2.5L omc overheating

nick_vw

Seaman
Joined
Jun 15, 2012
Messages
60
I posted a while back about losing power in my 86' 2.5 with the older stringer drive. I noticed it took quite a while to warm up, and when it did i got more power and less bog. Today i set off and within 5 mins temp was in the red, but when i throttle back the engine would cool off. My guess is thermostat. So really i have a few questions, first, can i just get an automotive t-stat? anyone know what model will cross reference to an 86 2.5omc? Also, if the impellers need looking at how big of a job is that on a stringer?


a few other things...when i throttle back i hear a loud whine almost like an electric pump, whats this about? Also, i know its a relic of a boat at this point but what should i watch out for on this OMC? any tips to keep it running smooth through the rest of the summer?

thanks for any input its appreciated
 

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: 2.5L omc overheating

when was the last time the swivel bearing in the outdrive was greased?

impeller issues affect cooling more at idle. Lack of grease in swivel bearing area allows exhaust gases into cooling water at higher speeds and loads - 20 mph and up.

but if the impeller is more than 3 years old, you need to go in there to change it and grease the w/p shaft splines.
 

nick_vw

Seaman
Joined
Jun 15, 2012
Messages
60
Re: 2.5L omc overheating

actually only owned the boat for a few months. previous owner had a bunch of paperwork for work he had done at a marina...unfortunately I forgot to take it all with me:facepalm: He did take it in for 'regular service'

Had the boat out 2 days ago and had no problems. Today, it got hot in the first 5-10 minutes. Shut it down, let it cool. What i found was once i throttled up a bit the temp. would start climbing, i could find a speed where the temperature wouldn't get into the red, but it was still higher than it should have been. Definitely not over 20 mph, more like 10. Pretty much anything over a slow crawl resulted in ever increasing temperature.

It almost seems like the t-stat is stuck only allowing enough water through to cool the engine at low RPM. Looking over the stern i can see water rolling up by the ball gear, so it seems its pumping properly. Should I just take the old t-stat out and take it for a run, or will the engine not run right without the t-stat?

Also, Is the thermostat specific to an OMC 2.5, or can it cross reference with other marine or possibly automotive engines? Local marinas cant look up old OMC stuff just mercruiser/volvo... so hoping i could pick up a merc tstat that will fit..
 

nick_vw

Seaman
Joined
Jun 15, 2012
Messages
60
Re: 2.5L omc overheating

OK i figured out the only t-stat i can use is a sierra part # 18-3558 used on OMC and Volvo. Will post back once installed and tested.
 

nick_vw

Seaman
Joined
Jun 15, 2012
Messages
60
Re: 2.5L omc overheating

OK got the thermostat replaced (a bunch of crusty rust built up in there) and while i was at it I noticed the belt was loose...i could spin the alternator pulley with my hand. So it was either the belt slipping on the water pump or a bad t-stat but one of those fixed the overheating. Darn water must be down quite a bit chipped my prop on my normal route out to Georgian bay..
 
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