Overheated GT150

[scott2000d]

OK, so I finally got the 86 GT150 going after replacing the flywheeel key. My brother had it out a couple days later and it overheated very quickly to the point that it melted wire covers and plastic around the coils. All the cylinders still seem fine, although the head and head cover bolts all have loosened up. I'm going to try retorking everything and hope it still works. What I'm trying to figure out is why it overheated in the first place. The thermostats are both fine as tested in boiling water, and the impeller is in great shape. My brother didn't notice if water was coming out or not before he shut it down. Any ideas what could have caused it to overheat. Thanks, Scott

[ta3834bbl]

Just had the same problem with my 89 200xp. I tested the t-stats in water also and they worked fine but still overheated. I removed them and it runs fine now. However, I still need to get replacements and install them to see what happens.

[scott2000d]

OK. I'll have to get it back together and try it myself. First I think I will try it with the same (but now cleaned) thermostats in it and see if it still overheats, but if it still does I will try it without thm and see if that makes a difference. What kind of water pressure should I expect to get when running at idle and also at different power settings? If it makes a diffrence my Pressure Guage is hooked in to the pee stream line.


Modified by scott2000d at 8:10 AM 5/25/2009

[ChampioNman]

Did you get the woodruff key on the impeller correctly? OMC changed over to a new design around that time.

[scott2000d]

I'm pretty sure I did. it's a directional key. Now my big problem is just getting it to start again. I got everything back together today and tried to start it, but it wouldn't start. I did manage to get it started once but I shut it down right away since it was idling at a lil over 3000RPM and sounded like crap. I didn't even get a chance to see if there was water coming out the pee hole. I think once I figure this one out the whole thing is going up for sale. This is the 3rd weekend in a row that i've wasted fixing the thing and I haven't had it out in that time at all. The only good thing about the whole situation is that I got 2 parts motors with it so a lot of the fixes have been free. When it overheated even the little valves below the thermostat melted and any plastic that was touching either head melted as well.

[ChampioNman]

Better check compression.

[scott2000d]

Alright, So I checked the compression and it is all still good. 85 - 92 all around. I have good spark all around. I can get it to start after much cranking , but it is idling at 3000 RPM and there is no water coming out. I have a feeling the impeller is shot so i'm thinking about ordering an impeller rebuild kit. That hopefully would solve the water issue. I also have to order a new starter as the one I have is now pretty much cooked since smoke started rolling from it today while I was cranking it over. Still will roll over the motor once it cools down tho so it isn't the first thing that needs to be replaced. However there is still the problem of the motor not wanting to start easily, and when it does it is running at 3K RPM with the throttle closed. Any ideas what could cause this?

[ChampioNman]

Yep make sure #1 is TDC with the flywheel. That is essential. Then you proceed to the sync n link.

[scott2000d]

At the risk of feeling really stupid. Can you please explain to me what you meant by "make sure #1 is TDC with the flywheel" and how I would do that. Also, do you think there is any point in pulling the flywheel again to see if the key somehow sheared again?

[ChampioNman]

You rotate the flywheel and make sure #1 is at TDC and the marks on the FW are at 0*. You need to put some type of indicator into the cylinder. I use a piston stop tool but if you have all the plugs out and use a pencil eraser end, hold the pencil in your hand and rotate the FW. When the piston reaches TDC mark the FW. Then go from there.

[scott2000d]

OK. Thanks, I'll check that first tomorrow. So from what I'm getting is that once I have #1 at TDC the FW should be pointing to 0*. If that is the case I should do a sync n link and that will hopefully fix my hard start and high idle issue. Would overheating very badly normally cause me to need a sync n link? Is there something that could have melted to cause this high idle and hard start? I have already replaced both poppers as they were melted to the point that they were running down the head covers so I know it got VERY hot in there.

[ChampioNman]

That will make the upper half right and the way to confirm is to do a compression test. The bottom half pumps the water and that MUST be right. No cool no go~~~!!!

[scott2000d]

So I went in and talked to a mechanic today and he told me that after the motor getting hot enough to melt the poppits the crank seal probably melted which will allow the motor to suck too much air causing it to idle at 3000RPM and will also be very hard to start. Also it made sence to him that the only way I could get it to start was with the choke on. He also said there is a good chance I blew a head gasket. He quoted me probably around $800 if I pull the powerhead off myself and bring everything to him. He will strip the motor and replace all seals and gaskets, as well as reassemble everything and put it back on the boat and make sure everything runs properly. He will also replace the impeller and check my lower unit seals. Does this diagnosis make sence and is this price reasonable?

[scott2000d]

Well I got an update from my mechanic. The crank seal was definately melted. Part of one of the crank barrings also melted. The heads both needed to be planed down .010. One of the head gaskets let go and was washing out cyl #5. The flywheel key was sheared again, and the impeller was shot. By some miracle the cylinders held up through all this. He even managed to rebuild the starter. Hopefully after all this the motor will get me through the rest of the summer. Just gotta wait for the gasket kit to come in. Thanks again for all your help, Scott