Overheating 350 MPI and B3 Moving Slow.

[fishmen111]

Been away for three years due to the wife being sick. I did search the other posts, but the answers varied a lot. 2003 SR 245 with 350 Mag MPI/B3 at 64 hours. Not properly put up, but at least I got the water out of it 2.5 years ago. Changed oil, lower unit fluid, checked plugs, pulled old gas and changed all three fuel filters. Much to my surprise after rotating it for 20 seconds (lanyard out) to build oil pressure, she fired right up and sounded great with perfect oil pressure. After ten minutes of very slow temp rise (on muffs, at idle), she jumped to 190, so I shut it down. Risers were cold, manifolds were hot, thermostat housing was warm and plenty of water was coming out of the starboard bypass on the gimbal. Raw water impeller was replaced right before I bought it and had zero hours on it. I know it should have an impeller every other year, just wondering if this sounds like the thermostat. If so, when I do replace the impeller, some folks remove the whole pump assembly and some just remove the rear casing. Which is easier as I am already hurting from getting my old butt in the compartment today. Also, the lower unit will move but very slowly and sounds like it is straining...gummed up pump valve? I appreciate any feedback to shorten the diagnosis.

Thanks a bunch!

 

[MarkSee]

Re: Overheating 350 MPI and B3 Moving Slow.

I'll join in on some of what you're wondering.

The temp issue could be the thermostat and some times it is recommended to verify the actual temperature with an IR gun at the sender unit so as to rule out the sender sending false readings and the engine really is getting that hot.
The risers staying cold is a good sign along with nice water flow out the idle relief ports.

On my Sea Ray, it is impossible to get to the back of the water pump housing in place to remove the hoses much less the housing.
I have to un-bolt the entire assembly including pulley from the block, pull it forward a little bit to remove the hoses then take the assembly out of the boat for replacing the impeller/housing.

Maybe you've already tried this on the lower unit but when my Maxum-alpha was doing similar, I put some grease on the exposed part of the rams, worked it up and down several times greasing it up and worked fine after that. Might see if that helps first.

Mark

 

[fishmen111]

Re: Overheating 350 MPI and B3 Moving Slow.

Thanks Mark. I hope to take a closer look this morning. I have several IR guns but it happened pretty quick (after 140) and I wanted to step back and re-evaluate with some advice. Had Alphas all my life and am just not familiar with the Bravo routing setup. I will pull the thermo in the morning and try again. I guess that will narrow it down a little. I will also try the ram lubrication as that could be an easy fix for the outdrive. I did read an update apparently from Mercruiser that you should not run Bravos on muffs at idle, only at 1300 rpms to prevent overheating. Have you heard of this? I was wondering how the heck I would get to the pump housing bolts in place though I have read several accounts where folks prefer that, so thanks for that info. I will pull the whole assembly (to match the two muscles I pulled yesterday doing the rest).

Thanks again,
Charles

 

[Fun Times]

Re: Overheating 350 MPI and B3 Moving Slow.

Thanks Mark. I did read an update apparently from Mercruiser that you should not run Bravos on muffs at idle, only at 1300 rpms to prevent overheating. Have you heard of this?

In this link below, Mark posted a mercruiser service bulletin explaining the correct running procedure that you may be interested in seeing if you haven't already.

I'd like to add that the running procedure i mentioned in the link could be at times a little more crucial on the bravo 3 drives vs some of the others in my experience.

Please bear in mind that the Bravo 3's do not have the low water pickups like some of the bravo 1's mentioned in this link.

http://forums.iboats.com/mercruiser...water-pump-running-muffs-question-597867.html

Hope you get things running correctly, Good luck.

 

[fishmen111]

Re: Overheating 350 MPI and B3 Moving Slow.

Thanks a bunch. That shows my lack of knowledge of the Bravos. I have never heard of such a thing and it was not in any of my manuals. I did at least "pre-fill" the block from the top vent/drain as I knew after that much time, the whole system was dry.

 

[fishmen111]

Re: Overheating 350 MPI and B3 Moving Slow.

OK...new observation. I ran it again two days ago and today as I have had stuck thermostats before that just needed a heat cycle after sitting to free up. I plan on getting into it this weekend, but both times I observed something different that i have not seen before. After 5-10 minutes of running, once again the gauge rapidly rises to 170-180 and then drops back to cold almost as fast and stays there as long as you leave it running. The cold temps before and after were verified with an IR gun @ about 85-90 degrees so I feel that rules out the sender. The warm temps were not verified as I was not about to leave the keyswitch unattended. I have never heard of a thermostat doing this, but i would think that would be the only possible answer for a cold running engine. Thoughts?
Thanks again!