ok so i sold my old V-18 to my nephew, and now it's my problem anyway because he calls me. 2019 Targa V-18 Combo, Merc 150 FourStroke, about 410 hours, Lake of the Ozarks. sunday it started beeping steady at about 4,500 rpm, went into guardian mode and wouldn't rev past about 3,000. telltale on the side of the cowl is weak, more of a dribble than a stream. idle it and it quits beeping after a while.
i know he's never done the impeller. i also know he runs it in the back of coves in two feet of muddy water. where would you start?
start with the cheap stuff. take a zip tie or a piece of wire and run it up into the telltale outlet. mud daubers love that hole, and so does lake silt. if the stream comes back strong you've found at least part of it.
then read the fault. that 150 will tell you on the SmartCraft gauge what it's mad about, overheat, low oil pressure, water in fuel, they all sound alike from the helm. don't guess.
and at 410 hours and never done, the impeller's due anyway. on that motor the schedule is every 300 hours or three years, whichever comes first. muddy cove running wears them faster. the vanes take a set and stop pushing water at higher rpm, which is right what you're describing.
water in fuel alarm sounds the same from the driver's seat, so do what ray said and read the fault before you buy anything. the water separating fuel filter has a sensor in it, and ethanol plus a tank that sat half empty all spring will set it off. if that's what it says, change the filter and pull a sample from the bowl.
zip tie came out with a wad of mud on the end. stream's better at idle, still not great. got the nephew to go through the gauge with me and it logged an engine overheat on sunday, nothing about fuel. impeller it is. he's got it in at a shop in Osage Beach for the impeller and thermostat because neither of us wants to drop a gearcase in the driveway in this heat.
for those of us too cheap for the shop, how bad is the impeller job on that motor? i've done one on a 90 years ago. is the 150 the same idea or worse?
same idea, a little heavier. tilt it up, shift into neutral, mark where the trim tab sits, pull the bolts and drop the gearcase straight down so you don't bend the driveshaft or the shift shaft. pump housing is right there. the kit has the impeller, the plate and the gaskets. grease the driveshaft splines when it goes back together and make sure the shift works in all three positions before you put the boat in the water.
two hours the first time if nothing's seized. under a hundred in parts. Mercury's owner's manuals and the maintenance schedules are on mercurymarine.com, look up your serial and you'll get the right one.
closing the loop. shop had it two weeks because everybody on this lake wants their boat back for the 4th. 410 dollars with the thermostat. they showed us the old impeller, every vane bent over in the same direction and one cracked at the base. telltale's like a garden hose now.
he ran it at 5,800 wide open on a weekday morning, no horn, and took his kids tubing for four hours saturday. i told him he's doing the next one himself and i'll stand there with a beer.
