View Full Version : Exhaust manifolds overhall or not

Worthing skier
01-04-2011, 04:07 PM
Hi All

Happy new year to you all ,

I have a 1993 prostar 190 with the 285hp inmar 800 pleasure hrs , which has served me very well .
I am looking at a bit of preventative maintenance but no sure if it is going to be more trouble than its worth .
Both the manifolds to risers are starting to bleed with rust from the riser gaskets and the manifolds are quite rusty at the area where it meets the head , there are no external water leaks of exhaust gas leak while running .
Been reading of a few instances where water has leaked internaly causing major engine problems .
My questions are
Is it worth pulling all the manifolds and risers off , then refacing all the gasket mounting surfaces and replacing all the fixing hardware.
Is the any manufacture recomendation for this job after a certain amount of hrs or age .

Any advice would be great.



01-04-2011, 04:55 PM
I just replaced the riser gaskets a few summers back for the same reason. Used a little aviation form-a-gasket to seal up the erosion on the machined surfaces. I can live with a little rust on the exhausted manifolds.

01-04-2011, 07:24 PM
I think your course of action is sound. Also, when the manifolds are apart, steam clean the ports and blow out the rust deposits.

01-05-2011, 06:27 PM
I just did my 93's manifolds and risers. Manifolds were good. Risers had a lot of rust and blockage. With a LOT of sanding and cleaning, and new gaskets, using Permatex #2 you will be fine. I had 669 hours on my boat 100 of them in salt. I also use the manifold drains from

01-05-2011, 06:45 PM
oops. Like I was saying the manifold drains from SKIDIM are a very good investment, along with new brass 3/4 pipe to 1"hose fittings. Do not skimp on the Permatex#2 and make sure the gaskets have openings that match exactly. The risers will have the most corrosion on the sealing surface. If its bad, they are very cheap,

Also, when removing the riser, make sure the mufflers are securely bolted down in the boat. If you start yanking them around, you could crack them, or worse the transom. Remove the hose clamps attaching the 3" hose to the muffler. Mark the exact position of the hose/riser. Break the seal carefully with butter knife or other dull tool. Spray WD40 in between the muffler and hose. NOW remove the riser bolts and carefully break it loose. The riser and hose will now come out of the muffler very easily. Repeat the butter knife wd 40 procedure with the hose attached to the riser outside the boat. Install in the exact reverse putting the hose and riser in its exact position, then sliding it on the muffler. Doing it yourself, wood blocks for support on the install make it easy. Also once removed a good time for plug removal and oil change.