View Full Version : 496 MAG HO temp issues at 1000 RPM

06-28-2010, 04:48 PM
Hey guys!

Iīm running a couple of 496 MAG HO in my Cobalt.
For some reason when I run them at 1000 RPM they seem to want to run at 185 degrease and thatīs exactly on the "high temp" marker and the alarm goes off. As soon as I get up to 1500 RPM or WOT they run great.

Could this be due to the ambient temperature (100) or the water temp (86) being really warm down here in Florida?

Usually I spend the summers in Sweden so I have not been running in real Florida heat.


06-28-2010, 05:25 PM
Where in Florida?

That sounds like the right temperature. I have two 496s and I think they run 180 degrees......either 160 or 180

06-28-2010, 06:44 PM
Hey Rich!

In Tampa / St. Pete.
This is Rickard with the yellow Donzi 33 you have been talking to on the phone.

This issue is how ever on my Cobalt....

I have never had an issue before at that RPM they usually run at 160.
I think this might be due to the ambient temperature is really high and there is nothing to worry about.
I changed the impellers about 10 hours ago and the engines are running great at higher rpm.

There are a lot of guys on this forum that knows a lot more than I do about these engines so I figured I post it here.

What temp are yours 496:es running at when 1000 RPM?


06-28-2010, 07:11 PM
Are you running in salt water..AND.. Do you have Closed Cooling.?. If you are RAW water cooled running in Salt water..180 temp is too high. Should be 140-160. If you flush after each run in salt..somewhat better. If you are Closed Cooling in Salt ..OR Fresh water there is no problen running at 180.

06-28-2010, 09:57 PM
Check the hose between the drive and the transom shield, if it has develop a leak it will do exactly what you are describing. Sitting in the water it will pump just fine but as you accelerate the boat clears the water away from the transom assy air will get sucked into the system. At higher speeds the drive develops enough pressure to overcome the leak keeping the air out.