Tstat question??

[Katemma Life]

Hi,
I have twin Mercruiser 350 MAG MPI's and am curious to know... when does the Tstat close?

Scenario: I'm winterizing my engine and am running one of the engines on the garden hose until temp reaches 150 degrees. Now I shut off engine, switch the garden hose over to the antifreeze bucket, open the valve on the bucket and turn on the engine. The engine was only off for 2 minutes but... does the Tstat close and then need time to re-open or does it stay open allowing the AF into the engine right on start up - the engine temp never drops below 145 during the transfer..
thanks!

 

[RollerCoastr]

I like to avoid the doubt. Even on my 20 year-old, rusty salties where every other bolt seems to be hopelessly seized, I can pull the t-stat housing in a matter of minutes.

 

[Katemma Life]

ok sure but how is it 'supposed to operate'?

 

[Lazy Daze]

We have to back up a bit. Your method of running AF into the engine is flawed. Because you didn't drain the water, first, you will only have "some" mixture rate of AF:Water. What it is, is anyone's guess. Even if you did drain the water, first, there is still some trapped raw water in the engine that may not get pushed out using the bucket method - unless you remove the t-stat, first. But pouring the AF into the engine is VERY easy and is GUARANTEED to work. On the plus side... you get a "re-do" and can practice more!

There's too many variables to say exactly when the t-stat closes in this situation, though. And, it's not an "immediate" close/open type thing. It's gradual.

 

[LUnaCY]

I did what Lazy Daze said above. Super easy to take off three tstat connections and dump 5 gallons in. After I drained the blocks I saw the colored antifreeze push some water out until it was mixed color and finally looked like unmixed.

 

[Katemma Life]

so, the approach to winterizing is noted.. I know that a 50/50 mix of AF and water will not freeze and ceretainly not expand so I am less concerned. I'm interested in knowing the mechanics of the Tstat.. maybe I need to google it.. Does the Tstat open and close on a temp? does it close on engine shut-off? How does it function?
Thanks

 

[Lazy Daze]

I'll assume that wherever you are that a 50/50 is OK for your worst temps. But you don't know, for a fact, that you have a true 50/50 mixture rate. As I mentioned, you have "some" mixture rate - and it may not be the same everywhere. But, if you're comfortable with it, it's your boat and your call. I'll just mention that every year I get to replace a few blocks in the Spring from customers that do it the way you did.

The t-stat starts to open at it's rated temp. It opens and closes based on temperature - not whether the engine is running, or not.

 

[CliffA]

as Dennis stated a t'stat will 'start' to open at the temp that is stamped on it...it will 'fully' open when the coolant or water is somewhere around 5 -10 degrees hotter than that....

and the reverse of that when the coolant or water cools down will cause the t'stat to close....

cliff

 

[RollerCoastr]

Pull it to add AF, and take it home to the kitchen (when you're admiral isn't watching.) Tie a string to it and and boil a pot of water. Dip the t-stat in alternating hot and cool water. It's a right-of-passage for every guy who wants to know how things work. It's worth at least 10 minutes of fun during the least-fun time of year.

I noticed last wkd that neither of my engines got above 140, even after a 10-mile run. I probably should've followed my own advice and yanked those t-stats...!

 

[Woody]

Depending on variables the thermostat may not get to full open before starting to close again. In the OP's case, if engine warmed until thermostat was fully open it would probably still be at least partially open if he changes his hose to the antifreeze jug quickly, but.....when the cold antifreeze hits the thermostat would the thermostat stay open long enough to circulate/fill the engine properly?

 

[Espos4]

Lots of good advice from some very experienced people here.
Stop worrying about when or if the thermostat is open.

My simple procedure is:
Disconnect the block drain hoses from the drain manifold below the crankshaft pulley.
Verify that the block drains aren't clogged, clear them if necessary and reattach to the drain manifold.
Remove plugs from under the exhaust manifolds and clear any debris from inside.
Run on muffs with fresh water for 15 minutes.
Change the oil
Run again to fog the motor and shut it down
Remove thermostat and pour in the antifreeze.
DONE

 

[Katemma Life]

this is an interesting thread.. So, thanks for all constructive guidance.

I am not thinking about winterizing at this time. I am considering the practice of flushing with saltaway during the boating season. This is why I need to understand the behavior of the Tstat. I think we all know when the Tstat opens (there abouts) the question is more geared towards when it shuts in relation to an engine shut off..

if folks dont know that is ok too!!

thanks again!

 

[Espos4]

Your original post was all about winterizing, thats why this thread has gone that way.

Regarding flushing with salt away, I would recommend draining the salt water and flushing immediately after returning to port. That’s your best chance at getting the best flush.

 

[Katemma Life]

So essentially running the engine on fresh water and then cutting over to the saltaway solution right? thats what I thought but this now is dependant on the Tstat opening..

 

[Espos4]

Yes. You're best chance at the thermostat being open, partially or fully, is to perform the flush immediately after returning to port.

You (and I) will never know how much the thermostat is open. I have the Mercruiser fresh water flush kit Tee'd into the raw water supply. This is how I flush mine and as far as I can tell, it does a good job of diluting the salt content of the water remaining in the block after shut down.

For my purposes, This is satisfactory for a fresh water flush, but not for winterizing.

 

[Katemma Life]

thank you!

 

[RollerCoastr]

Oh, yeah. Very different timing when flushing salt. No salt-away on this day. I think we ran each engine for 10 minutes, with a clear side-effect of boredom! IIRC, Salt-away says to inject the product for up to 1 minute.

 

[Lazy Daze]

OK, different direction than originally here, but...

Have the Salt Away hooked up and ready to go. Have it in the "Off" position. Run the engines up to temp and then a few minutes after that. Immediately switch over to the Salt Away for about a minute or so - you should see some foaming in the water. Shut 'er down.

Read the directions for Salt Away - they probably give you a better "time" than my memory. Directions tend to be good that way...

 

[CliffA]

well, we do know how a t'stat open and closes....not rocket science...

it is actually very easy to find out the exact temp for opening and closing if you really want to know....

put the t'stat in a clear pot of water on a stove.....put a thermometer in the water to monitor the water temp.....turn the heat on the burner high enough to bring the water to a boil and closely observe the t'stat....when it starts to open record the temp...keep watching the t'stat as the water continues to heat up and note the temp it fully opens....allow the water to reach a full boil...the t'stat will be fully open....turn off the burner and watch the t'stat again as the water cools.....you will be able to see the temp when it first starts to close which should be close to the temp it fully opens....it should be fully closed at about the same temp as it started to open....

but this info. may not help you since it will be difficult to monitor the exact temp of the coolant or water inside the engine when it is shut down after being run to normal operating temp.....i would not trust the dash gauge as an accurate temp reading....

cliff