Yamaha 100 telltale stream at 75%

[GxK]

Ahoy, C-Brats!

Despite my best efforts, the telltale stream on my starboard Yamaha 100 is peeing at about 75% at all engine speeds. I only have six more boating weekends this season before the TomCat goes up on the hard and can be fully inspected.

Am I at risk of damaging the Yamaha if I continue to run at 75% stream for another, say, 15 hours?

--Georgs

[thataway]

Hi Georgs!
Have you run a piece of lawn trimmer nylon line thru the tell tale tubing?

I assume that you mean that the flow now is 75% of what you saw earlier.

Is it both engines?

When was the last time that the engines had the impellers replaced?

Do you have an IR thermometer--and have you taken a reading of the heads of the outboard?

Regards!

[GxK]

Hello, Bob!

Only the starboard engine is affected. By 75%, I mean about 75% of full-strength stream. Which I can see on the port engine.

The impellers were replaced about a year ago, maybe 30 hours ago. Records not at hand.

I'll have to get my hands on an IR thermometer and the string you cited. Have been afraid to push a wire into the tube.

In the meantime, am I at risk running the engine for one to two hours?

--Georgs

[thataway]

I would suspect that there is some debris in the tell tail tubing. If the flow were impaired the temp alarm would go off.

I would run it and keep a close eye.

[GxK]

Bob and others--

I ran the Tomcat at cruising speed (4,200 RPM 22 MPH) for 30 minutes twice today.

At idle, both engines register about 100F on my IT gun. After 30 minutes, the problem engine warms up to 125F at the top cylinder, 110F at bottom. The other engine stays around 100F.

I only have about a dozen hours left in this season with the longest run being about 60 minutes. I'm tempted to keep operating, monitoring the temps every 20 minutes.

Once I'm on the hard for the winter, I'll fully flush both engines and thoroughly clear both telltale tubes—and hope that';s the end of it.

--Georgs

[potter water]

It is interesting that only those of us who have twin engines are constantly comparing. I doubt that you'll find anyone with a single engine boat who will be able to tell you from day to day whether they are at full pee or 75% pee. Lots of pee versus a dribble, yes, that is going to get attention.

So, my vote is that you are in fine condition and to enjoy your boat the rest of the season. These newer engines have the overheat alarm for a reason. If that isn't going off, relax. If it does, you have another nice engine on the other side of the stern. No if there is no pee or only a dribble, then the overheat alarm should be going off.

Note that the manufacturers instructions for you engine don't specify what is a 100% versus a 75% or 50% or 10% pee stream. They just want you to check that it is peeing. Me, I calibrate my Suzuki's using the comparison with what is happening when I pee.

[thataway]

Generally when there is just a diminished stream you think of a partial obstruction of the flow thru the telltale. I have not owned a 100 HP Yamaha, but my recollection is that on the 115 Yamaha and 90 Yamaha I owned the telltale stream was warm after running-ie that the telltale flow goes thru the head and is warmed vs those outboards which which the telltale flow does not go thru the head passages and comes directly from the water pump, and is always cool.

Were those engines run mostly in salt water before you bought the boat? What is the salinity of the water where you are boating now? If you are not running in fresh water there is less chance of salt build up in the heads, which has been a problem in some of these motors. I did have problems with the 90 due to salt shortly after I purchased the engine used. I had the passages cleaned and problem solved.

With these low temps after running for 30 minutes at cruising speed there does not seem to be any risk. The alarms go off at about 180--but even a short time at that temp should not cause any problems--and you would immediately shut the engine down with the alarm, and come home on the second motor. Let us know what you find.

[Will-C]

On our 150 Yamaha the pee stream goes thru an aluminum block that also has the fuel line running thru the same block to cool the fuel for better atomization I guess. It would be good to figure out now why the one engine runs 25 degrees hotter before you spend all winter thinking about it and then having to wait till next year to see if you really got it straightened out. At least with some season left it allows for testing before putting the boat up for the winter. I wonder how many years has it been since the water pump impellers have been changed?
D.D.

[potter water]

He said impellers were changed about one year/30 hours ago.

[C-jeep]

Mud dauber wasps love the tell tale openings and have clogged up mine more than a few times. Up here on Vancouver Island has been a great summer for cruising and wasps. Find a gauge of trimmer line that fits your telltale and keep it handy.

[Sunbeam]

Question: How does the tell-tale system relate to the actual cooling system? If I'm reading and understanding this correctly, the tell-tale stream itself can be clogged without the actual engine cooling system being clogged (not saying that's the case here, as one engine is running warmer).

If that's true, does it mean that a reduced tell-tale stream may or may not indicate an actual engine cooling problem; but that conversely, an actual engine cooling problem will be indicated by a reduced stream?

[Will-C]

I don't believe that if in fact the motor does not show a steady stream or no stream that the motor will necessarily over heat. But I have always looked for a problem if the stream was not present. I had an experience where my impellor had just been replaced. The not too long afterward on an outing I noticed to no stream before backing the boat off the trailer. I pulled the cowl and pulled off the water hoses on both sides of the aluminum block they run through before they exit the motor. As mentioned before the gas line also runs through the same aluminum block but adjacent to where there water line passes through. I ran a piece of rigging wire down through the water passage and hoses then blew them out important not to suck doing this. Then reinstalled everything started the motor and wa-la every was fine nice stream after the remaining sediment washed out. Since then I put apiece of duct tape over the hole to prevent unidentified flying objects from doing what they do in there. Sometimes the duct tape leaves a little residue which cleans off easily with a rag and some WD-40.
D.D.

[thataway]

Sunbeam it depends on the engine--and I don't have the answer as to which tell tails are after the water goes thru the cooling passages on the heads. If the water is warm then it goes thru the cooling passages. If it is cold, it does not.