Thermostat Bypass

[Sailing Amok]

Just curious how much flow there is through the thermostat bypass. I notice that Westerbeke indicates in the manual that the thermostat should be removed for coolant changes, but I've never seen that mentioned on this forum. Why would this be necessary given that there is, as I understand it, a bypass which allows continuous flow of the fresh water side? I assume this flow is fairly restricted to allow the engine to get to temperature in a cold body of water. Any ideas how long one would have to run the engine to fully circulate the system if trying to flush with distilled water? It seems to me that with the bypass, we shouldn't have to wait for the engine to come fully to temperature.

Regards,
Aaron

[KWKloeber]

Arron

It's irrelevant how much flow is thru the bypass when flushing.  Think of the engine block as a tank of coolant with two paths out of it.

The 1st path is to the WH.  The OEM Tstat bypass hose was there to keep coolant circulating in the block while the Tstst is closed to avoid hot-spots in the engine block. That original short bypass path was extended by CTY to run to the WH.

The 2nd path is up thru the Tstat, to the exhaust manifold, to the Hx, and back to the coolant pump. Until the Tstst opens that path is "essentially" closed off so the coolant in that circuit doesn't circulate.  (That's not exactly the case because there's a 1/8" hole in the Tstst to let a minimal flow thru the exhaust manifold so it doesn't overheat and warp but the flow isn't enough when trying to flush the entire cooling system.)

So to flush the system the Tstat MUST be open or removed. 

Even with "restricted" (as you put it) Tstat bypass flow the engine doesn't get to temp to open the Tstat. The engine needs to be under load (pushing the boat) in order to get up to temp and open the Tstat. That's WHY the WH is connected to the Tstat bypass. The older M25s (e.g. 1970s - mid-1980s C30) had the WH plumbed
in line with the Hx (the short Tstat hose was left in place) and one could not get hot water with the engine idling.  That's WHY the WH is hooked up to the bypass barbs, no other reason.

[Sailing Amok]

The 2nd path is up thru the Tstat, to the exhaust manifold, to the Hx, and back to the coolant pump. Until the Tstst opens that path is "essentially" closed off so the coolant in that circuit doesn't circulate.  (That's not exactly the case because there's a 1/8" hole in the Tstst to let a minimal flow thru the exhaust manifold

Thanks Ken, that answers my question. The flow through the hole is too minimal to be relevant. That said, I suppose the only option if a flush needs to be done on the hard is to remove the thermostat? Or could I essentially flush the two halves of the system as you described it, separately? Fill and drain from the hx, and from the hose below the pump plus wh loop?

[KWKloeber]

Are you looking to flush as much as possible (longest path) with the least number of hose connections/disconnections? 

Or naturally you could flush each separetly, i.e., engine block; WH loop; Exh manifold/Hx loop.

[Stu Jackson]

...

...Any ideas how long one would have to run the engine to fully circulate the system if trying to flush with distilled water?
...
...

Aaron,

Perhaps you may be over-complicating this.

If your goal is to flush the system, then draining as much of the old coolant out is the first step.

Using the Burp method of draining from the Toyota hose below the fresh water coolant pump would be the first step.  Then drain the water heater section.

Refill with distilled water via the coolant cap.  Run the engine for a while.  Whether it comes up to running temp or not should not matter, since the coolant is circulating.  If you feel you must, then put the engine in gear tied safely to your dock, or take it out for a spin, to "open" the thermostat.

Drain again and refill with your coolant of choice, and you are done.

It really is that simple.

[Sailing Amok]

Thanks guys! So here's where we're at. When I removed the hx and all hoses, all the coolant drained from those areas. I also sucked out the wh loop with a little hand pump. I believe this should have removed most of the coolant from the system, but as I did not drain through the incredibly inaccessible drain plug as suggested in the manual, I assume there is still some coolant in the block itself? I mean surrounding the cylinders, hopefully not in them! Everyone here seems to use the hose to drain, as described in the burp method post, rather than that plug.

The coolant and all internals I could see looked pretty clean, no sludge,  but I don't know if the previous owner had EG or PG in the system (just that it was green). So I want to do my best to remove all traces before refilling with new stuff. Launch is this weekend, and while we could probably get from the launch ramp to a slip before overheating, and deal with this in the water, I'd feel a whole lot more comfortable having the boat ready to go. Breaking down on the ramp and delaying everyone else, is not how I hope to start the season.

Run the engine for a while.  Whether it comes up to running temp or not should not matter, since the coolant is circulating.

This is where I'm confused. If the engine is not up to temperature, is it still circulating on the hx side, or just on the wh side? Looking at Ken's schematic, I'm understanding that the coolant only circulates on the wh side until the Tstat opens? I suppose the hx side gets flushed in a sense as you fill from the manifold. Anyway, that side doesn't really need a flush as it was just refurbished.

The alternative is to remove the hose from the Tstat cap to the exh manifold and adapt your garden hose to there.  BUT as you flush the block you'll get leakage out the Tstat cap (the 1/8" hole in the Tstat flange) plus the flush water coming out the WH hose you removed from the coolant pump.

Thanks for the very detailed reply Ken. I guess this is the method I would have to use, as my Tstat housing does not have the petcock. Would I not get the same result from putting the garden hose right to the manifold, rather than removing that Tstat-manifold hose?

Now I just need the yard to turn the water on. They're really waiting until the last minute. I realise it wouldn't be as thorough a flush, but could I just fill and drain the system a couple times from the manifold using jugs of water, to sufficiently dilute whatever coolant is left in the block? Or does it require the pressure of a garden hose to circulate, since the engine isn't running?

[KWKloeber]

Aaron

It depends on what you want to accomplish!!  To me a "flush" is a  "flush" — remember the old Flush-and-Fill kits Prestone used to?? sell in every Kmart auto aisle where you cut in a garden hose fitting into a heater hose and flushed up and out the radiator cap?

If you want to drain and rinse/dilute that's to me a different thing.

You could use the temp-gauge-sender port, which is larger than the petcock port. I didn't remember the 35 is petcock-free. 

I was just thinking that if one puts the garden hose on the removed heater hose, that would actually reverse-flush the block/manifold/Hx; just a point of information.
I was too concentrated on following the coolant flow.

[KWKloeber]

>> if a flush needs to be done on the hard <<<

Aaron
[EDITED]

I worked thru the flow schematic and here's how you can power flush (i.e., with a garden hose) the ENTIRE system on the hard w/o running the engine or removing the Tstat.

https://groups.io/g/Catalina30/wiki/9626

Drain the coolant.
Remove the 1/4" npt temp gauge sender on the Tstat cap and use a hose barb and reducing bushing/whatever fittings, etc., to attach a garden hose.
Remove the WH hose at the top of the coolant pump.
Put a short stub of hose on that open hose barb and pinch or block off the short hose.

Run water with the garden hose (throttle it back as you don't want huge pressure).  The fresh water will go:
Out the Tstat cap
Thru the exh manifold
Thru the Hx
Back to the coolant pump intake.
Thru the engine block.
To the base of the Tstst housing (the "water flange").
Out the bypass hose barb (the closed Tstat keeps it from short-circuiting back to the exh manifold.)
To the WH.
Thru the WH.
Back to the hose that you removed from the coolant pump.

NOTE: If one puts the garden hose on the removed heater hose it would be a reverse flush thru the WH/block/coolant pump/Hx/exh manifold.

It will be a continuous flow/flush but not a fantastic rate because getting past the coolant pump impeller is another bottleneck, but still free enough to flush the system.

The alternative is to remove the hose from the Tstat cap to the exh manifold and adapt your garden hose to there.  BUT as you flush the block you'll get leakage out the Tstat cap (the 1/8" hole in the Tstat flange) plus the flush water coming out the WH hose you removed from the coolant pump.

Drain and refill with distilled and fresh coolant (or 50/50 premix.)

Let me know if I mucked up what you're trying to accomplish and I'll take another look at it.

[KWKloeber]

>>> If the engine is not up to temperature, is it still circulating on the hx side<<<

No, thats what i explained firstly. The only flow would be thru the 1/8" hole in the Tstat flange,


>>Would I not get the same result from putting the garden hose right to the manifold, rather than removing that Tstat-manifold hose?<<<

"Right to" where?? 
The hose barb??  Sure, put it on the removed hose from the Tstat or on the manifold hose barb if you remove the other end of the hose.  It's more difficult adapting a garden hose to the 7/8" hose barb on the manifold.  Or remove the hose barb elbow and use the 3/4" npt manifold threads to adapt but I was trying to keep it simple. That's just make-work.

If you're suggesting simply filling at the pressure cap then that's not a power flush w/ a garden hose (I'm not sure of the relative heights but I guess it would "rinse" that loop by gravity?).  But certainly not work to flush the entire system as i described it.

There's also a drain plug on the M-25/xp manifold!! (not sure bout the 35)  But I think you 34 folks can't easily see/get to it.

[Sailing Amok]

Aaron

It depends on what you want to accomplish!!  To me a "flush" is a  "flush" — remember the old Flush-and-Fill kits Prestone used to?? sell in every Kmart auto aisle where you cut in a garden hose fitting into a heater hose and flushed up and out the radiator cap?

If you want to drain and rinse/dilute that's to me a different thing.

Thanks Ken,
I guess really all I'm looking to accomplish is a drain and rinse, as you put it. Everything seemed reasonably clean, so I'm not too worried about a power flush, though it would probably be a good idea. However, with the short timeline to launch, and the club still not having running water for a hose, I'm really just trying for the simplest option. I can do a proper flush another season, perhaps in the fall to avoid the spring time issues with the club water supply. At this point I'm basically just trying to avoid AF compatibility issues. I've heard horror stories of mixing PG and EG, and I have no idea what was in there.
So given that, would it be reasonable to fill the manifold and heater loop with water from a jug, drain, and do again, and then fill with 50/50 and burp the system? Would that get the rinse water throughout, without the Tstat opening? From looking at your schematic, it seems to me that it would.

[KWKloeber]

 Aaron

I've never dealt with EG/PG issues and know only what I'd do when there's something questionable - overkill it LOL!

Make sure it's all out of the block and coolant pump as it's going to be by gravity. 

[LogoFreak]

Aaron, what I've done worked like a charm. Unhook the return side hose from the water heater, and stick that in a empty bucket, then attach a hose to where the return connected to the thermostat housing and stick it inside a jug or bucket of distilled water or whatever you wanna flush it with. Remove the thermostat, and put the housing back on. Fire up the engine and watch all the coolant be flushed. Then you can repeat the process with your choice of coolant. Half hour job.

[waughoo]

^--- nifty idea logo!

[Sailing Amok]

I've never dealt with EG/PG issues and know only what I'd do when there's something questionable - overkill it LOL!

Make sure it's all out of the block and coolant pump as it's going to be by gravity. 

I tend to agree. I normally start by overthinking, and then proceed to overkilling!

Without using the engine drain plug, does anyone have any idea how much is left in the block after draining the wh loop and proprietary hose as described in the "burping method" post? I began with a low coolant situation, so measuring what came out was meaningless.

Aaron, what I've done worked like a charm. Unhook the return side hose from the water heater, and stick that in a empty bucket, then attach a hose to where the return connected to the thermostat housing and stick it inside a jug or bucket of distilled water or whatever you wanna flush it with. Remove the thermostat, and put the housing back on. Fire up the engine and watch all the coolant be flushed. Then you can repeat the process with your choice of coolant. Half hour job.

Am I correct in thinking that this method requires starting with the system full of either AF or water? I'm thinking that doing this with a dry system wouldn't create a prime to draw the water/af from the bucket.

[LogoFreak]

I'm not sure as I've never tried it with an empty system, missed the part where you said you've drained the system already. However, I also didn't fully explain my method it seems. Set the bucket on the floor by the engine, that's where the return goes (old liquid) and put the hose with fresh water/coolant on the upper step above the engine, that way it's fed by gravity. I've also used a funnel on the upper hose and just poured it in instead of relying on the engine creating a vacuum.

I'm not sure I'd want to start the engine with no coolant in it all though, I would personally fill it with water to start with.