1987 Suzuki DT85 overheats at high RPM

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

If you can rig something up I would think 1k rpm should show some pretty good volume and pressure. By keeping just the intakes underwater you could rule out a blockage to the water pump inlet or a crack or bad gasket that would allow sucking air. If you feel the pump is operating sufficiently I would adjust the flow on the hose to match it and slide it over the water tube to get a sense of where the water is going, increasing the flow until it fills the head and builds pressure.

The idle issue may just be setting the carb mixture screws. I would back them out a quarter turn to allow more air, sounds like it may be loading up.

Hope you have a lift or some friends to lift that beast off the transom.

Nothing wrong with a few choice words.

 

[mkrussow]

Re: 1987 Suzuki DT85 overheats at high RPM

It isn't possible to just immerse the intakes and have the pump work. These pumps can't suck up water from below - they must be fully immersed. After trying it, I had one of the those 'well, duh' moments.

Anyway, I rigged up the muffs and ran the shaft with a drill. Unfortunately, my corded drill shot cr*ps so I only have a 18V cordless which can't turn anywhere near 1k. Regardless, with the muffs attached, the drill hooked up and my finger partially covering the outlet port, I can get water to shoot up to the roof of my house. Some water also comes out around the main drive shaft, but I think that's by design.

I hooked the garden hose up to the water tube on the motor. When I look up the drive shaft housing, I don't see any water leaking from the top end of the water tube (good sign). I see water spilling out from the new lower gasket I just installed, but that had holes/perforations in it so I think that's by design, as well.

The attached picture is something I'm not sure about. Water is just pouring out of the main exhaust port below the power head. In this picture the pressure is about 10 psi on the pressure gage and the motor is not running. Should all that water be coming out of there?

 

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

I may be missing something but the pump should easily pull water the distance from the inlets. It should not have to be immersed. If you have a set of good muffs, install them with a little pressure, you might see a little leakage at the muffs, maybe a dribble from the pump outlet if you turn the shaft, but if you see water coming from anywhere else there is a crack or seal that is allowing the pump to suck air while its running. Let me know what you find.

Water from the exhaust port is normal, looks like K.C. has good water pressure, may have even given the relief valve some action.

 

[mkrussow]

Re: 1987 Suzuki DT85 overheats at high RPM

I didn't run the pump immersed for a long time with the motor. I was worried about mucking up the impeller. But, it seems like it would be tough for the pump to pull water up several inches.

When I hook the hose up with low pressure, I don't see water anywhere. As I bump up the pressure, I see water in both the outlet and around the drive shaft. But, there are two things that make that seem reasonable. First, there's a small relief in the pump housing that extends just beyond the inner 'seal' of the impeller. Secondly, there's an actual drilled relief hole that connects the outlet port and the opening where the drive shaft passes through. I'll include some pics.

On the pic of the impeller, you can see the raised ring near the ID. I assume this is the 'inner seal'.

On the pic of the inside of the housing, you can see the groove worn by the impeller's ID seal and the little 'port' that extends just past it. I assume that this will let some water pass.

On the pic of the top of the housing, you can see a small drilled hole. That hole runs over to the outlet port. I assume this must be some type of pressure relief?

Does my logic make sense?

 

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

Logic on the pump makes sense, but it should still be able to suck water through the inlets. Think of drinking through a straw with a hole in it. There has to be seals that keep air from the chamber that connects the inlets to the bottom of the pump, looking at the schematics, item 5 in the water pump, and item 36 in the gearcase would be worth a look.

Edit: Skip 36, it's an oil seal. Suzuki uses a RTV silicone to seal the mating surfaces of the gearcase to the half inch or so plate that holds the water pump. I have a Yam 50hp lower unit that I was able to draw water through just the inlets by turning the driveshaft by hand.

 

[mkrussow]

Re: 1987 Suzuki DT85 overheats at high RPM

Item 5 on the pump is new and I haven't ever see any water weeping from under that gasket.

I have never looked at 36 on the gearcase, but if that was bad, wouldn't I have water in the gearcase? I checked that recently just to be sure.

I can try to run the water pump longer tomorrow morning (I took the day off to swap motors) with a drill motor and see if I can get water to pull up.

The water dumping out the exhaust port isn't an issue? I suppose the water has to go somewhere and the poppet valve just let's it pass?

Thanks for the input. It seems like I'm so close, I don't imagine that I'll actually give up, but I have to get that other motor back on the boat.

 

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

Take a look at the edit on my last post, sorry to keep you from the swap, I was scrambling to try and keep the 85 on there. Have a great trip, if you're traveling through STL, throw that P.O.S. in the boat!

 

[mkrussow]

Re: 1987 Suzuki DT85 overheats at high RPM

For what its worth, I tried to run the pump with only the intakes immersed and the pump would not pull up any water. So, I'm into the removal process. Hopefully my trusty ol' 50 Mariner will fire right up!

BTW, I'd happily dump this thing in your garage and let you take a shot at it. If you lived in Des Moines you'd have a chance.

 

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

I think it's worth looking at after some R+R. Since you inherited the cooling issue, maybe someone replaced the lower unit oil seals and didn't know they were supposed to use RTV on the mating surfaces under the bearing plate. It seems like overheating occurs when the pump, which is several inches above the cavitation plate, raises out of the water.

 

[mkrussow]

Re: 1987 Suzuki DT85 overheats at high RPM

That's any easy area to check (after R&R).

So your theory is the pump is sucking air from the gap between the bearing housing (#1 on water pump diagram) and the main gear case (#1 on the gear case diagram)?

In good news, my old motor fired right up once I got it installed on the transom.

 

[mphelle8vld]

Re: 1987 Suzuki DT85 overheats at high RPM

That's a possibility, along with a crack somewhere. With my Yamaha 50 lower, it only took 6 rotations by hand to lift the water 5 inches and start pumping and that impeller had not been rotated for about 5 years, you can imagine what the fins looked like.

Removing the bearing carrier involves lifting out the driveshaft and shift rod with it so before doing that, as a quick test I would clean both sides of the intakes and cover them with duct tape. Remove the water pump and fill the chamber below it with water and see if it holds its level.

Nice that you had a backup motor.