Re: Tohatsu MD50 any questions
Oscar,
No, you don't need a lot of amps to start a TLDI... But, Yes, you do need at least an 840-amp-rated battery, 1000-amp preferred. It's not a how many amps are needed to spin the starter (at most, about 20 amps are needed for that). It's a matter of voltage drop while cranking. You want to maintain a solid 12v supply while cranking -- to preserve the integrity of, and get proper operation of, the ECU during cranking. The battery cables are about 6 gauge, and are intended to handle more than 50 amps with minimal voltage drop. The hefty battery is to minimize voltage drop during cranking. In the States, we can't even buy a decent group-24 marine starting battery that only has a puny 600-amp rating. Maybe a cheap garden tractor battery, but that doesn't belong on a boat. Just equip the boat with a good group-24 or group-27 starting battery, and you will have the rating you need. Run the isolated two-battery system that you mentioned you have been using, and you will minimize the possibility of accidentally draining the starting battery.
Regarding your car and a critically low battery... Yes, it can/will scramble a lot of data if the voltage drops too far... The car's TPS data, O2 sensor baseline data, and other critical things will need to be re-learned by the car's ECU. Even the non-critical memories in the clock and FM radio can be wiped out. The voltage drop will be exacerbated by cranking. Yes, it will probably restart once you get a good 12v supply, and so will the TLDI. That doesn't mean it's a good idea to operate that way all the time. The TLDI has two low-battery detection codes. One for generally low voltage, and another to indicate critically low voltage. And yes, it will still run even after those codes have been recorded.
Yes, TLDI motors are extremely reliable, and tolerant of brutal marine conditions. In general, they have comparable or better fuel economy -- with lower emissions -- than comparable 4-strokes, and they are as reliable as any, more so than many. Their torque curve begins very low in the RPM range, so they provide excellent hole-shot. Still, they are not intended to be hand cranked.
Hypothetically... If you truly needed a 3rd-world-reliable motor that would not require modern electrical technologies, the only option that comes to mind is an ancient "hot head" one-cylinder diesel. No battery, points, plugs, ECU, starter, nothing... Those motors are pre-heated with a blow torch, hand cranked to start, and will run on almost any fuel, even dirty bunker oil. They smoke like a chimney, have low hp output per displacement, get very poor fuel economy, and are very loud. If you were in a survival condition in a remote section of the Amazon, that might be an option. But for the rest of us... the TLDI is a much more practical choice, even though it needs a decent battery.
