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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 15919
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Mercruiser 350 mag engine overheating

Customer Question

mercruiser 350 mag engine overheating
Submitted: 9 months ago.
Category: Boat
Expert:  Jason replied 9 months ago.

Hi Ivan, my name is Jason.

Is this engine an inboard with a through hull pickup? Or is it a sterndrive using the sterndrive as a water pickup?

Customer: replied 9 months ago.
sterndrive
Expert:  Jason replied 9 months ago.

Does the engine run hot at all RPMS, or does it run cooler at a low rpm and hotter at a high rpm?

Customer: replied 9 months ago.
hoter at higher rpm. when guardian cuts in it limits to around 1200 rpm the the temperature drops
Expert:  Jason replied 9 months ago.

Got it. When was the last time the bellows, and more importantly, the water line that is in the outer transom replaced?

Customer: replied 9 months ago.
never but water flow looks ok when disconnect at cooler at rear of engine
Expert:  Jason replied 9 months ago.

Did you disconnect that when the engine is overheating and at high rpm, or did you disconnect it and check water flow just at idle and when the engine is cold?

Customer: replied 9 months ago.
at idle when engine cold. not safe checking when engine hot
Expert:  Jason replied 9 months ago.

Got it. You said the water line and bellows were never replaced. How old is this engine/boat?

Customer: replied 9 months ago.
think 8 years but less than 100 hours use
Customer: replied 9 months ago.
hi
Customer: replied 9 months ago.
are u there
Expert:  Jason replied 9 months ago.

Got it. All Bravo sterndrives have the same problem over time. That problem is the water line in the transom assembly eventually gets soft from the passage of time. The seawater pump has 2 sides to it, it has an inlet and an outlet. When you are running, the inlet side is always under a vacuum. The higher the engine RPM is, the higher the vacuum. When the water line gets old, it gets soft, and it eventually starts to suck itself flat at higher rpms, this causes a water restriction and causes the engine to starve for cooling water at higher engine RPM. In the shop we call this Bravoitis (similar to tonsillitis, except what you have is a sick bravo)

Customer: replied 9 months ago.
how is this problem rectified ?
Customer: replied 9 months ago.
big job ?
Expert:  Jason replied 9 months ago.

I am here, I am just trying to type you up a complete answer. I am not the fastest typer so I do apologize for any wait.

Click this link to pull up a new web page, this will help explain what is going on with your engine - http://www.amarket.com/BRAVOitis.htm

If you look at that page you can see what happens, the water line simply gets soft over time. Engine hours do not matter here, as rubber dry rots with the passage of time. Even if it was brand new and had zero hours on it, that water line would still become soft over time. On Mercruiser engines the bellows should be changed every 5 years, it is standard operating procedure to change that water line at the same time. What needs to happen on your boat is that water line needs to be changed. The best and most cost effective way to do this is to change the water line and bellows at the same time. Once it's done then you don't have to worry about it for another 5 years. This is a normal maintanence item, and part of normal wear and tear. Job wise, it's roughly 800 bucks total in parts and labor as long as there are no surprises. It's roughly 350 dollars in parts and the rest is labor. The job takes 5 to 6 hours to complete.

Expert:  Jason replied 9 months ago.

I don't know how you want to leave this but that is where you stand on your end and what needs to be done. I think that should do it but I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

Customer: replied 9 months ago.
i was told to replase that hose the engine and drive need to remove And further, the overheating caused one of the manifolds to have an extrenal crack. a mechanic told me this can possible be a head gasket
Customer: replied 9 months ago.
hey
Expert:  Jason replied 9 months ago.

No, a head gasket would not cause this problem.

Expert:  Jason replied 9 months ago.

The problem is going to be that water line. Did you have a chance to look at the link I sent you?

Expert:  Jason replied 9 months ago.

Did you have any further questions for me on the issue?

Customer: replied 9 months ago.
i saw it
Expert:  Jason replied 9 months ago.

Okay good. Did you have any further questions for me on the issue?

Customer: replied 9 months ago.
engine/drive has to be removed ? because the link looks like it had to be removed
Expert:  Jason replied 9 months ago.

The sterndrive has to be removed, but not the engine.

Expert:  Jason replied 9 months ago.

Also, to add to this, I know that you probably think that there is something "really wrong" with your engine. However, this problem is really just normal maintenance. This isn't something odd or out of the ordinary or some mystery. This is pretty normal, and a common complaint.

Customer: replied 9 months ago.
thanks
Expert:  Jason replied 9 months ago.

You are very welcome. The ratings box is located at the top of your screen, if you do not see it you might have to scroll up. If you still can not see it, or have a hard time when trying to select a rating for my help, please let me know and I will alert the moderators.

Thanks again and good luck!

Jason

Expert:  Jason replied 9 months ago.

Was there anything else?

Expert:  Jason replied 9 months ago.

It looks like you read my answer without replying back or putting through a rating for me. Please keep in mind the website did charge you to speak with me, but they will hold your money and not credit me for helping you out if no rating is put through. So far I have not been paid for any of the time I have spent with you. If you have a further question on the issue by all means please feel free to ask. If not, kindly select a rating for my service. If you have a problem with the ratings box or can not see it please let me know.

Thanks

Jason

Expert:  Jason replied 9 months ago.

Hi Ivan, Just checking in. No rating has been put through for me yet, did you still have questions on the issue? Jason

Expert:  Jason replied 8 months ago.

How did you end up making out?

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