Verado 350 temp fluctuations

[bloodman]

I just dont understand the wild fluctuations in the temps on this motor. It didn't start doing this until around 60 hours and now vary wildly between 134-188 degrees. Always ran constant 143-147 before.
I have flushed motor, cleaned thermostat, cleaned poppet and its still the same. I have read others with this problem and no cure has been found. Something had to change in this motor after 60 hours. I guess next I'll pull the lower unit and check the water pump.
Can anyone explain why this is going on? Thanks
Serial 2B549936

[howieranger]

Did you test theT stat when you had it out? My first guess would be a T stat is not consistent.

[bloodman]

Did you test theT stat when you had it out? My first guess would be a T stat is not consistent.

I did test in pan of hot water to see if it opened, which it did but did not test consistency

[EuropeanAM]

I have personally not seen a Verado 350 that ran a consistent 143-147 engine temp under a wide variety of conditions, UNLESS the lake or water temp the engine was being run in was elevated (such as higher than 80 degrees F, for instance).

The ones I've run did vary quite a bit depending on running conditions, especially when operating in cooler engine temps.

You could try a completely new thermostat assembly- but I suspect you will have very similar results.

[620Ranger]

Mine does that in water temps below 50. If the water temp is above 50, it will warm up to 160 then hold steady at 145. Once the water temp gets below 50 it constantly cycles. Will only get to 147 idling then run up to 161 on plane and drop instantly to 135. The process continues on plane, 135 to 161 to 135 to 161, continuously cycles . Slow down and idle it hold about 147. Curious to see if this is normal or not, it’s been that way since I’ve owned it. Runs great, never any alarms, serviced regularly.

[EuropeanAM]

From the considerable amount of testing we did on some early models, this is very similar to the results we had on two (new) engines.

[bloodman]

I just dont understand why my temps were so consistent until 60 hours. Something changed and I dont know what.

[EuropeanAM]

I suspect you are currently running in the coldest water and air temps your engine has encountered (at least since you put it into service June 10th).

Think back... when did you hit 60 hours?

[bloodman]

I suspect you are currently running in the coldest water and air temps your engine has encountered (at least since you put it into service June 10th).

Think back... when did you hit 60 hours?

You are right. I have thought about that since it was mentioned and probably its about the time the water was getting colder. I guess I will monitor this next spring/summer and see what happens. If this is the reason then I am guessing its a factory "slow opening" thermostat that is creating the issue. The motor must heat up faster than the thermostat allows and once open the rush of cold water cools it off fast. It could also be where the temp sensor is located on the motor.
Thanks

[Trond]

I just dont understand why my temps were so consistent until 60 hours. Something changed and I dont know what.

In advance thank you

Trond O

[bloodman]

In advance thank you

Trond O

I have no answer other than it still happens. It doesn't seem as much with warmer water. I wonder if there are some screens somewhere in the motor that need to be cleaned like the opti water intake compressor screen. Since this motor has an intercooler and uses cooling water is it possible?????
I wonder if any service bulletins address this issue?

[EuropeanAM]

No, but we do sometimes see that replacing the thermostat assembly helps. Running back as far as the first models (in the 2005 Production Vintage), I had a 250 and it did the exact same thing.

Was quite familiar with the 350 Sci version, but haven't spend a lot of time looking at what subtle differences occurred when it went to the Production 350 (cooling system, specifically). The Sci was a bear to get up to operating them when water temps were below 60 degrees.

[Trond]

Hi, I replaced the T.stat and it did help, bur mine also gave me
alarm high water temp as well. Verado 400R engine

[bloodman]

My 300 was never like this. It ran consistent temps all the time.
Just was thinking about some difference in the 300/350 and it's the poppet position. The poppet is lower in the midsection. Would th this have some effect.

[EuropeanAM]

Not only is it lower, I suspect it has a bypass and lacks a spray bar that the 300 has. Those were the BIG differences we saw with the 350 Sci...

[bloodman]

Hmmmmmm