Rusty Shackleford
New Member
I bought a '78 SRV 200 (305/Merc) a few months back, and have been catching up on the typical neglected maintenance issues that are typical of too many old boats out there. Anyway, after cleaning up hacked wiring, replacing a few small soft spots in the floor, and some new carpet and upholstery here and there I took her out for a test run.
As expected I found a few more issues to deal with, but mechanically she did pretty good over the three hours I was out. I did notice that the temperature fluctuated between 130-175 degrees, but never hotter. The next weekend I take the wife and kid out, and after about an hour of moderate use the engine started getting hotter, I shut her down when the gauge showed 200. I pulled the engine cover and the manifolds were pretty darned hot, enough to sizzle just a bit when I spit on them. After about 45 minutes of sitting, and swimming for the kid, I fired it back up. It went back to 200 pretty quick as I headed toward the launch, but after about a minute of running there the temp dropped quickly back to 135ish. We loaded up and came home.
Got home and took the t-stat housing apart, and no t-stat present. So I went and got a 165 to put in it, and buttoned it all back up.
I have ran the boat a couple more times since then usually less than 3-4hrs per trip, and have not had it get hot yet. It now warms up to 165 and stays there, as I think it should with the stat in it.
In doing research i read where the old manifolds/risers will get rusty inside and flakes of rust can block passages, and I've read multiple other reasons one would get hot, but no other explanation lean toward an intermittent overheat. My reasoning there is, if a pump or impeller went bad, it would still be getting hot.
I haven't pulled the manifolds/risers yet to inspect them, wanted to make sure I'm barking up the right tree before I do. I have no idea how old they are. The stat housing did have some surface rust showing inside, but no flakes or really nasty looking stuff.
Anyway, is my thinking correct? Should I be looking elsewhere first?
Thanks in advance for any advice. I'm a long time boater, and hotrodder, so working on stuff doesn't scare me. I'm just not as familiar with this type of cooling system so I thought I'd seek advice from those who are.
FYI, I'm inland and doubt the boat has ever seen saltwater, if that makes a difference.
As expected I found a few more issues to deal with, but mechanically she did pretty good over the three hours I was out. I did notice that the temperature fluctuated between 130-175 degrees, but never hotter. The next weekend I take the wife and kid out, and after about an hour of moderate use the engine started getting hotter, I shut her down when the gauge showed 200. I pulled the engine cover and the manifolds were pretty darned hot, enough to sizzle just a bit when I spit on them. After about 45 minutes of sitting, and swimming for the kid, I fired it back up. It went back to 200 pretty quick as I headed toward the launch, but after about a minute of running there the temp dropped quickly back to 135ish. We loaded up and came home.
Got home and took the t-stat housing apart, and no t-stat present. So I went and got a 165 to put in it, and buttoned it all back up.
I have ran the boat a couple more times since then usually less than 3-4hrs per trip, and have not had it get hot yet. It now warms up to 165 and stays there, as I think it should with the stat in it.
In doing research i read where the old manifolds/risers will get rusty inside and flakes of rust can block passages, and I've read multiple other reasons one would get hot, but no other explanation lean toward an intermittent overheat. My reasoning there is, if a pump or impeller went bad, it would still be getting hot.
I haven't pulled the manifolds/risers yet to inspect them, wanted to make sure I'm barking up the right tree before I do. I have no idea how old they are. The stat housing did have some surface rust showing inside, but no flakes or really nasty looking stuff.
Anyway, is my thinking correct? Should I be looking elsewhere first?
Thanks in advance for any advice. I'm a long time boater, and hotrodder, so working on stuff doesn't scare me. I'm just not as familiar with this type of cooling system so I thought I'd seek advice from those who are.
FYI, I'm inland and doubt the boat has ever seen saltwater, if that makes a difference.