Logo
FULL SITE MENU

Mercruiser 454 IO Alpha One STILL overheating

N

newboaters

New member
"Please bear with me, I'm

"Please bear with me, I'm the clueless wife of a semi-marine-mechanics-educated man who's quickly losing his "cool" because the boat is "hot".
wink.gif


We have a 1987 Imperial 270SF, Mercruiser 454 I/O, Alpha One - Running it in fresh water/Great Lakes. Runs GREAT up to about 2400 rpms. Then the alarm goes off. We've had the thermostat & the water pump kit/impeller replaced and had hoses blown out. They dropped it back in for us and it ran just fine on Saturday. Yesterday (Sunday), we took her out and ran just fine...until about three miles of consistent 2400-2500 rpms and then the alarm went off again. Thinking it didn't happen the day before because we didn't have it at 2400 for as long. ?? Backed down, ran at idle for just a minute and it cools right back down. Took her back into the marina at 2200-2300 rpms all the way....no problems.

We have three different props given to us with the boat. Wondering if a prop could be the culprit?? He was thinking that maybe the prop that's currently on the vessel is working too hard, not pulling enough water in? It's not the original prop for the boat.

*also* - when we got back in our slip yesterday he noticed there was a lot of water being pumped out of the bilge and was not sure why or where it was coming from???

Everyone we've talked to is pretty convinced that it's a simple solution...they're just not exactly sure what it is. They're also pretty confident that it's not an "engine" problem because it's not overheating consistently....meaning that it doesn't happen when it hits 2400 rpms.....only after it's "had enough" at that speed. ???

Thanks for any input you may have."
 
"Kim, There is a waterpump ou

"Kim, There is a waterpump output test for the Alpha 1. You run the motor at a prescribed RPM for a certain amount of time and collect the water pumped by the outdrive in a bucket. The volume of the water needs to be a certain amount, or the pump is faulty. The particulars are in the service manual.

Other causes of overheating: Plugged exhause manifolds and risers. If you feel the manifolds and risers while the motor is running, the should both be the same temperature, and you should be able to hold your hand on them for a few seconds w/o burning it.

Engine running too lean: Spark plugs will have white or nearly white deposits, or will have a green tinge. This indicated a too lean mixture or some other overheat condition.

How about the engine water pump. Maybe is has debris in it, so it doesn't pump well."
 
Thanks...we've narrowed th

Thanks...we've narrowed the problem down to a faulty/broken sensor/sender in the thermostat. The mechanic is getting us the parts and husband is going to put a new one in at the mechanic's suggestion so not to have to charge us a fortune for a simple job. Any suggestions on where to find an exploded view of the thermostat set up so he knows which pieces fit where???

Thanks a million!
 
"Kim:

Right now, TODAY, go

"Kim:

Right now, TODAY, go out and buy a laser pointed temperature gage and see what's reallly happening down there. Sweep the entire engine, starting by putting the 'red dot' on the temperature sender unit itself, then the rest of the motor, followed by the exhaust manifolds and risers. Do this first at idle (fully warmed up), then during a high speed run. The answers you seek will be readily apparent: it's either overheating, or the gages/ alarm system is lying to you (which I suspect).

Jeff

PS: For under 40 bucks these temp guns are incredibly useful. The wife uses it to determine temp inside/ outside the cabin, how warm the water is for her shower, the cat, etc. Great fun!"
 
Back
Top