Bypass Valve, Thermostat Question

[rpowers]

Over the weekend I constructed a cooling bypass valve.

My engine had been running hot, even after an acid flush.

What better way to force cooling water past the cylinders than with a bypass cutoff valve.

Question:

Should I leave the thermostat in, or take it out?

My first pressure test of the valve was today. No leaks. At first start-up, when open, good water flow out the back. While still cold, with valve closed, much less flow out the back (presumably the thermostat is closed).

I get it that with thermostat, you would want to leave the bypass valve open until warm, then close it.

But with no thermostat, couldn't the valve just be left closed? This is a warm climate here in California...

Thanks!

-Rick

[Al Schober]

Rick,
You'll get mixed responses on the thermostat question. My personal feeling is that you'll do less damage to the engine running cool vs overheating. Hence, I leave the thermostat out and adjust the bypass valve.
BTW, nice installation. I used a globe valve, hence have a few turns of the handwheel between open and closed. Good to see a properly screened alternator...

Al

[rpowers]

Alt

Al,

That's one of those new high-output alts from MMI.

-Rick

[Dave Neptune]

Bypass valve

The Thermostat "when operating properly" requires the bypass so the flow of water to the exhaust is not restricted by the thermostat being closed. As the thermostat opens it closses the bypass off and the "full flow" is diverted through the block.
Running without a thermastat requires the operator to set the temp by the position of the valve, however in this senario the "full flow of water" is not interupted to the exhaust either.
Using the bypass valve with the thermostat can restrict the water flow so be careful by paying attention to the amount of water going through the exhaust.
I have run without since I bought mine 26 years ago with no problems other than the normal flushing every four or five years. My beastie runs at around 130~140 when at cruise and all the raw water being pumped is not restricted from the exhaust.

Dave Neptune

[sastanley]

Rick, Keep in mind that valve doesn't have to be 100% open or 100% closed. I have mine somewhere in the middle, about 75% closed (a guess)..to still allow some water thru the bypass to get to the exhaust.. When the inside of the engine is clean, this gives me a very steady 165 degrees in 85 degree Chesapeake Bay water. When I close the bypass all the way (engine at temp) I can get it down to 155, but the t-stat is already opening.. If I open the bypass the temp fluctuates a little bit (155-185) but plenty of exhaust water..

I tend to tweak mine towards 'more open' to start and then after it is running and warm I'll tweak it back closed just a little bit to steady out the temp reading. In the C-30, I simply open one of my engine doors and can access the adjustment easily.

[rpowers]

Thanks

Sastanley,

I like that answer!

-Rick

[Jesse Delanoy]

I guess I don't quite understand.

Doesn't removing the thermostat will make the engine run cooler?

Then, wouldn't putting a valve in the bypass make it run cooler still, by preventing water from being diverted to the bypass and forcing it through the block?

'splain this to me.

Jesse Delanoy
1977 Catalina 30 "Off The Grid"
Baltimore/Pasadena, MD

[Dave Neptune]

The works

Jesse, the water from the pump goes to a Tee fitting on the side of the block, the line continues to the top of the thermostat housing so it can pass through to the manifold and on out then into the exhaust. The continuation line from the Tee to the thermostat is the bypass line.
We start with a cold engine and the thermostat closed so the water from the pump is going through the bypass to the thermostat housing and on~~~as the thermostat opens water can begin flowing through the thermostat itself which is fed by the Tee on the side of the block~~~as the thermostat opens it closes (restricts water flow) the bypoass at the top of the thermostat housing forcing more of the water through the block. All of this happens without comprimising the volume of water to the exhaust~important!
Without the thermostat you restrict (not close) the flow through the bypass line which forces water through the block. It takes a bit longer to get warm but you never have to deal with the thermostat as it is removed. You can control the operating temp by adjusting the valve. BTW if you have to close the valve to maintain temperature it is time to flush!

Hope this helps.
Dave Neptune

[sastanley]

Jesse, yes...the issue is if you close the bypass completely and the engine has a t-stat, the theme in this thread seems to be that there may not be sufficient water going to the mixing elbow until the t-stat opens.

I think I've found a median setting which steadies my engine temp readings, but also seems to allow enough water thru the bypass to cool the exhaust hose. My point to Rick was it isn't necessarily an off/on valve, but an adjustable valve based on conditions.

edit - what Dave Neptune said too!

[gary gerber]

I have been following this thread regarding the bypass valve on the hose to the thermostat ( after the "T" fitting ) but is the valve necessary? I ask this because I have been sailing my 1970 sloop fitted with the original A4 at times motoring for many hours. I have no valve installed and never experienced a problem but am I missing something.

I see a number of A4 owners have installed a valve. I welcome your comments.

[JOHN COOKSON]

Bypass Restriction Issues

It seems to me from my own experience and what I've read in the forum there is no "one size fits all" solution to bypass restriction issues. The correct amount of bypass restriction usually has to be found through experimentation.

My A4 was running ~195 degrees. (RWC) Rebuilt the H2O pump, correct thermostat function, acid flush, lots of water coming out of the hose on the end of the manifold. The engine was still running hot. Clamping the bypass hose brought the temp down to ~160. I ordered and installed the Moyer bypass kit.

After the Moyer kit the engine ran ~ 125 degrees. I removed the flow restrictor that came with the kit (but kept the ball valve that came with the kit). The engine now runs ~ 140-145 at any throttle setting for any length of time with the ball valve full open.

Apparently the small amount of restriction from the added plumbing is the correct amount of restriction for my A4.


TRUE GRIT

If your cooling system is working fine you don't need a valve. If it it's not broken don't fix it. If your engine is running hot clamping the bypass hose will indicate whether or not you need restriction in the form of a valve.

[ndutton]

Gary,

The valve is intended to provide the owner with some manual control to provide more engine cooling than a pure thermostat system. It's not meant to make the engine run warmer than it otherwise would. With the stat in place, it's an override-cool modification.

The consequence discussed is with the engine cold (thermostat closed) and the valve closed or partially so, the flow to the manifold and (if RWC) exhaust is reduced, a potentially damaging situation.

The are other reasons to dump the stat and go with the bypass valve like Dave has done. I'm currently installing FWC with an electric coolant pump rather than a belt driven flexible impeller pump. I want the electric pump to flow with as little restriction as possible so I've gone the no-stat route among other measures and will rely on the manual valve for temp control. No matter how the valve is set, I'll have full flow either through the engine, around the engine directly to the manifold or a combination of the two.

There are reasons to keep the system as Universal designed it too and your comments regarding zero issues for years tells me there's no incentive for you to change.

[BryanLee]

My understanding is that the original thermostats are variable, and do not have to open all the way or close all the way. But the are hell'a expensive. Newer, cheaper thermos are open or closed, no in between. My understanding is that the valve then allows you to mimic a partially open variable thermostat. Given relatively stable raw water temps, you should be able to tune the flow to the optimal open amount for your water temps, and only fiddle with it if the water temps are changing, and then the thermo going open and close will regulate temps correctly as the engine warms up.

Is this correct? I do not yet have any thermostat on my boat (or housing for one), but am planning to have one on the engine I am currently rebuilding, so I would like to understand this better, but have no experience of my own.

[Dave Neptune]

On the head!

Bryan, nice swing you hit the nail on the head. It is easy to visualize once you understand what is happening to the flow.

Dave Neptune

[rpowers]

Amazing Result

(See "Cool, is not cool" thread)

Amazingly, after installing the bypass valve, I am now running at ~130 degrees with the valve fully open.

Apparently, just the restriction of the valve plumbing is enough to divert flow to the main block via the T-fitting.

Awesome!

-Rick