The RPM is way off, has the boat been sitting derilict for awile, are you towing a ton of bottom growth when you are doing your speed check? Are the fuel filters clean? Is the engine smoking? Low compression will mainfest itself especialy on starting, how does the engine start, if it starts easily I would not suspect a compression issue. If these guys are mechanics they should have a compression gauge, have them use it.
I believe a gauge set is available through Toms tool box.

If the engine is toast, look it over for signs of corrosion, you can overhaul it but, if it shows a lot of corrosion it will turn into chore to refurb. At some point it becomes a draw between O/H and replacement. If you buy the boat right you may want to just plunk a new motor in the boat IF the rest of the vessel is worthy.

I posted an article about my rebuild that is toward the end of the opening page of this site. I also babbled on endlessly on the old web site regarding my engine dimise/Overhaul.

[QUOTE=benethridge;1212] I've had one diesel mechanic tell me ...he can turn the engine over by hand (indicating low compression).
Which mechanic is correct?[/QUOTE]

Ben, When my engine is OFF and the transmission is in neutral, I can turn the prop shaft by hand at the stuffing box, which is right behind the transmission, which is connected to the engine. I seriously doubt the veracity of the "mechanic" that told you that.

Trying to give you advice on an engine we can't see with that limited information is like trying to help you deal with smells, sounds, and "where does a wire on my boat end up?" We just can't do it from here.

A friend wrote this: [I]"My experience has been that a close observation of the seller and those things surrounding them can often give a clue as to the seller's approach to care & maintenance in general. Rare is the person who lets their car stay dirty, with leaking oil, grating brakes, etc., while meticulously caring for and maintaining their diesel engine & fiberglass boat."[/I]

What kind of condition is the engine? What do the hoses look like? Are they covered in engine paint or have they been replaced? What does the rest of the boat look like? Does the PO have maintenance records?

While many of us may have done a lot of homework on diesel engines before we bought our boats, many may not be inclined to get to that level of detail so early in their big boat ownership days.

Given that, I'd stay away from confusing mechanics ("qualified boat mechanics" is, to me, an oxymoron-ic statement, there almost aren't any), and find some folks you trust, ask around some more. We don't know where you are or what your boating experience is, and so, in reality, is almost impossible to answer your question as put.

You might also want to join the eList and ask the same ? there, it seems to reach more C36 IA members than this board...

Ben:

Just so your not confused with what has been posted so far about the diesel your looking at. With the motor off and the transmission in neutral one should be able to turn the prop shaft.

Yes the transmission is hooked to the motor but internally with it in neutral it is not connected to the motor via friction disk/compression plates. The disk and plates are not in the compression state but only floating. So turning the prop in neutral does not indicate any motor trouble.

Sometimes on here is it hard to depict what is conveyed as we all do want to help each other with our knowledge. Good luck with your search for a 36. Great boats.

Randy

A couple of things to consider:

1) Improperly adjusted decompression lever will cause engine to not make full power and may allow the crankshaft to be turned by hand. This would also give an indication of low compression.

2) what kind of boat speed do you get at 2000 RPM underway? If you get 5 to 6 knots, the tachometer may not be properly calibrated.

Ben:
I bought a 1989 model with the M25XP engine a couple of years ago. The boat had a recently upgraded heat exchanger, and I assumed it had overheated. The engine would not warm up at idle, and on checking, discovered that the thermostat was missing. When replaced, the engine warmed up properly at idle.

The engine started fine, and would rev up to the 3200 RPM redline when the transmission was out of gear. In gear, it would only get about 2400 RPM. When I hauled the boat, I discovered that the propeller had been repitched to 9", which should have increased RPM.

At one point the boat lost power, and started over heating. I noticed water coming out where the hose from the wet elbow connects to the muffler. On removing the hose, I discovered that the at some point the fiberglass muffler had overheated, burning all of the resin out of the inlet pipe. The raw fiberglass colapsed completely across the opening into the muffler.

I installed a new inlet into the muffler, and things improved a bit. However, I still could not get power. To make a long story short, I took off the wet elbow, and found that it was almost completely blocked just up stream of where the water is injected. The blockage was like a disc with about a 3/8" hole that the exhaust was going through. I replaced the wet elbow assembly, and the engine ran good with good power.

Unfortunately, all of the overheating cracked the head, so last year I had to replace it as well. With the new head, valves, and valve seals, the engine runs like new.

My engine has a little over 3000 hours, and I could see no sign of wear on the cylinders when the head was off.

For about 200 hours before removing the head, I ran Mobil 1 turbo diesel synthetic oil in the engine, with the idea that this would clean the engine up and perhaps free up any ring sticking or other problems. My observation was that it did clean the engine up nicely. The top of the engine was very clean for a diesel. Has anyone else had experience using synthetic oil in the M25XP engine?

Gary Teeter
1989 Cataline 36
AnnieG
Everett, Washington

Ben,
That is most likely the cause. You should have either a 15x10 two blade, or a 15x9 three blade prop. I would first check the tach, as all tachs are notorious for not being accurate. Next I would bring the prop to a good prop shop and have them scan it. They can tell you exactly what's wrong with it. (All of the above assumes a factory fixed prop - other styles/types would be different).