Somebody Explain this to me Re: T-Stats Question

[boscoe99]

Yamaha recommends inspection/replacement of the thermostat every year or 100 hours, whichever occurs first.

If it looks particularly grungy after that amount of time then maybe the inspection interval needs to be shortened. Try every nine months/75 hours and see what is to be seen. Adjust as necessary to fit whatever is happening with a particular motor.

Some may find they can go more than a year or 100 hours. Too many variables for a one size all inspection interval to fit everyone. Where I boated I had a several miles run up a fresh water river before I got to by storage place. My thermostats looked pristine for many years and many hours. Different salt water has diffferingg levels of salt and other minerals dissolved therein.

[panasonic]

Try just the muffs with the engine running and measure the temp at the thermostat housings then.
I suspect that when you have both the muffs and the engine flush connected there is just to much water being forced through the engine to allow it to come up to temp with the engine at idle. The water is removing the heat faster then the engine can produce it.

A engine at idle under no load is not workin very hard. A big engine like that has a lot mass to heat up to operating temp at idle..no load.

[HMBJack]

Okay thanks guys. It all seems like a total waste of time though.

If in 10 minutes, you're only flushing a Half Gallon, why bother doing it at all?

It seems like a bad design by Yamaha and bad advice to promote FW flushing like there's no tomorrow.
It just doesn't "work" as evidenced by my strict maintenance program (see T-stat bore photo after 14 months above).

Two final questions -

1. Going back to muffs with engine on Vs. no muffs and only flushing with the garden hose fitting - Since very little water passes through the closed T-stat - Does it make any difference in which way to flush? i.e. With Muffs engine on? OR With the garden hose fitting and engine off?

And,

2. Can a small hole be drilled into the face of the T-Stat cover to allow more water to pass through? Like a small hole drilled in the center of the blue mark in the photo above. A half gallon in 10 minutes is terrible! Maybe a small hole will allow a whopping 2 gallons in 10 minutes... Someone could actually measure this if they want.

Justification for drilling a small hole: If the T-stat "leaks" a little, so what? The engine will still warm up to 158 degrees - it just might take a couple minutes longer - so what? At least you won't lose the engine due to T-stat bore corrosion.

[fairdeal]

The thermostats should pass water even when they are fully closed.

They do indeed - although I suspect because they are designed to allow a small amount of air to pass when fully closed.

What you can do is to remove the dump hoses at the bottom fittings and then see for yourself how much water is bypassing the closed thermostat.

When I did that with my F225TXRD - using a 60 PSI, 5/8" garden hose connected to the flush port -

I measured flow through the closed thermostat of 200 mLs / minute. That's about 1/2 of a gallon in 10 minutes.

[boscoe99]

I can see the motor not getting hot enough to allow the thermostats to open when it is being idled. I instrumented an F150 to measure oil temperature and could never get the oil temperature up to a hundred degrees running the motor on flush muffs.

The thermostats should pass water even when they are fully closed.

What you can do is to remove the dump hoses at the bottom fittings and then see for yourself how much water is bypassing the closed thermostat. Then maybe remove the thermostat completely (simulating it being opened) and then see how much water flows out of the bottom of the dump tube.

[HMBJack]

Earlier this week, I put up a post titled "T-Stat Bore check - FW Flushing" because I had a good amount of salt crystal accumulation after just 14 months of use. See photo below.

I explained that I regularly flush with the engine OFF using the garden hose fitting. These are on a pair of 2006 F250TXR's.

Advice from some of you said I needed to flush with the engine ON using the muffs. For example:
" The thermostats will CERTAINLY OPEN when running on muffs and ALLOW flushing water on both sides of the stats.."

I am now of the opinion that the above is NOT at all true.
The T-stats stay locked shut and do NOT OPEN unless the internal water temps reach 158.

Here is a little experiment I performed today with my boat up on a lift:
1. Connected FW hoses to a set of muffs as well as to the garden hose fitting at the base of the powerhead.
2. Started the engine and let it idle in neutral which is about 600 RPM's.
3. With a digital heat sensing gun, during every minute of run time, I measured the temp of the starboard side T-Stat housing (outer casing where the T-stat sits inside).
4. Temperature was 74 degrees before I started the engine then it rose to 88 after 2 minutes then ranged between 90 and 98 until I shut off the engine after 20 minutes.
5. I repeated the above 4 steps on the other engine and experienced similar results. Temp range was 91 to 109 over a 17 minute run time on muffs + garden hose fitting.

When I returned home, I took a set of identical T-Stats I had removed from my F250's and placed them in a bowl of water measured at 100 degrees per a digital mouth thermometer.

None of the T-stats opened at 100 degrees. I warmed the water up to 109, my highest reading while idling, and again, none opened up - not even partially. They of course all opened when exposed to boiling water (~212).
This all makes sense since the T-stats for an F250 is set to open at 158 degrees.

So - per the above, I can conclude flushing with the engine ON with muffs does NOTHING to clean salt out of the T-stat bores.

My objective is to minimize corrosion in the T-stat bores with the premise that one needs to flush BOTH sides of the T-stat. Well, that does NOT happen in any FW flush procedure I can think of.

Please advise if you have a different view. Thanks, Jack