So I just bought a Mac X....

[Be Free]

Please don't get stressed about the engine running hot. Every part of the water pump can be rebuilt and/or replaced easily and economically. Keep looking. You'll find what is out of spec.

I had an impeller in a BF40A melt to the inner liner. I replaced the liner and the impeller and it was like new.

[opie]

Every new owner needs to carefully read BeFree's 649am last paragraph above regarding disconnecting shift linkage in order to separate lower unit to access water pump.

[Drifter]

I know I should't be so grumpy; i think it's just how I was already compromising after so much effort and fiddling, deciding to actually just use the thing, even if with just the engine and even if the test run was itself compromised by being a family fishing trip instead of a structured test.

As long as it did the big 3 - floats, goes and steers - we could have fun, right?

Well it floats, but rather failed the other 2

You appear to be going below hull speed in the video. At that speed, you can run with the rudders and keel down - which may help (believe svscott and Russ said this, too).

According to i-Boating app, I was averaging 11.5 kph, which is 7.15 mph or 6.2 knots, until giving it WOT throttle, where it overheated so fast the GPS didn't get around to updating the speed (briefly shows 18 kph but the boat surged forward fine, rose up out of the water and was going well above that, before the sudden siren and limp-mode)

It was actually rather scary because in my haste to throttle back I got it partially into reverse. I didn't realize at the time that the alarm actually gimps the engine, so from my perspective it was sudden loud alarm, I grabbed at the throttle but felt the boat suddenly slow before I even reached it, then after yanking it back I cut the ignition... At which point there was a metallic clackety-clack sound from behind me...

NOW I now the clacking was because it was trying to get into reverse, while the water was still spinning the prop, and the sudden slowing was because the Honda cuts the power when the alarm is triggered. At the time it felt and sounded like a catastrophic mechanical failure!

After leaving it for 10 minutes or so to cool I realized it was half in reverse when trying to re-start it. It started fine and we continued the journey but yes, I think on the way back I was even slower, more like 3300 rpm rather than the 3500 on the way out.

What prop are you running now (dia and pitch)? You could be over-propped with a 3-blade, too.

I'm not entirely sure but I am sure the 3 blade is the original supplied with the engine, as it has some wear but very little. The 4 blade has much more wear and has obviously been in use for a long time, so I think the 3 blade has been taken off and put to one side after they fitted the 4.

With 4 people, full ice box, a lot of water and a full tank, the engine/prop seemed quite comfortable and I was happy and impressed how hard it pulled (pushed) at WOT - until the alarm.

Please don't get stressed about the engine running hot. Every part of the water pump can be rebuilt and/or replaced easily and economically.

If it's just the impeller, thermostat or maybe some sensor, that can be done. If it turns out it needs a new ECU brain or the cooling channels are corroded, or the head gasket is leaking because the head is warped or cracked..? Realistically that would mean sourcing, transporting and trying to fit a replacement engine. Which locally is like buying a new car, in cash.

A quick look around at local versions of Craigslist, FB etc, shows no engines available. Best I could do is buy a disgusting old wreck of a boat that has a Yamaha 60 hp 2-stroke, for just under $7,000 USD. And who knows what's wrong with it. Or I could order an engine from Japan, with a shipping fee very close to the cost of shipping the Macgregor.

So yeah, I really hope it's just the thermostat!

I've ordered one, and have received 3 emails so far, that they got the order, that someone would get back to me about the order, and then today that the order is being processed. So that's nice No idea how long it will take to arrive though.

And I haven't mentioned the trailer wiring, or lack of it... That's a sad little saga all by itself, so I'm gonna shut up before I depress y'all

[Tomfoolery]

What prop are you running now (dia and pitch)? You could be over-propped with a 3-blade, too.

I'm not entirely sure but I am sure the 3 blade is the original supplied with the engine, as it has some wear but very little. The 4 blade has much more wear and has obviously been in use for a long time, so I think the 3 blade has been taken off and put to one side after they fitted the 4.

The 'standard' prop most folks use on the BF50 on a was a 3-blade 11-3/4" x 10" pitch, supplied by Honda. This allows the engine to get close to max rpm with no ballast.

I also have a 4-blade 11.8" x 9" pitch, which should work better for towing a wakeboard or other toys, but it makes a howl at my typical slow cruising speed (2000-2500 rpm on the tach) so I don't use it much.

Both were made by Solas, though the 3-blade was sold as a Honda part, with Honda silver paint. They don't seem to make it any more, at least with the Grim Reaper sickle blades.

The diameter and pitch should be on the prop hub, or possibly the back of one of the blades, near the hub. If the boat is on its trailer you can read it easily.

[Drifter]

I'll take a look tomorrow

[Be Free]

There are at least 17 stock 3-blade props for your engine. Almost all of them are wrong for a Mac. You will find the diameter and pitch of the prop stamped into the side of the hub. If the prop has been repainted it might be a little hard to read but it will be there.

While you are at it, what is the pitch and diameter of your 4-blade prop? It may be a better fit.

Am I correct that you were doing around 3500 RPM and running about 6.2 knots in a heavily loaded boat? I would expect closer to 8 knots if you have the right prop.

There is only one alarm buzzer but there are two conditions that will set it off while the engine is running. One is overheating and the other is low oil pressure. I don't suppose you noted which lights were lit on the remote control...

My (limited) experience with failing Engine Control Units is that they work or they don't. The circuitry in the ECU will note that the over-temperature alarm is on and will limit engine RPM to prevent damage. It could fail in a way where the over-temperature protection is always engaged or never engaged but it would take a very particular and very unusual set of conditions to have it fail intermittently. Your ECU is probably fine BUT if the engine is allowed to run hot (very hot) you will eventually damage the ECU, almost certainly the alternator coil, and probably the excitor coil. That's hot like blistering-the-paint-on-the-power-head hot.

[Drifter]

So I looked at the prop...

It says 11-3/4 x 10, which is standard

It also says 298x254. I'm guessing that's mm.

The 4 blade prop says 11.4x10

I'm not sure if that makes the 4 blade more torque or more speed? I'd presume it means more torque, right?

[Jimmyt]

About the only thing you can get from that info is, you don't appear to be grossly over-prop'd with either the 4 or 3 blade, such that rapid overheating would be expected. In fact, Tomfoolery mentions those specs above. Props wouldn't seem to be the issue.

What was your full throttle rpm?

I'm betting on impeller and/or thermostat.

If you run slow, can you run without overheating?

[Drifter]

Yes, we went 28 kilometres at lower throttle without problem.

I didn't get time to see what the revs were at full throttle before the alarm came on

PS: regarding the speed, we were going against the tide going out, and against the tide coming back (I was deliberately ensuring we'd have a high tide for launching and retrieve, rather than trying to save fuel on this occasion)

So yes, I'd say actual speed through the water was probably closer to 8 knots or even a bit more. The tides are very high here.

Edit: Reading up on props, it seems the "10" on the end is the pitch, so both the 3 and 4 blade have the same pitch? The 3 blade is a slightly wider diameter, but 3 blades instead of 4, is that right?

I've read on this forum that the props for a pontoon boat seem ideal for the Mac; is that what I already have?

Use-case: Kept pretty light, usually no more than 4 people on board, for one and two day fishing and sightseeing. Not expecting much in the way of extended cruising with a lot of water and supplies, so speed is more useful than torque. Sounds like the current 3 blade is ideal, right?

[opie]

one more thought, if not already suggested: Are lower unit intakes open and clear? Remove the two intake plastic grates and clean them and look inside as much as possible and look for grass, crud or debris.

second idea: Do you have one of those infrared heat sensors like they use to measure your forehead temperature? If so (or use hand?) run engine in water with cover off and measure the right and left manifold temperature. It should measure between 79 and 85 degrees centigrade.
(175 to 185 f).

third idea: If impeller proves ok, then check to see if intake tube from upper engine has the little rubber gasket in place in the intake hole on water pump housing.

fourth idea:
There is a metal key that slides against impeller that could have been left out (or fell out during assembly) of the impeller by an inexperienced mechanic. This absence could allow impeller to pump at low speed but slip during high speed.

[dlandersson]

Pretty slick

second idea: Do you have one of those infrared heat sensors like they use to measure your forehead temperature? If so (or use hand?) run engine in water with cover off and measure the right and left manifold temperature. It should measure between 79 and 85 degrees centigrade.
(175 to 185 f).

[Tomfoolery]

one more thought, if not already suggested: Are lower unit intakes open and clear? Remove the two intake plastic grates and clean them and look inside as much as possible and look for grass, crud or debris.

And don't forget the third one, under the anti-ventilation plate, forward of the trim tab. Don't know about other brands, but the BF50 has that third one, which you have to tape over to use muffs when on the hard.

[Be Free]

You are not going to do much better than the prop you have on it. The speed estimate I gave you were for a 12x10 so you are definitely in the right ballpark.

+1 on Opie and Tomfoolery. It sounds like something is keeping you from getting all of the water you need at full throttle.

When your boat is in the water is the cavitation plate submerged? Is it still submerged when you are at full throttle? If the engine is mounted too high your intakes for the water pump may be above the water when you are moving faster.

[OverEasy]

Maybe with the boat on the trailer, you can take a photo with the engine down from the side and rear with a straight edge along the hull keel extending back to the engine.

My local engine service department mentioned that the cooling ports need to be well below the keel line to ensure proper cooling, especially at speed or on plane.

Obstructions such as transom mounted transducers ( depth, fish, etc...) can also have a negative impact on engine cooling water if the transducer is too close to the engine and causes cavitation which can starve the engine cooling inlets.

[Drifter]

Away from the house, PC or boat at the moment but seeing as the Honda BF50 was a standard fitting on the 26X I think it's unlikely this specimen was fitted too high.

The guy with the tractor was a bit of a... Yes, so it's possible with his ignoring the word "stop" and then our haste to get away from him once we could, that the engine wasn't 100% lowered.

However I'm very confident that it is some engine issue, rather than the tilt or even fitting, because the previous owner had reported (admitted) that the engine would overheat above 3500 rpm. He seemed to think it was because of the 4 blade prop he fitted.

At this stage I am somewhat optimistic that a new thermostat will let it cool properly.

I do intend to change the impeller but I must say it squirts with considerable force and volume. I really couldn't ask for more and it does seem it's sucking plenty of water in and pushing it with enough power.

My impression is either the thermostat is blocking the flow through the engine or something else is.

My big concern is that it might be heavily corroded inside the cooling channels, with no way of repairing that.

I guess while I'm waiting for the thermostat to arrive I could try taking the current one out and seeing if it works, and perhaps seeing inside at least some of the channel?

Right now I feel like walking away from the thing for a few weeks - but I also want to get on with it! Gah...