1988 Mercruiser 3.7 over-heating

[mgilker]

working on a Mercruiser 3.7 and its over-heating. had it out on the water recently before the problem was detected and shortly noticed that the heat exchanger was pouring out water from the back of it [back plate]. took the plate off which seemed to be pretty much only finger-tight to inspect the plate and gasket. i had the plate off while the engine was started to see if water poured out like i thought it would, but nothing came out, so i thought it might need pressure. i put the cap back on and i also had the exaust pipe off too and thought water might flow out of there as well but again, nothing. it also dosent SEEM to be sucking up water from the lower unit [was in a container with wate]. i have worked on a few boats with water that flows though the manifold and out, no self contained units like this one... could use some help.

 

[86 century]

Re: 1988 Mercruiser 3.7 over-heating

The container maybe the problem you haft to get above the impeller witch is real hard with a mercruiser.

Get yourself a good set of muffs on a garden hose after you have replaced the impeller that was most likely toasted by running with no water.

If I read this correctly you had a big leak of sea water out the back of your heat exchanger.
After inspecting it you reinstall run with drive in tub and have no flow.

 

[Eric 3.7LX Alpha 1]

Re: 1988 Mercruiser 3.7 over-heating

Your impeller is probably shot.
Here is a flow diagram for the engine, before the seawater gets to the exchanger it goes thru the voltage regulator which is the first thing the seawater hits as it enters the boat. You can disconnect the hose off the stern side of the V.R. and see what the flow is like.

The first thumbnail pic is the backside of the voltage regulator, basically just a piece of copper pipe strapped to it to help cool it down.

 

[mgilker]

Re: 1988 Mercruiser 3.7 over-heating

i have run a few different engines without water, for a short time before, and didnt noticed any problems with the inpeller. this time, this impeller SEEMS to be noisey, but it was hard to tell listening to it as the engines loud. how high would the water have to be in the container? just so high so its above the water in-let screens? the water in the container i have is high enough to almost be to the top of the fin thingy [don't know wha its called] but the containers about 2 feet and the lower unit is touching the bottom.

 

[mgilker]

Re: 1988 Mercruiser 3.7 over-heating

-Update- so, the water pump was completely shot, only a half of one of the impeller blades left, getting a new one soon.

 

[Eric 3.7LX Alpha 1]

Re: 1988 Mercruiser 3.7 over-heating

Get the complete water pump kit, including the upper and lower housing, and make sure you find those impeller pieces or you will still have overheat issues. They find their way in the front half the exchanger many times.

Complete kit here at Iboats:
http://www.iboats.com/mall/partfind...&gd_poid=110924&gd_row=3&session_id=644704424

 

[stonyloam]

Re: 1988 Mercruiser 3.7 over-heating

The impeller does not "suck up water" it must be totally submerges to push the water into the exchanger. Do as Eric suggests, new pump and impeller OEM Mercruiser if you can get them. The pieces of the old impeller will be under the front endplate of the heat exchanger. With that engine you should replace the impeller every other year at least.

 

[dead_soul79]

Re: 1988 Mercruiser 3.7 over-heating

i just bought a 1987 larson runabout with a mercruiser 3.7 liter inboard motor trying to find a service manual for it can anyone help with this

 

[Eric 3.7LX Alpha 1]

Re: 1988 Mercruiser 3.7 over-heating

i just bought a 1987 larson runabout with a mercruiser 3.7 liter inboard motor trying to find a service manual for it can anyone help with this

Welcome dead soul!! .... you need to start your own thread with your question, and not add it to the end of another's thread from last year. Your not going to get the responses your after.