Dt 9.9 cooling problem

[Billwrd]

My dt 9.9 has exactly the same problem as reported by Chris p everything is fine whilst in gear forward and reverse everything fine at idle revs in neutral, up the revs in neutral and the cooling water stops pumping as Chris p had changed all the gaskets and impeller I thought the problem must be elsewhere so I took the prop off and ran the engine and hey presto the problem disappeared but I still can't figure out what's going on. Any ideas would greatly appreciated

[keakar]

its the prop wash vortex causing it then. whats happening is the prop is causing water not to be drawn into the intake.

I don't know what it looks like but try a different style of prop before you start thinking of ways to block the prop wash from hitting the water intake directly.

I hope you sent chris a PM telling him about your discovery

[Billwrd]

I wonder if changing the spacers on the prop might make a difference? I think I have to bring the engine ashore and experiment. I can't seem to can't seem to contact Chris p on the forum or I would try and have a talk with him

[keakar]

I wonder if changing the spacers on the prop might make a difference? I think I have to bring the engine ashore and experiment. I can't seem to can't seem to contact Chris p on the forum or I would try and have a talk with him

maybe a smaller diameter prop would not interfere with the water intake since the blades wont be as close to it.

definitely experiment on shore and I hope you can find access to different prop sizes to test since its not realistic to go buy a bunch of different props just to play around with it

[Billwrd]

What really confuses me is why this only occurs when the engine is in neutral with the prop at rest ?

[Moonlighter]

Ok, i have resisted so far, but now i will ask the obvious question:

Why the heck are you revving the engine in neutral anyway???

And if I understand you correctly, in gear at any revs it is fine, yes?? And at idle in neutral it is also fine, right??

If it ONLY ever overheats in neutral when you rev it up, well, don't rev it up in neutral would seem to be the sensible solution.....

Not trying to be smart, I am just completely bemused as to why you would rev it up in neutral, it seems to be a pretty well pointless thing to do.

[Solarman]

dt 9.9 cooling issues.

There are a couple possibilities...In the gear case picture: part # 25 & 26 (both exhaust seal parts) might be worn/damaged allowing exhaust to access/ block water entering the pump if more than low idle in neutral. Likewise, part #11 may be damaged/ corroded allowing escape of exhaust into the pickup screen located just above. Maybe the propeller is not fitting inside part # 11 properly because it is shimmed out to far.
In the same parts picture it does not show any shims behind the propeller, therefore any shims under the prop could also cause such a problem.

[keakar]

What really confuses me is why this only occurs when the engine is in neutral with the prop at rest ?

ok, forget what I dsaid about prop wash, it no longer applies.

as I understood it, chris p reported he had this issue with it only in forward gear not in reverse or neutral and just between idle and just starting to increase rpm

if its doing it in neutral then it might be the engine isn't efficient at getting the exhaust out without some forward movement to help draw it out and as the other guy said, why are you revving it up in neutral? you may only do this to warm up a cold engine and then only a few rpms so just don't rev it up in neutral and there is no problem to solve.

[Billwrd]

Ok I'll ignore the comment about why rev it when it's in neutral whether you do or not is not relevant it should still pump water. Anyway I found the problem, there is a spacer at the rear of the prop if it is put in the wrong way round it pushes the prop further aft and creates a gap between the back of the prop and the cowl it fits into, this gap allows the exhaust gases when in neutral to escape behind the prop tube and stop the cooling water entering the intake this only happens at revs over idle. This gap is small about a quarter inch so is hard to spot unless you look. Anyway turn that spacer around and the problem is gone

[keakar]

well glad you got it all sorted out.

was this something you did or was the washer on backwards from the factory?