OK, its labor day weekend... I'm hydrolocked with a good compression test (not a leakdown). All the parts stores are officially closed till Tuesday. I have a bad exhaust manifold. But I have some old ones I saved in the garage from when I replaced the other engine.

Question is: can I reuse the exhaust manifold gaskets or do I need to wait and buy new ones?

Also, is there a way to test the old manifolds I have in my garage so I know or can be reasonably assured they are good?

Points to consider:
1. Labor day weekend.
2. This is the first time I've worked on a aside from filling the drive oil reservoirs. Which doesn't really count.

I wouldn't reuse old gaskets there has to be a marina open tomorrow in your area that would have riser gaskets

Exhaust manifold gaskets? Auto parts store should be ok to use for exaust and for the manifold to risers they might carry some sheets of exhaust gasket material to cut your own. For testing you need to block off any water passages then put pressure to one of the fittings and do a leak down on it.

Sorry, but would you mind elaborating on how I might test the manifolds? I'm admittedly a noob when it comes to any sort of mechanical issues but I feel confident in my ability to follow detailed instructions.

Greatly appreciated!

You have to build a block off plate for the riser end. Then i like to fill with hot water and add a few pounds of air pressure then look for leaks.
And yes most auto places will have exhaust gaskets. Riser gaskets may be another story.

STOCK MANIFOLDS? yOU CAN USE A PIECE OF WOOD AND A PIECE OF INNERTUBE FOR THE RISER BLOCK OFF PLATE THEN PLUG THE FITTINGS AT EITHER ENG OF THE MANIFOLD AND INSTALL AN AIR LINE FITTING TO ONE OF THEM. fILL WITH WATER AS STATED AND APPLY A LITTLE PRESSURE TO THE FITTING AND LOOK FOR LEAKS, 20 POUNDS IS PLENTY. SORRY FOR THE CAPS, I WASN'T LOOKING WHILE TYPING.

OK, an update:

I don't have air tools or a compressor for that matter, so I did some research and found out that acetone has 1/5 the molecular density of water and at average atmospheric pressure will seep into cracks like water at 20lbs psi. So I used acetone to check my manifolds. Both of my "spares" have now been deemed scrap metal. I ran out of day light so ill check the one I pulled off the boat tomorrow when I get home from work.

Question: will a headless exhaust manifold bolt allow enough water through to fill cylinders? Because o found a broken (headless) bolt on my exhaust maniflod...

Headless between the manifold and the block or between the manifold and riser. If the second it will fill that side for sure.

It wasn't the riser bolts, they were all there. It was the exhaust manifold bolt on the starboard engine starboard side, the bolt closest to the front of the engine.

I'm not to sure about your actone working like water at 20 psi. are you taking ing to acount that you are roughly at 14.6 psiA depend on your elevation... You need to test it at psiG. Also I would concider the rate at that actone evaporates. I am not trying to sound like a jerk but if you don't have a compressor in your shop or at very least a friend that had one you might be over your head. I would wait to get the job done right unless you have a cash sitting around to make larger repairs.