One riser overheating/steam/thermo fine - Toubleshooting help

[nutshellml]

Hi,

I have a 94' Chaparral w/a 5.7L Mercruiser 350MAG. Looking for some advice on pinpointing a problem. Here's the story:

Last year everything was running fine. Beginning of this season i had the outdrive/impeller serviced. After dropping it in the water i noticed that one Riser gets extremely hot. This is def not the norm. The temp is constant at 160 (thermostat setting). I took off the entire thermostat housing (everything was fine), replaced the thermostat, took off the Riser (everything fine), checked the exhaust flaps (everything fine), and all hoses looked good. I can?t figure out what could be the problem? My two thoughts, either something happened over the course of the winter, but what? or when the marina serviced the outdrive something got screwed up? but if it was an water intake problem wouldn?t both risers get really hot?

Any help troubleshooting is greatly appreciated.

Thanks!!

 

[nutshellml]

Re: One riser overheating / thermo fine Mercruiser 5.7 V8 350Mag Toubleshooting help

Re: One riser overheating / thermo fine Mercruiser 5.7 V8 350Mag Toubleshooting help

Forgot to mention, when running on earmuffs steam comes out (never happened before). When running in water and revving little hard, riser is extremely extremely hot and steam is coming out. All manifolds and risers were replaced two years ago and good condition.

I know that one riser is usually a little hotter than the other, but i have had the boat for over 7 years now, and know that it's not normal. Especailly while running under a load (on the lake), stop for a sec and check the risers, one i can't even touch for 1/2 second, where as the other is fine. And up until this point i was always able to touch both. Also alot of steam.

Thanks

 

[bruceb58]

Re: One riser overheating/steam/thermo fine - Toubleshooting help

Check that the outlet of the thermostat housing is not clogged up. Somehow, the water is not making it to that manifold.

 

[nutshellml]

Re: One riser overheating/steam/thermo fine - Toubleshooting help

Thermostat housing isn't clogged. I tooke the entire housing out, scraped it, replaced the thermostat, still same problem... any other ideas?

 

[nutshellml]

Re: One riser overheating/steam/thermo fine - Toubleshooting help

Thermostat housing isn't clogged. I tooke the entire housing out, scraped it, replaced the thermostat, still same problem... any other ideas?

bumpbump, any other advice?

 

[DockedPay]

Re: One riser overheating/steam/thermo fine - Toubleshooting help

I have had this problem and it was the o/d impellar. I know you said it was replaced but so was mine. I replaced it again using the whole kit (housing, etc, cost about $50 in parts). Ran like a top after that. If you have twin motors check my threads re trouble shooting an overheating problem...just do a search under my user name. I have twin motors and trouble shooted by swapping the water pump hoses to isolate the drives. If you don't have twins then I would give a impellar kit replacement a shot..its not that expensive if you can do it yourself...good luck