Questions about M25XP
The 1987 Catalina 30 MKII I just purchased has a Universal
M25XP engine with a 2-blade fixed prop. I have a some questions for those of
you with a similar configuration: "Alan Gomes"
I have a 1986 Catalina 30 (original before "Mark"
designations) with a M-25 engine. I understand the engines are the
same except for piston size. "George F. Goodall"
(Q1) At what RPM is this engine supposed to idle? With the throttle lever
all the way back mine drops down to about 750 or so, but seems to idle more
smoothly at about 900. Is this in the ballpark?
(A1) I get about the same results as you at idle. 800-900 can
be even smoother without hurting the engine or
(Q2) What is the max RPM that you achieve? Running flat out I
can hit about 2600. (I did not run it at this RPM for any length of time,
only for a brief test.)
(A2) I get about the same max rpm. The book says that
the engine governer is set at the factory for 3000 rpm. However,
remember that the rpm gage is NOT reading the engine RPM. Since
diesels don't have ignition pulses to count, the RPM is taken off the
alternator. My rpm gage is generic with switch settings to approximate
the engine rpm. Alternator pulse output will vary with the pulley
ratio and type of alternator (# of windings, etc) and belt slippage.
I.E. Don't expect the rpm gage to be an exact match of real engine rpm.
(Q3) What is a good cruising RPM? I've been running it between 1900
and 2100. Temperature seems to hover between 160 and 170 deg. at this
RPM, which seems reasonable to me. I noticed that the temp began to
climb somewhat when I was running it at 2600, but did not do so for long
enough to see how high it would go. It was still under 180 before I
(A3) The big boys tell me that good cruise rpm is between
80-90 % of max. This vintage M-25 with hot water heater in the cockpit
lazerette is known to have a slightly under designed cooling system.
If you have a 100% efficient cooling system, the eng temp will stay at 160
(or thermostat setting) regardless of engine rpm. There are several
upgrades and things to check. First check for obstructions in sea
water cooling, grass in filter, broken impellor blades down stream from
pump, and pencil zinc pieces plugging heat exchanger core holes. (The only
way to do this is to remove
h.e. and shake. If it rattles, you have got them.) Have radiator
shop boil out H.E. Make sure impellor is fairly new and flexible with
all blades still attached. Best bet is to upgrade from 2" to 3" h.e.
Replumb hot water heater from bypass system around heat exchanger to
attached direct to thermostat bypass connectors. This will help
eliminate air locks on the fresh water side of the cooling system.
(Q4) What kind of speed might I expect to make with this engine? At 2100 RPM
in flat water I'm around 6 kts or a bit shy of that. Adding any headwind or
chop drops me to the lower to mid-5's.
(A4) Sounds about right. Big fat boat will slow down
considerably in chop. Thats why Catalina went from 11 hp engine std with 21
hp (M-25) optional to 21 hp std.
(Q5) What are your experiences with prop walk? Compared to my 27 footer the
kick to port seems more substantial. My technique at this point has been to
goose the throttle to get the boat moving at sufficient speed in reverse to
overcome the prop walk. This means that at first I'm actually going somewhat
the wrong way but I find that as the boat gains speed the rudder takes over
and the boat begins to go where I want it. I tried using less throttle but
found that it did not correct itself as readily.
(A5) I use the same technique except after I goose the engine
in reverse, I go to neutral shift. Rudder immediately becomes more