coolant intake manifold, sputtering

[BobCT]

I took out my mid cabin again today, doing some short sea trials before she gets hauled.

This morning, i was working on the throttle linkage and removed the two bolts that hold the bracket to the intake manifold. I noticed that one of the bolt holes had coolant inside the hole.

I thought that didn't seem right but buttoned everything up and took it for a test run. Over 2,500 rpms's it starts to stutter and sounds like it's misfiring. It's also throwing a lot of steam out of the exhaust but running around 180F. Below 2,500 it ran ok.

Is this a sign of a bad exhaust manifold? I'm pretty sure I'm burning some coolant based on what I see. It also did this last week, total coincidence that I was working on the throttle cable and removed the mounting bolts and saw what I did.

I checked the oil and it looked ok. Maybe I should remove some plugs?
The risers and elbows were done at some point, not sure if the exh manifolds are original. BTW, the boat is an 88, freshwater cooled 454's.

The port engine is fine.

thanks,
Bob

[prowlersfish]

The coolant could have gotten on the bolt when you lossen them if the are the back 2 or front 2 bolts on that side ( coolant is at the manafold front and rear . the sputting could be due to a dirty bottom as could the steam increse due to load the cooler the out side tempstemps the more steam . are the exhust manafolds fresh or raw water cooled ? also cheak the risers to see if one is a lot hotter then the other it could be stoped up . look at the water in take to see if pluged when you pull it .

if you were burning coolant it wold likely be running poorer at low speeds Are you losing coolant ? if the steam was from coolant you would be losing a lot .

[BobCT]

After talking to Bob he said start with the fuel filters. I never saw the big inline filters because they were painted the engine color years ago. I changed both and the carb filters as well. It runs out great to 4k RPM's so problem solved.

I still have this weird coolant issue though. The engines run great (at all RPM's now), I'm not loosing any coolant and I don't see any in the oil.

BUT, if I remove the mounting bolts for throttle cable, coolant is right to the top of the bolt hole. I started the engine with the bolt removed and coolant will start to overflow. It's not shooting out but now I know it's not residual coolant from another job. The intake manifold was removed at some point, the gasket doesn't look original.

If I re-install the bolt, it doesn't leak. I did the same thing on the other engine and no coolant.

Am I just catching the start of an intake manifold leak?