V8 overheating problem ( 5.7 mercruiser)

B

bassarama

Junior Member
Hey gang

Yeah yeah I know.... it's an I/O ::)

Anyways, I took this boat for a test drive and 1/4 of a mile odwn to the river the darn motor overheated...

The owner( geez THAT never happened before) :D

Me: Riiiiiight!!! uuuuhh uh :o.


At any rate, The guy says the problem is a raw water pump.

Optimistically, I say it's blown head gasket/s. Now in case I'm right do you think that the overheating may have cause severe damage to the heads/ block ?

Thanks for any advise.


Joe
 
How hot did it get? I would suspect the raw water pump as well, but if it got really hot, then yeah, the heads could be trash. There is also the water pump on the front of the engine to consider as well. What makes you think head gasket (just curious, not argumentative)?
 
a raw water pump is probably what is wrong, they are notorious for going out. a simple compresion check will tell you if the head gaskets are shot( it may not indicate if they are cracked however). An easy way to check the water pump is to pull the hose off the thermostat housing that comes from the power steering cooler, look in there to see if you see any pieces of impeller, hook a flusher up and crank the engine up with the hose off, you should get a nice steady stream of water, about what you would get if you cut the end off a garden hose and turned the spigot on. Another thing to check is the exhaust risers and manifolds, not a real good way to check them other than looking at the condition, and questioning the age, if the boat is in salt and the engine has been flushed regularly, expect 5 to 7 seasons if you're lucky, if the engine hasn't been flushed regularly, figure 3 to 4 seasons at best. The manifolds will stop up, not allowing the hot water to exit the engine, you may notice a burnt rubber smell associated with either of these problems, its the exhaust hose burning up due to lask of water mixing with it. A bad circulation pump can cause the engine to heat but usually the bearing will go out, allowing the main pulley to wobble noticably( i have seen the circulation pump impeller rust off inside the block,its rare but can happen).  Stuck thermostats can cause overheating as well. If the alarm went off, they are usually set at 215( what good is an alarm that tells you its too hot too late?), most new cars run that temp everyday, so you may be ok on the engine

Check the water pump first, then inquire to the age of the manifolds( they can be expensive)
 
Re: V8 overheating problem ( 5.7 mercruiser)pumpen

Did I say I hate I/O yet??

On mine first the Out drive pump went, then the water pump on the engine, then the Manifold let go. O yea then the exhaust bellows

If fresh water cooled the the exchange boxes might have rotted threw mixing salt with antifreeze.

O yea the list goes on!! and nothing is cheap either!!
 
Thanks guys

I consulted a couple of marine mechanics and they told me it could be the head gaskets.

The motor is 9 years old so I assume the risers and manifolds are shot, again my worst fear is the induced heat on the motor causing internal damage like on the heads etc. etc.

I really don't know how hot it got but I saw the temp. Gauge maxed out.

Funny thing was, even overheating this frigging motor revved up quite well, the motor responded to the throttle when trailing on the boat.

Thanks
 
Re: V8 overheating problem ( 5.7 mercruiser)pumpen

macojoe said:
Did I say I hate I/O yet??

!!
Click to expand...


i have to say this agian

whats wrong with i/os

i think that a muscle boat cant be a true muscle boat enless it an i/o
 
no my has a fresh water holding tank i have to fill if it get low.
 
This particular set up has a through hull intake leading to water pump and then heat exchanger, the outdrive pump cools off the outdrive only…I think ???
 
if it closed cooling, that opens up more posibilities and options, first, if the manifolds are included in the closed cooling( full cooled system vs half cooled), your maniolds are probably OK. If it uses the belt driven water pump, just take the end cap off the heat exchanger or pull the raw water hoes off the exchanger, you should see pieces of impeller in there, if you replace the impeller, use the late style impeller kit that uses a one piece housing, it pumps more water and is easier to install. Verify that the raw water is pumping to the heat exchanger, you may still have a problem with the risers, you'll get that burning rubber smell. While you have the end cap off the exchanger, take the one off the other end and shine a lighht thru the tubes, if you see any blockage, blast some water thru there, or use a rifle cleaning rod to clean the passages. Once you get water going to it, let the engine run with the radiator cap off the heat exchanger,if you have a blown head gasket, you should get a lot of air bubbles in the exchanger, check the oil and see if it has gotten milky( an indication of water leaking past the head gasket). If it checks out, you may want to keep going with this boat, not many engines in boats this size come with cloosed cooling, it is an expensive option when new, and really extends the life of the engine and manifolds( if included in the system) form corrosion. Those motors are pretty tough, if a 5.7 blew its headgasket everytime it ran hot, i would'nt have to work on anything else but putting heads on these motors for a living.

PS, have the thing checked out by a mechanic that is familure with Mercruisers, there is still a lot of other things you could get burned on with an boat engine( I/O or OB)
 
Thanks to all

First, let's see if we agree on the price, if I buy the boat I'll get back to troubleshooting with you guys. Thanks again :)
 
Hey Bassarama, I had a 5.0L Volvo, One time I was about 15 miles south of the inlet and 3 miles out. I had some old a s s manifolds and risers on my boat and that particular day the port side manifold decided to quit flowing water, I ideled it in the whole way. No damage to the engine. Another time I'm about in the middle of the chesapeake bay, 7 or 8 miles out of lynnhaven inlet and my raw water pump came apart, barley pumped any water. Again it got hot, but I idled in again and didn't popa head gasket. If that was the first time it got hot I wouldn't worry about it too much. You really have to scorch one to burn one up. And usually there are other symptoms. If you lose a headgasket you usually will find signs of coolant in the cylinders, just pull a couple of plugs and look for really clean plugs. With the plogs out, turn over the motor and see if it pumps water out of the cylinders. If none comes out, you have a good chance of no problem with the head gaskets. Those motors are pretty rugged, although the manifokds and risers take a beating.
 
Well I'm still waiting for the owner's decision, I made an offer assuming I was gonna spend 1000 bucks for parts.

My hope's were not to high on this boat anyways, so I'm gonna keep on looking... Thanks for all the help guys, I really appreciate it.

Joe
 
I've never had an i/o, and in this forum I have read all the pro's and cons. One of the major downsides of the i/o, IMO, is the space it takes away. Me, personally, I'd stay w/an outboard. Plenty of v20's out there...keep looking ;)
 
Might be the circulating pump as well.  I had a boat once with a brand new raw water pump and the circulating pump went bad.  The raw water pump didn't have enough "umph" to keep the engine cool and it overheated.  Speaking of exhaust bellows, its always fun when you're out with your wife and the darn thing catches fire.  Now (after putting the fire out) in order to get home your engine exhaust fills your bilge with water and you're praying the bilge pump can keep up! :-/ Isn't boating fun?!!!!!!!!!!!!!! 8) 8) 8)
 
With the 350 Chevy, head gasket problems are rare.  The motor is very good at holding on to head gaskets.  Even if the motor is fresh water cooled, a bad raw water pump will still cause overheating.  The raw water pump on a fresh water cooled engine is like the cooling fan in your car.  If that goes, you have no cooling water through the heat exchanger and your engine overheats.  The heat exchanger itself may also be plugged.  These are usually easily serviced.  After leaving the heat exchanger, the raw water is dumped overboard through the exhaust manifolds.  If these are plugged, there will be no water flow and the engine will overheat. Circulating pump problems are also very rare.  There just isn't much to go wrong inside of that pump.  
 
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