Does my 25hp have to have a thermostat?

[cliffblue]

I have a 1999 25HP model 25M serial # OG874716C. My buddy has a 25HP serial #OD813999. I bought mine as a program motor with a new power head. He bought his used a few years before I got mine. While his has a thermostat housing, it's never had a thermostat as long as he has had it. Mine has always had one. We run them in a shallow muddy lake with a lot of vegetation. His flows a lot of water out of the "pee" hole all the time. Mine flows about half of his when the stat is open. We serviced both water pumps today because mine quit pumping water. Mine was 3-4 years old and completely shredded. His was 5-6 years old and looked brand new. WTH??? I can't find if his is supposed to run a stat and it was removed before he got it or not. His actually has 2-3 times the hours last year as we took his way more than mine. Is the combination of less water flow and vegetation matter staying in my cooling system longer causing mine to die a early death. Do I really need the stat in Louisiana? Thanks, Cliff

 

[Fun Times]

Re: Does my 25hp have to have a thermostat?

I have a 1999 25HP model 25M serial # OG874716C. My buddy has a 25HP serial #OD813999. His actually has 2-3 times the hours last year as we took his way more than mine.

Hi there, your serial number on your engine is showing one to many letters at the end. Your number is 0G874716. No C at the end.

Your friends serial number (0D813999) appears incorrect as it's coming up as an I/O MERCRUISER - (5.7L H.P. BRAVO (1992) Serial No: 0D813999 Model No: 457B110ES.

So you may want to double check that number.

Keep in mind that not using your boat allowing the rubber impeller to dry out can be worse then actual use. Using it keeps it wet/lubed. That could be why yours went sooner.

 

[cliffblue]

Re: Does my 25hp have to have a thermostat?

Hi Fun Times, I have problems with my serial # and while I can't double check my friends # today, I have been getting parts for his motor using that number. I have tried to check to see if he is supposed to have a thermostat on his motor using the reference material here on iboats. His motor has been running fine for years and if that is the case, I will try removing mine. Here is my sticker on my motor.

 

[achris]

Re: Does my 25hp have to have a thermostat?

In the parts diagram your engine shows a thermostat.... So yes, it's a good idea to have one. There was an era where the telltale was from the thermostat cover, so the water was only present when the thermostat was open, and even then it wasn't very strong. Merc changed that pretty quick... The easiest way to tell if you have enough cooling water is to put your hand on the exhaust cover. It should be coolish to the touch...

I don't have a problem with that serial number. It (minus the 'C') comes back as a 1999 25hp, Manual start, standard (15") shaft, model # 1025201VD.

Using the serial number form one engine to get parts for another can cause issues... Can you get your friends' number?

Chris.....

 

[carholme]

Re: Does my 25hp have to have a thermostat?

You will see at the bottom of the s/n sticker in your post #3, that it says "Factory Reconditioned" and I don't doubt that is what the C is referring to. Faztbullet may be able to confirm that. Most manufacturers have a method of identifying a product which, after delivery from the assembly line, has to return for major work. 0G874716 is the correct s/n.

Gerry

 

[cliffblue]

Re: Does my 25hp have to have a thermostat?

Thanks Gerry, hey Chris, I meant that I picked up parts for my friends motor using his serial #. After the parts guy waded through the part numbers updating swamp, we both used the same water pump and carb/fuel pump kit. I don't guess that it would be easy for me to update to whatever Merc did to improve the telltale problem? I was hoping to get some input on ditching the stat. Yes-no, possible problems? Thanks all.

 

[cliffblue]

Re: Does my 25hp have to have a thermostat?

Well I had the parts guy look up my friends motor and its a 92 model. His came with a stat new and either its stuck very open or it's gone. When I clean mine, it's out! I'll put it back if I have trouble.

 

[Texasmark]

Re: Does my 25hp have to have a thermostat?

Well I had the parts guy look up my friends motor and its a 92 model. His came with a stat new and either its stuck very open or it's gone. When I clean mine, it's out! I'll put it back if I have trouble.

"Trouble" may come at a cost. Depending on location, and operating rpms....aka water volume, the top of your top cylinder may not get submerged in cooling water. I know on Merc 90 and 150 engines it won't be. I wouldn't want that. Back before the stats were used on Mercs, there was no problem as they were designed to fill the block as the stat hole was nonexistent.

Mark

 

[25xs]

Re: Does my 25hp have to have a thermostat?

If your engine has a thermostat housing; then it uses a thermostat. The early 1980's Mercury 18/20/25hp engines did not have a thermostat and only have 6 bolts retaining the waterjacket cover around the sparkplugs. All the later engines have thermostats and the waterjacket cover has 7 retaining bolts due to the t-stat housing. Best to keep it installed and check its function by observing the waterflow increase from the telltale stream as it warms up. The powerhead was designed to run at a certain temperature, and without a t-stat, the combustion chamber temperature will be lower. If you run in tropical waters, you likely won't see a problem, but lakes/rivers/ocean water temps below 60degrees could cause oil to form carbon in the combustion chamber. Too much, and you'll stick a piston ring and ruin the powerhead.

IF you remove the t-stat, I would suggest you keep the restrictor in the end of the telltale hose to keep the telltale stream volume low. all the cooling water should be kept in the powerhead rather than dumped overboard from an empty t-stat housing.

I run that powerhead on my hydroplane well above 60mph and above 6500rpm and I run a thermostat.

Regarding the water quality & debris, the intake filter on the gearcase will keep pretty much anything big enough to clog the t-stat from entering the powerhead...

Tom