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Poppet Valve 2106 Verado 350ís

Old 01-08-2019, 07:27 AM
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Default Poppet Valve 2106 Verado 350ís

Iíll make this a quick question and couldít find any threads on this:

I have a set of 2016 Merc Verado 350ís...

Assuming the thermostate and water pumps/impellers are good and new, would a bad or old poppet cause oscillating temp gauge and overheat? Even though the water pressure is good? Oscillating temps as low as 111 degrees, bouncing up and down to a high of 200+ and then alarms and limp mode.

I can go into more detail, but curious of the function or malfunction of the poppets...

Thanks!
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Old 01-08-2019, 08:47 AM
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Originally Posted by Kiedroj View Post
Iíll make this a quick question and couldít find any threads on this:

I have a set of 2016 Merc Verado 350ís...

Assuming the thermostate and water pumps/impellers are good and new, would a bad or old poppet cause oscillating temp gauge and overheat? Even though the water pressure is good? Oscillating temps as low as 111 degrees, bouncing up and down to a high of 200+ and then alarms and limp mode.

I can go into more detail, but curious of the function or malfunction of the poppets...

Thanks!
Check spring and for corrosion in thermostat.
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Old 01-08-2019, 08:49 AM
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I searched your manual for a poppet and it doesn't list one.
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Old 01-08-2019, 08:56 AM
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Originally Posted by Kiedroj View Post
I have a set of 2016 Merc Verado 350’s...

Assuming the thermostate and water pumps/impellers are good and new, would a bad or old poppet cause oscillating temp gauge and overheat? Even though the water pressure is good? Oscillating temps as low as 111 degrees, bouncing up and down to a high of 200+ and then alarms and limp mode.
I had the same problem with my 300's. It only happens when the sea water is below 65*. When the water is warm, my temps barely move from 150*. I had some small holes drilled in my t-stats and it helped but didn't completely fix the issue. I think Merc has finally issued a service bulletin. I've been mentioning this on every forum I can and starting to see others with the same issue. I guess a lot of guys don't use their boats when it's cold and never noticed this.
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Old 01-08-2019, 08:59 AM
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Originally Posted by SWF Pontoon Angler View Post
I searched your manual for a poppet and it doesn't list one.
I does have a poppet, but I thought the purpose was to bleed off excess water pressure?
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Old 01-08-2019, 10:54 AM
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I’ll have to see if I search for the service bulletin on it. I’d find it odd that an engine goes through this kind of oscillating of temps when the water are below 65 and not have a service bulletin right?

We use our boat a lot in the spring and late fall to fish...

We did replace the poppets, thermostates, water pump (impellers) and if I have to, I’ll even change out the temp sensor...

It keeps me awake at night... lol
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Old 01-08-2019, 11:37 AM
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I have 2017 350's and experienced the same issue on one motor which started after a high speed turn. Mechanics found pieces of wood in the thermostat. The last 3 trips were in the bay. No problems in the ocean.
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Old 01-08-2019, 11:56 AM
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Thanks! I wished we would have found something like wood in the thermostate, but we replaced them anyways... still randomly did the same thing...
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Old 03-03-2019, 10:11 AM
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I’m slow on my response on this... I searched for a service bulletin and never found one... anyone else have any luck? I asked my mechanic and he didn’t see any bulletins by Mercury... we did replace impellers and poppets and next would be the sensor... but until we splash the boat in a few weeks, we won’t know if it’s solved or not
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Old 03-03-2019, 01:56 PM
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Posted on another web site. Allowing some water to leak around the Tstat will allow the tstat sensor and the temp gauge to see the actual water temp from the block.


How cold is the water you boat in when you see the temp variations? The poppet is most likely not the issue.

More likely scenario:

The coolant temp sensor is downstream of the thermostat.
The thermostat actually makes a good seal preventing any/most flow from the block to the temp sensor when it is closed.
As the motor runs in very cold water the temp goes down to the point where the thermostat closes.
The temp sensor then shows a low temp.
The water holding up in the block heats up very quickly due to no/low flow through the thermostat.
When the thermostat finally opens, the hot water then contacts the temp sensor and causes the temp to go up.
As the hot water is replaced by cooler water in the block the temp sensor comes down and Tstat shuts.
Cycle continues over and over.

Usually this occurs in colder water. In LA I have only seen this temp swing in the cold, cold winter (for LA). Could imagine a very common occurrence in the north.

Recently I have seen some posts on another web site where techs are drilling small holes in the thermostat to provide flow to the temp sensor all the time which has alleviated the temp swings. Interesting thought right there.
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Old 03-04-2019, 03:18 AM
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We see this issue during the winter from Verado powered boats running in The Mississippi River. Itís the thermostat causing the temperature fluctuations. Some only see major fluctuations while others will actually get an alarm. Drilling the 1/8Ē bypass hole has worked, but it can easily become clogged with debris. We have been trying to come up with a way to use a small bypass hose. Just need some extra time to test a few different ideas.
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Old 03-04-2019, 06:13 AM
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Originally Posted by davidwademarine View Post
We see this issue during the winter from Verado powered boats running in The Mississippi River. Itís the thermostat causing the temperature fluctuations. Some only see major fluctuations while others will actually get an alarm. Drilling the 1/8Ē bypass hole has worked, but it can easily become clogged with debris. We have been trying to come up with a way to use a small bypass hose. Just need some extra time to test a few different ideas.

Yes just need some way for the water from inside the block to flow at a slow rate to the TStat sensor on the downstream side of the tstat. That way the thermostat sees the actual water temp in the block and will even the temp out at the temp sensor.

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Old 03-05-2019, 11:47 AM
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Thanks!

I won’t be able to launch my boat until the end of March, so I won’t know how the new impellers, Thermostat and Poppets will help or not until then.
Are you all saying that once the Chesapeake Bay water warms up, this issue is likely to go away?
What about changing the sensors? They seem inexpensive and way not?

Seems crazy this is an issue on such an expensive 350 and so new (240hours) to be happening..

thoughts?
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Old 03-05-2019, 03:54 PM
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Originally Posted by Kiedroj View Post
Are you all saying that once the Chesapeake Bay water warms up, this issue is likely to go away?
My issues go away completely once the water is 70*. Between 65-70* I get some temp fluctuation, below 65 the temps swing up and down and the motors will sometimes alarm. Here's a page from the manual. It looks like if you are running in cold water, or running fast, more water psi is needed.

Last edited by 30Concept; 03-05-2019 at 04:06 PM. Reason: add picture
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Old 03-05-2019, 04:06 PM
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..
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Old 03-05-2019, 04:13 PM
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Originally Posted by davidwademarine View Post
We see this issue during the winter from Verado powered boats running in The Mississippi River. Itís the thermostat causing the temperature fluctuations. Some only see major fluctuations while others will actually get an alarm. Drilling the 1/8Ē bypass hole has worked, but it can easily become clogged with debris. We have been trying to come up with a way to use a small bypass hose. Just need some extra time to test a few different ideas.
Happened to me on my port and starboard engines, the bypass hole worked for me as well
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Old 03-06-2019, 02:24 AM
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Originally Posted by z3axv View Post
Happened to me on my port and starboard engines, the bypass hole worked for me as well
On the new 350's? I have yet to run mine up this way, but certainly our early season water temps will be in the high 50's low 60's. I'll have to keep a close eye on them.
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Old 03-06-2019, 05:26 AM
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Originally Posted by Greene Machine View Post
On the new 350's? I have yet to run mine up this way, but certainly our early season water temps will be in the high 50's low 60's. I'll have to keep a close eye on them.
Yes, fluctuations from 145 rising rapidly past 215, overheat alarm would sound. Bring it back to idle and temp drops immediately to 145. Funny thing is that past 4000 rpm motors ran under 150 degrees all day long. The drilling of the thermostat prevented the overheat and kept the temp fluctuations at a minimum. This happened multiple times on my port engine, once on my starboard engine, no issues on my center engine. Heard it also happened on a quad 350 Invincible cat and drilling the thermostats solved the issue.
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Old 03-06-2019, 05:46 AM
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Well if your overheat problems are at speed,look to the poppet as being the issue.The basic function is that the stats control temps at idle and the poppet at speed.Function is based on water pump pressure and the poppet acts as a pressure relief valve.With a good pump,pressure exceeds the poppet spring pressure at say 2500 rpms and after that any pressure above the spring rate is bled off through the poppet valve.The result is better cooling at high speeds.You can alter the stock spring tension by clipping a coil or two off the spring which would open the poppet sooner and in theory stop the temp spiking and allow for better high speed cooling..A water pressure gauge is a great indicator of what your cooling system is doing.
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Old 03-12-2019, 07:09 AM
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I am having the same issue. I thought I got trash in the cooling system but I took it to the shop and that was not the case.

It was throwing error code of 206 according to the tech. He said the pressure was low so they replaced water pumps on both engines. This was August 2018. I ran the boat several times with no issues through October. I just put her in the water this past weekend for first run and same issue. Starboard engine threw up a fault at ĺ throttle temp jumped to 217. When I backed down it immediately dropped to 143. The port engine was not behaving exactly like that but was still fluctuating more than expected.

I pulled her out and went directly to Leisure Marine in DíIberville. This was last Saturday.

What if anything should I tell them to help with their diagnosis. I really donít like giving advice to folks where I am no expert. But I am not sure if they are aware this may not be an isolated issue. Has anyone gotten direction from other Mercury authorized techs?

suggestions?

thanks
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