Mercruiser 1987 260/5.7 thermostat/water priming before startup

[Rderrick121]

Hello, I just put my motor into my boat and have just about everything ready to go minus priming the oil pump and putting in my distributor. The old motor I replaced did not have a thermostat so I purchased one from the parts store to install (hopefully now my temp gauge will read something...) The thermostat is in and I am worried to start the motor now because I am not sure the engine will ever have any water in it and the t-stat will keep any water pushed up against it out of the motor. Do I need to prime the cooling system somehow? If not how will the water get past the t stat to cool the motor? Or does the t stat only let water out of the motor?

Thank you,

Richie

 

[nola mike]

The point of the thermostat is to bypass the engine until it's warm, so that's not a problem. Using an auto tstat is a problem though. Wrong temperature and made to run in antifreeze not straight water. Get a proper marine stat

 

[Rderrick121]

Hi Nola, I will order the marine t stat today.. what temp should I get? So if its a bypass and there is no water in it initially after a swap then nothing will warm the thermostat and it will never open?

 

[Scott Danforth]

you are over-thinking it

unlike a car that requires you to pre-fill the motor.......marine thermostat housings are a mix housing. water flows into the block and heads and the thermostat then mixes incoming water to control temp. water is always flowing to the discharge which is what cools the manifolds.

water is always flowing in the system as long as your raw water pump is flowing.

for your motor, a 140F thermostat.

 

[Rderrick121]

Hello all, so I finally got it back together after letting it sit for about 2 weeks and its running good minus the fact that it is really hot about 200 after letting it sit on high idle for 10 minutes.. I haven't yet put the marine thermostat in because I wanted to see if it would run first. so currently its on a 180 degree auto t stat. Before I test it in the river I will install the marine 140 degree one. I am having another problem though.. I am getting very little water out of my through hull exhausts. 99% of it is coming from the gimbal housing itself. Yesterday when I ran it it was the first time I ran it sitting in a drum full of water and not on muffs, never had any water problems getting to and exiting through the through hull.. why would this water be coming from the gimbal housing

 

[tank1949]

Is your motor closed cooled or does it have a heat exchanger? U have an Alpha or Bravo? Most Alphas pull water through OD's foot. You must connect muffs there! Some Bravos pull from foot or water pickup via hull. I am assuming (1987) that yours is a raw water cooled Alpha and there is no heat exchanger or hull pickup? However, it could have been retro-fitted many times since 1987. Mine has.

 

[Rderrick121]

Hi Tank, I had the outdrive in a 55 gallon drum cut in half. It's an alpha 1 that sucks up water from the water you're floating on. I assume this would be just like running it in a river or lake?

 

[nola mike]

Nope, not the same. The impeller in an alpha needs to be submerged, which it isn't in a drum. It is normal for water to exit the gimbal idle relief ports at idle. Maybe you had enough flow to keep from frying your impellerand exhaust bits, but with your overheat that should be the first thing to check anyways. Get the 180 out of there, it's going to hurt the situation. You'll now need to check your exhaust boots after the elbow as well as the shutters in the y pipe...

 

[Lou C]

Agreed the problem with running an outdrive in a drum is that it can’t go up high enough to fully submerge the impeller and keep it from sucking in air. Also your exhaust water is heating the water in the drum as well. Get a marine thermostat 140 if in salt water 160 if in fresh water and use the Merc/Quicksilver muffs with the circular cups and the metal rod clamp that goes thru the water intakes. These are the best I have used as far as having the impeller prime quickly.
And while its probably not necessary I have filled the engine & manifolds if dry before a start up....

https://www.dropbox.com/s/ysj65t93un...0hose.MOV?dl=0

note the good flow of water coming from under the transom mount/exhaust bellows, that's what you want to see, this means your impeller is really sucking in enough water to keep the engine and exhaust cool.

I don't know what they changed but I used to use the Tempo dual inlet style muffs and the last pair I bought the rubber was too stiff to conform to the lower unit and I had trouble with it priming, not so with the Merc/Quicksilver ones.

 

[Rderrick121]

I have muffs.. Just thought the drum was a better option. I had the water level well above the pickups where the muffs go... I am putting the new t stat in today and will hook it to the muffs and let you guys know what unfolds. Also, as far a y pipe flaps I don't have a hole in my transom for the exhaust I am full through hull, I don't even run an exhaust bellow exhaust is always above the water.. annoying i know, my exhaust system is the manifolds, risers, and 6 inch rubber pipes about 2 feet long that run to flappers on the transom. Thank you, Richie