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Water Temp Gauge stops working after 10-15 Min of Run Time
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Author:  partschaser [ Tue Jun 14, 2011 3:05 pm ]
Post subject:  Water Temp Gauge stops working after 10-15 Min of Run Time
Hey guys, first time, long time.

I have an 87 Horizon 170 with the 4.3 Merc, and I have what I hope to be a simple problem. I know the Water Temp gauge is good, as it will work for the first 10 minutes or so of use, then the gauge begins to waiver and drop to zero. Usually have to let the boat cool all the way down and re-start for it to work again (for a few minutes).

My question is that would it be a ground issue if it works initially, then fails? or is there something in the harness that may be having issues once the engine is up to temp?

Thanks in advance!
Author:  Walt [ Tue Jun 14, 2011 5:00 pm ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
That actually sounds more like a bad t-stat or impeller to me... are you sure your engine temp is ok? Mine did the same 2 seasons ago; at that time, I knew what it was and replaced a shredded impeller.
Author:  aguyindallas [ Tue Jun 14, 2011 5:32 pm ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
I was thinking impeller also. Typically what you are describing is a result of steam at or near the sender...which is a result of improper coolant (water) flow.
Author:  Paul I. [ Tue Jun 14, 2011 9:16 pm ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
aguyindallas wrote:
I was thinking impeller also. Typically what you are describing is a result of steam at or near the sender...which is a result of improper coolant (water) flow.


I never would have thought of that!! But, at 200 deg, your alarm should have started beeping and the on-board-computer would have shut the engine down. At lest thats happened to me on a 2007 Merc. not sure on a "87".
Author:  Walt [ Wed Jun 15, 2011 4:25 am ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
Paul I. wrote:
I never would have thought of that!! But, at 200 deg, your alarm should have started beeping and the on-board-computer would have shut the engine down. At lest thats happened to me on a 2007 Merc. not sure on a "87".


I'm fairly certain an '87 doesn't have an on-board computer
Author:  partschaser [ Wed Jun 15, 2011 8:17 am ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
I actually replaced the impeller this year (last year the temp would soar and I'd shut it off) so I know the gauge is good to 200. This year its rock steady at 140ish, with plenty of water coming back out the exhaust when its on the muffs, so I am more satisfied that its cooling properly now.

I am thinking it may be something up near the sender that is affected when its warm, as the issue doesn't show up when the engine is cold.

Thanks for the tips guys, keep'em comin!
Author:  Jammer864 [ Mon Jun 20, 2011 11:21 pm ]
Post subject:  Re: Water Temp Gauge stops working after 10-15 Min of Run Time
How about checking the sender itself. Remove it, rig it up to hang in water that you heat up on the stove. Check the resistance with a multi-meter between the terminals and see if the resistance does something wacky as it heats up.
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