Reply
 
Thread Tools Search this Thread Display Modes
 
Old 09-19-2013, 03:52 PM   #1
Senior Member
 
City: Madisonville
Vessel Name: Aku Uka
Vessel Model: 43’ DeFever
Join Date: Feb 2011
Posts: 213
Onan Running Hot

Has anyone got an idea what would cause my Onan to run hot. I've checked both water systems; everything OK. It will run about 45 min. and then the HT switch (mounted on the block not the exh.) shuts it down. I took a temp reading in the switch area, it was around 250 deg.. Can there be a problem other than the water system causing it to over heat. BTW, I did removed the water thermostat; same thing. Any suggestions?
Dixie Life is offline   Reply With Quote
Old 09-19-2013, 03:54 PM   #2
Guru
 
obthomas's Avatar
 
City: Seabrook Texas
Vessel Name: TheVenture
Vessel Model: 1985 Bestway Labelle Sundeck 40ft
Join Date: May 2013
Posts: 560
fresh water circulating pump deteriorated? , fanbelt worn or loose?
obthomas is offline   Reply With Quote
Old 09-19-2013, 05:28 PM   #3
Guru
 
Edelweiss's Avatar
 
City: PNW
Vessel Model: 1976 Californian Tricabin LRC
Join Date: May 2011
Posts: 1,860
What model Onan??

Check the exhaust water flow. If it is normal flow amount and lukewarm, no steam, then it's the freshwater side of the cooling circuit. Fresh water pump or plugged heat exchanger.

If there is not enough flow at the exhaust, then check the sea strainer for blockage. Be sure and open the seacock and make sure you have flow in through the through hull. (Sucked up an eel one time and only his head was visible inside the strainer. Had to take the basket out to see it. He had a bad day and didn't survive the ordeal !!) If that is ok then check the raw water pump, impeller and bearings. Even a good impeller will not pump if the shaft and bearing are gone.
__________________
Larry B
Careful . . .I Have a Generator and I'm not afraid to use it !
Edelweiss is offline   Reply With Quote
Old 09-19-2013, 08:08 PM   #4
Guru
 
swampu's Avatar


 
City: Biloxi, MS
Vessel Name: Cajun Rose
Vessel Model: Biloxi Lugger
Join Date: Jul 2011
Posts: 1,384
Check your cap on your heat exchanger. Mine was spitting water out of the overflow and then it would over heat. Also check the hoses and make sure nothing is kinked. Let me know what you find out. I'm still trouble shooting on one of my onans....
swampu is offline   Reply With Quote
Old 09-20-2013, 01:15 PM   #5
Guru
 
CaptTom's Avatar
 
City: Southern Maine
Vessel Model: Prairie 36 Coastal Cruiser
Join Date: Dec 2012
Posts: 2,717
If the raw water flow is low (little or no water coming out the exhaust, or exhaust hose too hot to touch) then check for leaks on the intake side. I had to connect a garden hose into the system to find where a little water was squirting out. Of course, if water can squirt out then air can get in. And if the pump is sucking air, it isn't sucking as much water.
CaptTom is offline   Reply With Quote
Old 11-21-2013, 03:03 PM   #6
Member
 
moonchaser's Avatar
 
City: Melbourne
Join Date: Nov 2012
Posts: 13
Quote:
Originally Posted by CaptTom View Post
If the raw water flow is low (little or no water coming out the exhaust, or exhaust hose too hot to touch) then check for leaks on the intake side. I had to connect a garden hose into the system to find where a little water was squirting out. Of course, if water can squirt out then air can get in. And if the pump is sucking air, it isn't sucking as much water.
I have an Onan MDKC 4 & am looking for the zinc(s). Any help locating ? Jim
moonchaser is offline   Reply With Quote
Old 11-21-2013, 03:55 PM   #7
Senior Member
 
City: Seattle
Vessel Name: Poach
Vessel Model: Sabreline Trawler
Join Date: Aug 2013
Posts: 234
250 is way too hot and can cause serious damage. If you have looked at your belts and they are not excessively worn, checked the coolant and it's ok, there is no water in the oil, oil in coolant or staining on the block--then this strongly suggests to me that the raw water cooling side is not working. Is the raw water seacock open, is the raw water strainer clean?

I am betting on the raw water side myself. If that stuff's ok pull the impeller on the raw water pump. It is the cause of many if not most overheats. It is a relatively simple task, requires a gasket , a new impeller and your time. You could merely inspect it--looking for cracks at the base of the fins, or excessively soft fins or even missing rubber, but the defects can be quite microscopic and still cause a problem. In MHO, replace the impeller to be sure you have eliminated the problem--they are cheap. If you find missing chunks of rubber from the impeller, try to get as many out of the heat exchanger tube as possible. They will clog the heat exchanger which will definitely cause overheating. If that doesn't solve the problem, remove the heat exchanger, take it it a radiator shop and have it pressure tested for leaks (pinholes)--those can be fixed usually--and have it "boiled" as you may have built up scale that is impeding flow and quantity. All of this stuff on the raw water side is routine maintenance which should be done periodically on all marine engines anyway and will improve the performance once you get it all back together. AND by all means, replace the zinc pencils while you have the thing apart--it's easier. If that doesn't fix it, then look into the other stuff.
Poach is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 06:16 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012