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2000 yamaha 70 overheat horn on, not hot
Tim Erwin	#1  Posted on 12/18/10 - 4:57 PM
Member Personal Page Posts: 44 Comments: 1 Joined: 05/04/08	Merry Christmas to all. My 2000 yam. 70 2str. has the overheat horn on and the motor isn't hot. I'm running it with the garden hose on with the water coming out everywhere it's supposed to. Telltale has high pressure and water coming out the exhaust. It' running just fine? Appreciate your input. I don't want to take it in if it is something I can do. Peace Tim Tim Erwin -1975 Montauk II, Yamaha 70 2cycle
Ralph Iorio	#2  Posted on 12/18/10 - 8:19 PM
Member Personal Page Posts: 86 Comments: 1 Joined: 06/30/10	Tim, check your owner's manual. I have a Johnson 90...the horn sounds for one of 3 reasons...Overheat; INSUFFICIENT FUEL FEED; or, it's broken. I found out about the fuel feed situation when mine did it this past Spring. As soon as I changed to a larger diameter fuel line and changed the primer bulb which I felt was too small, the horn began behaving properly...Ralph 1989 Montauk 17 w 1989 Johnson 90
gawhalerfan	#3  Posted on 12/19/10 - 3:59 PM
Member Personal Page Posts: 1 Comments: 0 Joined: 11/28/10	Replace the impeller anyway. My telltale was very misleading, all the obvious signs of lack of water were not present. I fiddled around thinking that it was not the impeller for over year. Changed the impeller, all was fine. The old one did not look bad either, but lessen learned. It's cheap, it's easy and then at least you'll know it's something else.
WhalerDan	#4  Posted on 12/19/10 - 5:47 PM
Member Personal Page Posts: 245 Comments: 1 Joined: 11/13/05	My guess -- replace the thermostat.
Derwd24	#5  Posted on 12/19/10 - 9:07 PM
Member Posts: 1607 Comments: 9 Joined: 05/09/07	Does the horn sound when you first start it up cold? If so, as Ralph suggests, check for restrictions in the fuel line, even the under cowling fuel filter. Even a portable tank vent not fully open can cause the warning, though usually at higher rpm. Also, on the Evinrude/Johnson engines there's a temp switch in the head, easily detectible by the single wire coming off it. Has a blade connector that's easy to disconnect and makes checking that simple. Not sure if Yamaha is the same but it's worth a look. If the horn doesn't start as soon as the engine is running when cold but sounds when it's had time to run a bit, it could well be cooling related. Edited by Derwd24 on 12/19/10 - 9:30 PM Dave - 1983 Outrage 22
Whaler27	#6  Posted on 12/21/10 - 5:26 AM
Member Personal Page Posts: 32 Comments: 1 Joined: 10/11/06	The 2000 Yamaha 70 does not have any sensor or switch that can detect vacuum caused by a restriction in the fuel system. It may have some salt buildup in the cooling passages. Pull the thermostat and see if there is a salt buildup.
tedious	#7  Posted on 12/21/10 - 5:37 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	As mentioned before, the key to figuring out what's wrong is to start the motor up cold. If the horn starts sounding immediately, you have an electrical problem in the horn circuit, most likely a short. If it takes a while for the horn to come on, then you probably really are overheating, and you'll need to find out why. Flow from the telltale and exhaust is not a reliable indicator that cooling water is going everywhere it needs to.
seahorse	#8  Posted on 12/31/10 - 7:38 AM
Member Posts: 103 Comments: 0 Joined: 05/21/06	Tim Erwin wrote: My 2000 yam. 70 2str. has the overheat horn on and the motor isn't hot. I'm running it with the garden hose on with the water coming out everywhere it's supposed to. You cannot troubleshoot a cooling problem on a hose. Float or back the boat into the water to the correct depth, then run it and check the engine cylinderhead using an infrared temp gun. You first have to determine if the motor is actually overheating or if it was just sucking air thru the garden hose and flusher attachment. It is possible that the temp switch or wiring has a short, but that is super rare. Edited by seahorse on 12/31/10 - 7:43 AM
rlryder	#9  Posted on 01/01/11 - 3:34 PM
Member Personal Page Posts: 22 Comments: 0 Joined: 06/24/09	I had similiar problem on my 70 hp Mercury 2000, if the symptoms are the same. My steady alarm occured with the engine cold. Turned out to be a sensor in the oil resovoir was inorperative. Had to replace the oil tank for about $75. This was not, however, a overheat alarm. It was a steady alarm when the ignition key was turned on, engine not running. Good luck. Rock Ryder
CES	#10  Posted on 01/03/11 - 5:35 AM
Member Personal Page Photo Albums Project Albums Posts: 2681 Comments: 7 Joined: 04/27/07	Tim, Did you ever figure out the problem? Cliff 1966 13' Sport with a 1993 40hp Yamaha 2 Smoker