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1983 Suzuki DT40 overheating and not pumping

L

Lachlan

New member
The motor is running fine on muffs and it cools properly with water coming from the telltale and the exhaust when the thermostat opens, but when running it in a bucket or in the water, there is no water from the telltale and water does not reach the top of the engine and it gets very hot. I know it's not the depth of the bucket because I have tested it at the boat ramp and there was no water out of the tell tale. I have also tried with the lower unit off and a hose connected to the water pipe and the water circulates fine.
With the lower unit in a bucket and turning the shaft with a drill, water comes out of the pipe but also slightly around the driveshaft. Is this normal?
I have already changed the head gasket, water jacket gasket, thermostat, impeller and gasket, and exhaust cover gaskets, so I'm not sure what else it could be.
 
I had a 140 Suzuki at my shop a couple of years ago doing pretty much the same thing.I took the cylinder head off and the head gasket was burned out.
 
You mention changing the impeller and gasket(part #8?) but not the base plate(part #7), the key(part #5) or the water pump case(part #2), unfortunately case is no longer available. I’m thinking if the base plate might be warped ever so slightly and the water pump case is worn from 40 years of a spinning impeller against the water pump housing. My Suzuki(2009) has a cup that fits into the water pump casing so my impeller vanes are spinning against an aluminum cup not a plastic water pump. IF the base plate is warped and the water pump case is slightly larger or out of round than OEM specs your pump will pump but not at 100% efficiency.
An other thought is the rubber grommet that is usually at the top of the water tube has deteriorated and effecting water pump performance in a negative way.
As far as water coming out around the drive shaft I’d GUESS that shouldn’t happen.
If you don’t already have a genuine Suzuki service manual I’d recommend you get one, only $12US in pdf form

Suzuki 30-40HP outboard motor Service Manual

Suzuki's condensed service manual covers the following models: - Suzuki DT30 prior to 1988 - Suzuki DT30C after 1987 - Suzuki DT40 prior to 1984 - Suzuki DT35 after 1986 - Suzuki DT40 after 1983 Manual is searchable, printable and indexed.
www.selffixer.com www.selffixer.com

Just because Boats.net show your water pump case is no longer available only means it’s not available in North America. Suzuki still makes 2 stroke outboards for other markets with less stringent environmental laws so parts MIGHT be available offshore. That being said it’s a 40 year old engine.

Good luck
 
Thanks guys.
I had a second look and the plate looks very flat and no leak on the edges. This water pump casing is metal inside and is not scorched.
I tend to agree with William that the top grommet could be damaged but I was not keen to disconnect the powerhead to check this.
One additional info is that with the lower unit off, if you connect the hose to the tube directly and turned the water on a little bit (low pressure), water is going up the pipe but some of it is coming down from the exhaust side of the leg. When increasing the water pressure slightly, the water comes out the tell tale too. Note that this is with the engine not running.
So we'll probably have to disconnect the powerhead to check the top tube/grommet.
 
Water coming out of your exhaust could be coming thru your water pressure valve (aka popit valve). The water pressure valve is designed to allow water to exit the engine via the exhaust when cylinder water pressure is high buy opening the valve. IF your pressure valve is stuck/seized open it’s possible water will escape before ever reaching the engine. Just a guess but worth checking out before tearing into the power head. I have read on other forums that if the chamber that separates the incoming water (front) and the exhaust passage (back) corrodes to a point where a hole is formed the outgoing exhaust pressure will interfere with the incoming water. Worth looking into, especially since you have the lower off anyways. Fresh or salt water engine?
 
From a 2009 DF90A service manual. Don’t know how helpful this screenshot will be or how valid it is compared to your 1983 model.
 

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Hi, William
i don’t think this dt40 2 strokes has a pop it valve but will check diagrams just in case.
Since in salt water (Sydney, Australia), your corrosion point is definitely worth checking.
when replacing the Exhaust gaskets, we noticed that the top half was dry so the water was not going up enough. Previous owner had red RTV instead of proper gasket. After replacing them, water was reaching the thermostat ok…..but with muff only. There was not too much corrosion in the plates and the head/water jacket. But again it doesn’t mean that there is some exhaust gas stuffing up the water pressure.
a bit busy this week…but will update when we have news.
 
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