Mercruiser 165 Over heat problem

[FreeBeeTony]

On my first trip with my newly rebuilt '78 mercruiser it seemed to run hot when at higher RPM's. When at lower rpm's (2500) it seemed to run around 160 deg. Is this too hot for normal? When I tried to open her up the temp shot past 180! This is the first time out for me in this boat. I rebuilt the engine myself. New water pump on engine and new water pump in outdrive. I couldn't even try to see what the wot rpm's were because it got too hot. The boat is a '78 20' Grady white. I think the prop is a 19" pitch. I am new to I/O's but it seemed like the engine was working hard. May be my imagination because I don't have anything to compare it to. Any help with the high temp would be appreciated. I also noticed a little bit of smoke comong out of th beather cap on top of the valve cover where you add oil, what does this mean?

 

[fishing2hightide]

Re: Mercruiser 165 Over heat problem

what size outdrive? ihave 165 with 1.50.1 i had to go down to 14.25\15 ss. are you trying to run fresh water through your exhaust manifold ?

 

[Trent]

Re: Mercruiser 165 Over heat problem

Engine that old......Manafold and risers need replacement!

 

[FreeBeeTony]

Re: Mercruiser 165 Over heat problem

Engine is 165, outdrive is 1.65:1. Riser is new. How can I check the manifold?

 

[akriverrat]

Re: Mercruiser 165 Over heat problem

how complete a rebuild? what was your breakin procedure? how many hours on engine since rebuild? you don't want to take fresh engine out and just start running it hard.

 

[FreeBeeTony]

Re: Mercruiser 165 Over heat problem

The rebuild consisted of the following: bored 0.030 over with new pistons, rings, bearings, <br />oil pump, water pump, fuel pump and lifters. Rebuilt carb and installed electronic ignition conversion kit. Only has about 2 hours on it, half of that was probably in the driway on the muffs. Starts right up and seems to run strong. I didn't run it hard for long. I was cycling the RPM's between idle and about 2800, then I tried to see what the WOT RPM's were and noticed the temp rising. Could the trim cause the temp to rise like that? I didn't really try to adjust the trim. It was the first time out and i decided not to push it. Other than the temp and low RPM's it seemed to run fine! Also, what temp should this engine (Mercruiser 165 IL6 250 cui) run at? This is my first I/O, I am used to outboards running at ~150.

 

[Juancho]

Re: Mercruiser 165 Over heat problem

My Volvo AQ125 runs at 180 degrees dead on.

 

[akriverrat]

Re: Mercruiser 165 Over heat problem

http://www.marinemechanic.com/2000/chfacts/engine_break-in.htm take a look here.

 

[galaxy]

Re: Mercruiser 165 Over heat problem

My 165 stays around 160 to 165 degrees. I had to replace temp sending unit and also installed a 140 degree thermostat. I thought my guage was bad because it kept reading 260 degrees. I changed sending unit and it fixed that problem.

 

[FreeBeeTony]

Re: Mercruiser 165 Over heat problem

Is it possible I put the thermostat upside down? And if I did would it make a difference?

 

[llerrad]

Re: Mercruiser 165 Over heat problem

Didn't see mention of water pump in lower unit what condition is the impeller, old or new?

 

[FreeBeeTony]

Re: Mercruiser 165 Over heat problem

As stated in original post both water pumps are new. I verified the water flow out of the outdrive last night, looked like a garden hose.

 

[akriverrat]

Re: Mercruiser 165 Over heat problem

tight rebuilt engine produces more heat. if cooling system not 100% it may just not be able to handle it till you get a few more hours on the breakin.

 

[horndog]

Re: Mercruiser 165 Over heat problem

if you put the thermostat in upside down, you would know! I wouldn't open. Just follow the break-in procedure in the link above and you will be OK! <br /><br />Running near 180 degrees is normal at higher rpms. remember, the water isn't 40 degrees anymore!

 

[FreeBeeTony]

Re: Mercruiser 165 Over heat problem

Maybe it's not opening? Is that possible?

 

[galaxy]

Re: Mercruiser 165 Over heat problem

If it wasn't opening it would be burning the paint off the engine, not to mention your oil. It must be opening. Not sure what degree thermostat you've got. Mine has gotten up to 180 at WOT. Sustained, that is. I agree with the breakin period as stated above. Go thru the process and see how it reads at a steady 20 to 25 mph.