Suzuki DT9.9c water cooling stopping

[Chris P]

I have a problem with irregular cooling in my 1995 DT9.9C outboard. Right now I am running it in a deep tub.

At low rpms (at a very low idle) the engine runs great. Water flows out both the telltale and the main discharge nicely. It will run fine like this for a long time. But as soon as I increase the throttle slightly (not much - not even a fast idle), water stops coming out the main discharge, then after another 10 seconds or so stops coming out the telltale. Then I only feel hot exhaust coming out both. The engine temps start to climb at this point. If I back the throttle off to a very low rpm, water starts to discharge again out both outlets, and temps return to normal. This cycle repeats every time I increase the throttle.

This happens whether the thermostat is in or not (thinking it was heat related, I thought the thermostat might be causing the issue).

I can blow compressed air through the cooling system and use a hand pump to force water through it as well with no problems.

I have replaced the following items so far (most needed to be replaced):

thermostat
thermostat gasket
thermostat cover
water pump case bushing
impeller
oil and water seals for upper water pump housing
plate under water pump (pump case under panel)
Cylinder head gasket

I initially thought it was blockage as the old impeller wore out from the previous owner. But everything seems to run through the cooling system when it is running, and the telltale is strong at the low rpm. I have removed the cylinder head, water pump, etc... and have found no blockage. I am assuming if there was blockage, no water would come out the telltale at low rpm (or at least it wouldn't come and go like it does).

I thought it might also be a vacuum leak in the water cooling, but all gaskets seem good and it runs well at the low rpm.

The two possibilities I am leaning towards now are:

1. Right now I am just running the motor in a deep tub and possibly in the confined area the exhaust coming out the leg is interrupting the water intake for the pump at higher rpms. If I ran the engine in open water, perhaps this might disappear. This seems unlikely though.

2. There is a leak between the exhaust and the water cooling. Perhaps a bad gasket under the powerhead. As I rev the engine up, the exhaust leaks into the cooling passages, blocks off the water, and that's why I feel only hot exhaust coming out the outlets. When I decrease throttle, the exhaust output lowers, and the water cooling starts again.

I am thinking it may be the latter, but I am wondering if I might be missing anything?

[keakar]

#2 is possible but first when you replaced the impeller and water pump housing seal did you put the water pump housing seal in upside down? that is with the open lip spring side visible on top? if not you put it in backwards and it will not hold pressure to pump through the cooling system. this seal gets installed upside down compared to how you normally install seals.

also you didn't mention the water tube seal, is it in good condition? did you replace that?

[Chris P]

Are you referring to the two seals at the TOP of the housing? The oil seal and the Water seal that insert into the top of the water pump housing and go over the driveshaft? If those, then the open lip spring side is still visible on top - but that is how the old one was and how my manual seems to show it.

If you are referring to the gaskets BELOW the water pump case panel and gasket, I haven't replaced those. I have replaced the Under Case panel and gasket though, just not the oil seal below that.

Yes, the water tube seal appears in good condition.

Thanks!

[keakar]

sounds like you did it right.

most oil seals have the spring lip side to the inside but the water pump housing seal put them on the outside facing up. if you put it in wrong the water pressure just squirts out around the shaft rather then up the water tube.

as long as you put it all back the same as original there are no issues but some people forget to take note of such simple things and can make mistakes.

I think you need to seriously investigate #2 to try and find the leak

[Chris P]

Thanks for the feedback Keakar. Good to get some reassurance that I may be on the right path. I just hope I eventually clear up the issue!

sounds like you did it right.

most oil seals have the spring lip side to the inside but the water pump housing seal put them on the outside facing up. if you put it in wrong the water pressure just squirts out around the shaft rather then up the water tube.

as long as you put it all back the same as original there are no issues but some people forget to take note of such simple things and can make mistakes.

I think you need to seriously investigate #2 to try and find the leak

[Solarman]

before checking power head...

Am not sure of the dt9.9...if it is like my dt140's. I had to rebuild the sub-water pickup, located under the water pump, because as exaust pressure increased, it was pushing the water back out of the pump. This caused my engines to overheat after 2500 rpms. I also had to repair the housing that separates the exaust passage from water passage with some epoxy (corrosion had eaten through the aluminum webbing - where the foot bolts together with the housing). If you're looking at the foot off the housing, just above the prop a stainless tube runs through the exaust passage to under the water pump. On the 140's there is a rubber grommet that seals the 2 passages. I do not know your motor, but by chance this might help...
It is easier than the head... Hope this helps.

[Chris P]

Thanks Solarman - I am thinking something similar may be happening in my engine.

Will let you know what I eventually find.

[Chris P]

Just a quick update. I ran the outboard in open water yesterday for the first time in a year or so, and it exhibited the same issue.

It is still a bit of a mystery to me. I had a friend come out who is far more knowledgeable on motors than I, and he had never seen anything like it before - he was even suggesting it might be a flaw in the engine design.

Just to recap, here is what it did in open water:

1. In gear, it ran flawless. Forward or Reverse, from 10%-100% throttle it ran perfectly. Ran cool with good cooling.

2. In Neutral at LOW rpms (just above stalling), it ran flawless. Idled like that no problem.

3. In Neutral at slightly higher rpms (maybe 100-200 rpm higher at most - less than a 1/4" turn of the throttle), after 10-15 seconds the cooling completely cuts out and the engine overheats. Turn back the throttle a tiny bit and the cooling restarts.

Essentially it seems I can run the engine all day as long as I keep it very low at idle or in gear. Turn up the idle a nudge and the cooling shuts down. Fortunately this way I think can still use the engine, as long as I don't idle tool fast (which there is no need to) 0 but I will have to monitor the issue to ensure it doesn't get worse.

But if anyone has any further suggestions as to why this happens ONLY in a fast Idle, I'd love to hear from them.

[Solarman]

overheats at idle up?

I might think the screen, or water passage leading to the water pump may have a slight blockage.

[keakar]

very strange since water pressure really wouldn't have changed in your idle to just above idle issue so if the boat were moving I would think its a prop or boat issue where the water intake is in disturbed water (bubbles) or prop wash creates a vaccum at the intake ports and not able to get enough water into the intakes but it does this in neutral when your not moving so it cant be that.

I guess you just have to adjust to not using that idle speed and learn to live with it, if it were a design flaw with the motor it would be a well known issue by now

if it bugds you and you want to try to fix it all I can suggest is you take the midsection apart and replace and inspect all seals, gaskets, and matting surfaces between the lower unit and the engine itself and inspect the housings for corrosion pin holes between any chambers and if you find nothing, reseal them so you know nothing is leaking there.

I might think the screen, or water passage leading to the water pump may have a slight blockage.

but if this were true he wouldn't cool fine at idle because any blockage or restriction would stop water flow and cause overheating then too.

[Chris P]

Thanks guys. Keakar, that is my line of reasoning too.

I will update if I ever find otherwise.

[Solarman]

reply to keaker

keaker...but if this were true he wouldn't cool fine at idle because any blockage or restriction would stop water flow and cause overheating then too.

I would agree if totally blocked, but in neutral the water is only flowing from the movement of the impeller. A slow idle, maybe enough water gets through, but slightly higher idle causes overheating... I feel a partial blockage before the pump might be the first check point. I might also look at the exhaust ports while checking there.
I know i'm not familiar with the 9.9, and I tried to pull up a diagram of the parts, but couldn't get that either. So am trying to visualize in my mind all the aspects of water flow.
I would not think design flaw either.
Good luck in the search.

[keakar]

keaker...but if this were true he wouldn't cool fine at idle because any blockage or restriction would stop water flow and cause overheating then too.

I would agree if totally blocked, but in neutral the water is only flowing from the movement of the impeller. A slow idle, maybe enough water gets through, but slightly higher idle causes overheating... I feel a partial blockage before the pump might be the first check point. I might also look at the exhaust ports while checking there.
I know i'm not familiar with the 9.9, and I tried to pull up a diagram of the parts, but couldn't get that either. So am trying to visualize in my mind all the aspects of water flow.
I would not think design flaw either.
Good luck in the search.

I mentioned that because he noted that the water would stop coming out of the tattle tail at just above idle so I suppose it could be trash that doesn't restrict at idle but just above gives it enough flow for the trash to move and block flow and when more speed is given it forces its way around it.

that's what it sounds like to me that is happening but the fact this problem is shared by other motors is strange and makes no sense because a random new motor may have trash or foreign body in a water passage but i wouldn't think it could happen to other motors too

[Chris P]

Just to recap:

Essentially it runs all day at a very slow idle (just above stall), or at any RPM in gear (Forward or Rev). The only place it cuts out is when I throttle up a little in neutral... then like clockwork, the discharge out the main port at the top of the leg stops in ~10 seconds... then the telltale stops ~another 5 seconds later. The it overheats.

No form of throttle in Neutral will restart the water flow. Only turning the throttle back down to above stall restarts the water again (after maybe 10 seconds).

This happens in moving water, Stillwater, and a bucket.

I can run compressed air and water (with a hand pump) through the passages without a problem.

It COULD be a blockage issue I guess, but so many signs show that water flows excellent 98% of the time that I keep ruling that out.

[keakar]

do a muriatic acid flush just to rule out any corrosion issues and if its a tiny leak somewhere the flush will make it more obvious to find

also did you ecver replace the water pump housing shaft seal? that might just be your gremlin