1977 evinrude 25 hp overheating

[zxstingerxz]

i have a 1977 evinrude 25 hp, on a 14 ft alumacraft. About a week ago i was heading up river when i noticed the pisser had stopped. before i could shut the motor down a puff or steam/water shot out of the pisser and the motor died. i waited about an hour for it to cool. checked the plugs, they were fouled. so i replaced the plugs, and the motor started on the first pull and the pisser was working. headed back to the launch (about 3 miles) with no problem. went to the evinrude dealer in mobile, AL and purchased a new water pump. replaced pump. tested motor in a drum, the water pump worked properly. went to the river agin yesterday for the 4th, used the motor most of the day with no problems. when i was headed back to the launch, same problem happened. water pump stopped pumping and the motor overheated and fouled the plugs. i would bring it to the shop but mechanics in my area are swamped with bp "oil clean-up boat" repairs. Any help would be greatly appreciated. thanks.

 

[AlTn]

Re: 1977 evinrude 25 hp overheating

drop the lower unit again and check the wp function by submersing it in a 5 gal. bucket and spinning the drive shaft with an electric drill attached ( there's a vid on you tube of a guy doing this with a 6hp. I believe)...while you have the lu off...force water up the water tube to the power head and check that it circulates up to the thermostat by removing the thermostat and leaving the cover off, it should "pour" from here with the thermostat out...finally...I'd suggest you check your compression as with 2 overheating episodes you may have blown the head gasket; also it'd be a good idea to check for scale between the block and the cylinder liners anyway

 

[zxstingerxz]

Re: 1977 evinrude 25 hp overheating

I pulled the t-stat cover off and found that it was stuck closed. I bought a new t-stat, water jacket gasket and head gasket. Cleaned all scale out between the block and cylinder liners. I put everything back together. Checked compression, had 91 and 89 psi. Installed the new plugs. I started the motor. It ran good. The pisser was working great. But there was barely any water coming from the exaust. Usually there was alot coming from the exaust. The pisser had alot of pressure though. Any advice?

 

[AlTn]

Re: 1977 evinrude 25 hp overheating

I'd put the boat in....idle it to warm it up...run it up and down the lake/river..no more than paddling distance away...and check the head temps after 10 minutes or so....140 to 160 should be about normal...I think the common wisdom is you should be able to hold your fingers on for 3 seconds or so at any time if all is well cooling wise

 

[scskinny]

Re: 1977 evinrude 25 hp overheating

I too have a 77 25 seems to be overheating. new impellar and plate and have pulled head cover and removed thermo for troubleshooting. seems to run well,start idle and full trottle but a bit noisey. maybe time for bearings or total rebuild but thought I would run it til it dies. problem is after a good run water coming out of exhaust is HOT possibly with steam not sure. have not run without cowl to put hands on but when i run in barrel till exhaust gets pretty hot, exhaust cover and head dont seem to be that hot to touch. 2-3 sec hands on no problemo. any other place i could look for blockage or could bearing wear and slop be creating eccess heat? thanks for any input