Mercruiser - Chevy 350 overheating - Badly need help!
Nancy P
the detail of what we've done to solve this problem.
Have a 1977 20' SeaRay with Mercruiser 228 (actually 260 with this
engine) I/O Chevy 350 engine. (repowered 2 years ago) Sea water cooled
engine.
Back in June, I had the lower seal in the outdrive resealed up because
of
water in the oil. As soon as I got it back from the shop, the boat
began
heating up and has since that time.
Took it back to the shop, and they said that there was a burr on the
drive shaft of the outdrive that had been missed, and it fried the water
pump. So, they fixed the burr, replaced the water pump, (at their
expense) and sent the boat back to me, saying that the drive shaft was
worn, but useable. It continued to overheat, so back to the shop it
went.
Next they said that one of the exhaust manifolds was cracked, (which you
could see the crack with water leaking from it), so we replaced the
manifolds, and checked out the risers at the same time. The risers were
only 2 years old, and still in good condition, so put it back together.
No rust or water noted around the exhaust ports on the block, so there
was no crack on the critical areas of the manifolds. There was a lot of
loose scaling noted inside of the end caps of the manifolds though,
especially the one that was cracked.
Again, put the boat in only to have it overheat once again, so back to
the shop it went. This time, they pulled and replaced the thermostat
housing. Apparently someone in the boats past had put marine tek on the
bottom side of the housing to seal up a leak. They're saying that there
was a lot of growth inside of there, and that it was plugged. So, they
put another housing on, with a new thermostat, figuring that would take
care of the problem. It didn't.
Engine still overheated. This last time I took it back, they removed
the
outdrive, and checked it over again. Checked the water pump, it is ok,
checked the lower housing, it was ok. They back flushed through the
engine, without a problem. Water put in the thermostat housing drains
through the block without a problem. No scaling noted inside of the
block water jacket. They put it all back together, and it still
overheated.
Yesterday, (thursday), they replaced the engine water pump, figuring
that
possibly the impeller was slipping on the shaft (which it was actually
according to the mechanic). Back into the water this morning, it's
still
overheating. It takes a few minutes to heat up, and does so only at
higher running. At low speed (5-8mph), it cooled back down to make it
back to dock.
NOW, the shop is saying that the problem is the drive shaft in the
outdrive that is bad, and keeping the water pump from pumping enough
volume to keep the engine cool. They're suggesting placing a raw-water
pump with a through-hull fitting on the front of the engine, and
basically bypassing the outdrives water pump completely (as far as
engine
cooling goes), saying this would be less expensive than a new drive
shaft, and prevent this problem from re-occuring in the future.
We know the sending unit is accurate since they placed a digital meter
on
the engine to get accurate running temps. It only heats up when the
boat
is in the water and under way. Sitting on the trailer, even in the
water
in gear, it won't overheat.
I'm looking for suggestions, or new ideas here. Has anyone here ran
into
anything like this before, or had to make the modification with the raw
water pump like I described above? Is what they've done so far
reasonable trouble shooting method, or am I just throwing money down the
drain by replacing all of these parts? Should they have been able to
tell me $1000+ ago what was wrong and fixed it without replacing parts
unnecessarily? I'm not informed enough to know for sure if I'm being
taken for a ride here, or if this is all just a matter of bad timing and
numerous failure of parts that normally wear out anyway, and really had
to be replaced.
I would appreciate any help anyone can offer here.
Thanks
NP
Gator
just mentioned (the lower unit water pump, the thermostat and the engine
circulating pump) I separated the hose leading from the lower unit to the
engine circulating pump to take the lower unit out of the equation and
connected a garden hose directly to the hose leading from the lower unit as
well as placed the earmuffs on the lower unit to avoid frying the lower unit
water pump (I connected another hose from the inlet from the lower unit to
feed the water coming in from the lower unit over the side), and then ran
the engine until it started to heat up. Using an infrared thermometer, I
checked the heads and the manifolds, it had all the symptoms of a blown head
gasket. Took the boat back to the shop, informed the mechanic of the
readings, he did not think it was a head gasket, because when he ran a
compression test, it showed even compression. They did all the
troubleshooting you mentioned, including aciding the heads and manifolds to
no avail, they finally removed the heads, and sure enough, the head gasket
was starting to go, just enough to cause it to overheat. After replacing the
head gaskets, and putting the engine back together it ran better than it did
before and I have not had a problem since. Hope this gives you some help.
"Nancy P" <por...@centurytel.net> wrote in message
news:3B621C46...@centurytel.net...
Larry
or adjust carb, change engine oil etc?) when they replaced the original
seal?
Could it be they put in the wrong plugs or set the timeing wrong or mis
adjusted the carb? Any of these things can cause over heating. Pull a plug
or two and look at them. What color are they?
Also look at the water inlet screen on the outdrive. Mabey it is pluged.
The idea that a worn drive shaft is preventing the water pump from pumping
does NOT sound likely to me. If the drive shaft were not turning the pump
then it would not be turning the prop and you would not go anywhere.
Unless the impeller key is sheared off internally, but then I would expect
it to overheat at all speeds. You can check this yourself with 2 garden
hoses and a little plumbinbg work. Connect one hose to the outdrive as
usuall ( to protect the lower unit pump). Inside the boat disconnect the
hose from the lower unit at the point it enters the engine and connect a
second hose directly to the engine water inlet. This second hose will now
cool the engine. Run the disconected hose from the outdrive over the side so
you don't fill the boat up with water. Now turn on both hoses and start the
engine. As you increase engine speed you should see a definite increase in
water comeing from the lower unit hose ( the one hanging over the side).
Hope this helps.
Good luck!
Larry
"Nancy P" <por...@centurytel.net> wrote in message
news:3B621C46...@centurytel.net...
JDW
all you can do. Sounds like there is a passage plugged - maybe?! Have
you measured water flow through the system at low pressure - pressures
like you should encounter when underway? Thru hull fittings, etc sound
like major surgury that may be unneccessary. I assume you had no
problems right after installing the new engine. Are you sure all of
the hoses are going where they are supposed to and that none of them
are colaspsing or dirty. Have you run the engine with NO thermostat
installed? Do not leave it out forever, just long enough to see if it
makes a difference. You did not state how how you are getting. If it
is only 175-190F, do you have the correct thermostat? I'd take care of
some more little things (reflush even?) before major surgury. Good
luck
Charlie
One of the modifications that the dealer had to make was the addition of a
seacock (thru-hull) and a raw-water pickup pump.
The old engine setup was fed water by the outdrive's impeller (Alpha 1, Gen.
1), but they said that the new engine wanted more water than the impeller
could supply.
The only other comment I can offer from a distance is that if a mechanic is
trying to fix an overheating problem, he should TEST the boat after each
repair attempt to be sure that it's fixed. Not doing so suggests shoddy
workmanship.
Good luck with ti.
Charlie
M/V Wavelength
Lloyd Sumpter
As someone else suggested, you might try a different mechanic. First, as
someone else said, they should check their work. Second, it sounds like
they're using the ol' "shotgun" approach to solve the problem: ie "let's
try replacing this and see if that solves the problem". For instance, I
can't see how a cracked manifold would cause overheating (sure, it should
be replaced, but it won't solve the problem)
As for fixing the problem, the idea described elsewhere of "splitting"
the cooling system so you can see what's going on would be my next step.
Lloyd Sumpter
"Free Time" Campion 18
NP
>
> Was the engine tuned up or did you do anything else (change plugs, rebuild
> or adjust carb, change engine oil etc?) when they replaced the original
> seal?
At the beginning of the season I had the carb rebuilt, and changed the
plugs with identical plugs to what was in there. It ran very cool after
that work. The only other thing they did when they did the seal was to
replace a cracked bellows in the intermediate housing that was allowing
sea water to leak through into the bildge.
> Could it be they put in the wrong plugs or set the timeing wrong or mis
> adjusted the carb? Any of these things can cause over heating. Pull a plug
> or two and look at them. What color are they?
Just the other day they did an entire tune up, points, cap, rotor, plugs
(again), wires, timing, etc. It physically ran much better after the
tune up, but the heating problem still occured.
> Also look at the water inlet screen on the outdrive. Mabey it is pluged.
Without seeing the outdrive when it was apart, I can't say there. I
know they've checked through that area pretty completly though, although
I will remention it to them. I know that when we've taken the hose from
the outdrive to the engine off and started it, there was a lot of water
pressure coming from the outdrive.
> The idea that a worn drive shaft is preventing the water pump from pumping
> does NOT sound likely to me. If the drive shaft were not turning the pump
> then it would not be turning the prop and you would not go anywhere.
hmmm...
> Unless the impeller key is sheared off internally, but then I would expect
> it to overheat at all speeds.
Ok, so there is a key on the impeller to keep it from slipping on the
outdrive then?
> You can check this yourself with 2 garden
> hoses and a little plumbinbg work. Connect one hose to the outdrive as
> usuall ( to protect the lower unit pump). Inside the boat disconnect the
> hose from the lower unit at the point it enters the engine and connect a
> second hose directly to the engine water inlet. This second hose will now
> cool the engine. Run the disconected hose from the outdrive over the side so
> you don't fill the boat up with water. Now turn on both hoses and start the
> engine. As you increase engine speed you should see a definite increase in
> water comeing from the lower unit hose ( the one hanging over the side).
Ok, will suggest this. Thank you very much for the help and ideas.
NP
>
> Get a new mechanic is one idea. It looks like you are doing just about
> all you can do. Sounds like there is a passage plugged - maybe?! Have
> you measured water flow through the system at low pressure - pressures
> like you should encounter when underway?
I know that they've tried back flushing through the engine. Basically
connected up a hose to the water inlet from the outdrive and flushed it
through.
> Thru hull fittings, etc sound like major surgury that may be
> unneccessary. I assume you had no problems right after installing
> the new engine.
Correct. The setup ran perfectly all last year with no problems
whatsoever.
> Are you sure all of the hoses are going where they are supposed to
> and that none of them are colaspsing or dirty.
Yes, we've checked and rechecked all of the hoses multiple times.
They're all in good shape and correctly aligned to the right spots on
the engine.
> Have you run the engine with NO thermostat
> installed? Do not leave it out forever, just long enough to see if it
> makes a difference.
Tried that, it made no difference at all.
> You did not state how how you are getting. If it is only 175-190F,
> do you have the correct thermostat?
The thermostat is a 143F one, which is what is supposed to be in there.
The exhaust manifolds are getting 200-210F, which is normal for them.
The heads are getting about 195-200. We're not letting them get that
hot though. What is odd though, is that the thermostat housing is not
getting that hot. It gets upto about 150F or so maximum. Even when
the engine is 'hot' you can place your hand on the thermostat housing
and not get burned.
> I'd take care of some more little things (reflush even?) before major surgury. Good
> luck
Thank you for the suggestions.
NP
>
> FWIW, I just repowered my 25' cruiser with another 5.7 Merc.
>
> One of the modifications that the dealer had to make was the addition of a
> seacock (thru-hull) and a raw-water pickup pump.
>
> The old engine setup was fed water by the outdrive's impeller (Alpha 1, Gen.
> 1), but they said that the new engine wanted more water than the impeller
> could supply.
Ok, this is exactly what they're suggesting to do on my boat next. The
thing that has me stumped is that the engine got plenty of water before
they resealed the outdrive.
> The only other comment I can offer from a distance is that if a mechanic is
> trying to fix an overheating problem, he should TEST the boat after each
> repair attempt to be sure that it's fixed. Not doing so suggests shoddy
> workmanship.
They have been testing after each attempt. Part of the problem had been
that they were originally testing it on the trailer, which doesn't cause
the problem to show up. It's only in the water and under way that it
heats up, so now that is what they've been doing.
> Good luck with ti.
Thanks much Charlie. Appreciate any and all advice.
NP
NP
>
> As someone else suggested, you might try a different mechanic. First, as
> someone else said, they should check their work. Second, it sounds like
> they're using the ol' "shotgun" approach to solve the problem: ie "let's
> try replacing this and see if that solves the problem". For instance, I
> can't see how a cracked manifold would cause overheating (sure, it should
> be replaced, but it won't solve the problem)
Well, they were pretty well plugged up with scaling inside of the end
caps. Whether that was at minimum contributing to the problem I don't
know. I can see how all of the stuff inside of them could at least keep
water from flowing well through them though.
> As for fixing the problem, the idea described elsewhere of "splitting"
> the cooling system so you can see what's going on would be my next step.
Thank you. I'm going to talk to them about this too.
NP
NP
Ok, I just got off the phone with the head mechanic who's working on my
boat. (it was his brother who's suggesting the raw water pump). The
head
mechanic is saying that with this being a raw-water cooling system, they
have to rule out these other things first. (the things that've been done
so far). They're going to do a pressure check and 'leak-down test' on
monday to check the heads next.
He says that the drive shaft problem won't cause this problem with the
over heating like we've been getting. So, he agrees with you all
basically.
Thanks for the suggestions so far.
Noname
repairs and it does afterward? Find another marine mechanic.... who can find
what they did wrong instead of guessing with your money and parts!
"Nancy P" <por...@centurytel.net> wrote in message
news:3B621C46...@centurytel.net...
Twin Boat
ago and got the wrong ones. When the drive was down they kinked causing
overheat at 3500rpm and up
icediver
developed a leak, and had to be replaced last summer, for about $1500.
I asked about replacing the starboard gasket too, but that wasn't done
because those cylinders passed the compression test. But I'll be watching!
Just curious how many Merc's have done this.
"Gator" <gato...@excite.com> wrote in message news:<Sgq87.2708$m8.7...@news1.rdc1.md.home.com>...
Andrew Martin
the trailer, even in the
water in gear, it won't overheat."
If true that says-it-all.
Look at the lower gearbox on the outdrive (in front of the prop). Above it
is the water intake slats. One on each side. Look at them. Are they
installed crooked so there is an edge sticking out on the the forward-edge
(towards the bow)? That would prevent proper water flow into the outdrive's
water pump under speed. You can remove them with a phillips screwdriver.
Inspect them and the area inside for blockage, obstruction (like a clogged
screen, piece of plastic, or something). If it's equipped with sand screens
consider replacing them with larger screening or simply remove them. Clean
any debris off the slats and their matching surfaces so they fit properly
back on. Reinstall them. There should be a SMOOTH transition from the
lower gearcase housing to the water slats. Or even a bump downwards onto
the slats. If you want to 'tweak' it you can make it so the Trailing Edge
has a ridge to it. That will tilt the slats forward, which will make it
easier to pull in water when underway. This sets-up a greater venturi
suction which the slats are designed to do in the first place. TIlting them
forward just magnifies it. Run you fingers over the slats to be sure of a
good alignment. Black on black is hard to see.
Even a slight lip on the leading egde of the pickup slats can disrupt water
flow into the slats and therefore the water pump and the engine when under
way which = overheating.
If this is it then I'd hope you'd told the mechanics about the overheating
when underway only. If you did and they still charged you for all that work
they did then "Yeah, you got ripped off". Knowing "It only heats up when
the boat is in the water and under way. Sitting on the trailer, even in the
water in gear, it won't overheat" i.d.'s the pickup slats as the prime
suspect.
Good luck,
-Andrew.
"Nancy P" <por...@centurytel.net> wrote in message
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Lloyd Sumpter
> "It only heats up when the boat is in the water and under way. Sitting on
> the trailer, even in the
> water in gear, it won't overheat."
>
> If true that says-it-all.
>
Not neces-celery.
"in the water and underway" is also "under load". On the trailer, even
in gear, the engine isn't working at all. It takes WAY more cooling for an
engine under load than an engine just spinning (obviously).
But your solution may be the one - wouldn't take much to check it!
khay...@webtv.net
person nuts trying to find a overheat problem. They are usually a real
bitch to replace, and look fine from the outside when the inside has
collapsed. If you replace it I would recommend only using the Mercruser
hose. It may look like garden hose, and though expensive it works for a
long time where most other hose fails, and who wants the problems you
have had on a regular basis.
Khayes
NP
They checked the compression and did a leak down on both of the heads.
Everything did fine, and no problems.
He changed the way that the water flows through the engine and that
solved the problem. Apparently the older style mercruiser was set up to
have the water that goes through the exhaust manifolds go back through
the engine, before it goes out to the risers/exhaust. He made some
changes to the flow, so that the water comes in from the outdrive, goes
through the block, then out the exhaust manifolds, and on out the risers
and exhaust. This way the block is isolated from the manifolds, and it
solved the problem. Interestingly, he put clear tubing on when he first
did this, and it blew a bunch of crap out through the exhaust when it
first started up. So, I guess changing the flow of water around made it
so whatever junk was in the engine was able to blow out, and clear.
Heating problem resolved. Thankfully!
Thanks to all of you for your suggestions, and advice.
NP