DT 115 cooling puzzle

[Jayster]

Hi all,

After getting my 1983 DT 115 finally firing on all cylinders, I have some issues with my cooling but I feel it may be due to one of or a variety of reasons so I'm turning to you all for help...

I've been using muffs but have recently found a tank that allows water to cover the cavitation plate by about 1cm.

Sometimes water jets out the tell tale but then goes to a boiling hot dribble. No water coming from the top exhaust on the lower leg... ever. Loads of water coming out from the prop. Water p1ss1ng out of the plastic gearbox cover plate nearest to the transom.

I've had muffs on the lower leg whilst it was off the engine and loads of water was coming out the top of the impeller housing (which is why it's coming out of the gearbox cover).... is this normal?

And what is this sub water pickup tube all about? My lower leg was missing the plates, bung and filter but I missed it when I bought it. Is it meant to suck because mine throws water out when the muffs are connected? Can it just be plugged? I've tried this but it doesn't seem to make any difference.

I've looked at so many threads but I'm getting a little confused which admittedly doesn't take much so any help would be very warmly accepted. New CDI, stator, magneto... great... now this.

Thanks in advance,

Jamie.

[artdf175]

couple of thoughts
1cm over the cavitation plate, in my opinion, is not enough- should be deeper
you didn't mention the impeller - how old is this part?
and from your comment I am wondering if it is installed correctly
impellers should be replaced at a minimum every two years regardless of use

Art

[Jayster]

Thanks for the quick reply Art.

You're right... I don't know how old the impeller is and although it looked okay it should be changed as a matter of course.

I can't actually get a bucket to go any higher as it gets fouled by the transom brackets and tilt/trim gear, but I've seen engines on Youtube throwing water out of the top exhaust just using muffs?

I think my main query is can I block the sub water pickup or do I need the super expensive kit to put it back into operation. Apparently it was an optional extra on my unit? And... should there be any water coming out of the top of the impeller housing (which isn't cracked, it's coming out of the hole at the top where the drive shaft goes).

Also I'm saying it's getting hot but that is the exhaust plate.... it's not cool by any means but you can leave your hand on it.

Thanks again.

[Solarman]

I'm not sure what you mean in this statement:

"And what is this sub water pickup tube all about? My lower leg was missing the plates, bung and filter but I missed it when I bought it. Is it meant to suck because mine throws water out when the muffs are connected? Can it just be plugged? I've tried this but it doesn't seem to make any difference."

What plates are missing, and is there a plug/ grommet/ plate under the impeller housing (the casting between the water pump cavity, and the exhaust cavity (where the sub-water tube should connect)?

Are the mating surfaces (aluminum webbing/walls separating the exhaust and water pump channels) intact, where the lower unit bolts to the mid-section? If the mating surfaces are deteriorated then high pressure exhaust when running higher speeds can push into the other channels.

If able to take pics of those areas (using good lighting) and posting them in your next reply, this could be helpful?

If the water pump housing is worn out inside, you could have excessive loss of pressure around main shaft?

The only area that sucks water in, is the impeller and housing (water pump). If you have the sub-water tube, it mostly helps out during higher speeds, to keep plenty of water flowing into water pump cavity for impeller to pull in.

Water coming out of prop is normal if on muffs. Can try putting rag on hand over face of prop (idling in neutral), to block exhaust, should come out of exhaust hole on midsection because of the back pressure at prop (when motor is in water back pressure is created by weight of water against exhaust.

Post back when able to let us know.

[Jayster]

Thanks for that Solarman,

I won't be with the boat till Friday but I've ordered a new impeller kit to eliminate one issue. Yes I'm sorry about that vague statement about the sub water pickup but I've never encountered one before so didn't really know it's function. There are no plates, filters or bungs under the water pump but I'll be sure to take a few detailed pics on Friday when the lower unit is off and examine the mesh between the exhaust and water ways.

Thanks again for both your help.

Jamie.

[Jayster]

Hi guys,

The new impeller kit has arrived but I'm dubious about putting it on as something doesn't look right with the housing. I can't find a pic or part no for the housing to compare my one to but it looks bodged. Perhaps that's why I had water coming out of the driveshaft hole or is that just because water was being forced into the unit by the muffs and the impeller wasn't turning?

The exhaust plate and rubber broke as I tried to get them off so I'll need to source new ones and the view of the underside of the unit is all that came with the engine. That is what you see there is what I got.

It's firing up and sounding great now due to a new/second hand CDI, magneto and stator and the compression is good over all 4 cylinders. £500 for this much horsepower is great so I don't mind spending a little time and money if only I could be pointed in the right direction with this cooling.

I hope this is how you add photos, never done it befor but it looks a bit long winded!

Cheers for your help!



https://lh3.googleusercontent.com/59...U=w497-h662-no

[Jayster]

I'll try that again!

[Solarman]

that tube is your sub-water pick-up pipe.

I would also say that there could be quite a bit of deterioration under, and around your watery pump, judging by all the sealant that's there.

I can not tell what condition the grommets are in, but i don't think the one around the sub-water pipe under the water pump is tight? I can not tell if the stainless plate is covering the grommet around the pipe, it should have one. But all of the exhaust makes all of it look black.

You will probably have to take it apart just to see if parts are still good? The water pump housing on the outside looks ok, but still need to see the inside.

Take more pics as you go to post.