running to maintain level). You may need a bigger test barrel.

 

[Kymc3000@gmail.com]

Ok thanks

 

[jimmbo]

How old is the impeller, the pump liner, and bottom plate?

 

[Kymc3000@gmail.com]

Brand new

 

[Kymc3000@gmail.com]

Oldboat1 you were correct I didn’t have the engine submerged deep enough to test. Do have another question tho. When running I’m charging at 12.7V at all rpms? What should I be charging at? I would think 13.5-14. How can I test to determine the issue?
Thanks

 

[oldboat1]

Start with a fully charged battery before testing. Around 14 volts would be about right if the system is working. If the Javelin has a separate rectifier, I would be inclined to just replace it (not too expensive). But they are not difficult to test (essentially looking for conductivity in only one direction).

Glad the cooling issue appears to be solved. Check the temp on the top of the heads to make sure it's not overheating (Too hot to touch is too hot to run.)

 

[Kymc3000@gmail.com]

Do you know a link on how to test the rectifier?

 

[Kymc3000@gmail.com]

It the rectifier your talking about a round unit with 3 wires?

 

[oldboat1]

Yes (triangular base). Do a search here for "rectifier testing" or something similar.

Here's a brief description:

Use a high ohms setting on your multimeter and test resistance from each lead to an engine ground, then reverse probes. A high reading in one direction and a low reading in the other means the diode is good.

Do the same test between the red lead and each of the other leads (and reverse). Again, a high reading in one direction and a low reading in the other means the diode is good.

 

[Kymc3000@gmail.com]

Tested it and it’s shot, has continuity both directions on all wires. No working dioed anymore. They joy of fixing up and older boat, thanks a lot for your help

 

[oldboat1]

You're welcome. Best bet is usually oem. Not much difference in price, I think.

 

[Kymc3000@gmail.com]

I got the rectifier on today and it charges now but at idle it’s around 14.5v and when I’m reving it up the charging voltage goes to 16.8v?? Could the base of the rectifier not be grounding well enough?

 

[oldboat1]

sounds like you're golden.

 

[Kymc3000@gmail.com]

It’s supposed to charge that high when reving the engine up? Im used to automotive and Diesel engines that charge at 14-14.5 on a 12v system
thanks