We have a 1984 Caravelle with a Mercruiser 140 engine. This is the 4 cylinder GM engine, with an Alpha 1 outdrive. The engine serial number is 6045155. This boat has been in the “family” since 1986. It was owned by a close friend until 95 when I bought it. I sold it back to the friend in 2005, and last month he sold it to my brother. When he sold it to my brother he said it wasn’t running well, and he had paid for a tune up that did not cure the problem.
We took the boat out to the lake. It was hard to start, but it started eventually. After running it for a few minutes we noticed that the vent hose from the valve cover to the carburetor had slipped off the carb, and there appeared to be a lot of steam coming from the hose. After a few more minutes these steam started looking like a brownish oily mix, and we went back to the dock. We went home and changed the oil. The oil was a brown watery mess.
I suspected the problem was the exhaust/intake manifold. I know that I replaced the riser some time in the early 2000’s, but the exhaust manifold has never been changed. But I also thought it could be cracked block or something else, so we ran a compression test. We warmed up the engine, and did the test. We got dry compression values of (starting from the front of the engine) 55, 125, 105 and 150. We then added a bit of oil to the first cylinder and the compression value jumped up to about 65.
One more thing—when we were doing the compression test we noticed that there was a decent amount of what looked like water squirting out spark plug hole of the back cylinder.
At this point we are not sure what to do. My best guess is that we have a leak in the exhaust manifold somewhere near the back cylinder. I am inclined just to replace the exhaust manifold and see what happens. I have another boat that had low compression in one cylinder and that boat has ran just fine for 10 years.
The boat does not have a lot of value. I am not sure what it would cost to fix the low compression, but it might exceed the value of the boat. OTOH, it is a fun little boat when it is running well, and given how much we use it, the engine might last a long time just like it is.
So what should we do? Should we just replace the exhaust manifold and see what happens? Or is it foolish to not deal with the compression issue at the same time? And should I replace the riser again?
Jared
We took the boat out to the lake. It was hard to start, but it started eventually. After running it for a few minutes we noticed that the vent hose from the valve cover to the carburetor had slipped off the carb, and there appeared to be a lot of steam coming from the hose. After a few more minutes these steam started looking like a brownish oily mix, and we went back to the dock. We went home and changed the oil. The oil was a brown watery mess.
I suspected the problem was the exhaust/intake manifold. I know that I replaced the riser some time in the early 2000’s, but the exhaust manifold has never been changed. But I also thought it could be cracked block or something else, so we ran a compression test. We warmed up the engine, and did the test. We got dry compression values of (starting from the front of the engine) 55, 125, 105 and 150. We then added a bit of oil to the first cylinder and the compression value jumped up to about 65.
One more thing—when we were doing the compression test we noticed that there was a decent amount of what looked like water squirting out spark plug hole of the back cylinder.
At this point we are not sure what to do. My best guess is that we have a leak in the exhaust manifold somewhere near the back cylinder. I am inclined just to replace the exhaust manifold and see what happens. I have another boat that had low compression in one cylinder and that boat has ran just fine for 10 years.
The boat does not have a lot of value. I am not sure what it would cost to fix the low compression, but it might exceed the value of the boat. OTOH, it is a fun little boat when it is running well, and given how much we use it, the engine might last a long time just like it is.
So what should we do? Should we just replace the exhaust manifold and see what happens? Or is it foolish to not deal with the compression issue at the same time? And should I replace the riser again?
Jared