Overheating GT-40

[DanielC]

RE: " T "

I have had to deal with two different GT-40 motors thet started to have minor overheat problems, both with high hours, more than 1000. Replacing the raw water pump solved the problem.
The raw water pump is the one with the rubber impeller that is driven by a belt on a GT-40 motor.
If my memory serves me correctly, the raw water pump should fill a 5 gallon bucket in less than 15 seconds, at 3000 engine rpm.
See also this thread:
http://planetnautique.com/index.php?...amp;highlight=

[mndanielsncsu]

RE: " T "

I've pulled all of the hoses leading from the RWP to the T'stat along with the t'stat housing but haven't found anything yet. When the guy at the dealership was helping me, he did mention that he couldn't figure out why the driver's side exhaust manifold was getting hotter than the passenger. He pulled the head with the hose leading to the exhaust off and checked for blockages but didn't see any. I'm wondering if that's still where the problem is. What's the best way to fish around in there? Wire coat hanger or is that too abrasive?

Just an FYI, the boat has 348 hours on it.

What does an RWP rebuild usually cost on average?

Figures that my first time out on this thing would turn into a small nightmare.

[jward]

RE: " T "

You should be able to order the rebuild kit from your dealer for under $40. As far as the manilolds, you can connect a garden hose to the intake side of the manifold (one at a time) turn on the hose, do not start the engine and see if there is any difference in the water flow. there should be good flow through the hose and out the back of the boat. Feel the water hose and make sure it doesn't expand as it would if there was any kind of blockage. Hope this helps

[M3Fan]

Re: RE: " T "

When the guy at the dealership was helping me, he did mention that he couldn't figure out why the driver's side exhaust manifold was getting hotter than the passenger.

Funny that he'd say that- this is completely normal. The flow of the RWP naturally directs a little more pressure to the port side. It shouldn't be a huge difference, but some difference is pretty par for the course.

[M3Fan]

Re: Overheating GT-40

Let's slow down for a second and take a look at the original post:

The temp got back to around 195, but as I slowed to the dock, it dropped back down to 180 or so. Any thoughts on the culprit? Thermostat?

If you are running around 180, my guess is that they put a 160 Tstat in rather than a 143 Tstat. That's my bet for what the culprit is. It's worth double checking. That, combined with maybe a very common low voltage situation might have that gauge reading 180-195. Keep it simple!

[M3Fan]

RE: Re: Overheating GT-40

I just re-read all of the posts and it looks like you're saying the temp climbed higher than 195 after the impeller replacement. Still worth checking the stat type anyway. I like jward's advice on checking manifold water flow. A clogged exhaust manifold water jacket can cause an overheat because hot water is not able to escape the engine efficiently.

[DanielC]

RE: Re: Overheating GT-40

At 348 hours, I would think the raw water pump should be good with a new impeller, unless the previous owners beached the boat, and sucked sand into the engine, wearing the raw water pump.
When I lay the boat up for the winter, or recommission the boat, I polish the brass plate on the surface that is next to the impeller.
Part of my winterizing steps is after I pull the plugs on the exhaust manifolds, I stick a finger in the hole, and feel for any loose rust. If there is rust flakes, I disconnect the host that goes to the exhaust manifold, from the thermostat cover, hook a garden hose up to it, and try to flush any rust out. Digging into the cooling passages of the manifold from the plugged end with a wire also helps to get the rust out.
Some water always bypasses the thermostat, and goes straight out the exhaust manifolds, to cool the exhaust. When the engine gets hot, and the thermostat opens, hot water in the block is allowed to exit out the exhaust manifolds, and the hot water is replaced with cool lake water.
If the engine is really overheating, there is not enough cool lake (or river) water coming into the engine. Either the flow is restricted, or the pump is not supplying enough water. The thermostat can restrict the flow.
You can remove the thermostat, and cook it on the stove in a pot of boiling water, to see if it opens. It actually should open before the water boils.
See this thread:
http://planetnautique.com/index.php?...amp;highlight=
With the flushing adapter, I can pressurize the hoses up to the raw water pump. I can see leaks, which will leak air when the boat is running normally, and fix them. leaks on the intake side of the raw water pump reduce the amount of water the raw water pump moves, and in severe cases allow the raw water pump to run dry, destroying the impeller.
I do not ever crank or start the boat without supplying water to the raw water pump. It can destroy the impeller.

Some will argue with this, saying they have got away with it. It is their boat. They can run the boat without water to the pump if they want. They can risk damageing their engine, and putting their passengers and or family if they want. I choose not to.

With my flushing adapter, I can also turn off the hose supply, and run the boat engine off the bucket, and see if there is suction from the raw water pump.
With the flushing adapter hooked up to the two different GT-40 motors I commonly work on, at idle, with both the bucket valve fully open, and the hose valve fully open, the bucket very slowly fills. A brand new good raw water pump will slowly drain the bucket. at 1000 RPM, I expect the engine to start using all the water from the hose, and to start draining the bucket. If it does not, I try to find out why.

[mndanielsncsu]

RE: Re: Overheating GT-40

I made a rookie mistake upon looking for blockages. I took the RWP off to check for pieces of the old impeller and realized that I don't know which direction to install it back. I didn't think to mark it before removal. I have a PCM 351 Pro Boss with a Sherwood RWP. I'm assuming that these things aren't multi-directional. If you're looking at the front of the engine, so the RWP is in the bottom left corner of the engine, do the hoses connect on right side of the center point or on hte left side of the center point? Hopefully this makes sense. The hoses could connect either way, depending on if the pump is oriented in the right direction. I can try to take pictures to clarify if need be...

I feel like I'm dragging this thread out, so I apologize.

[DanielC]

RE: Re: Overheating GT-40

Looking at the front of your engine, you facing to the rear of the boat, does the engine run in a clockwise direction? If that is the case, the screw on the side of the pump body goes toward the engine. the inlet and outlet fittings on the pump are on the engine side of a verticle centerline of the pump.
Your engine will turn clockwise if you have the gear reduction transmission.

[jos]

RE: Re: Overheating GT-40

Its easy to check for air leak and also check the RWP. Pull a hose far as possible from the RWP. Put your hand on the hose to close the hose. Start the engine. At idle it already should sucks massive vacuum.
Last year i had an air leak under the hoseclamp of the oil cooler, the oilcooler had a flat spot. I had no vacuum at all idleing.
This methode only can be quick, before the RWP running dry too long and the engine heating.
Best to do the trick before the strainer, thats not easy but the best.

I suggest to put a database on this forum, wikipedia like, so that these repeating cases can be found easily.

[SquamInboards]

RE: Re: Overheating GT-40

Pretty sure DanielC has that right - I looked at some pictures of 2 different 351's I have and of course you can't see it perfectly in either... BUT if you install that pump upside-down, you would definitely have some overheating issues, though they might be more serious than what you're describing... either way check to be sure the thing's in right-side-up.

[midtennwake]

RE: " T "

i am experiencing the same problem, the starboard manifold and riser starts getting hot in a few minutes time and the port side is extremely cool. I have taken out the thermostat and left it out all together, the impeller is in good shape also. I have recently removed the manifold and riser cleaning them both and had to replace the exhaust hose. Cranked it up today and its still running hot. I can tell that the water strainer is drawing a little air, could this be the problem with the starboard side manifold? or do i possibly need a new raw water pump?

[Rock_Toy]

I just took the boat out today for the first time this season. Ran in straight up to about 180 degrees and then under load, it shot up to 200+ degrees. Dropped it to an idle and the temp dropped to about 180. Ran it back up to 3500 RPM and back to 200+. I just changed the impeller a week ago. Maybe I installed the RWP backwards but I think that the results would be a little more extreme, right?

How much is a new RWP? When I pulled mine, there were loose metal pieces in it....

[Rock_Toy]

OK, so I did some troubleshooting this weekend. Disconnected the strainer and hooked a water hose directly to the Hose running to the RWP. Ran water through it and it came out the back. Turned on the motor and the water started gushing out in spurts. I figure that this means that I don't have any blockages in the system. Still have to check the thermostat though. I then pulled the RWP (I'm going to rebuild it just in case) and it appears as though it was installed backwards. I had the screw facing the motor. Does anyone know if my motor turns counterclockwise? I forgot to check while it was running. Its a 1996 Super Sport Nautique with the GT-40 motor in it.

[Rock_Toy]

Anyone?