remove thermostat?

[bison716]

I have a '93 Johnson 15 hp. Replaced waterpump and housing, plus a new thermostat as well. Finally could try it out today. Engine runs hot and the tell tale just barely comes out at idle. Water coming out is very hot and the head will sizzle if you put some water on it. Definitely too hot. I'm on vacation and away from my home shop. My question is if I can remove the thermostat and run the engine? Will it still cool the engine properly? That's about the only trouble shooting I can do here. Would appreciate any quick advise. Thanks.

 

[Cofe]

Re: remove thermostat?

Yes you can run the motor ok without the thermostat. Let your motor warm up good before you get on it..... or motor could cold seize......

If your old impeller had chunks missing out of it, they may be lodged somewhere in the water passages.

 

[kenmyfam]

Re: remove thermostat?

Check that your stat is functioning correctly.
What was the reason for the impeller change ???
You may well have a blockage somewhere.
Sizzling head is bad news in my opinion.
How close to a parts source are you ???

 

[F_R]

Re: remove thermostat?

Removing the thermostat probably won't help. You are going to have to find the real problem.

 

[bison716]

Re: remove thermostat?

Bought the engine used and replaced impeller and stat to be safe. Water pump housing looked worn so replaced that too. Ran great but telltale was very hot. Stream was strong off idle. I will try it without the stat. Thanks for the replies.

 

[bison716]

Re: remove thermostat?

Removing the thermostat probably won't help. You are going to have to find the real problem.

You are probably correct about bigger problems. I removed the stat, taped up the wires that got melted yesterday and tried it again. It was hard to start but definitely runs cooler. At speed the tell tale is barely off cold and only warm at idle. However now it is off on power and really sluggish to get up on plane. 3/4 to wide open does nothing. When my test was over, I see a grey slimy paste forming in the prop hub. What the heck is that? I'm on vacation in the moutains and 2 hours from a marine dealer. Any more ideas to try? Compression still seems good on the rope, it did have 90 per side when I left home. Tell tale is good and strong, not sure what to check next.
thanks.

 

[Cofe]

Re: remove thermostat?

You probably got it so hot that it could have warped the head enough to leak water into the cylinders, or the exhaust chamber water cooling passages are leaking into the cylinders. That grey stuff in the exhaust hub is evidence of water ingestion.

 

[snowman48047]

Re: remove thermostat?

I don't think removing the T-stat will work for long and I don't think it will run right as it won't run warm enough without the T-stat. As for the original problem, I am going through this same issue on my 25hp. Telltale water EXTREMELY hot, barely any water out at idle at first then nothing but steam. My pin for the impeller came out and there looks like a piece of impeller is missing. Mine probably has that piece jammed somewhere and I suspect you have one or both of the same issues. Maybe you don't have impeller pieces anywhere but it sounds like lack of water circulating to me. Let us know what you find.

 

[jmendoza]

Re: remove thermostat?

Suspect upper water tube grommet may be deteriorated and folds over when the block gets warm and restricts cooling water flow, and it also can be leaking water so you will not get enough to cool properly
Water will spray out of the upper water tube grommet and mix with exhaust, possibly forming that emulsified oil you are seeing. You can take out the upper vent screw on your lower unit and see if the gearcase oil is OK and not emulsified. If it is, then you prop seals are bad. Be sure to tighten the vent and drain screws after this because they will leak...I always use new nylon sealing gaskets when replacing the screws.

I had a 9.9 I ran with no thermostat, it would foul plugs at idle because it never warmed up. The water tube grommet is suspect, but if you know the engine was used in salt water, remove the head and check the block for corrosion.