Overheating!! Head gasket? Blockage? Other causes?

[Cofe]

Re: Overheating!! Head gasket? Blockage? Other causes?

This is on a 2000 model Johnson 30 2 cylinder two stroke.

After extensive diagnosis, it was determined that the motor was overheating. Overheating causes the overheat sensor to cut back the RPMs until the engine cools. (The motor surges but will not build RPMs again until it cools. It has been determined that this is not a fuel problem and that the engine is overheating.)

The Johnson dealer replaced the water pump, thermostat, and overheat sensor. That has not fixed the problem. It does exactly the same thing - surges and will only idle until motor cools. Water flow out the indicator tube is good. Compression is good.

The dealer seems to be out of ideas, so I'm hoping someone here can help with this.

After doing some research (including looking through the repair manual), several possibilities stand out.
- leaking head gasket that overheats the water and/or allows compression gases to escape into the cooling water jacket.
-blockage or other water flow problem in the water jackets around powerhead. This motor has only been used in fresh water and shows no signs of corrosion.

Can anyone tell us what diagnosis procedures to follow to determine if head gasket needs replacement? Or is this a case of taking it apart and replacing the head gasket and hoping for the best?

And how and where would one look for and fix a blockage in the powerhead area?

This motor you have really isn't that old to be having these problems. You stated that it surges....."could be fuel pump diaphram leaking fuel to the bottom cylinder. Just a thought

 

[northernmerc]

Re: Overheating!! Head gasket? Blockage? Other causes?

Cofe, no it's definitely overheating. Without the overheat sensor connected, the temp just keeps climbing until it will self destruct.

On the water deflectors, since there are two types in there - one hollow and the other solid - I'm pretty sure someone was in there before.

In your other post - the one you provided the link to - I thought that you indicated that you seated the water deflectors as far as they could go. That would not leave a space behind the top deflector and the bottom starboard deflector. Now I'm confused. Are you now saying to leave a space behind those two? Or maybe just behind the top one?

 

[Cofe]

Re: Overheating!! Head gasket? Blockage? Other causes?

Hey Northermerc.
The bottom two deflectors were inserted all the way they would go. But there is a small water passage behind the starboard one. The top deflector area "tapers" {can only push the deflector in sofar} there is a space behind that one.
As far as overheating goes, a fuel pump diaphragm leaking fuel back thru the vacuum tube to the lower cylinder can cause overheating and poor performance. The added fuel at WOT will burn hot.
Then at lower rpms, it makes the engine load up on the bottom cylinder. About all I can come up with. Hope this helps

 

[northernmerc]

Re: Overheating!! Head gasket? Blockage? Other causes?

Hey Northermerc.
The bottom two deflectors were inserted all the way they would go. But there is a small water passage behind the starboard one. The top deflector area "tapers" {can only push the deflector in sofar} there is a space behind that one.

Can you tell me more about that "small water passage behind the starboard one." How small, and where does it lead to? Will the deflector block it if I push it all the way back, or is the small water passage behind the metal that the deflector bottoms out on. I can quite easily push the deflector back to completely block the main passage that goes up the starboard side of the block. But as I mentioned earlier, the deflector then is about an inch further into the block than when I took it apart.

 

[Cofe]

Re: Overheating!! Head gasket? Blockage? Other causes?

Mine may be different than yours, Back on the other thread there is a picture taken with a mirror. Note where the deflector will stop and the water passage behind.....Had to see this with a mirror.

 

[northernmerc]

Re: Overheating!! Head gasket? Blockage? Other causes?

Mine may be different than yours, Back on the other thread there is a picture taken with a mirror. Note where the deflector will stop and the water passage behind.....Had to see this with a mirror.

You must be quite the photographer to take that picture. I have a hard time just seeing in there, even with a mirror.

I'm still kind of stumped on this water deflector thing. What surprises me is that there don't seem to be any specs on the length of these deflectors. Why don't the manuals state the length or give more detailed instructions on their installation? Maybe it's like someone said - that working on outboard motors is a "black art."

 

[Cofe]

Re: Overheating!! Head gasket? Blockage? Other causes?

Your motor is a 2000. Chances are nobody messed with the deflectors. My advise is put the old ones back in or cut new ones the same length. My oem manual says nothing about deflectors. Guess it is some kinda secret.

 

[Cofe]

Re: Overheating!! Head gasket? Blockage? Other causes?

I sent you a private message....

 

[northernmerc]

Re: Overheating!! Head gasket? Blockage? Other causes?

Here's an update on this P*S. For lack of more information on the water deflectors length, ended up putting the same three water deflectors back in. That leaves a space behind two of them for the water to flow. (If anyone ever sees this thread and can offer more advice on this, please post and/or send me a PM)

Took leg and water pump apart to confirm that shop did it right. Also made sure that the tube from the water pump was clear (took it off, poked wire through it, and blew compressed air through it). Also blew high pressure compressed air (150+ psi) through system from below and through all orifices around the head. No blockages found - everything squeaky clean with no corrosion evident.

Checked new 143 degree thermostat to make sure it opened. According to infrared temp. sensor, thermostat opened within a few degrees of 143 degrees. Put head back on with new head gasket.

Went to lake and tried out boat, expecting little. I was not disappointed. Made it less than one mile before engine overheated and overheat sensor cut back the power. Indicator stream great, but still overheating.

Back at dock, removed thermostat. Took boat out again. Ran perfect. Full throttle for about five miles, with no overheating.

The logical thing seems to be to keep running it without a thermostat. What harm can it do?
If it wants to run that way, who am I to argue with it?

Comments appreciated.

 

[northernmerc]

Re: Overheating!! Head gasket? Blockage? Other causes?

Another update. In the past week, we used this motor for three days of fishing. That included quite a few hours of trolling and some long runs across the lakes. It hasn't missed a beat running without a thermostat. So far, so good!