Engine Overheating problem

Okay, here's the story - 2001 Tige 23V. Put the boat in the water with the wife at the helm. While I was parking the truck, the wife was idling around and said she heard a squealing noise coming from the rear of the boat at which time she turned the motor off. When I got to the dock, she fired it back up and and idled over to pick me up - No noise. I took the wheel and before I even got out of the 'no wake' zone, the motor over heated.

My first guess is the impeller since I've heard your supposed to replace them every 2 years or so. The reported squealing is throwing me off though. After the motor cooled off I cranked it back up and checked the belts - everything looked OK. I pulled the hoses off both sides of the V-drive to check for trash, but it appears unobstructed. I pulled the hose off the hull intake and water was flowing through it quite well also.

I'm a pretty good backyard mechanic, but this is my first inboard. If it is the impeller, could someone tell me where to find it?

Any help would be appreciated.

ok i am pointing out the obvious, but have you looked at your owners manual?

the squeeling might have been the impellor seizing and the belt running over the seazed pulley, put your boat on a fake a lake and start it up and watch your pulleys also keep your eye on the temp!! e-mail me and i'll give you mu number and i'll walk you thru it all if you want

I agree - when my impeller went it initially seized up and made a very loud squeal. If the impeller broke into pieces then it's likely that it wouldn't still be seized and so the noise would go away but the engine would almost immediately overheat. Oh, and mine seized about 20 seconds after dropping it in the lake too.

Find the water inlet hose from the bottom of the boat. Follow it up to the impeller housing. You should be able to take out a few screws and look inside. Use a mirror if needed. It will be very obvious if your impeller disintegrated. If it did, you have other issues to contend with that I am sure the board can help you with. Check inside the housing first. It only takes a couple of minutes.

Tim - yes, I looked at my owners manual, but it doesn't have that kind of info.

Maverick - I did look at all the pulley's while the boat was running and all were turning.

Gary - I have traced the water inlet hose. It runs to the V-drive and then to what looks like a belt driven pump on the starboard side of the motor down low. The water inlet hose and another radiator hose are connected to the back. I guess this is the impeller?

Thanks for all the help guys.

mike, i guess mercruiser doesn't have as detailed of a manual as indmar.

Tim, I misunderstood you. I looked at my Tige owner's manual. I don't have a Mercruiser owner's manual, but I will have a service manual before the end of the week.

Mike,
sounds like a impeller. And yes, they are a annual maintanance item. Though most don't, me included.

Mike:

Yes, the pump that has the water inlet hose attached to it would be the one you need to change the impeller on.

There are different styles of pumps, so the directions can vary. On the boats I have had, the impeller could be changed with the pump in place, no need to remove the belt. On this arrangment, there is a cover held on with four screws. Remove the screws and the the impeller is accesible inside.

When you get the cover off you should be able to look inside and see the impeller. It should look as if it is a bit off center in the opening, such that on one side the vanes are nearly extended and on the other side they are squished down a bunch.

If the impeller has been destroyed, you may not see any vanes at all.

Either way, you need to reach in with a pair of needle nose and try to pull what's left of the impeller out. It should be on a keyed shaft, so it should pull out without too much difficulty. Sometimes, especially on really old units, the impeller gets frozen on the shaft and then it can be a bitch, but generally just a pull from the needle nose is enough.

If you get the impeller out and it still has al the vanes then it probably wasn't what was wrong. Replace it anyway.

If what you pull out is a chewed up, knobby looking rubber thingy then it was destroyed. Worse, all the missing vanes are somewhere in the engine. With luck, they will continue to pass through the system and go out with the exhaust. It is possible, however, that a chunck of rubber can lodge into some critical spot and cause problems.

When you install the new impeller it will help a bunch if you apply a little bit of grease to the vanes. You will need to twist the impeller as you push it onto the shaft to get the vanes to bend. Try to establish which direction the engine turns and twist it that direction as you push it on. If you twisted in on the wrong direction it isn't a big thing, a fresh impeller is flexible enough that it will fold over and lay the correct direction one you crank the engine.

On my old direct drive boat it was a ten minute job to replace the impeller, the only tools needed was a screw driver and a pair of needle nose pliers. The pump was right there in the middle of the boat, easy access.

I haven't tried it yet on my new V-drive boat. I am sure the pump is a lot harder to get to.....

Oh, there are three spares that I usually carry with me on my boat: impeller, fan belts, and fuel filter. Even if you aren't enough of a mechanic to change any of these yourself, having the spares along will enable some other mechanic to help you out.