thermostat

I have a 1997 25 hp mariner.was told that it has a thermostat that is way it does not have a study stream of water from pisser. not comforable with this.would like to know if the thermostat can be removed with out causeing any problems

Re: thermostat

the motor has to stay warm to run right, running it cold will cause problems, thats why it's there. i could be wrong but i think the telltale bypasses the thermostat

Re: thermostat

I would imagine that you should always see a pee stream but you may notice it **** "harder" when the tstat is closed.

Re: thermostat

mercurymang said:

I would imagine that you should always see a pee stream but you may notice it **** "harder" when the tstat is closed.

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Yes the tell tail should run most all the time as stated, unless the bypass is pluged, or it needs to be replaced from a overheat at some point. Running a motor without the stat will cause the fuel not to addemise as needed and will cause damage if run as so. JMO
Oldman570

Re: thermostat

Also depending on flow rate and location of the stat, take Starboard bank of Merc V6 engines, if the stat isn't installed, the top of the block on that side could be void of water causing serious cylinder overheating.

I wouldn't run without it.

Mark

Re: thermostat

Before I replaced my tstat, I had several folks tell me I could run without it. I opted to keep it. I'm glad I did.

Re: thermostat

mercurymang said:

Before I replaced my tstat, I had several folks tell me I could run without it. I opted to keep it. I'm glad I did.

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Back in the early days, we would pull the stats out of cars and things but OB's had none. Funny, in OB's with stats, I have had probably half a dozen or so engines with them and 2 of those had stat failures. The first was an OMC '75 70 hp with no OT warning and the second was my current engine I bought used and on the first outing I got an OT alarm and found a frozen shut stat.

Mark

Re: thermostat

When was last time the water impellar was changed? That year motor may or may not have come with t/stat. got to find that out.

Re: thermostat

Let's start over (for me). I just looked in a '94 and '97 sales brochure for Merc/Mariner 25 hp and cooling has an option of a thermostat. Pop the cowl and look at the rear of the engine. You have 2 spark plugs embedded in a plate which is the water jacket cover for the cylinders cooling passages. If you have a stat, you will have a bulge on that plate probably a cover held in place with 2 bolts. The bulge in the plate will probably be about the size of a Nickel coin.

Probably the pee comes from a tube routed off the exhaust manifold, or could come from a plug on the rear of the block to the side of the mentioned cover. It may come from the cover described. I don't know but a quick look will tell you.

If it comes from anywhere other than the stat cover, you should have pee within a minute of firing up the engine on muffs, or sitting in the water with the boat stopped....aka water pump is under the surface of the water. If not, check the tube for clogging. If not clogged then the "when did you change the water pump last" from Mr. duckdown is the next question.

If it is plumbed off the rear of the stat cover, the stat has to open to get any water which means the engine internal temp is at least 143F and every time the stat closes back, the water shuts off.

HTH,
Mark

Re: thermostat

Mercury Parts, 20/25 H.P. 15/20/25 SEA PRO/MARATHON SUPER 15

See 120 degree thermostat as item 37 under CYLINDER BLOCK AND COVERS

Gerry

Re: thermostat

carholme said:

Mercury Parts, 20/25 H.P. 15/20/25 SEA PRO/MARATHON SUPER 15

See 120 degree thermostat as item 37 under CYLINDER BLOCK AND COVERS

Gerry

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I said 143 as my 90 and 150 have that temp. Sorry for the disinfo.

However, even though it is on the PL, the engine may not have one. Surely there is a foot note in the PL attesting to "when equipped". Just guessing, the manual start may not have one and the ES would. Part of the extra ES upgrade.

Mark

Re: thermostat

If something were optional, it would state so or show the serial numbers of the affected engines. There is reason it is in the service manual.

However, I leave it up to you.

Gerry

Re: thermostat

carholme said:

If something were optional, it would state so or show the serial numbers of the affected engines. There is reason it is in the service manual.

However, I leave it up to you.

Gerry

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Yes I hear you and most of the PL's I have viewed in my life that is true. However, on my 90, with respect to the water pump and associated components, the PL didn't provide a foot note for a variance in models covered. It just showed one way and a couple of X's and beside it a different option. I guess they figured that once you looked at the hardware you would figure out which version you had. I guess that's an ok line of thinking, but if it's like old farm tractors, what you see is what others did over the years to solve problems and may have no resemblance whatsoever to the original design.

Mark

Re: thermostat

AS I said, I leave it up to you.

Gerry

Re: thermostat

thanks for the help. but i think it is time to go to the shop.

Re: thermostat

Ok may be nothing but on some engines it,s essetial and other not so important Important on my 40 HP> The line for water out of the exhaust cover went through a nylon fitting( Impellor fin clogged it) and then went to the fuel pump where it connects and cools the fuel pump then out to the pisser. I had to remove the fuel pump and reem the salt corrosion out to get it to pee. On the other hand My 70 HP has a hose that runs from the top of the rear block water jacket cover staright to the pisser and has a hose running from the base plate to the fuel pump to cool it then back to the rear of the base plate where it spits water even before the tell tale starts as it is a diriect flow and doesn,t have to fill the Jackets. Being a 25 HP I don,t know what you have. I never ran a T stat after removing it from my 40 and never had an issue with temp after that, My 70 did not have a T stat and I don,t run one in it either. I,m in florida and do not run in cold weather below 55 degrees as a base. Lots of people say it,s nessecary for proper fuel burning and that may be so but the only reason you need a T stat on a car is for heat in the winter and you can run your engine without it and actually get better fuel mileage and a cooler running condition as well as water flow with it removed. Back in the old days of the dinosars when I wa born 1962 The cars had a t stat for several reason #1 Heat the block and keep it at a certain tem for the heater core. #2 Let the engine block heat up to a cetain temp so the spring would react to the heat and open the choke and open the butterfly to let the kickdown loe=wer the idol. #3 To help the ngine in cold weather fire the cylinders in a proper way as a cold running engine might not fire correctly due to fuel and the cold condition not being up to temp. Carburetor adjusment may have to be made to compensate for the lower running temp on an outboard but unless you going Ice fishing there is no need for a T stat on a carburetor model. This may not ring true for fuel injected models. JMO

Re: thermostat

The engine will have a thermostat. Engines must be warm to properly operate, that's why the t-stat is there - to let the engine warm up. You can take it out , descale it, and check it in a hot water bath and using a good thermometer [dial or thermocouple] watch it open and close- and then put it back in. If I recall correctly, the pee line comes off the jacket, but a quick check will tell - and flow is regulated by the stat. All in all - after the engine has run a few minutes, you'll be getting water out the pee line . If not, you may have some plugged passages....and how's your impeller working ?

Re: thermostat

Easier to heat water in a container in a microwave for 2 minute and through the T stat in it to see if it opens then clean it if it does