Engine overheating at higher rpms

sreill

sreill

New Member
Jul 18, 2008
104
Long Island, NY
Boat Info
sundeck
Engines
496 mag
Took the boat out yesterday. Boat idles fine at 165. As i get up to cruising speed the temp slowly climbs up to 190 and the alarms start going on. When i slow back down to 5mph the temp slowly drops back down. Obviously there seems to be a water flow issue that isnt keeping up with the engine rpms. Last year i had the same issue and i had a mechanic replace the water pump and impeller. Boat has had about 100 hours since then. So far, I took the ends off of the heat exchanger and it was clear with no clogs. Any ideas? Can the impeller or pump have gone in a year?
 
impellars wear out , wear out quickly if you boat in water with high amounts of sand and grit or industrial waste like fly ash
 
UPDATE:
Went down to the boat today (Its in a wet slip)

I took apart the heat exchanger and cleaned it out. There was a very little bit of sea weed, but I thought "Hey..heres my problem" Took it out for a quick run and the smart craft alarm starting going off again. The temps didnt get too high, but the water pressure was low (4psi) As I revved the engine it went up to 5.5 but no higher. I am pretty sure it should be around 12psi at 25oo rpms.

So Im thinking maybe a clog in the system? I am trying to exhaust all of the easy options before getting into the bilge and taking off the pump assembly.
 
Update:
Changed the impeller yesterday (what a job) Old one looked fine. Didnt get a chance to give it a test run but I think that Im going to get the same results. Im going out today. Will post back.
 
I'm having the same trouble with mine (port engine only). Haven't started to troubleshoot yet but we have huge barnacle growth in the upper Narragansett bay...gonna have a diver check out the outdrives and intake.
 
My mechanic thinks it is the through transome hose collapsing. He tells me it is very common on the BIII outdrives. We are going to bypass that intake and put a sea trainer through the hull for my intake
 
Have you checked the thermostats? I had the same issue on one of my 5.0BrIII, would over heat at higher RPM's. Mechanic found it was not the impeller but a corroded thermostat sticking.
 
That pretty much leaves the exhaust manifolds or elbows where the raw water leaves the system. I'm taking into consideration that you removed any pieces of the old impellor that might be in the system as well.
 
The old impeller was in good condition. It was the hose between the bravo 3 and the pump. It was collapsed. Problem solved Thanks for the input guys
 
I just started with this problem today. Everything ran fine on the way out.. spent a few hours at our favorite spot behind Sandy Hook.

I took some time to dive under to check for growth and barnacles. My Bravo II was loaded. I cleaned it up and concentrated on the intake ports.

On the trip home I started experiencing high temps at higher RPMs, slowed down, temp went down.

Thinking I pushed barnacle debris in, thus clogging something or... thoughts? seems like strange timing

Tiki Foot
1998 270 DA
7.4 MPI
Monmouth Beach, NJ
 
Tiki, again, this same thing happened to me. I cleaned out the intake holes on my stern drive (found them clogged) and it didn't seem to help.
Maybe the barnacles grow up inside the intake space?
 
I just finished and think I've got it. Took off the hose the brings the water to the impeller. Water was coming in but VERY slow. pushed it to the stern and the pulled it up above the water line.

Proceeded to blow into the hose until my Son could see bubbling coming up under the swim platform. continued this for a while and the got hit with a blast of water in the face. As i was pulled the hose back into place I held my hand over the opening and felt a lot of debris coming out... mostly barnacle debris.

Ran the engine to temp and then went out and ran her with no problems. Keep your fingers crossed. :thumbsup:
 
Very interesting....so the damn barnacle debris was trapped between the intake holes and the impeller hose. Is there something that prevented the debris from getting into the impeller? Was it just stuck in the hose?
What a vexxing problem!!! I hate barnacles. I just watched the Deadliest Catch on Discovery Channel and they had to throw back hundreds of alaskan crabs simply because they had 2 or 3 barnacles on them...perfectly good but un-aesthetic looking and restaurants won't buy them!
 
haha I saw that one too.

I think the only was to prevent it is to run the boat as often as possible. I now think I have to pull the impeller and change, just in case some of those sharp SOB got in there...
 
You must log in or register to reply here.

Forum statistics

Threads
113,224
Messages
1,428,905
Members
61,116
Latest member
Gardnersf
Back
Top