Overheat after high RPM run 350 MPI from 2001 with bravo one

[jkaetz]

Was out with the family today and ended up racing a storm back to the ramp. We spent about 9 minutes at either WOT or above 4k RPM. As we approached the ramp idle zone I noticed the temp was around 180 which is a little higher than the 160 I usually see but then I noticed it was climbing so I backed down a little to 3500 RPM and then came down to idle to approach the ramp. The temp then spiked up to 200 and the overtemp alarm came on but then the temp dropped quickly back to 160 and then up to 180 again over the next 30 seconds or so. The temp stayed at 180 for the idle to the ramp and the overtemp alarm silenced itself after a minute or two. Thoughts? Tests?

Engine Serial: 0M079526
Drive Serial: 0M115493

 

[kenny nunez]

Have you replaced the impeller in the sea water pump recently?
Worse case scenario could be a case of Bravoitis.

 

[jkaetz]

I have seen the seawater impeller/pump mentioned frequently. I can't say when it was replaced last. Would it just decide it had enough after an extended high load like that or cause the large temp fluctuations after we came back down to idle? I believe I have located the pump and can access it. How can I determine what parts are needed for our engine?

 

[Scott Danforth]

Would it just decide it had enough after an extended high load like that or cause the large temp fluctuations after we came back down to idle?

no, you have a flow issue

use your serial number to order parts on BAM or other marine parts houses.

BAM Marine - Mercury Marine & Mercruiser engines and parts, Cyborg transmissions > Our Stuff > Mercury & Mercruiser > Mercury & Mercruiser Parts

 

[cyclops222]

Junk covering most of the water inlet openings ? It did occur while at sea. Floating plastic stuff ?

 

[jkaetz]

Junk covering most of the water inlet openings ? It did occur while at sea. Floating plastic stuff ?

Local freshwater lake. Boat spends most of its time on the trailer. Not too much gunk in the lake.

 

[Bondo]

I have seen the seawater impeller/pump mentioned frequently. I can't say when it was replaced last. Would it just decide it had enough after an extended high load like that or cause the large temp fluctuations after we came back down to idle? I believe I have located the pump and can access it. How can I determine what parts are needed for our engine?

Ayuh,..... That's reason enough to start there,.....

 

[jkaetz]

Ayuh,..... That's reason enough to start there,.....

And so it shall be done. I see kits with just the impeller and others that include the housing. Given this one may be far too many years old should I go ahead and get the housing as well? Presumably I should stick with the OEM Mercruiser/Quicksliver parts or are the aftermarket parts capable when replaced regularly?

 

[Bondo]

And so it shall be done. I see kits with just the impeller and others that include the housing. Given this one may be far too many years old should I go ahead and get the housing as well? Presumably I should stick with the OEM Mercruiser/Quicksliver parts or are the aftermarket parts capable when replaced regularly?

Yes, 'n Yes,.....

 

[tpenfield]

It sounds like you have an open cooling system (i.e. raw water cooling). One thing that can happen with this type of system is that the water running through the engine can/will come to a boil if the engine gets too hot and cause the temperature fluctuations that you mentioned.

As mentioned, it sounds like a water flow issue ( not enough at high speeds) so it is a matter of finding out what/where is the cause. the impeller is always a good place to start, but you will also want to check the intake line for blockage, especially at the coolers along the way up to the thermostat housing. Then, there is the exhaust manifolds and risers to consider.

Is this ocean or lake?

 

[jkaetz]

It sounds like you have an open cooling system (i.e. raw water cooling). One thing that can happen with this type of system is that the water running through the engine can/will come to a boil if the engine gets too hot and cause the temperature fluctuations that you mentioned.

As mentioned, it sounds like a water flow issue ( not enough at high speeds) so it is a matter of finding out what/where is the cause. the impeller is always a good place to start, but you will also want to check the intake line for blockage, especially at the coolers along the way up to the thermostat housing. Then, there is the exhaust manifolds and risers to consider.

Is this ocean or lake?

Freshwater lake. It does spend most of its days on the trailer though. We actually hadn't been able to use it for a couple years prior to this summer. Has been out maybe a half dozen times this year with no issue. Haven't had the opportunity to run that hard for that long though. Going to throw in my IR thermometer next time we're out to verify temp readings after I get the raw water impeller and housing replaced. Might try to find a tote/tub that I can run it with here in the yard to test too. I have the muffs but know they can mask problems due to the hose pressure.

Any chance there are service manuals around for our engine? I have one from 2001 but not sure it's exactly the same as it shows a different raw water pump. I'd be interested to see how the water flows from the raw water pump. I can follow the hoses a little but like diagrams if I can find them.

 

[Bondo]

Might try to find a tote/tub that I can run it with here in the yard to test too. I have the muffs but know they can mask problems due to the hose pressure.

Ayuh,...... Don't do that,...... Anything less that an in-ground pool is to small to get the water over the hump, 'n down to the raw water pump,......
Especially with the Bravo drive,......
Use yer muffs,.......

 

[alldodge]

Any chance there are service manuals around for our engine? I have one from 2001 but not sure it's exactly the same as it shows a different raw water pump. I'd be interested to see how the water flows from the raw water pump. I can follow the hoses a little but like diagrams if I can find them.

Your manual should be number 24

 

[jkaetz]

Ayuh,...... Don't do that,...... Anything less that an in-ground pool is to small to get the water over the hump, 'n down to the raw water pump,......
Especially with the Bravo drive,......
Use yer muffs,.......

Good point. Brain failure. I'm thinking of things that have the impeller in the drive.

 

[Scott Danforth]

Good point. Brain failure. I'm thinking of things that have the impeller in the drive.

Even with impeller in drive, use the muffs

 

[cyclops222]

Using a LONG adjustable hose clamp to hold the mufflers in place is a good idea. Just be sure the clamp does not flatten the muffler over the holes.

 

[jkaetz]

Impeller and housing changed. Old impeller was definitely on its way out. Temp seems to be good at the thermostat housing. Having never had the IR gun I also checked the exhaust risers and saw that the starboard riser was up to ~177 after running and cooled down to ~150 at idle. The port side was considerably less and I've seen that a temp difference between the two is normal. What would an upper limit temp on the risers be? Water flow coming out the exhaust ports seems to be the same on both sides and I believe we've always seen more steam from the starboard exhaust.

 

[alldodge]

One side is always hotter then the other, just the way water flows the path of least resistance

 

[Stinnett21]

Exhaust shutters have dislodged and are blocking exhaust ways in drive. At lower speeds the relief ports are enough to handle it. At WOT they cannot. Check your exhaust shutters. Exact same thing happened to mine but I'm talking Alpha 2 so not sure the same.

 

[tank1949]

Might want to replace thermostat just to be sure.