Motor???

[pab1981]

A friend of mine has a motor that he took to the shop because it was getting hot when idling. Mechanic replaced impeller on water pump and checked all ports for blockages, or so he told my friend anyway. Motor is still doing the same thing now, getting overheat alarm while idling, but runs fine at WOT. Says he doesn't think he's getting the same amount of water out the hole while idling than he used to, but not sure how to procede. Is there anything that can cause this other than what the mechanic was supposed to have checked/replaced?

[sparky]

Does the motor have a thermostat? Could be a faulty switch. Maybe he didn't replace the impeller right. Is the motor sitting low enough to pick up water (saw that happen twice, the guy who replaced the impeller took the motor off and when it was replaced he changed the settings, "height", and there was no water pick up? Worked fine in the tank but not when on the transome.

[Scrapper]

I agree thermostat is a probable cause. What kind of engine?? The 80's and earlier 90's merc's would idle hot if you putted around alot. Change termostat or thermostats....many of the kits come with the poppet valves also...go ahead and replace them if you can.

Get some heat sticks or a heat gun and find out what the real temp is. If you can take the alarm switchs out you can put them in hot water with a thermometer and watch the temp...use a mutimeter to test...you can do this with your thermostats too...but if its out I think I'd go ahead and replace it. Just my .02 cents

[crapDADDIE]

im gonna agree with sparky we had a boat a while ago and that alarm would go off and we would get it "fixed" and it would keep doing it until one mechanic was smart enough to check the electrical work and found a loose wire that would just chose when to activate the alarm

[pab1981]

His outboard is an 88 Mercury 150. I talked a little more with him today about it and he said he had this problem before and a different mechanic had to put a new baseplate in. Also said same mechanic told him he was better off without thermostats and took them out at the same time. Boat idled fine for several years up until end of last year.What do the poppet valves do? I'm not real motor savvy and trying to learn a little on this forum.

[Scrapper]

Those engines are NOTOERIOUS to run hot when idling around. The poppet valves are the ones that open when you are running. Depending on what state you are in...you need the thermostats. Many people take the thermos out...problem is not in the summer, its in the fall and winter. Engine doesn't get warm enough and will load up...if you are not up to operating temperature you take the chance on not burning all the fuel and oil completely...like a smoking two stroke on a cold morning. You will also have more coking or carbon build up due to lower temps. There could very well be a blockage somewhere. Check the switch, pull lower and look at the water pump...make sure ALL gaskets were put back. If not when idling there can be enough water leaking past gaskets that it doesn't cool very well. That engine does run hot when idling though...they are known for it. I would put thermostats in it...check switchs...and check water pump install.