Engine warms up-stalls out

[skiman53]

I have the 1995 Maristar 225 with the LT-1. Bought it brand new, have replaced the impellars every 2-three years religiously. Last fall, boat running well, no problem. Winterized it, checked the plugs, fogged the cylinders, changed oil, only Mobil 1 15W50 ever went in this puppy. Have over 715 hours on boat. Pulled the intake hose and put in bucket of water, sucks up and spits out with no problem.

The problem: Boat will go for 15-45 minutes at all speeds/rpms and then start to bog down and sounds/feels like fuel starvation. I have noticed the temperature gauge starts to climb and when it gets to 180 degrees or a little over, that's when I have the problems. I've researched the older threads about over heating, but this just warms up above normal and then the engine bogs down. I go to idle for a minute or two, than slowly increase speed, the temp drops to normal or below, and the LT-1 is alive and kicking again. When we board, at low RPMs 2,000 or less, it has no problems...only when I get over the 2,500-3,000 rpm range. I changed the fuel filter last fall when I winterized it and all other maintenance is up to par and current. I have not checked the thermostat. However, have never had a reason to, but not too sure where thermostat is, unless it is just in front of the impellar housing. This boat has been great. Never stranded me and never been a problem....until now.....I wouldn't want to trade it for a new one, I like to ski and kids like to board, it is perfect compromise for us both, with the flat bottom and the fatsacks and Rat Cage.

Any suggestions and help would be appreciated. Boat is kept 3.5 hours from dealer and dealer will have it for over two months, not good since we're in the middle of our season. Thanks for any thoughts..

Skiman53
'95 Maristar 225
LT-1
Rat Cage
fat sacks

[Britt]

have had same symptoms on many cars. WEAK COIL...Although if I recall your reverse coolant flow LT1 has individual coil packs..is this correct? Also, say you had a problem with vapor lock...The engine could start to bog and get hotter due to lean mixture then quit. Check these few things out.

Britt

[JimN]

First of all, depending on where you live, 2-3 years is too long for an impeller to stay in the motor. They lose stiffness very soon and don't push the water through as effectively as necessary. If you did overheat, the ECM went into RPM reduction mode and when this happens, shut it down immediately! There is no "limp home mode" on a boat. The only reason it doesn't quit due to the ECM shutting it down is that they don't want to put anyone in a dangerous situation due to engine problems. Better to kill the motor than the boat owners/passengers. Once it's in RPM rediction, you won't get more than 2000 RPM. If the motor cools down and this still seems to be the problem, the ECM may have a stored code that causes it to run this way.

Any time a motor starts to act like it's got a fuel problem, check the fuel pressure.

The first thing to do is check the motor out thoroughly for any damage. Clear out the oil cooler, make sure the impeller is indeed good and that the bleeder lines(thin rubber lines going from the heads to the exhaust manifolds) are clear. Check the exhaust tubes and flaps for damage.

There isn't much chance of vapor lock unless the vent is clogged and the pump is moving enough gas to create a negative pressure situation in the tank. There is, however, a check valve(anti-siphon) just after the fuel cut-off on the tank. Make sure this is open completely. Also, check the fuel pickup tube for any debris.

If the tank has run dry more than once, I would be surprised if the impeller isn't bad. The gas keeps the fuel pump impeller cool and in good condition.

The LTI has two thermostats- one is behind the water pump and the other is on top of the motor, in the triangular housing with two hoses going to the exhaust manifolds. Make sure you get the right ones. One is a normal 160 degree and the other is a 143 degree with bleeder holes. DO NOT just go to an auto parts store for the 143 degree unless they know what you need. If the water circulating pump was replaced and you went to a car parts store, you have the wrong one. Your LT-1 has reverse cooling and the water goes to the heads before the block. This will kill your heads($1500 each).

I'm not trying to be all doom and gloom, but you need to know these things about your LT-1.

[LakePirate]

SkiMan listen to JimN--he is the man.

[gtink]

JimN, I just got a new 160 and 140 from my dealer. the 160 has the bleeder holes, but the 140 does not.

I would like to confirm if both need bleeder holes, (I can drill a hole) :)

[Thrall]

You didn't say if your at the end of your 2-3 yr schedule on impeller replacement or not. If you are, I'd start there. Otherwise, make sure all the water passages/hoses, trans cooler are clear.
Fuel pressure would be the next step. Fuel pump may be going south.

[JimN]

Only one has the holes. Look at the original thermostats and see what the temperature is(stamped in the metal) to verify that your replacements are correct. I could swear the lower temp one is 143 degrees, but I would call MC and get their part # to compare.