I have a 1998 mercruiser 5.7 v8 250 hp, I had the exhaust manifold,riser and outdrive impeller changed this spring. The boat ran fine for last month, I was out yesterday running for about 15 mins at 3800 rpm and the engine temp alarm went on, the temp >180's. I immediately shut down the engine and opened the engine hatch and felt the risers, the starboard riser was hot to touch and port was warm. After a while started back up and headed for the dock, keeping rpm's below 3500 and the engine temp at 170. After I got back I felt the risers again and the starboard was hot and the port was warm. I didn't notice anything blocking water intake on the outdrive. Any suggestions??
hot riser
- Thread starter JJO
- Start date
Asureyez
New Member
- Apr 22, 2007
- 1,535
- Boat Info
- Sea Ray 460 Sundancer Hardtop 2001 - SOLD
- Engines
- Cummins 450 Diesels
Check that raw water strainer and impeller ...
New or not impellers can go in a heart beat. You could have sucked up a fish in the strainer or plastic bag but the trouble is too little water .
New or not impellers can go in a heart beat. You could have sucked up a fish in the strainer or plastic bag but the trouble is too little water .
PlayDate
Well-Known Member
JJO,
As you can tell by some of the other threads, this is a common issue which can be caused by a number of things. What would really help is if you can get your hands on an Infared Temp gun. They can be had for about $70 and make the job of finding heat related issues quickly.
Taking temp readings on the exhaust manifolds, elbows and the tstat housing with the engine hot will tell if there is a blockage issue. Posting the results will make it alot easier to figure out. Generally, a blockage at the impeller heats the whole engine up. So, it could be a couple of things. Can you also post how many hours are on the engine and if it is raw water cooled.
-John
As you can tell by some of the other threads, this is a common issue which can be caused by a number of things. What would really help is if you can get your hands on an Infared Temp gun. They can be had for about $70 and make the job of finding heat related issues quickly.
Taking temp readings on the exhaust manifolds, elbows and the tstat housing with the engine hot will tell if there is a blockage issue. Posting the results will make it alot easier to figure out. Generally, a blockage at the impeller heats the whole engine up. So, it could be a couple of things. Can you also post how many hours are on the engine and if it is raw water cooled.
-John
The boat is RWC and in now overheating at anything over 2000 rpm, the starboard riser is still hotter then port. I pull off the hose to the thermostat housing on the port side and at idle speed it has a good flow of water, but when i throttle up the flow goes to a trickle, does this sound like the outdrive impeller?? I had it replaced in april, the boat sits in saltwater slip, I did run aground once could i have sucked up sand and slowly destroyed it?
PlayDate
Well-Known Member
JJO said:
Definitely, sounds like there is an issue with water pressure falling with rpms increasing. Usually, that is a sign that the impeller is failing or has failed causing it to cavitate with higher rpms. I wish I had better news....that is a pain to deal with.
-John
