Finally Changing Manifolds, Got a Question

[FastFred]

Putting aside changing the exhaust manufolds on my 340 with Mercruiser manifolds I ordered the coated version of the mercrusier mainfolds for my 89 340 with 454's. I hav not yet taken the old ones off but looking at the elbows and what the gaskets it calls for seems strange to me. The pictures of the underside of the elbows seem to show 4 slots for water along the side of the elbow. The ones I got in have a releaf at the bottom of the base where water may circulate freely between these slots. They are located by the bolt holes.

What I do not understand is the gaskets have 2 slots and 2 small "steam" holes. I do not see the reasoning here, do I have the wrong parts?

 

[Happy Hour IV]

Different styles of gaskets for different cooling systems. If you have closed cooling then the gasket has no slots or holes at all. If you have raw water cooling then I believe you get 4 slots. I believe a partial closed system gets 2 slots and 2 holes.

You will also have to clarify if you have riser spacers and if so will they be closed or raw water cooled. I understand that most spacers are
raw cooled but I run mine on the closed sided with no problems.

 

[FastFred]

Happy Hour, Thanks for the responce, it is a fresh water system, not a partial system and from what I can see regarding the gaskets, the fresh water system calls out the 2 slots and 2 holes which to me is the wrong way to go. Also I do not have the extra 4 inch riser block, just the standard risers. Since this is on a 1989 engine and these are the orginals I'm replacing, had Merc made a change in the base of the elbows? I called several Mechanics and they all seem to have a different answer on what gasket goes to what elbows. I guess I'm going to pull the risers and see what the old OEM is and go from there.

 

[Happy Hour IV]

In a full freshwater cooling system the manifolds have coolant and the elbows (risers) have raw water in them. They do not mix. Between your
manifold and riser you will find a stainless blanking plate with a gasket on each side. The plate stops the flow of water/coolant and the gaskets simply seal the plate. In theory you can use any style gasket. I like to error on the side of caution so I use gaskets with no openings at all on each side of the plate. So I guess the mechanics could pick whatever style gasket they want and still be right.

 

[rondds]

Mike
Just seeing this...
First, let's get the nomenclature right. The elbow is one thing, the riser is the small extension block that fits btwn the elbow and manifold. Are you saying you have NO riser, only the manifold and the elbow (not familiar with the setup on a 340DA but my DB [and yours] has NO riser).

If you have true factory "closed cooling," then you need the gasket that has no holes or slots other than the holes for the bolts. As Happy said above, there is NO co-mingling of seawater and coolant in these systems, and the thing that separates the two fluids is that gasket.

This is the exploded diagram for my (our) engines. Item 11 is the ELBOW - note that there is no RISER. You need Item #10, which is merc part #27-8637251

 

[FastFred]

Ron, thank you for the diagram. In my post I did not mention a riser, only referred to an elbow so I think it was the responce from Happy Hour regarding the riser. I met with my local parts manager who confirmed the serial number of the engines to the correct gaskets which was the one with the 2 slots and 2 small holes. Mercrusier calls out this gasket for only the "Raw Water" system which is what I have. Planning on the first weekend of November to pull the manifolds and do some updating on tune up parts, much like what you did with the trigger sensors. May as well as its almost apart anyway.

 

[Happy Hour IV]

FastFred, in your response to me you said you had a closed system. Now you say you have a raw water system. They are totally different and require different gaskets. The original engine serial number simply says how the engine left the factory and does not include any modifications such as closed cooling additions.

The best way to clarify......Do you use any antifreeze in the engine ?

 

[tdschafer]

This is getting confusing?? I also thought the OP earlier stated he had a closed cooling system and has now said it is raw water?

 

[FastFred]

Guys, Read my responce to Happy Hour where I stated "Fresh Water", meaning its a Raw Water system not "closed cooling". From the area we boat most locals call the water intake systems "fresh water" so hense I called it a Fresh water system, my bad! I never mentioned having a closed system nor having a riser in any of my responces . Whats so confusing about this?? Raw Water systems calls out the 2 slots and 2 holes in the Gaskets not the 4 slotted gasket. I checked with Mercrusier using the serial number from the engines to order the correct Gaskets. I do want to thank all that did respond.

 

[rondds]

Mike
You are absolutely right! Someone else mentioned RISER and the other misunderstanding here is us not understanding that where you boat, raw water is FRESH water! So you need the slots. Guess it's gonna look like item #9 in post #5 above.

Now that we've got that settled, good luck getting the cruddy old manifold bolts off! Don't break an ez-out in the bolt hole. It creates all sorts of problems - don't ask me how I know.

 

[dicor]

I replaced mine last year and used an old Street-Rodder trick. You may already know about it but just in case here it is. Get (2) 5 inch long bolts with the same thread as the ones holding the manifold on. Cut off the heads, round off the edges and drill a 1/8 inch hole 1 inch from the top (unthreaded end) this hole is so you can put a Allen wrench or nail in it to install and de-install it now that the head is gone. Remove the 2 outer bolts and install the studs you just made, remove the rest of the bolts, now you can easily slide the heavy manifold off. The best part is when you install the new stuff, slide the new gasket onto the studs which will hold it in place then install the new manifold. Simple!

 

[boatrboy]

I replaced mine last year and used an old Street-Rodder trick. You may already know about it but just in case here it is. Get (2) 5 inch long bolts with the same thread as the ones holding the manifold on. Cut off the heads, round off the edges and drill a 1/8 inch hole 1 inch from the top (unthreaded end) this hole is so you can put a Allen wrench or nail in it to install and de-install it now that the head is gone. Remove the 2 outer bolts and install the studs you just made, remove the rest of the bolts, now you can easily slide the heavy manifold off. The best part is when you install the new stuff, slide the new gasket onto the studs which will hold it in place then install the new manifold. Simple!

This is great advice - and I will go further and say if it is too hard to drill the small hole grind flats on the end so you can use a wrench. I personally never did this as most of the time finger tight works or vice-grips in a pinch will get your studs back out. I have changed manifold gaskets many times and its easy with these studs.