rising temp at low idle

[crazy charlie]

My port 230 mercr i/o rwc, has experienced rising temp only at low idle.As a matter of fact the idle is lower on this motor than my stbd.When I tap up the throttle while idling to about 700,which is as little as I can,the temp does not climb.New this season is o/d impeller,circ pump,thermostat.I replaced the manifolds and risers on the strbd motor last year and the old ones were in such good condition I was not in a hurry to replace them on the port motor.Anyone ever heard of a low idle not cooling properly?????I guess I should just turn the idle up and find out for myself but I wont have a chance any time soon.

 

[crazy charlie]

Re: rising temp at low idle

Cmon guys,all I am looking for is an opinion ot two.I hate pondering things all by myself.

 

[KM2]

Re: rising temp at low idle

Charlie, My boat runs warmer at idle too. Up to 175 on the temp gauge but it always runs around 140 to 150 when I'm running at planning speeds. Since it has done this since new, I assumed it's the way it is suppose to be.

 

[crazy charlie]

Re: rising temp at low idle

KM2,I have had several i/os and they have all run at about 145 except immediately after throttle down.The temp usually spikes for a minute or two 10-15 degrees,after coming off of plane.My starboard engine is consistantly 145-150.Since thats all my i/os have done ,I assume thats how they are supposed to be.I guess we may both learn something here.Charlie

 

[rbezdon]

Re: rising temp at low idle

Charlie, I have had the same issue. Turned out to be an air leak in the water pick up in the lower unit. I also have seen a posting where ultimately it was an air leak in the lower also. Search the site more and you'll find this is not uncommon (or normal). The engine should get enough water to run pretty much the same temp at low or higher speeds.

 

[crazy charlie]

Re: rising temp at low idle

If I dont figure it out by the end of this season I will use a spare drive that I keep ,next year on the port side to help determine if that is it..I want to do the exhaust in the off season but I hate to do too many things and thus never figure out the definite fix.Thanks for the heads up!!! Charlie

 

[crazy charlie]

Re: rising temp at low idle

I pulled off a riser today to have a look and it was in very good condition so I dont think it is the risers.Charlie

 

[Ralph 123]

Re: rising temp at low idle

I had the exact same problem at the end of the season a couple back - the impeller went even though it had been replaced the season before - I'd take that engine out of gear, bump the idle to cool the engine (in no wake zone) and then re-engage and at idle it would heat back up. Finally put aside my disbelief it could be the impeller and took a look and sure enough it was chewed up... otherwise both of my I/Os run at the same temp it seems regardless of speed.

 

[canufixit]

Re: rising temp at low idle

Ok, You may not believe this - but this happend to me. I lost a "vane" on my 120hp outdrive impeller - and it showed up in the hose at the thermostat. As you just replaced yours - were you missing a vane ?? Or as another thought - did can you pull of the feed watrer hose at the engine and run in for a few seconds to check th flow ??

 

[crazy charlie]

Re: rising temp at low idle

The impeller was fine but I replaced it anyway in the spring.I used the boat this weekend and tapped the idle up a bit with the throttle while going up the canals and through the no wake zones and the temp did not climb at all until I pulled back on that little tap.The difference was only 1-2000 rpms but that made a difference.Charlie

 

[AdamB]

Re: rising temp at low idle

Besides the impellor and housing, you have a top water cover and lower cover.. did you try to change those? I had the same problem and it went away after changing out the lower base.

 

[crazy charlie]

Re: rising temp at low idle

I always change the housing and tube when I do an impeller but I have never done the base.Since I can control the temp I will just be extra careful until it is haul out time.Short hauls cost too much on a 10,000 lb boat so I will do it when we get her home in October.Charlie

 

[KM2]

Re: rising temp at low idle

I replaced the impeller, but still have the high temp at idle. 160 or so and 120 during high rpm operation. The old one was chewed up so I will look in the thermostat housing and for debris. <br /><br />Since my thermostat is a 160 i think. I don't really have a high temp problem I have a low temp problem above 1000 rpms. <br /><br />Any more ideas out there? <br /><br />Can someone explain air leak? I don't see how that can happen.

 

[rbezdon]

Re: rising temp at low idle

Some kind of a leak on the vacuum side (intake) of the pump. If for example, a hose clamp were loose then air can be drawn into the water stream along with water reducing the water flow substantially. You can detect this by temporarily replacing part of the water delivery hose with a clear hose and looking for bubbles in the water stream. Common causes are cracks in housings, water passages etc, loose hoses/clamps, cracks in hoses, poor gasket sealing on housing mating surfaces to name a few.