3.0 overheating

[bohen]

Got a 1989 Citation 1900 CC cudy with a Merc 3.0. Boat is overheating only while up on plane. Boat runs perfect while sitting at dock even at full throttle. Once boat gets up on plane temps gradually rise. Have run boat for 5 minutes under heavy throttle and tems stay 140-160. Sonn as on plane temps rise. Help

 

[ktbarrentine]

Possible cavitation getting into the water pump/impeller while on plane (drive is higher out of water then). When was the last time impeller was changed? Could also have a leak at the water-pocket cover or elsewhere in the water circuit that is letting the exhaust gasses get into the water circuit. There are troubleshooting methods that involve hooking up a temporary clear hose/tube in the water supply to the engine from the drive and checking for air bubbles while in plane. Check the adults only sticky for more information, too.
Has this boat have a previous serious overheat condition? A melted water pocket cover can easily leak exhaust gasses into the water circuit at high RPM. Just a thought.

 

[bohen]

Did notice that the water supply line looks a little brittle. Impeller changed 3 yrs ago. Recently had heads checked new valves installed new head gasket complete tuneup ect. Weird that it runs perfect till on plane even at high RPM ful throttle

 

[Scott Danforth]

pull your lower and change your impeller

also, while at idle, or in neutral, you are not loading the motor, so it is not generating heat. so doing so does nothing but run your motor at high RPM's

 

[stonyloam]

Could be lots of things, but I'm with Scott, by far the most overheating problems are impeller related. Anyway kinda like chicken soup, couldn't hurt

 

[bohen]

Will replace impeller, also doesn't make sense that even at full throttle in water for 15 minutes it does not overheat. I understand that there is not as much load but still motor is running flat out with no movement in guage or overheating. Running motor =heat . thanks

 

[Bondo]

Will replace impeller, also doesn't make sense that even at full throttle in water for 15 minutes it does not overheat. I understand that there is not as much load but still motor is running flat out with no movement in guage or overheating. Running motor =heat . thanks

Ayuh,.... Welcome Aboard,.... Actually, it makes Perfect sense,....

No Work(Load),.... No Heat,............................................. .................................

Runnin' yer motor at Wot for 15 minutes at the dock, Tests absolutely Nothin',....
It mighta burnt a cup of fuel,..... with a Load, it'd burn a Gallon,........................................... .................................................. .......................................................................
Yer darn Lucky ya still got a Runnin' motor,.....
They tend to come Unglued screamin' along with No Load,...... Long before a motor runnin' Wot, With it's full load,....
Hi-idle at the dock, I run 1200, maybe 1500 rpms,.....

 

[bohen]

just ordered new impeller kit along with complete Bellows kit. Through process of elimination willl move on to Riser if problem not fixed. Still think that at 4000+ rpm for 15 minutes motor shoul overheat if riser was issue. leaning toward impeller or exhaust gasses

 

[H20Rat]

You ran the motor 15 minutes at WOT with no load, presumably bouncing off the rev limiter the entire time? Wow! I'm surprised you aren't worried about a new problem... Like why your engine blew up into a whole pile of pieces!

 

[dubs283]

all the advice for a new impeller is right on, i will add this

high rpm/on plane overheat is textbook lower base assy gasket failure

order a new water pump base assy and gasket along with the complete water pump kit

 

[bohen]

Impeller and water intake hose was the issue! fixed and running great

 

[stonyloam]

just ordered new impeller kit along with complete Bellows kit. Through process of elimination willl move on to Riser if problem not fixed. Still think that at 4000+ rpm for 15 minutes motor shoul overheat if riser was issue. leaning toward impeller or exhaust gasses

Easy, under no load the impeller was pumping enough water to cool the engine, under load it did not.