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DT30C Overheating problem

W

Wynand

New member
My DT30 3 cylinder two stroke engine overheats and I cannot find the problem.

When starting the engine, the water pump seems to be working as it discharge water at the piss hole and the water is warm. However, after about half a minute it stop and the motor overheats rapidly - usually after revving it above fast idle. The engine casing at the top cylinder shows some scars of overheating (spot lightly scarred and engine has a slight piston slap as a result at rpm over about 4000 but otherwise fine)

I did lowered the gearbox and checked the impeller and it seems fine - also pushed water up the water pipe in leg with a hose and the water exits the piss hole first, then work its way up and the out the thermostat opening (thermostat cover removed). When pouring water into the top at the thermostat hole with the hose, it flows out the pee hole and the tube that connects to water pump. IOW, no obvious obstruction I can find.
When the motor is started with thermostat casing removed, water does not makes it way out there...


What can be at fault? The engine was rebuilt after oil injection failure and the oil injection disconnect as a result by the previous owner. Currently it does not have a thermostat fitted - and I know the importance of the thermostat but if water does not reach it, how would it help:confused:

Any help or suggestions would be greatly be appreciated. Thanks
 
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New impeller fitted and the squash plate and pump casing in nick condition. Removed cylinder head and head cover, exhaust covers and clean all water passages that was foiled with lime?, fitted new gaskets and the problem is now worse with no water pissing.

The pee hole blows out hot air and I then removed the thermostat casing and started engine again and have exhaust smoke coming out of the casing big time. Perhaps this exhaust pressure in the water ports in head prevent the pump pushing water into the head.
And this begs the question; how does exhaust smoke/pressure getting into the head waterways? Suspecting the head gasket, I took the cylinder head off again and can see no evidence where the cylinder gases blew through the gasket. Cylinder sleeves and head has no cracks or damage...

However, the owner before me removed the cylinder head and replaced with same gasket, I did the same and the gasket still looks fine. Can the gasket be at fault and need to be replaced. (damn expensive in my country). As a precaution I will get the cylinder head skimmed at an engineering shop.
 
Simple ------If there is no water in the block then the exhaust will enter the water jackets where it would normally discharge the water into the exhaust.
 
Thanks for advice thus far but still no cigar.:confused:

Had the water-pump out at least a dozen times.
Took the gearbox and pump off motor and run in container with water (level just above cavitation plate) with drill press at about 2300rpm. No water ejected but only "slurping" sound from the outlet hole on pump.
Opened the pump again and since there was some minor wear scrape marks on the pump casing top, took it to engineering works and they faced it smooth on a lathe and skimmed the same amount off flange so the same dimensions are still intact and nothing wrapped. Assembled again and still no go on the drill and tub of water.

I then stripped again and took the gear casing and pump, squash plate and impeller to local boat repair guru's shop and he said that unit is perfect and should pump. I mentioned that some water leaked out between the gearbox and the g/b drive shaft bearing housing plate, he suspected that to be the problem (bubble formed?) and suggest I strip it off, clean and put some sealer between the gearbox housing and this plate and re-assemble again.
This I duly did.

Back on the drill and water bucket the pump spurted a solid stream of water about 1 inch high out of the hole. I assembled the unit to the motor and started it - after about 30 seconds water pissed out of the pee hole but sporadic and hot air with it. After another 30 seconds or so the water stopped and only hot exhaust air exits the pee hole.
After restarting again the water do not reach the engine, even with the thermostat out and its cover removed...

Im desperate with this motor that's otherwise perfect, starts with just one pull everytime and runs sweet.
Im thinking of stripping the gearbox again and have the drive shaft bearing housing plate machine faced (skimmed) and refitted - suspect the problem lies there or am I missing something. :confused:
 
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You do have the drive pin for the impeller installed ??----------------Have you measured the width of the new impeller ( if aftermarket ) and compared to the depth of the housing ??
 
Yip, the drive pin (shaft key) is installed. The old impeller is thrown away and therefor cannot check the replacement unit's width. How tight must the impeller run when the casing is tightened to squash plate? Must the impeller width be smaller, same or larger than the housing depth?

Edit: Aftermarket impeller
 
I have seen problems with aftermarket impellers ( refuse to use them )----------------There should be very little clearance between the housing and the impeller.-----------Say if the impeller is too big you can back off the fasteners holding the housing down to see if that improves it ( testing ) with the drill press.----------If it is not wide enuff say more than 0.010" clearance then get a factory impeller.---------------------In 40 years of repairs I have never had a problem such as you describe after repairing a pump.
 
Some results at last but still no cigar...

Took the gearbox off again this morning and connected to the drill press and run at 2300rpm. No water - release the casing bolts whilst running and when I re-tighten them again, suddenly the pump start pumping, slowly at first and after 10 seconds or so at full blast with water all over the garage. It spray up about 12-14 inches high unrestricted.
Assembled the box to motor and start - you guessed it, no water in the engine and heated up fast. Removed the powerhead and took the driveshaft housing to the big drill press and into the container water again and run the drill. Immediately water pissed out at the top of the housing where the water pump pipe discharges. Trying to press the hole shut with the thumb is like trying to close off the end of hosepipe at full tap, such is the pressure.

Million dollar question; why no water going up stairs into the engine, to the thermostat housing and pee hole??

When I checked the drive-shaft housing spares list at Brownspoint http://store.brownspoint.com/DT30c/fig020-30c8897.asp I noticed a part (no 29 - waterplug) on the drawing that is not present on my engine. What is the purpose of this water plug and can it be the culprit?
Or is the problem in the powerhead?
I appreciate all the help this far.

PS: Nearest Suzuki dealer is about 310km from me so I have to battle this alone.:)
 
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justintime said:
that would cause no water!!!!
Click to expand...

Seems then that the culprit is identified :)) Previous owner stripped the motor after oil pump failure, then sold the engine to me and mentioned overheating problem and I thought that could easily be sorted out at the price I paid, but was I wrong - perhaps he never noticed the waterplug missing when he re-assembled everything.....

Believe it or not, Suzuki South Africa does not have a single said waterplug (or piston rings and cylinder-head gasket for this engine) in stock and have to be ordered from Japan that can take up to 6 weeks!!
That leave me to do some internet transaction with Brownpoint or similar in the USA - at least will have the spares in 5-7 days. Pity, the postage freight/cost will be 8 times more than the part asking price??
 
PROBLEM SOLVED at last.....but not where it was expected to be.

Got this water plug after 22 days ex Japan, but when inspecting it and where it goes, failed to see how this could be the problem other than restricting the water a bit. Anyhow, I installed it and guess what, no joy. Still no water going upstairs to the power-head and only hot air and smoke out of the pee hole.

This made me think. It is easier for a pump to lift/pump air or exhaust gasses than water and off the gearbox again. Stripped the waterpump off, removed the gears etc and remove the drive shaft housing end plate under the waterpump to check for cracks or air leaks and bingo....at the back is a water port that dump/suck? water to below the cavitation plate just in front of the trim tab. The cover, identified as the "gearcase under cover" in the parts micro-fish was missing and left two holes where it clip in from the inside open ABOVE the cavitation plate sucking air into the pump.


Not wanting to wait another 3 weeks ex Japan for this cover and failing to see why that particular port is there, I simply blocked the hole off solidly with epoxy at the top where it entered the water canal on the gearbox casing.
Started the motor and immediately she pissed a solid stream of water out off the pee hole like there's no tomorrow. Took the engine to the local dam in town, run it hard for about 40 minutes and the motor stayed as cool as a rap singer, water still peeing a strong solid stream meaning the blocking off the hole expained had no ill effect on the cooling.

Lastly, thanks for all the input from you guys, but a lesson learned is that nothing is really as it seems to be. In fact, I saw the cover missing below the cavitation plate and never gave it a second thought assuming that since it is a water port, it will actually work better without any interference of the cover....

Edit: In hindsight, the reason I had water pumping as described in post #12, was simply because the water container was filled well above the cavitation plate at the time, hence water covering the two culprit holes and the bottom hole and the pump sucked water. But when I started the motor today, the water level was just touching the cavitation plate and the pump sucked air through the two little holes and not pumping...
 
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No, have short shaft motor on short shaft transom - cavitation plate level with bottom of boat hull. (centre chine)

But everything is well and the problem was not the water pump but something else.:)

Usually when there is an overheating problem, one assume it is waterpump related.
In fact, I grind about 2mm off the impeller top on the sander, skimmed the casing flange off on the lathe this morning until I felt that the impeller and casing is a good match before I put everything back again, plugging the said hole and its pumping like a new engine.
This shows that the impeller is not that sensitive to wear as one often read to be the case - actually, when I spun the impeller at high speed (+-3400rpm) in the casing without the squash plate, I noticed the impeller blades "pulling" themselves closer to the hub and not making contact with the casing sides anymore (perhaps a safety feature to prevent over pumping?) , thus blowing the argument of slightly worn impellers out of the door so to speak.:confused:
 
Wrong---------------The impeller behaves as a " positive displacement pump " at lower speeds ( vanes touch the outside of housing ) -----------then at higher speeds it becomes a " centrifugal pump " ----------Nothing to do with being a safety feature !!!!------------That is the way they have been designed and have worked for some 60 years of outboarding.-------------------Aftermarket impellers have been know to be out of spec.------------I always install FACTORY impellers and have done so for many , many years.
 
Some outboard motor impellers work as displacement pumps at low speeds, such as idling and trolling .----The same impeller then becomes a centrifugal pump at high speed !!!
 
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