Overheating 454 Mag Bravo Gen IV
 

Hey All - I'm hoping the collective intelligence of the readers can assist me. I have a 270 Sea Ray with a Single I/O upgraded from a Bravo 2 to a Bravo 3. It has a Mag Bravo Gen IV. The motor is Raw Water Cooled, 140 deg thermostat.

A few years ago I installed a freshly rebuilt Long Block. I replaced all hoses, belts and accessories on the engine. I rebuilt the raw water pump and upgraded to a Mallory electronic ignition. I ran the boat for 2 seasons with no issues. Last season, early on I noticed the water temp, which normally runs dead on 140 deg which I could watch creep up to 150 then drop to around 120 when the thermostat opens, creep up to 170 - 180 deg's., and never move. No matter if it was at Idle or WOT it stayed at the 170 - 180. I did my due dilligence and started with the easy stuff. Changed the thermostat, guage, sending unit, none of which affected the value. I then moved the the bigger stuff, and replaced the raw water pump. I changed from the sierra composite to a brand new Bronze housing pump. I also changed the circulating pump, inspected all the hoses, oil cooler, and back flushed the block. As a last resort, I changed the manifolds and risers ( I always wanted to upgrade to Aluminum and used this issue as an excuse). Unfortunately not one thing I did changed the now higher temperature. Using a non-contact temp guage the manifolds / risers are very cool the engine is around 165deg. and is close to the gage value. In my frustration I ended up shoring the boat for the season and found other ways to spend my time. Now that the new season is a few months away I have regained my motivation to re-look at the issue. Has anyone had any issues like this? Any thoughts on the next step? I would also like to note that I did a compression check and found 115-120 on all cylinders except 1 which read around 106-110. I'm wondering if a slight head gasket leak could cause this issue?

Any thoughts would be appreciated.

Eric

I just pulled apart the same motor/problem and found a cracked head. #4 combustion chamber from the intake valve to the sparkplug:ernaehrung004:

Pressure test the cooling system.

How did you diagnose the cracked head?

How do you suggest I pressure test the cooling system? I have done it on cars with radiator caps, but what about the bypass to the manifolds? Won't this just pass the pressure through?

Is there a pressure test kit I can buy?

Also - I attempted to leak test the cylinder with low compression but I couldn't hold the engine from turning? Any suggestions to lock the crank to keep it from turning?

Thanks for the suggestions so far!

Eric

the leakdown test will require a big wrench (in my work we have a 6' or 7' long prop to hold). in a boat use a breaker bar I would assume. I just ripped them apart and inspected.. saw it as soon as I looked
I wanna know about cams HE HE
be safe
Bobbo:ernaehrung004:

Pressure test isn't too hard but your right, you will need to close off the hoses going to the exhaust. You can loop the hoses back into the water neck to seal them off.
Disconnect hose at the cooler and make up a fitting for your radiator test pump/gauge.
Did you ever run without a T/stat for kicks? Another thing if your exhaust is cold could you be bypassing the block somewhat?

Remove the intake water hose that connects at the transom and check to see that the pipe going thrue the transom is open.

One would think; if you had a cracked head or bad head gasket, you would have water in the oil or on a spark plug.

One more thing to look at
 

and those that know me will say I mention this alot - but it's often overlooked and has been the case of trouble for numerous boats I've worked on over the past couple of years ...

Take the hose off at the transom that feeds the raw water pump and make sure you don't have a blockage at the transom end...

In many cases the corrosion around the hose will push in and eventually collapse the inner fitting that holds the hose in place. If you can't get your pinky inside - you have a problem. On some boats you can fix it with the engine in - but some there just isn't the room to do the work. I have a 382 Formula lined up right now that we're pulling both motors to fix the stbd which overheats and also knock out the port motor while we're in there.

The other option is to install a thru hull pickup..... if you find a blockage....

Good Luck

I saw neither, just high water temp

very common ...... DT270 .where do you boat?

Amen

Check the hose barb where the water comes through the transom assbly. It is held on with two bolts. Problem is that the barb covers the aluminum around the inlet hose and lets water come in contact with the aluminum and stays there. The corrosion pinches the water flow. There is a little plastic insert that holds the hose that comes from the drive securely in the transom assbly. The insert gets crunched and limits water flow.

pull the cooler, not just backflush,,,,, remove the end caps and check for debris.

Pull the block drain plugs and see if water flows or it got packed with sand/debris

OK I will admit I'm a newbe here but I have put a boat (and engine) or two together but you obviously have something here.. what comes first, a hot motor or a cracked head?? I will be ripping my seawater pickups apart. the BAJA has these angled assemblies bolted to the transom. one thing I did notice was a #$#k load of zebra muscles on my drives when I pulled it out (was in from jul to oct) but I looked at the inlets and they looked ok. most of the zebras looked small enough to pass thru the grate of the pickups..

you don't suppose?????:eek:

The shells have a hard time getting into the raw water system but the mussel eggs or babies or whatever will get into the system and grow. Time to pull the hose barb on the transom assembly.

I believe that restrictions in the suction side of the raw water pump are worse than restrictions on the discharge side of the water pump so check the inlet side very closely. Hell, you've changed everything else!!!

R/H exhaust manifold would not drain till I poked it w/stick but then pretty much flowed out fine?? funny #4 is on the R/H and there is where the crack is.

I now picture DR evil with pinky:ernaehrung004:

Thankyou for your knowlege. we're talkin babies here these shells would easily fit thru the grates. I will tear them apart and inspect.

are there any upgrade options here?

Bobbo:boat: