water temp prob

[justincase]

Hi folks im new here, ive been a boat owner for 20 some years, just picked up a starcraft american 18 witha a 5.7 stringer 1978, took it out for first time tue and ran perfect except once i was idling for about 3 min and temp went to 195, ran it some more came down to 175, stopped and idled for about 5 min and temp stayed 175. then when idling to load it on the trailer temp went to 200.....but each time temp went up you could lay your hand on the motor with out getting burned. also if running it on the muffs in the drive temp never goes above 175. any ideas on this....thanks

 

[Haut Medoc]

Re: water temp prob

Sounds like it needs a new water pump impeller......​

 

[DHPMARINE]

Re: water temp prob

Actually 175 is too hot,never mind 200.But IF you can keep your hand on the manifold or riser,you are not reaching that temp,and have a temp gauge/sender problem.

Never hurts to replace the water pump impeller,though.

DHP

 

[Boomyal]

Re: water temp prob

The laser thermometer has become an indespensable tool for el mechanico. You can point it at every critical point and see what is really going on.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91778

One thing that does point to a potential problem, regardless the specific numbers, is the wide fluctuation in temp between idle and speed. On the surface it does appear that your impeller is marginalized but I would check one thing before I ripped the OD off. OMC impellers are not as fragile as are Merc impellars.

a) when you are in the water, at idle, pull of the line from the OD, and watch the flow. Quickly have someone slowly accelerate and watch what happens. This will verify an impeller problem.

b) have you verified the existance of a thermostat and what it's rating is?

 

[justincase]

Re: water temp prob

ok ive replaced impellers on outboards and a mercruiser, but how do u go about changing one in a omc 800 post 1976, and are there any special instructions to do it and can u just take off the lower unit?

 

[justincase]

Re: water temp prob

sorry got ahead of myself with last post, i have not verified anything yet such as thermostat,just went by feel

 

[justincase]

Re: water temp prob

thanks for the help, i dont know why everyone thinks its a hard job? no manual and had the impeller out in 15 minutes, i dont see where they get 2.5 hrs for it.

 

[whywhyzed]

Re: water temp prob

Well, to do it right takes a good 2 hours....and as soon as 1 bolt breaks it doubles the time. Having a wire wheel on a bench grinder helpful to get all the old sealant off the impeller side plate, or just replace the plate it if you bought the full kit. Then, cleaning the threads of the bolts (sealant again), cleaning out the oring groove. Cleaning all the old grease out of the w/p shaft splines and regreasing. Having a look at the upper gears while in that deep always part of my routine...
You definitely want a new "cog seal" for the spline, and use Castrol Pyroplex blue or Mercruiser spline grease on those splines not regular grease.

 

[justincase]

Re: water temp prob

thanks guys it was the impeller, took it to the lake and all is well.