1990 Merc 3.0l alpha one ...Overheating at idle

[sully123]

Hi all
I would like to know if anyone has any ideas as to why this happened. I was out on the lake all day and had no problems. While waiting for someone to get their boat loaded, I had to keep the engine at idle inorder to avoid hitting other boats...I watched the temp, which is normally at 150 to 160, go over 200 and close to 250 but not over the 250 mark. I shut the engine down but had to keep starting inorder to stay in position. (prob at low ildle for like 15-20 mins). Btw, idle is around 800 rpm and I was using forward and reverse. Earlier, while boating, no problems at all...When I got boat home ,I hooked up the ears with water turned on (few turns)...ran engine for like 5-10 mins at idle and temp was fine...holding at around 150...

Any ideas would be welcomed

P.S. Someone said that the impeller could be wearing....if so, where can I get info on how to change, and is it a hard job?

 

[maxxman04]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

worn impeller sound logical. water/coolant level. didn't say tho if this is a raw water or closed cooling system. makes difference in diagnosis

 

[cooter2506]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

When was the last time the impeller in outdrive was replaced. If you dont know change it. I personally would change it anyway. Look up at the adult sticky at top of page. Download your manual. It has how to change your impeller. Also you idle is alittle high. should be around 650.

 

[sully123]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

Hey guys.....thanks for the responses....its a raw water system...and I will adjust the idle to 650....
So the amout of time running hot should not be a problem? Like I said, it never went over the 250 mark, it was up high but only at idle and maybe just for few mins...I would say over 200 and under 250 for a max of 3-5 mins.

 

[maxxman04]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

idling for longer than 5 minutes or so will cause temp to rise for sure. even in autos this occurs. this happens because the water is not circulating as fast at idle as it is higher rpm's. pretty common. it's hard to do in a boat, but if idling for more than a couple minutes, might not hurt to shut engine off. again, i know this is hard to do sometimes.

 

[sully123]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

Can't seem to find the manual under the adult sticky...say's NLA...Anywhere else I could get some info on the changing of the impeller?

 

[Bt Doctur]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf
Make sure you save it.

 

[sully123]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

Bt Doctur....Thanks Alot!

 

[sully123]

Re: 1990 Merc 3.0l alpha one ...Overheating at idle

Installed the impeller today....no problems at all....old impeller was toast.
Just worried about tightness of bolts on water pump. Read somewhere not to over tighten or water pump will fail. Was not sure of specs so just tightened little over hand tight. Hooked up ears and ran hose and it worked fine. I guess the real test will be when out on lake. First time doing this job and took about 2 hrs.