thermostat opens and stays open

[jwilkey84]

I just changed the thermostat on my Johnson 50 hp (J50BELCTA) and when I was done someone told me I should check the old one. So I put it in some boinling water and it opened after a few seconds, but then it stays open. What should this tell me? The reason I changed it was because this motor is new to me, and it felt like the motor was hot to the touch, and there wasn't much water coming out of the tell tale, so I figured I would investigate. I just like tearing into this stuff for a hobby, and I had never done a thermostat so I figured it would be a learning experience. I did check the impellor prior to doing this, and it looked ok and the flaps felt pretty good. I haven't started the motor since the new thermostat installation because I have some old gas lines to replace, but what should I expect when I fire it up again?

 

[Texasmark]

Re: thermostat opens and stays open

Looks like it was binding on the shaft. In your engine it may have done that upon opening also.

Mark

 

[tashasdaddy]

Re: thermostat opens and stays open

change the impeller any way. you have no idea how old it is. they will disintergrate.

 

[Benny1963]

Re: thermostat opens and stays open

cahnge pump kit with new brp kit worth every penny
benny b

 

[Silvertip]

Re: thermostat opens and stays open

If the tell tale stream was not very strong, that should be the clue that the water pump impeller, the housing, or both should be replaced. If you merely dropped the thermostat in boiling water so it layed on the bottom of the pan, that is not the way to test it. Laying on the bottom it is subject to the heat of the flame (gas) or heating element (electric) and not the water temp. You need to suspend a thermostat and use a candy or digital thermometer to get an accurate reading. It's also a good idea to test a new thermostat before installation. As they say -- stuff happens. If the thermostat stayed open at room temperature, then it was indeed defective and allows over cooling at idle. It would not cause an over heat condition.

 

[jwilkey84]

Re: thermostat opens and stays open

That's the part that doesn't make sense to me, if it was stuck open, why would the motor feel hot? And, no I didn't drop the tstat to the bottom of the pan, I suspended it with a pair of tongs in boiling water. What temp should it operate at anyway? This particular motor also has a temp sensor, what does that do exactly? Does is simply tell you when it is too hot by way of an alarm, or will it shut the motor off? (BTW I have not run the motor long enough to make it do either) I just thought the motor felt hot to the touch, maybe it is supposed to be that hot, but I could not hold my hand on ther for 3 seconds. Could there be something blocking enough water from getting into the motor, could that be why the tell tale is weak. I also bought a gasket for the water passage cover, so would it be the next step to look in there for blockage?

 

[F_R]

Re: thermostat opens and stays open

99.9% percent of the time when a thermostat fails, it fails in the open position. The same thing (corrosionof the plunger) that is holding it open can also make it stick closed till you get it hot enough to pop it loose, then it stays open. Most of them open at around 140 degrees. The overheat alarm only goes off after the motor is already overheated. It does not shut the motor down. (Some models like S.L.O.W. excepted) Any time there is suspected overheating, you should always first suspect the water pump. Only after you are certain that the pump is A-1 should you go looking for something exotic.

 

[mikesea]

Re: thermostat opens and stays open

Pretty much ditto with all already said.As FR stated,the boiling water,close to 212,is alot hotter than the 140 it is designed to react to,with expansion,contracting of metals and the higher heat,the thermo probably was forced to open,but it still has a problem and wont close,The tell tale is telling you (my opinion)impeller needs changing.Ive changed many over the yrs,and what seems to be okay ,isnt always so.Kinda sorry you didnt post before you put it back together.Its suggested by many mechanics to change it every yr.

 

[Silvertip]

Re: thermostat opens and stays open

1) Do you hear a single beep when you turn the key on? No = fix warning horn. Yes = thats the signal the overheat warning is functional.
2) Disconnect the brown wire from the overheat sensor. With the key on, touch the wire (non sender end) to ground. The warning horn should sound as long as you have the wire grounded. Yes = ok, No = fix the system.
3) If the engine overheats the warning horn should sound continuously. That means stop the engine now -- not next week or whenever I get a chance.
4) An ohmeter test on the sender should show open circuit with the engine cold. You would need to remove the sender and heat it with a hair dryer or or in hot water to get it to the trigger point at which time it should measure closed circuit. If it shows closed circuit cold -- that means replacement. If it doesn't show closed circuit when heated to trigger point, that means it needs to be replaced.

 

[jwilkey84]

Re: thermostat opens and stays open

thanks, I will try unhooking the brown wire and grounding the non-sending side of the circuit. There is no audible sound when I turn the key on. Should the sound be coming from the motor iteself or from in the control setup?

 

[Solittle]

Re: thermostat opens and stays open

Sound cones from speaker in the control box.

 

[Texasmark]

Re: thermostat opens and stays open

On Mercs in my current life, stat is set to 120F on midrange and on big engines to 143 but OT alarm is at 195. The NORMAL setting on most USA domestic hot water heaters is 140F to give you an idea what the engine would feel like (to the touch) at that temp.

Mark

 

[jwilkey84]

Re: thermostat opens and stays open

OK guys, I got the tstat replaced and I started the motor tonight. It seemed to run good, but it took like 15 seconds and some slight revving of the engine to get water to come out of the tell tale. I have been told that water should come out of the tell tale almost immediately after starting, is that true? Since water was coming out of the tell tale now, I let it run for about 4-5 minutes and then the overheat alarm started to sound, so I shut it off. I then waited for about 5 minutes and turned on the key and the alarm did not sound, so I started it again and let it run for probably 1-2 minutes before the alarm sounded again. I think the next thing I will try is the new impellor. Does anyone have any suggestions before I order parts. I am getting tired of paying shipping for one item, so if there are other parts anyone would suggest, I would like to order them all at once. Thanks!!

 

[Texasmark]

Re: thermostat opens and stays open

Time to pee depends upon how fast water is pumped in and how much volume you have to fill to pressurize and push the water out the pee tube.......or how it's plumbed.

Some plumb off the exhaust manifold, some off the top of the block, and some off the output of the tstat.

The first two require waiting for the block to fill. The later has to wait for the stat to open.

Don't have enough details to comment on whether or not your impeller needs to be changed, but with OT alarms, something needs attention as you must not be getting adequate water flow.

Mark

 

[ezeke]

Re: thermostat opens and stays open

Unless it has been upgraded, your early-eighties control does not have the three wire horn that beeps when you first turn the key. Those come much later.

SOME of the 1980's controls have a slot above the ignition that you can shove another key in to test the horn. You have to raise the warm up lever to get to it.

 

[jwilkey84]

Re: thermostat opens and stays open

yeah, the alarm does not come on until it overheats, so it must be equipped with the original early 80's setup. So what do I do next?

 

[jwilkey84]

Re: thermostat opens and stays open

Texasmark, I am not sure about all you said, but here is what I know. The tell tale comes out of the lower side of the water passage area. Does this mean that water should come out of the tell tale as soon as water comes up the water tube into the water passage area? If that is the case, then it is taking way too long for water to get to that point, and I probably will try a new impellor. Please give me your thoughts on this logic.

 

[Texasmark]

Re: thermostat opens and stays open

Don't understand what the lower side of the water passage area means.

The powerhead is filled from a tube coming up inside the midsection to the bottom of the block from the water pump located in the top of the lower unit. Water goes to the exhaust manifold cover and into the block directly, and to the top of the pistons (head water jacket) where it is restricted by the stat. You may also have a popoff valve that works with the stat to control head temp.....stat for slow speeds, popoff for higher speeds where more water is required and higher temp is not that important.

I have seen pee plumbed to the exhaust manifold cover, the top of the block, or from the stat discharge. Most engines have tubes going into the mid section just below the block to discharge excess water, or to provide for constant water flow.

The time to fill depends on the volume of water coming in and the volume of the water channels.

You probably ought to look at your impeller just for the heck of it. Then you'll know where you are with it and it will fix your problem or you will at least know it's not the problem. If it hasn't been changed in the past year or so, probably ought to go ahead and change it while you're there. It only costs about $10.

Mark

 

[BruceAML]

Re: thermostat opens and stays open

If it were my engine I would replace the complete water pump assembly with a genuine one. The thermostats usually have the temperature engraved on them in small numbers. A thermostat slows the water flow so that heat can be extracted more efficiently. When the water flow is too fast there is often not time to transfer the engine heat to the cooling medium (water in an outboard or antifreeze mixture in a closed system). A warmer engine can be more economical because it can run well on a leaner mixture than a cold engine.

 

[iwombat]

Re: thermostat opens and stays open

I don't know of any tell-tales that are plumbed in on the back side of the t-stats. That would be a really poor place to put an indicator. They should output water as soon as the jackets are filled. Water should come out within 2 or 3 seconds of ignition. If that is not happening, replace the impeller.