58 Johnson Super Seahorse 35 Needs Help

Hi All,

Having a few problems with the old Johnson. Took the boat across from Whidbey to Marrowstone Island. Seemed a bit sluggish on the way but we were weighted down with camping gear so we thought that was part of the problem.

When we got there, we unloaded and went out again to check out Mystery Bay. Didn't make it very far before we saw lots of smoke / steam? and lost half our power. We turned around and went back to the dock. The next morning we limped her over to Port Townsend.

A mechanic has diagnosed the problem as follows: Thermostat stuck, caused overheating, blew a head gasket, water in the chamber, lost compression. Apparently when he pulled out one of the spark plugs it was all wet.

A new head gasket is on order. The thermostat has been removed and he does not want to replace it. Says it will run fine without it at about 150 degrees. Just double checking on this because this particular mechanic does not usually work on these old Johnsons. Does this sound logical to those of you that have experience with these older Johnsons?

Thanks,

Lauryn

Anybody out there?

Hello Again,

If all goes well on the Super Seahorse 35 repairs today, and the blown head gasket was in fact the culprit, I'm picking up the boat tomorrow. I'm really wondering about the idea of not replacing the thermostat - just leaving it off- if anyone out there can give me some feedback on this I would greatly appreciate it. I have searched all the threads I can find on the internet and have not been able to find anything - good or bad - about removing the thermostat and not replacing it.

Thanks!

[ChuckB]

Lauryn:
Lot's of mechanics like to leave out T-stats as they can stick closed and cause overheating. Without the T-stat the motor will take longer to warm up and thus run smokey and cough more. Other than the longer warming to operating temp, it should be OK.
ChuckB

[halffast32]

Don't know much about t-stats on outboards, as the old mercs don't use them. On the race cars, I gut the t-stat. Remove the inner "plug", but leave the rest. Gives the system something to slow the flow, but eliminates the "stuck" possibility.

[McSkagit Tim Jones]

Salt water thermostats

Salt water cooled thermostats are set at 143 degrees. Any hotter and the salt begins to precipitate out. No problem running with it out, but the motor runs better and less wear with it in presuming the water pump is good.

Also the exhaust cover gaskets may have been damaged by the overheat. Best check them too. If the paint on the exhaust cover is burned or black, better change the gaskets. Else you may have more water in the cylinders and a scored piston and/or sleeve.

How's the water pump impeller? Sometimes the rubber grommet where the water pipe from the pump enters the power head gets compressed by salt build up and chokes off the water flow. This is just under the power head and requires removal of the power head. Not a big deal unless you have frozen bolts.

My two cents worth.......
McSkagit.

[Tim_Mattson]

Tim has a good point,bolts will loosen thru-out the motor if if got that hot.
Might be worth a test turn on some exhaust cover bolts,and even up near the carb intake....basically all of the motor bolts should be checked.Tighten as needed.
The T-stat does regulate temp and a warmer motor does burn more of the fuel.
I`d only pull T-stat if it is repeatedly clogging......replaced with new it shouldn`t stick until it gets dosed with salt and left to harden.
A temp gauge can easily be added too,one metal strap thru one of the head bolts and a single wire to a grounded gauge on dash will give you an idea of it`s temp visually.
TM