Riser gasket question

[SCORPIO]

Replaced the four season old risers on my 1989 5.7 Merc I/O raw water cooled engines as part of a process of elimination to find an overheating condition at high rpm. The risers are standard Merc center riser 4" units. The gaskets that came with the risers are of the 'Restrictor' type. That is to say they have two oval slots on the sides and two tiny holes one on each end of the riser. It would seem to me that the four slot gaskets would flow alot more water and reduce both riser and engine temps. I am going to sea trial the boat tomorrow to see what effect the new risers had on the over heat problem. I have run it in the slip and noted the starboard engnie risers run hotter than the port engines by about 35 degrees. If I still have a heating condition or hot risers, could I switch to the open style gaskets and would this harm anything?

 

[boatrboy]

Replaced the four season old risers on my 1989 5.7 Merc I/O raw water cooled engines as part of a process of elimination to find an overheating condition at high rpm. The risers are standard Merc center riser 4" units. The gaskets that came with the risers are of the 'Restrictor' type. That is to say they have two oval slots on the sides and two tiny holes one on each end of the riser. It would seem to me that the four slot gaskets would flow alot more water and reduce both riser and engine temps. I am going to sea trial the boat tomorrow to see what effect the new risers had on the over heat problem. I have run it in the slip and noted the starboard engnie risers run hotter than the port engines by about 35 degrees. If I still have a heating condition or hot risers, could I switch to the open style gaskets and would this harm anything?

http://www.perfprotech.com/store/as...ST-ELBOW-(CAST-IRON-EXH.-ELBOW),1014-190.aspx

Take a look at this website - I'm not sure if i have the correct motor picked but this one show with risers the gaskets are 4 slots.
good luck - mark

 

[kaz911]

Replaced the four season old risers on my 1989 5.7 Merc I/O raw water cooled engines as part of a process of elimination to find an overheating condition at high rpm. The risers are standard Merc center riser 4" units. The gaskets that came with the risers are of the 'Restrictor' type. That is to say they have two oval slots on the sides and two tiny holes one on each end of the riser. It would seem to me that the four slot gaskets would flow alot more water and reduce both riser and engine temps. I am going to sea trial the boat tomorrow to see what effect the new risers had on the over heat problem. I have run it in the slip and noted the starboard engnie risers run hotter than the port engines by about 35 degrees. If I still have a heating condition or hot risers, could I switch to the open style gaskets and would this harm anything?

Have you tried flushing the cooling system?

Read here for a success story:
http://clubsearay.com/showthread.php/53140-Merc-225-302-Ford-Running-hotter-than-I-would-like?

 

[njmello]

I had a similar overheating problem (at higher RPM - otherwise normal at idle) with my '78 Cuddy/350 Chevy engine and asked the boat mechanic the same question re: the separater 'blocking' the larger holes. The risers are cast to accommodate several different applications and if your separater blocks the larger holes that is by design. You have to use the correct seperater to match your engine. The small holes allow steam that accumulates in the exhaust manifolds to escape BEFORE returning to the T-block (steam is ALWAYS over 212 degrees)and have nothing to do with restrictions in the overboard water flow. The inner parts (where you can't see - behind the casting plugs) of the riser water jacket will scale up and clog/restrict the overboard water flow - which is the actual problem.

When I got the new risers they arrived without the casting plugs installed. I discarded the cast iron plugs and installed brass plugs instead - which will not 'freeze' in place, over time. By removing the risers (and taking out the plugs) I can give the risers a caustic soda bath to remove scale buildup every couple of years and nearly double their life expentantcy. It's the carbon buildup in the riser that clings to the rust scale that is the killer - minimizing the rust scale minimizes the carbon build up.

Just my 2 cents.