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Okay.....Riser Question......

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Old 03-18-2002, 01:26 PM
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Default Okay.....Riser Question......

I've had some heating issues for a little while now.........1988 5.7 merc........I know the impeller housing and impeller are gonna be changed shortly.......at idle she will heat up to about 200.....but bump the throttle a little say to about 1000rpm's and it will run right at 165...

I noticed today that the left hand side riser is much hotter than the right hand side.......this is new.......they were about the same the last time it was used....both rather hot.........you could touch both at full warm....but not for a long time..........

Now the right-hand riser is cooler by far and the left hand riser is too hot to touch for more than a few seconds......all this is on the hose........and the motor temp is good the whole time.....

Oh and BTW I got the belt problems fixed......

What I need to know is if this is a riser needing to be replaced or if it is just an extension of ther impeller housing being warn....?..the risers are merc items and use four-inch thru-hulls after....
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Old 03-18-2002, 02:03 PM
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Hey Shorgasm
I went through this a while back. Be very careful
of the riser getting to hot. I have a 1987 donzi
with twin engines 454 motors. The port engine riser was bad and got so hot the engine caught on fire which i quickly put out. Come to find out it was clogged with rust. I just had the whole exhaust system redone.Totally cleaned with muratic acid and everthing. I would suggest to replace both riser and check your water flow from your pickup. Hope this helps. If you need futher info feel free to call me at 704-634-9004
good luck
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Old 03-18-2002, 04:39 PM
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Thanks man......it's not soo hot that it would burn anything other than baby skin.........but it's still to hot to hold on to.....The fnny thing is that BOTH of the risers were hot before...and by before i mean since I have had the boat........NOW the Right riser is cool and you could holdd it indefinitly......and the left riser is about the same as it was before....maybe a touch warmer.......

What's goin on here?????.......I had some weird wear on the upper housing when I changed the impeller last year....some kind of melted mess were the tube goes into the upper housing.....
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Old 03-18-2002, 05:24 PM
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Someimes when on the hose water does not circulate well. Make sure it does it when the boat is in the water before you go thru too much trouble.
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Old 03-18-2002, 05:36 PM
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Have you looke for bits of the impeller in the riser, thermostat housing/bypass, or the hoses. Not sure of the plumbing on a small block motor, but I pull a couple impeller blades from the water inlet on the riser of a big block motor. It had the same symptoms as yours right after a water pump failure.
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Old 03-19-2002, 12:04 AM
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First drop a new impeller on there. If you find that when you take the old one out it is missing parts then you may have clogged your riser or some were else. However you know that thing is old to replace it anyhow. From there if you still have the problem on the hose then get the boat in the water and test it there. I know on my Formula with 454's they will run uneven teps as the hose can not give enough water preasure for the motor. The always equalizes in the wter. If you still have the problem then I think you have a clogged riser on the hot side. This will make the other riser run cooler as you have more water flowing through that one. If there is a clog then pull it and do the acid dip.

Jon
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Old 03-19-2002, 08:32 PM
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shore my motor runs the water temps all whacky when on the hose scares me so much i try not to do it much. i would check it in the water before you get too worried about it.
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