1996 DT150S Overheat buzzer and light problem at low speed and idle.

[N2 Fishing]

Ok I pulled the VST off and removed the needle and seat. I did not observe any trash in the top half of the VST or cap plumbing going into the needle and seat. So I adjusted the needle tang on the float so it barely opens and put it back together. Primed it good and tight again and left the two top vent hoses off of the VST cap so I could observe for any flooding coming out of the two top vent hose barbs. I did not detect any.

Time to get a gallon of 50:1 premix set up to test run the engine on a satellite tank and observe to flow rate of oil from the oil pump. Thinking it might be a good idea to replace all of the check valves. One on the oil hose between the pump and the VST and one between the lower engine crank case vent and the VST.

I’m excited but not counting my chickens just yet.

[N2 Fishing]

Got it put back together with oil reservoir hooked up but the oil tube to the VST unplugged to look at oil flow from the pump. I also have it running on a satellite fuel tank with 50:1 gas mix. It started right up and and sounds good but I still get no water pee stream from the tell tell hole.

I think it is missing parts to the water intake tube that sits just above the pump housing. That is the only thing that I can think of to explain it. When I put a garden hose on that tube with thermostats out I observed plenty of water flow on both cylinder sides.

[N2 Fishing]

I figured I better pull a T stat to see what king of water flow I'm getting. So after pulling the stat and starting the engine I discovered not a drop of water flowing through the water jacket.

I'm thinking some parts are missing on the tube that sit on the tube just outside/above the water pump housing.

I don't see parts #8, #14, #15 on the tube that sits above the water pump housing.

[N2 Fishing]

Broke a T stat bolt off in the head :/

https://m.youtube.com/watch?v=RIdUqJ...ature=youtu.be

[N2 Fishing]

What is the best way to remove cylinder head bolts with out braking them?

[Solarman]

There is not a guaranteed way to prevent bolts breaking off?

You mentioned adjusting the tang on the VST float at a minimum? It must be set where the manual tells you. If the float is set too high excess gas will get pulled into the motor. If the float is set too low then the motor will act like it is running out if fuel at higher rpms.

Try connecting your water hose directly to the tube the water pump connects to, just to see if there is any water going to the powerhead and pee-tube?

If the bolts that broke off do not leak (water or compression), leave them alone for now.

Run the anti-corrosion solution as soon as you can start the motor and let it idle like I said. After trying the hose like I said, and putting the lower unit back on if correctly put together?

Good luck, post back on what you find out.

[N2 Fishing]

I’m ordering the parts for the tube that sits just above the water pump housing.

I have always been able to see plenty of water flow with a water hose pushing water up through the tube that sits just above the water pump.

It has to be missing bushing parts etc on that tube above the water pump housing.

OK I’ll hold off on the head bolts until I get the water situation figured out.

When I measure the float per the manual instructions It measured ok but the float if suppose to be free floating turned sideways. However there is a little spring loaded pin that sits against the float tang that changes the way the float will rest if I lean the float inwards towards the needle when resting the floats sideways per the manual instructions. The manual does not give all the details required in my opinion to properly set the float tab.

I’ll leave the floats set how they are for now. There is not a lot of movement as it is so there is very little wiggle room for adjustment. I can always readjust the floats if need be later once I get this thing back out on the water and see how it runs at wide open throttle.

[Solarman]

If you have good water flow going up the tube from the hose, then a good water pump should also send good pressure up the tube. It sounds like you need to flush the powerhead with vinegar or other corrosion solution as mentioned earlier. Inside each head there are by-pass valves that may be stuck open from corrosion. Flushing is the best way to clean those water jackets around the cylinders.

Post back to let us know what's up.

[N2 Fishing]

I believe it is just missing pick up water tube bushing parts which explains low water pressure at low RPM’s and overheating under load at lower RPM’s. I purchased the upper and lower tube bushings. As soon as the parts arrive I’ll try the lower bushings first before pulling the power head to inspectfor the upper bushing.

[N2 Fishing]

Inside each head there are by-pass valves that may be stuck open from corrosion. Flushing is the best way to clean those water jackets around the cylinders. Post back to let us know what's up.

I put all 3 of the new parts that arrived this past Monday to the pick up tube just about the water pump and it still gets no water pressure to the T-Stats.

I made a video I'll upload later. It shows the water flowing through the water pump with dog ears on the lower unit while the lower unit is not on the engine. I also talked about how water is flowing back down the drive shaft tube hole as well as the exhaust ports at the bottom when pressing a garden hose against the pick up tube with low water pressure from the garden hose.

You mentioned in this quote ^ that flushing is the best way to clear out the water jackets. Is that also the best way to get the by-pass valves to close if they are stuck open or does some things need to come off to remove to clean or replace the by-pass valves? Honestly I have not seen any by-pass valves in the service manual but I have not been looking for them either.

I was thinking of using a bin with some water in it sitting under the engine with an electric pump recirculating a corrosion remover through the engine? You say run the engine but if no water is getting up there during idle then it won't take long for the engine to start to over heat. Thinking it might be better to recirculate water using an electric pump to prevent overheating? what do you all think about that?



Oh and if things are not bad enough with this engine I have some other bad news to share. I started the engine with the oil floats unplugged and now the lights for the oil level no longer work on the display

[N2 Fishing]

[QUOTE=Solarman;n65189]Inside each head there are by-pass valves that may be stuck open from corrosion. Flushing is the best way to clean those water jackets around the cylinders. Post back to let us know what's up./QUOTE]

I put all 3 of the new parts that arrived this past Monday to the pick up tube just about the water pump and it still gets no water pressure to the T-Stats.

I made a video I'll upload later. It shows the water flowing through the water pump with dog ears on the lower unit while the lower unit is not on the engine. I also talked about how water is flowing back down the drive shaft tube hole as well as the exhaust ports at the bottom when pressing a garden hose against the pick up tube with low water pressure from the garden hose.

You mentioned in this quote ^ that flushing is the best way to clear out the water jackets. Is that also the best way to get the by-pass valves to close if they are stuck open or does some things need to come off to remove to clean or replace the by-pass valves? Honestly I have not seen any by-pass valves in the service manual but I have not been looking for them either.

I was thinking of using a bin with some water in it sitting under the engine with an electric pump recirculating a corrosion remover through the engine? You say run the engine but if no water is getting up there during idle then it won't take long for the engine to start to over heat. Thinking it might be better to recirculate water using an electric pump to prevent overheating? what do you all think about that?



Oh and if things are not bad enough with this engine I have some other bad news to share. I started the engine with the oil floats unplugged and now the lights for the oil level no longer work on the display

[N2 Fishing]

Ok video uploaded https://m.youtube.com/watch?v=RbkGYR4mMkk

[N2 Fishing]

oil reservoir level lights are solved. I have two more alarm displays from previous diagnostic attemps. Anyway I was getting down under the helm to remove and replace the alarm unit with a different one when I discovered some unplugged wires.

Very frustrated at this point because that meant I had to snake my a$$ back out of there after unplugging the wires to plug the battery wires back in.

Bottom line, it was a couple of unplugged wires keeping the lights from illuminating. I'll chalk it up to a ferrel animal messing around under the helm.

One less problem to solve

Now back to figuring out what is wrong with the cooling system on this engine.

[N2 Fishing]

I'm ready to try some calcium deposit remover like RydLyme, Barnacle Buster or West Marine has one called Descaling fluid.

[N2 Fishing]

Update:

I did the flush with Barnacle Buster for a couple days and then took the boat out for a couple of test drives trying to force a over heat condition driving it slow at idle, and barely over 25 on plane then mid throttle and full throttle. 2 Days in a row I was not able to force an over heat alarm.

The tell tell pee stream is very strong now. The strongest I can ever recall it ever being.

Additionally I am able to hold my hand on both sides of the engine heads with out having to pull it away from the heads. Temps on the port side reached close to 150-160F When idling in a trash can with fresh water running into it from the bottom. The trash can was new.

Other problems that still exist is loosing prime. I have replaced all the fuel lines from the VST all the way back to the Yamaha Fuel / Water separator filter. I have a new Suzuki Primer bulb as well.

With all that in mind I just placed an order for 2 new fuel pumps after opening both of them up to inspect and found cracks and some missing material on the clear plastic check valves. It's a shame I have to buy new fuel pumps for a couple of 0.02¢ broken pieces of plastic :/ The diaphragm and gasket were still good in both pumps.

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