Thermostat stuck open

[bluefin87]

I have an outboard 40 hp mariner serial # 40 el 6e9 l 418332. I think the thermostat is stuck open because it doesn't get hot on the housing.

Is this okay to leave? or should I replace it and why?

Thanks for your help,

Jake

 

[aussieflash]

Re: Thermostat stuck open

Take Tstat out and have a look.Are you putting your hand on the head cover/block?
Mine (both) were stuck open so when up on plane she always ran cold which is not good for motor.Runs best when up to temp around 140.I replaced both Tstats though havnt run boat yet.Your lucky there not seized shut.

 

[Faztbullet]

Re: Thermostat stuck open

Remove it and inspect to see if held open by debris or if defective. If I remember it a 122? t-stat and the part numbers are 11752M or 814554001, and are a dealer item only as no one carries them aftermarket that I know of.

 

[Texasmark]

Re: Thermostat stuck open

You are lucky. I had 2 stick closed. First was on a '75 rude triple and cost me an engine overhaul as there was no over temp warning horn. The second was on a '02 90 Merc and it had a warning horn which saved the engine. Don't know about the designer's decision on your engine but mine, the 90 Merc, the stat pellet is stamped 143F which is the opening temp and at full open the water will be somewhat higher.....10 degr.?

Mark

 

[bluefin87]

Re: Thermostat stuck open

I just bought motor having it tank tested in the town i got it from. Mechanic said it wasn't getting up to temp, when he put hand on it. I haven't ran it yet myself until i got some advice and owner manual.

Question: If I replace it will it mess up fuel mixture and cause it to run different?
Will it change the amount of water the motor pisses? Because it was a real strong stream (i assume because it is stuck open?)

Thanks all

 

[oldman570]

Re: Thermostat stuck open

I would adjust the carbs as the motor will be runnig hotter and it will affect the fuel mixture. You might see a diffrence in the tell tail stream till the motor warms to temp., but none after it is warmed up, as the stats will have opened. If the motor is a remote steer, you might consider getting a water pressure gauge for on the consol to help keep a closer eye on the pump condition, and water flow thru the motor, without haveing to become an owl.
Best of Boating,
Oldman570

 

[aussieflash]

Re: Thermostat stuck open

Yes,it will run different.It will run more efficiently.The motor will thank you by saving a little on fuel.
Picture of my stuck open Tstats below.......maybe not.(stupid Ipad)You can view on my recent thread if you like.

 

[badfish888]

Re: Thermostat stuck open

^^ if the themostats were to stay closed, would it stop discharging water from the weep hole?

 

[aussieflash]

Re: Thermostat stuck open

In most models yes.Will also cook your engine.

 

[1nebel0]

Re: Thermostat stuck open

The most important thing that can happen without runnng stats is to cold seize the motor...very simpley stated, the piston expands and the cylinder doesn't because it is cold..next thing that happens is piston scuffing cylinder wall and the motor is ready for a rebuild..I have a mint 200h.p. purchased from a guy who thought colder was better..WRONG..........now I have to bore the cylinder, replace the piston and spent a lot of time that really was unecessary.. It you run in salt water, change then every year....whats $30 for the pair for piece of mind..Same goes for the water pump...The big motors use a small pump that should be replaced every year..less use even more important due to the impeller taking a set... I have seen impellers with zero hours on them that I have thrown away as they sat for a couple of years in one position....Run the stats.........

 

[bluefin87]

Re: Thermostat stuck open

I am waiting for the thermostat to get here.....when i get into the thermostat what about the valve, grommet, and spring that are next to the thermostat. How often do those need to be replaced?

 

[oldman570]

Re: Thermostat stuck open

The valve next to the stat is called popit valve and can be replaced when the stats are. Don't cost much and they do go bad also.I would replace them at the same time if it were mine.
Oldman570

 

[Texasmark]

Re: Thermostat stuck open

I am waiting for the thermostat to get here.....when i get into the thermostat what about the valve, grommet, and spring that are next to the thermostat. How often do those need to be replaced?

Hard to say. I bought a 2 year old engine used in fresh water and the stat was stuck closed. I replaced it in spring '05 and had no more problems.....pop off was ok and is still in there.