I bet the issue is a combination of cold temperatures, low battery power, and bad glow plugs.
-Diesels don't like to start when the temperature is cold
-Diesels don't like to start when they don't spin fast enough
Here's some suggestions for you:
-charge the batteries
-make sure all batteries are paralleled when you try to start the engine (if you don't know about boats then this involves using the battery switch to use the house and engine batteries together to provide as much power as possible for starting)
-power up the glow plugs for at least 30 seconds before starting the engine.
If those don't work I would:
-use a hair drier or heat gun to warm up the engine and the air going into the engine. This assumes you have A/C power available. If not, or if that doesn't work
-Use a short spray of starting fluid
I had a Universal Diesel M25 in one of my boats. If the air temp was below 50 the engine would not start unless I gave it a shot of starting fluid. When the air temp was warm the boat started right up.
Many people will tell you not to use starting fluid, your engine will blow up, your hair will fall out, the boat will sink. I would not recommend using starting fluid on a regular basis, but to get a very cold engine running, one that hasn't run in a long time, would be a good thing. Way better than spinning the starter for a minute and pumping the engine full of unburned diesel fuel.
Oh - one more thing. Boat's don't have fan belts. Assuming your M18 is fresh water cooled then it has a belt to drive the water pump. This is an external pump that is used to pump seawater through a heat exchanger (HX). There is another water pump that is used to circulate coolant through the engine block. The HX is used to cool the engine coolant. Note that the engine coolant and seawater to NOT mix. There are tubes in the HX that the coolant flows through. The HX is full of seawater and that cools the engine coolant. The raw water pump suck up sea water and pumps it through the HX and then into the engine exhaust. If the raw water pump is not being driven by the engine then the engine will quickly overheat.
After doing some reading around the web it’s worth noting that the batts only had 11.5v each and although the starter spins it’s a little sluggish.
Other forums indicate this matters especially in colder weather.
Next weekend we’ll charge then batteries, check the injectors and glow plugs and perform a compression test.
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