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Mercuiser 7.4MPI running hot

dspracing

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98 Mercrusier 7.4 MPI
Bravo one, side water pickup

The issue began on our last trip out. The alarm buzzer would go off while getting on plane. After installing new gauges it turns out my water temp is hovering around 210.

Temp is OK at idle
Temp is OK at cruise speed
Starboard side exhaust riser warmer than port side but not overly hot, I can still rest my hand on it. Seems to me like this would point towards low flow?

Installed a new impeller assembly yesterday. The old impeller was on its way out but completely intact. The issue remained the same.

Hoses from the thermostat housing to the exhaust risers are clear/no restrictions.

Did my internet research but no clear path to a solution so I thought I would see what the brain trust had to say. Here is what I am suspecting could be the culprits. What do you all think I should throw parts at first?

Blockage between drive and impeller causing reduced flow
Bad/failing water circulating pump
Bad thermostat
 

Dalton

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Look at the first heat exchanger/cooler after the impeller, take the hose off the inlet, look/feel inside and make sure there’s not a bunch of old impeller pieces in there


Sent from my iPhone using Tapatalk
 

BDMar

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They are famous for building corrosion around the water supply hose where it goes into the gimbal housing. The hose is held in place with a plastic internal "nut" that will crush closed from the corrosion. You can see it by removing the water supply fitting inside the boat on the gimbal where the 1 1/4" hose connects.
 

dspracing

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They are famous for building corrosion around the water supply hose where it goes into the gimbal housing. The hose is held in place with a plastic internal "nut" that will crush closed from the corrosion. You can see it by removing the water supply fitting inside the boat on the gimbal where the 1 1/4" hose connects.

I think this is what I have seen people refer to as bravoitis? It will be tricky to get back there to check it internally, if the part needs to be replaced would this be accomplished from the inside or the outside of the boat? Trying to figure out if I would be better off to just go ahead and pull the drive to do the inspection.
 

BDMar

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You can't see if the sleeve is crushed from the outside. You'll have to remove some things to get to it to remove the fitting to get a good look. The corrosion will never go away even if you could get to it to clean it. To do it with any chance of lasting you would have to pull the engine. The best fix is to put a cover plate over it and either put a thru-hull pickup inside (my preference) or transom mounted pickup. Permanent fix.
 

Fun Times

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if you happen to have access to a digital inspection camera, it may help find any signs of bravoitis, rocks, seashells, etc. inside the the inlet water hose between the bell housing on up to the engine or back down depending on if you pull the drive or water pickup fitting inside the boat.

Also check the outside hose for cracks/cuts or kinks, etc..

Fresh or salt water use?
 

dspracing

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if you happen to have access to a digital inspection camera, it may help find any signs of bravoitis, rocks, seashells, etc. inside the the inlet water hose between the bell housing on up to the engine or back down depending on if you pull the drive or water pickup fitting inside the boat.

Also check the outside hose for cracks/cuts or kinks, etc..

Fresh or salt water use?

An inspection cam is a great idea! I'll give that a try first.

Freshwater boat, 350 original hours.

You can't see if the sleeve is crushed from the outside. You'll have to remove some things to get to it to remove the fitting to get a good look. The corrosion will never go away even if you could get to it to clean it. To do it with any chance of lasting you would have to pull the engine. The best fix is to put a cover plate over it and either put a thru-hull pickup inside (my preference) or transom mounted pickup. Permanent fix.

If the nut is crushed, does a block off plate require the motor to be pulled?

Any thoughts on the other two avenues? Thermostat or water circulating pump?
 

shunter2005

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If you are a tiny guy or know one, you can get back to it and take the plastic outlet piece off. I think it has two 7/16" bolts. Looks kinda like an old school Chevy t-stat housing. Probably a swivel socket with a long extension would make it a little easier. Take that outlet off and it will be clear if you have Bravoitis or not. Even if you don't have it bad, it will eventually get worse, fresh or salt (salt is just faster). It's probably worth it just to go ahead a replace it if you have the cover off. You can pull the drive and replace the hose. Merc finally fixed the replacement hose using a metal sleeve instead of plastic. There is also another company that makes one as well. Hardin Marine/CCPerformance sells them. Costs about $85 plus about $400 for the cuss jar to get it done.
 

shunter2005

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98 Mercrusier 7.4 MPI
Bravo one, side water pickup

The issue began on our last trip out. The alarm buzzer would go off while getting on plane. After installing new gauges it turns out my water temp is hovering around 210.

Temp is OK at idle
Temp is OK at cruise speed
Starboard side exhaust riser warmer than port side but not overly hot, I can still rest my hand on it. Seems to me like this would point towards low flow?

Installed a new impeller assembly yesterday. The old impeller was on its way out but completely intact. The issue remained the same.

Hoses from the thermostat housing to the exhaust risers are clear/no restrictions.

Did my internet research but no clear path to a solution so I thought I would see what the brain trust had to say. Here is what I am suspecting could be the culprits. What do you all think I should throw parts at first?

Blockage between drive and impeller causing reduced flow
Bad/failing water circulating pump
Bad thermostat
Have been thinking about this and have a couple of questions I would want to answer BEFORE I jacked with the transom inlet hose.
Sorry for the length, but one question leads to another, at least for me.
1. When is the temp at 210*?
All the time or just when getting on plane? Have you checked the temp with an infrared temp gun? Could the new gauge be off or even bad? Has t-stat ever been changed? If so, what degree t-stat was installed?
2. How is the water flow out of the exhaust?
I would suspect flow to be ok if the manifolds/risers are cool enough to hold you hand on, but you might take a look anyway. Check the flow with your hand to see how hot the water on each side is. Starboard exhaust should be a little warmer to touch than port.
3. Did you check the inlet side of the oil cooler for debris?
Could be rocks, etc and even old impeller pieces. Pull hoses from each end and shine light from the bottom. Clear any restrictive junk on the inlet side and then run a straight piece of coat hangar wire down the capillaries to make sure they are not plugged.
4. Starboard manifold/riser will always be warmer than port side.
20*-30* difference is pretty normal. Mine runs around 90* port side and 110*-120* starboard side.
5. T-stat is easy enough to check.
6. Circulating pumps aren't typically bad, but if you can somehow look under and check the weep hole for leakage. If it's weeping, I would change it out. Mine was weeping a little last year. I decided to replace it. Peace of mind for me. Also, with the belt off, check the pulley for any play. If there is any play at all, I would change it.

If all that checks out ok and the problem still exists, then I would consider checking for the dreaded "Bravoitis" and replacing the transom inlet water hose. Oh, and let us know if you can get a camera in to check out the inlet hose. I had no luck at all trying to use mine, but I tried to go thru the hose from the sea pump end to the transom. I did not take the hose off at the transom.

Again, sorry for the length, but I am curious as to what you find to solve the issue.
 

dspracing

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Have been thinking about this and have a couple of questions I would want to answer BEFORE I jacked with the transom inlet hose.
Sorry for the length, but one question leads to another, at least for me.
1. When is the temp at 210*?
All the time or just when getting on plane? Have you checked the temp with an infrared temp gun? Could the new gauge be off or even bad? Has t-stat ever been changed? If so, what degree t-stat was installed?
- Once it warms up the temp pretty much stays there, plus or minus 5 degrees I would say. Idle, cruise or otherwise. Have not checked the temp in any other way. based on the way the paint looks on the bolt heads, I would say the thermostat has never been changed
2. How is the water flow out of the exhaust?
I would suspect flow to be ok if the manifolds/risers are cool enough to hold you hand on, but you might take a look anyway. Check the flow with your hand to see how hot the water on each side is. Starboard exhaust should be a little warmer to touch than port.
- My exhaust is through transom but below the water line. I could try dipping the boat deep enough to check this on the trailer or perhaps check when its on the hose?
3. Did you check the inlet side of the oil cooler for debris?
Could be rocks, etc and even old impeller pieces. Pull hoses from each end and shine light from the bottom. Clear any restrictive junk on the inlet side and then run a straight piece of coat hangar wire down the capillaries to make sure they are not plugged.
- I haven't yet but certainly plan to tonight.
4. Starboard manifold/riser will always be warmer than port side.
20*-30* difference is pretty normal. Mine runs around 90* port side and 110*-120* starboard side.

5. T-stat is easy enough to check.
6. Circulating pumps aren't typically bad, but if you can somehow look under and check the weep hole for leakage. If it's weeping, I would change it out. Mine was weeping a little last year. I decided to replace it. Peace of mind for me. Also, with the belt off, check the pulley for any play. If there is any play at all, I would change it.
- No weeps at all.

If all that checks out ok and the problem still exists, then I would consider checking for the dreaded "Bravoitis" and replacing the transom inlet water hose. Oh, and let us know if you can get a camera in to check out the inlet hose. I had no luck at all trying to use mine, but I tried to go thru the hose from the sea pump end to the transom. I did not take the hose off at the transom.

- The more I research bravoitis the more I start to doubt. I see photos of these nasty transom assemblies with leaks, dirt and salt everywhere. This is a damn clean boat inside and out, I just can't imagine that there could be that level of corrosion anywhere. And if my boat could get it, damn near every boat of its age would have to have it as well.

As of now my plan will be -
inspection cam through inlet water hose to check for bravoitis
check/replace thermostat
check oil cooler for debris
check circ pump pulley for play
If no smoking guns found -
run the boat check water flow through exhaust, scan for temps throughout
pull drive and check for debris

Thoughts?

Again, sorry for the length, but I am curious as to what you find to solve the issue.
 

shunter2005

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Have been thinking about this and have a couple of questions I would want to answer BEFORE I jacked with the transom inlet hose.
Sorry for the length, but one question leads to another, at least for me.
1. When is the temp at 210*?
All the time or just when getting on plane? Have you checked the temp with an infrared temp gun? Could the new gauge be off or even bad? Has t-stat ever been changed? If so, what degree t-stat was installed?
- Once it warms up the temp pretty much stays there, plus or minus 5 degrees I would say. Idle, cruise or otherwise. Have not checked the temp in any other way. based on the way the paint looks on the bolt heads, I would say the thermostat has never been changed
2. How is the water flow out of the exhaust?
I would suspect flow to be ok if the manifolds/risers are cool enough to hold you hand on, but you might take a look anyway. Check the flow with your hand to see how hot the water on each side is. Starboard exhaust should be a little warmer to touch than port.
- My exhaust is through transom but below the water line. I could try dipping the boat deep enough to check this on the trailer or perhaps check when its on the hose?
3. Did you check the inlet side of the oil cooler for debris?
Could be rocks, etc and even old impeller pieces. Pull hoses from each end and shine light from the bottom. Clear any restrictive junk on the inlet side and then run a straight piece of coat hangar wire down the capillaries to make sure they are not plugged.
- I haven't yet but certainly plan to tonight.
4. Starboard manifold/riser will always be warmer than port side.
20*-30* difference is pretty normal. Mine runs around 90* port side and 110*-120* starboard side.

5. T-stat is easy enough to check.
6. Circulating pumps aren't typically bad, but if you can somehow look under and check the weep hole for leakage. If it's weeping, I would change it out. Mine was weeping a little last year. I decided to replace it. Peace of mind for me. Also, with the belt off, check the pulley for any play. If there is any play at all, I would change it.
- No weeps at all.

If all that checks out ok and the problem still exists, then I would consider checking for the dreaded "Bravoitis" and replacing the transom inlet water hose. Oh, and let us know if you can get a camera in to check out the inlet hose. I had no luck at all trying to use mine, but I tried to go thru the hose from the sea pump end to the transom. I did not take the hose off at the transom.

- The more I research bravoitis the more I start to doubt. I see photos of these nasty transom assemblies with leaks, dirt and salt everywhere. This is a damn clean boat inside and out, I just can't imagine that there could be that level of corrosion anywhere. And if my boat could get it, damn near every boat of its age would have to have it as well.

As of now my plan will be -
inspection cam through inlet water hose to check for bravoitis
check/replace thermostat
check oil cooler for debris
check circ pump pulley for play
If no smoking guns found -
run the boat check water flow through exhaust, scan for temps throughout
pull drive and check for debris

Thoughts?
1. I am certainly no expert, but I would think, unless that t-stat is stuck partially closed, there could be an issue with the gauge or maybe even the sending unit. Just my way of thinking it through. What was usual running the temp with the old gauge? If you still have it and it was working when you changed it, why not put it back in and run the boat up to temp. If the water is really that hot, the alarm should go off at around 190* or close to that I don't think you wouldn't be able to touch the risers, much less put your hand on them for a bit. But, a t-stat is pretty cheap and easy to change as is a sending unit.
2. Check it on hose at idle. I check mine that way all the time, just to see and feel the flow.
3. Oil cooler is my #1 go to for high engine temp or flow issues. That is where I find all of the debris that inhibits water flow. You can check the other coolers also, by back flushing from the oil cooler to the sea pump.

Bravoitis is non-discriminating. It screws up nice boats just like crappy boats. Taken care of boat, with 350 hrs in fresh water, I wouldn't be too worried about that yet, but that's just me. Again, that would be my last check. I would start at the front with the easiest and progress through the system till everything else was eliminated before messing with the huge PITA transom inlet hose.
 

dspracing

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1. I am certainly no expert, but I would think, unless that t-stat is stuck partially closed, there could be an issue with the gauge or maybe even the sending unit. Just my way of thinking it through. What was usual running the temp with the old gauge? If you still have it and it was working when you changed it, why not put it back in and run the boat up to temp. If the water is really that hot, the alarm should go off at around 190* or close to that I don't think you wouldn't be able to touch the risers, much less put your hand on them for a bit. But, a t-stat is pretty cheap and easy to change as is a sending unit.
2. Check it on hose at idle. I check mine that way all the time, just to see and feel the flow.
3. Oil cooler is my #1 go to for high engine temp or flow issues. That is where I find all of the debris that inhibits water flow. You can check the other coolers also, by back flushing from the oil cooler to the sea pump.

Bravoitis is non-discriminating. It screws up nice boats just like crappy boats. Taken care of boat, with 350 hrs in fresh water, I wouldn't be too worried about that yet, but that's just me. Again, that would be my last check. I would start at the front with the easiest and progress through the system till everything else was eliminated before messing with the huge PITA transom inlet hose.

Pulled thermostat and tested in boiling water. Open and closed properly. Don’t have the old gauge. The fact the gauge reads high and the buzzer alarm goes off I’m pretty confident that the temp is in fact an issue.

oil cooler is free and clear of debris. Pulled upper and lower hose, nothing there. Backflushed through inlet hose, seemed to run fine.

circ pump has no play. I don’t know how it’s supposed to feel but it seems to spin pretty damn freely.

ran the cam up the intake hose. No bravoitis!

going to prestige in the morning, I’ll try to get two new senders and a new thermostat. Button it back up and run it on the hose.

thanks for the help!
 
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mattyc

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Did you put the thermostat in the pot then bring to a boil? Or put it in after the water was boiling?

Could the buzzer be an alert for something else? Does it sound constantly once that temperature is reached?

An infrared thermometer is very helpful for looking at temperatures of various locations
 

dspracing

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Free and clear of bravoitis though!

IMG_4440.jpeg
 

MK1MOD0

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Damn. That’s a lot of extra work. But at least ya know your cooling system is GTG for the summer. Party on!
 

Todd Mohr

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What about the gauge reading the wrong temp? Did you swap the sender? I purchased a boat 2 months ago (350 Mag) the temp gauge was reading 210, we put a heat gun on it and it showed 160. Swapped the sender, it had some plumbers tape on it. Put the new sender in with no tape and it now reads correctly.
 

dspracing

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What about the gauge reading the wrong temp? Did you swap the sender? I purchased a boat 2 months ago (350 Mag) the temp gauge was reading 210, we put a heat gun on it and it showed 160. Swapped the sender, it had some plumbers tape on it. Put the new sender in with no tape and it now reads correctly.
I've got a new sender on order, that should solve the temp reading issue.
 

shunter2005

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Right? I know my entire cooling system is 100% GTG!
Well, I did mention the gauge and the sending unit among a multitude of other things, so I was partially in the game. LOL..
Hope that gets it done for you.
 
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