Overheated

[River Rider]

I have a question for you pros. I have a 1985 30 horse Evinrude that ran like a top until last weekend. I was running the river fine and got to an area I had to keep my eye out in front when my motor slowly died out. I first thought I was out of gas, but saw some light smoke behind me. I opened the cowl and realized my impeller must have felled becuase my eninge was boiling. I let it cool and later on try to see if it would at least turn over and I got it to crank, but I did not run it again until I replaced the damaged impeller and the plastic housing that melted a little. My is now that it is all back together I am having problems starting it. Out of an hour I got it to start up once and idle perfect again, but it died once I throttled it back down a little. What could be the problem?

 

[wilde1j]

Re: Overheated

You may have done internal engine damage or the head gasket is blown. Start with a compression test and go from there. Post the results.

 

[River Rider]

Re: Overheated

Thanks, I will be doing that later tonight once I get my compression tester back.

 

[River Rider]

Re: Overheated

Ok, so I got home yesterday pondering how to get my engine warm for the test, but to my amazement one hit on the starter switch and she fired right up. I let her idle for a little while and then killed her. I then did the compression test to each cylinder a few times and came up with 80-85 PSI in both cylinders. I am wondering if it may be the head gasket should I go ahead and by a whole gasket set and redo the whole block or just start with the head incase it is a lost cause. Thanks.

 

[HybridMX6]

Re: Overheated

Those #'s do seem low, but then again all gauges will read differently. At least they are close to each other. I'd just pull the head for now and take a look at the cylinders. You can go from there as far as what parts you may need.

 

[River Rider]

Re: Overheated

I am going to pull the head tonight. I went ahead and ordered a whole top end gasket set just in case, might as well get everything up to snuff if my motor will make it a little longer. I will post my results. Thanks for the help so far.

 

[River Rider]

Re: Overheated

Just out of curiousity, what should my compression be? I know 80 seems low but again when it did start up and idle it sounded to be about the same as it was before, but I am know trained outboard guru. Thanks.

 

[petryshyn]

Re: Overheated

hi
An exact compression reading is seldom given as it is too subjective to:

-number of cranks
-speed of cranking (battery/starter condition)
-throttle open or closed
-engine temperature
-elevation compared to sea level

A compression test is not a "know all" "be all" test. Its information that helps troubleshooting. If your readings are within 10% of each other, you are likely OK. BUT REMEMBER, its a good idea to replace the head gasket after an overheat condition, as gasket damage can occur. It also gives you an opportunity to inspect "some" of the cylinder wall and piston tops.

Cheers

 

[pmat1]

Re: Overheated

Just out of curiousity, what should my compression be? I know 80 seems low but again when it did start up and idle it sounded to be about the same as it was before, but I am know trained outboard guru. Thanks.

110+ is good

 

[HybridMX6]

Re: Overheated

hi
An exact compression reading is seldom given as it is too subjective to:

-number of cranks
-speed of cranking (battery/starter condition)
-throttle open or closed
-engine temperature
-elevation compared to sea level

A compression test is not a "know all" "be all" test. Its information that helps troubleshooting. If your readings are within 10% of each other, you are likely OK. BUT REMEMBER, its a good idea to replace the head gasket after an overheat condition, as gasket damage can occur. It also gives you an opportunity to inspect "some" of the cylinder wall and piston tops.

Cheers

Agreed. It varies too much just by different gauges, not to mention all the other factors involved in that.
I'd pull the head, check out the cylinder walls and piston tops, thoroughly inspect the old gasket to make sure it wasn't compromised in any way, then also check the head for levelness using a sheet of glass. You lay the head down on it with the flat side down and see if it wobles, or if you can look under it and see if anywhere appears to be not even. If you can't tell, use a piece of fine grit sandpaper on the glass and move the head gently in a figure 8 motion over it. It will lightly scuff the areas touching, but not too much to make it not seal. If you see any areas not scuffed, then that area is not level, and you will repeat the sanding process until you get it all even. Just be sure to go in small increments, a little bit can go a long way on something like this.

 

[River Rider]

Re: Overheated

Thanks for all the help guys. After an hour and a six pack I found the problem for the over heat. When the impeller chunked a vien it lodge in the thermostat causing it to not open. I checked the cylinders and the rings everything was amazingly slick and clean. I replaced the head gasket as well as some of the other gaskets. I then tested compression and got 125lbs out of both cylinders. I ran the river this weekend and it was great. I do have another question. I took the thermostat out until I could a new one. Was that a bad idea to run my motor without the thermostat? Can you run the motor without a thermostat? Thanks.

 

[HybridMX6]

Re: Overheated

You can, but it is advised to go ahead and get another one. Outboards are designed to run at a specified temp range, too cold and it will cause excess carbon buildup and cause premature spark plug fouling.

 

[wilde1j]

Re: Overheated

Don't run too long w/o it ... the motor will run too cold and carbon up.