Overheating 4.3 Mercruiser
05-25-2009, 03:00 PM
#1
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Overheating 4.3 Mercruiser
Just need some advise, or collaboration on my newly experianced overheating issue. I have a Tahoe 2006 q4 ski and fish with the 4.3 Mercruiser. I have owned it since 2007 bought it used.
Well, we took it out for the start of summer for a wonderful Memorial weekend. Well within 15 min. we were overheating...
Here is the scene. I launched no problem. Idled a while to get things going went for a nice little ride, never going faster than idle (for about 15 min.). Then opened her up for a little jaunt. Within 3 min. or so the alarm went off and I was at 200 degrees.
So I checked the raw water intake for blockage... Nothing.
I replaced the thermostat (had to get one from autozone)...
There seems to be water running in the cooling tubes...
Still overheating....
One other note... The tach is jumping from accurate to pegged once and a while. Related?
I am thinking that the ability to drive at idle for 15 - 20 min. without overheating means I have a blockage somewhere. I am thinking in the exhaust risers? When I had things apart and looking into the area below the thermostat I have to say there was a lot of rust and scale in there, is this normal?
Anyone have a good link to a trouble shooting guide, or know of a good chilton's type manual for the mercruiser?
If you concur, let me know if tearing the exhaust risers apart is something the moderately inclined gear head could accomplish?
Anyway, the weekend was not ruined. We had fun fishing with the trolling motor which worked great. The bass and crappies were biting!
Well, we took it out for the start of summer for a wonderful Memorial weekend. Well within 15 min. we were overheating...
Here is the scene. I launched no problem. Idled a while to get things going went for a nice little ride, never going faster than idle (for about 15 min.). Then opened her up for a little jaunt. Within 3 min. or so the alarm went off and I was at 200 degrees.
So I checked the raw water intake for blockage... Nothing.
I replaced the thermostat (had to get one from autozone)...
There seems to be water running in the cooling tubes...
Still overheating....
One other note... The tach is jumping from accurate to pegged once and a while. Related?
I am thinking that the ability to drive at idle for 15 - 20 min. without overheating means I have a blockage somewhere. I am thinking in the exhaust risers? When I had things apart and looking into the area below the thermostat I have to say there was a lot of rust and scale in there, is this normal?
Anyone have a good link to a trouble shooting guide, or know of a good chilton's type manual for the mercruiser?
If you concur, let me know if tearing the exhaust risers apart is something the moderately inclined gear head could accomplish?
Anyway, the weekend was not ruined. We had fun fishing with the trolling motor which worked great. The bass and crappies were biting!
Last edited by Covert_Ops; 05-25-2009 at 03:40 PM.
07-16-2009, 05:13 PM
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Did dealer inform you that the impeller should be changed every year? Same with lower unit lube, I take my lower down also to check the alignment (engine-lower unit) and to grease the CV joint in the upper driveshaft
08-13-2010, 08:36 AM
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yup , you need a new impeller ... 4.3's are good engines and don't have many problems as long as they're maintained .... i've never seen many thermostats go bad in them