DT 85 overheats

[2004 Voyager]

New impeller installed by reputable shop. Thermostat tested, then ultimately removed with no difference. At 3500 rpms or less, runs all day long with no problems. At or above 4000 rpms, alarm goes off. Cavitation does not seem to be the problem, motor is deep in the water. This is on an 18' pontoon.
At a loss here, could use any help- suggestions.
What other factors can cause overheating?
I'm a v-8 Chevy man, not a 2 stroke engine mechanic (yet!)

 

[99yam40]

Re: DT 85 overheats

put the stat back in or better yet put in a new one.
even the v-8 Chevy's need stat in place to help force the water to all areas to cool properly

what did the passages look like as far as deposits?
Did they replace water pump with a kit or just the impeller?

Have heard some motors had problems with exhaust getting into water intake due to corrosion in lower leg, something to look at

 

[2004 Voyager]

Re: DT 85 overheats

put the stat back in or better yet put in a new one.
even the v-8 Chevy's need stat in place to help force the water to all areas to cool properly

what did the passages look like as far as deposits?
Did they replace water pump with a kit or just the impeller?

Have heard some motors had problems with exhaust getting into water intake due to corrosionin loser leg, something to look at

Do not believe t-stat is the problem, will put back in for further testing. It opened in a pan of water on the stove fairly quickly and all the way. I believe just the impeller was replaced, are you suggesting a problem with impeller housing? What is a "loser leg" as you called it? Deposits in passages appeared minimal, nothing looked clogged up. Water squirts out of pee hole in strong stream, fairly warm even with t-stat out.
Any more ideas?

 

[99yam40]

Re: DT 85 overheats

Sorry, that was lower leg or lower unit.

There is the housing, cup, and wear plate that the impeller runs in that need replacing if they have problems

 

[2004 Voyager]

Re: DT 85 overheats

Did not want to, but maybe I should pull the lower unit to check for issues. Fitment between lower unit and upper portion is not "tight", a screwdriver had been used to pry the two apart, and it's either water or exhaust that bubbles out in small quantity when run on the muffs. Don't know if this is a problem, is this a gasketed connection?

 

[2004 Voyager]

Re: DT 85 overheats

Please, anybody else with any thoughts? Timing issues perhaps? Water passages blocked? I need all the help I can get here.
Thanks in advance, Larry

 

[stylesabu]

Re: DT 85 overheats

how hot is motor getting? use a digital pyrometer, its a lazer thermoeter, i believe outboards run at about 150-170 degrees check what temp you have at 3500 and then again at 4000. maybe sending unit is faulty

 

[2004 Voyager]

Re: DT 85 overheats

Thanks for the suggestion, I need an excuse to buy new tools! I wonder if instead of running in the lake, I can leave it on the trailer backed into the water and test run it? Anybody ever try this? It would remain stable on the trailer, easier to get behind it to shoot with a pyrometer, wouldnt have to worry about water sloshing into an open engine or worse yet, dropping the cover as I remove it out on the water.
Any thoughts on this anybody?

 

[stylesabu]

Re: DT 85 overheats

try running with cover off. its noisier but you can point pyrometer at it from drivers seat. as long as your at same distance should tell you if you r running hotter.it don't see why you cant run it on the trailer except you won't be able to put it gear to duplicate the load of running at speed

 

[2004 Voyager]

Re: DT 85 overheats

Can you think of any reason I can't run it in gear while still strapped on the trailer? Too much load on the trailer? Seems I want the motor on full load, simulating the load it would feel traveling while at 4000 RPMs. Ramps are concrete, wash out will not be an issue.
Anybody ever load test a boat in this manner?
Thanks in advance, Larry

 

[99yam40]

Re: DT 85 overheats

Do it with the Yamaha test prop like I said before, that is what they are designed for.
Do it with the normal prop and it is like the prop is pitched way too high and overloads motor just like when boat is way too heavy to get out of the water on plane

 

[2004 Voyager]

Re: DT 85 overheats

I see now where another poster has suggested trailer testing also. A DT 85 is actually a Suzuki motor, if I had a Suzuki test prop I would try it. Would trailer testing with regular prop put too much strain on motor, resulting in overheating? Just asking here, want to get this overheating issue resolved before this season is over.
After searching past postings, seems a lot of overheating problems are from some grommett and or tube being pinched. Are DT 85s built in a manner that this could happen?

 

[gbak]

Re: DT 85 overheats

You might have the same problem as I, took me half the summer to find it!

Check the intake direct below the impeller steel panel!
The upper shaft seal can (if lockring rusts off) get loose and block the water intake to the impeller.
Motor runs fine and on low rpm, but when rpm rise the water will suck the seal up against the panel and block 80% of the water intake.

 

[2004 Voyager]

Re: DT 85 overheats

Sounds like time to pull the lower unit! Was hoping to avoid this, but seems everything is pointing to a problem down there somewhere. Saw a video of this on You Tube, anything I should be advised of before I tear into this?
Thanks for all the advise from fellow IBoaters, Larry