Engine Temp Rises/Overheats at Idle, Cools to Normal Temps while Moving...?

jts4486

Cadet
Joined
Sep 18, 2014
Messages
10
Thank you all again for the help correctly diagnosing the bad ground wire issue from my previous thread. Hopefully this issue is similarly easy to diagnose and fix.

As mentioned in the thread topic, my engine temperature rises/overheats at idle both in the driveway and in the water but cools to normal operating temps while moving. The boat had sat for 3 years prior to me buying it this summer. My research points to impeller as it sounds like sitting is not good for them.

I am guessing the impeller needs replacing. Does a bad impeller cause the issue I'm experiencing? Other possible causes or things to check?

Thank you in advance!
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Thank you all again for the help correctly diagnosing the bad ground wire issue from my previous thread. Hopefully this issue is similarly easy to diagnose and fix.

As mentioned in the thread topic, my engine temperature rises/overheats at idle both in the driveway and in the water but cools to normal operating temps while moving. The boat had sat for 3 years prior to me buying it this summer. My research points to impeller as it sounds like sitting is not good for them.

I am guessing the impeller needs replacing. Does a bad impeller cause the issue I'm experiencing? Other possible causes or things to check?

Thank you in advance!

Ayuh,.... The impeller is Always the 1st place to look, in any overheat situation,....
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
The impeller should be replaced at least every other year. I would get the whole kit with the housing and everything since you don't know the history.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Have a look at my video up in the sticky section and you'll have an idea of what to look for once you start getting into the pump...

Chris....
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Mine did that at one point when I had a tired impeller.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Yep, tired impeller can't pump enough water at low speed ('displacement' mode), but once it's running a bit quicker (into 'centrifugal' mode) it pumps just fine...
 

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,759
Full kit is on order. Thanks again! You guys are top shelf!
Pull hoses at risers/stat housing and see if passing water. Your cir pump may be worned. I had seals in one only a year old that went bad.
 

888

Petty Officer 1st Class
Joined
Jan 7, 2012
Messages
358
Thank you all again for the help correctly diagnosing the bad ground wire issue from my previous thread. Hopefully this issue is similarly easy to diagnose and fix.

As mentioned in the thread topic, my engine temperature rises/overheats at idle both in the driveway and in the water but cools to normal operating temps while moving. The boat had sat for 3 years prior to me buying it this summer. My research points to impeller as it sounds like sitting is not good for them.

I am guessing the impeller needs replacing. Does a bad impeller cause the issue I'm experiencing? Other possible causes or things to check?

Thank you in advance!
check balls...stretch the springs or replace
 

four winns 214

Senior Chief Petty Officer
Joined
Oct 25, 2008
Messages
757
I had a similar situation after a Merc authorized shop installed a new impeller. The young, inexperienced and unsupervised tech did not reinstall the water tube properly after replacing the impeller. Not enough water was getting through to the engine at low RPM, but enough made it at higher RPM. Unlikely your problem, but I mention it for those readers who run into overheating problems after impeller replacement.
 
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tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,759
I had a similar situation after a Merc authorized shop installed a new impeller. The young, inexperienced and unsupervised tech did not reinstall the water tube properly after replacing the impeller. Not enough water was getting through to the engine at low RPM, but enough made it at higher RPM. Unlikely your problem, but I mention it for those readers who run into overheating problems after impeller replacement.
That is why I DON'T let any person work on mine that I don't know for a long time.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
That is why I DON'T let any person work on mine that I don't know for a long time.

Ah, we have another certified Merc mechanic in our fold, excellent. We need all the qualified help we can get here... Thanks for putting your hand up as an experienced tech. Now, get to work. :D

Chris...... ;)
 

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,759
Ah, we have another certified Merc mechanic in our fold, excellent. We need all the qualified help we can get here... Thanks for putting your hand up as an experienced tech. Now, get to work. :D

Chris...... ;)

Just yelled a lot of "aw-****" then solved it.
 
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