1990 Mercruiser 5.0L Exhaust Riser Gasket

[OMARiverRat]

Hello again everybody. Another stupid newby boater question. Just got the boat out of storage and I pulled off the exhaust risers to discover they were severely deteriorated and rusty. Picked up a new set of risers from the local marine center and brought them home. When I compare the gaskets that were included with the risers to the gaskets currently on the vessel, they do not match up. The used gaskets only have 2 holes for water flow... I've looked around on the web and they call this the "Restrictor" gasket set. The gaskets that came with the risers have 4 holes for "Standard cooling operation". Should I buy a set of these restrictor gaskets, or will the standard cooling gaskets work for my application? Boat is 1990 Wellcraft 197xl Eclipse, w/ 1990 Mercruiser 5.0L & Alpha One Drive. Any help would be greatly appreciated. Thank you.

 

[crazy charlie]

Re: 1990 Mercruiser 5.0L Exhaust Riser Gasket

I did the same change on an older merc and the only difference i saw was that the riser and manifold ran a little cooler than before.So I left the new style gasket on.Ran the motor for a few more years and sold it.Guy that bought it ran it for 3 years w/o a problem.I still see it around once in a while.Charlie

 

[yoced]

Re: 1990 Mercruiser 5.0L Exhaust Riser Gasket

This is what was related by an ex Merc engineer:<br /><br />Merc was trying to solve the problem of risers which overheated at lower engine rpm. The risers were overheating because the water flowing up over the riser was flowing slowly - slow enough to not fill the riser's water passages all the way, but instead just barely make it over the top and out.<br /><br />The theory was that if they could pressurize the water in the manifold, they could get some extra oomph out of the water flow at lower RPM.<br /><br />In my opinion (and the engineer did not disagree), it was a rather misguided attempt and never really helped much at all. <br /><br />However, whenever the big M does something they do it in quantity, and therefore a lot of those gaskets are out there being replaced with the same.<br /><br />And, in all fairness, not many people like to second guess an OEM choice of gasket style. Those who do are more often than not wrong, and often wrong to the point of wrecking things.