deteriorating exhaust manifolds

[Ron Everson]

My 1975 225 OMC (305 Chevy) I/O appears to have the original exhaust manifolds - at least they don't appear to be any newer than the rest of the engine. I've had the boat for 8 years or so, and every fall when I drain the exhaust manifolds, I get a lot of rust chips coming out of the drains. I've even flushed them out in the middle of the season to see what's accumulating and got quite a bit. I'm assuming that after all these years, there can't be much left of whatever internal baffles are in the mainfolds (I'm assuming that's what is deteriorating) and I,m wondering whether I should replace them. The engine runs at normal temperature, neither hot nor cold, although, when the water is 40 degrees in the spring, it runs several degrees cooler than in summer. Will the $700.00 that I'll have to spend on replacement manifolds be worth the peace of mind, or am I worrying to much? I have replaced the thermostat and water pump since I got the boat. What are your thoughts?<br /><br /> Ron

 

[snapperbait]

Re: deteriorating exhaust manifolds

I'd say you've been running on borrowed time... <br /><br />Thats a big yes on replacing them...

 

[dmorley]

Re: deteriorating exhaust manifolds

Ron,<br />You have to look at your situation to answer that question. Specifically, ask yourself what the consequences of an unexpected break down will be? First, there is the mechanical possibility of rust through resulting in water finding its way to cold valves and then you'll be looking at a minimum of a valve job. Second, if the boat is central to a much looked forward to vacation that could be another big loss. Third, I noticed that you are in southwest Colorado. I know that on the Colorado front range it takes weeks to get in and see a boat mechanic during the summer. Finally, you might let the people on this forum know if you use the boat in salt or just fresh water. That will let them give you a better guess at manifold life expectancy.<br /><br />Don

 

[crazy charlie]

Re: deteriorating exhaust manifolds

Compare the 700 to the cost of replacing the motor and it is a cheap investment.Your manifolds must be related to the 114 year old guy that died today.Its hard to believe they lasted that long.Call the Giness book of records.Charlie

 

[biloxiriver]

Re: deteriorating exhaust manifolds

It just depends on how much you value the boat. Can you replace it for $700.00? I doubt it. If the boat met my needs and I intended to keep it, it would be well worth it to me.

 

[Trent]

Re: deteriorating exhaust manifolds

Make sure to replace the risers also.

 

[Ron Everson]

Re: deteriorating exhaust manifolds

Believe it or not, these things are so old that the risers are rubber hoses (replaced when I got the boat). The OMC manifolds that I've seen in the catalogs all have cast iron risers. The last time I checked with Seaway Marine a year or two ago, they still had the original replacement parts, so that's probably where I'll go to get the parts. Definitely a shortage of qualified marine mechanics around here, so I do almost everything myself. I only use the boat in fresh water, and as far as I know, that's all it's ever seen. You've all confirmed what I thought. It's time to replace! Now I've just got to break the news to the better half. It will be a good early spring project, while the boat canopy is still surrounded by snow. Speaking of long life, I sold my 1977 ford F150 4x4(351M, 122,000 miles) late last fall, since it was getting too weak to pull the boat to Powell. Since I drove it since it was new, I've kind of figured out how to make things last a long time. I'm hoping the boat will be no exception. Thanks for your help!<br /><br /> Ron

 

[rodbolt]

Re: deteriorating exhaust manifolds

what? sold a truck that was barley broke in?<br /> my old rusty chebby still has to haul the occasional 25 hydra-sports with a pair of 225's but its got about 290K on it <br /> do the risers and manifolds replace all the rubber parts, do a water pump job and enjoy the boat. some freshwater boats I know are at the 15 year mark and still running original risers. in my salt pond I say scrap them every 3 years.<br />good luck and keep posting

 

[biloxiriver]

Re: deteriorating exhaust manifolds

Wow, I am impressed! You actually sold your 1977 truck with such low mileage!!!! My 1995 F150 w/302, has 260K and still pulls my boat just fine! Just like anything else, if you maintain 'em they will last!

 

[crazy charlie]

Re: deteriorating exhaust manifolds

Good luck breaking,I mean removing the bolts.Charlie

 

[Ron Everson]

Re: deteriorating exhaust manifolds

From my experience with old outboards (5), you're probably right - the bolts should break right off, and then I'll spend a lot of time drilling them out. However, I'm counting on the fact that the marine mechanic that did the valve job on it for me 4 years ago pre-loosened them for me. By the way, when I asked the mechanic about the condition of the exhaust manifolds, he thought they looked ok. This is the same guy that couldn't help me with the Rochester carburetor and sent me to the auto mechanic down the road that "knew" Rochester carburetors. The auto mechanic replaced the Rochester with a marine model of a major carburetor manufacturer that I can't recall the name of right now (wasn't Holley). The boat has run well since. I need to shovel enough snow away from the boat canopy so that I can get in there and get to work. Of course, the boat canopy isn't rated for snow, ice, or high winds, all of which we have a lot of. I got my moneys worth when I bought that.<br /><br /> Ron