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Old 03-05-2012, 08:51 AM
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Controlling and affecting proper operating temp

Thought I'd start a new thread on this, rather than hijack Marian Clare's thread...

All this talk of flow and heat exchange reminded me - when I brought my boat back to her slip last weekend, I noticed that the temp never got much above 150 on the gauge. Now I never ran her hard, but I would have thought that even just running along at around 1200-1400 RPM would have made the engine get up to full operating temp. So if that is the case, then it would seem that "full operating temp" in this case was only 150.

I'm thinking I'm going to need to play around with the bypass valve to see what effect it has when I slightly open or slightly close it.

What about slightly hotter plugs? The engine was a little hard to start, to my surprise. I am using the plugs that were in it when I took it out, because they seemed to be fine. But I could easily decided to yank them out and put new ones in.

I also don't know if maybe I need to to a little tinkering with the carb. I kinda don't want to.
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Old 03-05-2012, 09:20 AM
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Rust: I look at the water temp as a guide. A warning of to hot or to cold. What I do check is the condition of the plugs. If they are staying clean then the running temp must be close IMO. Dan S/V Marian Claire
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Old 03-05-2012, 09:23 AM
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Bill,
150 for temp...nothing wrong with that. Might be hard to start if the carb is leaned out a bit too much.

As for plugs, I use NGK XR4'S. Nova Automotive suggested them and I've had them in since last spring. Nova automotive does A4 rebuilding here in the area, they rebuild just about any engine. My engine never ran as good since I started running with those.

That said, Dave Neptune thought they were too much for that engine and he has some sound reasoning for his opinion. I respected Daves opinion so much that I went back to Nova Automotive to double check. They told me NGK will help the engine perform better. Phil said that they will keep the combustion chamber cleaner. They run hotter and are a bit deeper in the combustion chamber...they said they've never seen damage related to it...they told me to run them and see for myself. All I can say is that the engine has never run as smooth or as well. I have the carb leaned out nicely and my fuel consumption is right in the ballpark.

Please note I don't use a T-stat and my operating temp is always low side...around 130-140 if pushing it. Engine doesn't use oil to speak of and the plugs are consistently clean don`t leave much residue in the combustion chamber.

So basically, I'm FWC no T-stat, by-valve open about 1/2, and hotter plugs maintaining clean combustion chamber.
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Old 03-05-2012, 10:07 AM
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Question

So, to continue the discussion, have we established that faster flow rate tends to more uniform temperatures throughout the system? This, of course, applys only to FWC.
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Old 03-05-2012, 10:10 AM
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I had understood that a more optimal operating temp, with FWC, was 180 F, and that running too cool will lead to fouling on the valves.
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Old 03-05-2012, 10:19 AM
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Quote:
Originally Posted by ILikeRust View Post
I had understood that a more optimal operating temp, with FWC, was 180 F, and that running too cool will lead to fouling on the valves.
I think for those who run their A4 mostly to get in and out of the harbor 180 is good; but for sustained long range running I have found that 165 or so with FWC is better. What concerns me is that looking at the gauge, what you see may not really be what you get. I have been toying with the idea of installing a sensor where the coolant should be the coolest, and then switching between the other sensor, where the coolant should be hottest, and monitoring the differential.
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Old 03-05-2012, 11:11 AM
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Thumbs up Cool!

I have been thinking of the electric conversion for my beastie so I am very interested in this thread. I have run at 130~140 as Mo for 26 years now and no stuck valves (I have filled the crankcase with saltwater too many times tough) and very clean J8 plugs. I will say I am a bit of a carb nut and the carb is very close to spot on. I don't feel that there are any real adverse issues running "cool" albeit cooler running can increase wear on rotating parts., however once the "operating temp" is achieved the wear factor pretty much becomes a non factor.

Mo, I'm a bit intrigued by the plugs you are trying out. The extended tip is a must for some applications and I am a bit suprised that they are working better. Did they state the heat range comparisons with what you were running?

Bill, it should be a bit hard to start if the idle is correct. Didn't you say you were fouling plugs before?
And yes the valve adjusting makes a differance however it will take more than a few minutes for temps to settle. I suggest if you are going to "set" the temp you do so just above your "max crusing speed", take your time and enjoy some liquid bread. After setting like that you will notice the temp will rise only as the load increases and idle warm up will be slow and and drop to around 100+ degrees in 50 degree water. After running and the engine has set for about 5 minutes switch on the ign and see what the core of the beastie was running, it will usually rise around 20 degrees because the heat can radciate into the block and not be carried away by the cooling fluid.

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Old 03-05-2012, 12:00 PM
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Quote:
Originally Posted by Dave Neptune View Post
Bill, it should be a bit hard to start if the idle is correct. Didn't you say you were fouling plugs before?
No. I owned the boat only for about 5 months before I pulled the engine out, and probably put only a few hours on the engine during that time. The plugs were a little dirty when I pulled them out for the overhaul, but nothing I would consider "fouling."

I'm thinking I need to take a careful look at the idle setting on the carb. I fiddled with the screw last time I was out there, and it didn't seem to have much effect until I got to one extreme end of travel or the other. So I probably need to start over - although it seemed to be idling pretty well.

I also lowered the idle speed, because it was idling a bit too high. It always was that way since I got the boat, though. I don't know if the P.O. purposely set the idle at that level or just didn't understand that it wasn't necessary to have the engine idling at 1,000 or 1,100 RPM.

Another factor of course is that my temperature observations were made cruising through water that probably was around 40 degrees or so. It will be interesting to see what the engine temp does when cruising later this year, when the water temps will be up around 70.
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Old 03-05-2012, 12:00 PM
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Another thing - the valves did have a bunch of baked-on crud around their necks.
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Old 03-05-2012, 12:04 PM
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FWIW: I have been running my FWC at the same temp as I did my RWC, 140-150 F. My thoughts are, same temp sensor location, same 100% flow thru the block and head, same valve in the recirculating loop to control the mix of cooled and un cooled liquid entering the pump. The only thing that has changed is the type of fluid running thru that loop. Am I missing something here? Dan S/V Marian Claire
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Old 03-05-2012, 12:36 PM
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Quote:
Originally Posted by edwardc View Post
Running coolant faster lowers it's temperature and increases the heat transfer rate.
How does solely running coolant faster lower its temperature? Does running hot coolant faster make it cooler? Using another thought experiment of an extreme example, could we run the coolant fast enough to eliminate the need for a heat exchanger??

Without consideration of the variables of exchange efficiency, heat exchanger capacity, raw water temperature and raw water flow rate, inside the heat exchanger the longer the coolant remains there the more heat is extracted and the cooler it is delivered to the block until it reaches equilibrium with the raw water. I agree that beyond that point more time is meaningless. The delicate balance in the entire system (block and heat exchanger) comes from a corresponding lower flow rate in the block heating the coolant up more.

With a massive HX this topic isn't an issue. With a smaller or marginal HX due to space constraints, the idea of balance comes into play and flow rate is but one of several factors acting in concert.

The positive effect of faster coolant flow in the block is a negative in the heat exchanger and as I offered in the original post, within limitations.
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Old 03-05-2012, 12:38 PM
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In the same waters as Bill just cruised thru, my engine at cruise Never comes off 100, (the lowest mark on the gauge)
I have to run at full WOT for at least 10-15 minutes to go to 130.
If you lift off the throttle at all back to dead cold.

I have RWC and a thick shoe in the water pump.
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Old 03-05-2012, 12:47 PM
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Question Hmm

Daniel, are you using a valve in the bypass or is it blocked off? You may want to try the smaller shoe.

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Old 03-05-2012, 01:05 PM
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Daniel, in the cooler months mine runs cold too. I remember the first winter I had the boat, we motored it down to the marina to haul out in late November. I was a little worried that the water temp would not come up barely above the bottom of the gauge @ 100, but I also didn't want to mess with it because it was colder than crap and raining (of course!) and I just needed to get to the marina. This was stock cooling config...202m3, OEM Holley t-stat and failing original t-stat housing, so I was still getting a lot of bypass leaking & had no valve. I also have no idea in what condition the cooling passages were or when the last acid flush had been.

Once the Bay is up to 60F or so, I run 160-170 RWC..Below 60 at creek cruise RPM (1,500 or so) it stays down below that..120-140..but 2,000 RPM or greater it will come up to 160. Tied to the dock at a high idle it also barely gets above 140 unless the creek water is 65+F. I have to run WOT at the dock to get 160F.

Just some comparison numbers for you.
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Old 03-05-2012, 01:29 PM
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Talking Back at it...

Quote:
Originally Posted by ndutton View Post
How does solely running coolant faster lower its temperature? Does running hot coolant faster make it cooler? Using another thought experiment of an extreme example, could we run the coolant fast enough to eliminate the need for a heat exchanger??

Without consideration of the variables of exchange efficiency, heat exchanger capacity, raw water temperature and raw water flow rate, inside the heat exchanger the longer the coolant remains there the more heat is extracted and the cooler it is delivered to the block until it reaches equilibrium with the raw water. I agree that beyond that point more time is meaningless. The delicate balance in the entire system (block and heat exchanger) comes from a corresponding lower flow rate in the block heating the coolant up more.

With a massive HX this topic isn't an issue. With a smaller or marginal HX due to space constraints, the idea of balance comes into play and flow rate is but one of several factors acting in concert.

The positive effect of faster coolant flow in the block is a negative in the heat exchanger and as I offered in the original post, within limitations.
The point here is that the temperature of the block, not the coolant, is the issue. Certainly by slowing the coolant in the exchanger we can extract more heat and deliver a cooler product to the block. But while this is occuring the block is heating up at different rates at various points in the block. The question then becomes; can we achieve a lower and more uniform average temperature throughout the block, notwithstanding we are injecting coolant at a hotter temp than is potentially available?
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Old 03-05-2012, 03:25 PM
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Quote:
Originally Posted by Dave Neptune View Post
Daniel, are you using a valve in the bypass or is it blocked off? You may want to try the smaller shoe.

Dave Neptune
I have the moyer check valve and ball valve conversion, along with the adaptor plate, and a 160 thermostat.
I have the gate valve turned so it a straight shot, as to help make heat.
If I close the valve, the block never warms even at WOT...
But my block only has about 150 ish miles on it since I rebuilt it, and all the passages are clean.

That being said back in november when the creek was warmer I was getting 150 at WOT, but if I slow down, the temp is back to nothing.

The big shoe came with the pump, and I Love how it makes my exhaust sound
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Old 03-05-2012, 03:38 PM
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Quote:
Originally Posted by Ball Racing View Post
I have the gate valve turned so it a straight shot, as to help make heat.
I think you meant ball valve.

I'll have to try this next time I'm motoring anywhere. I think I turned it so it was maybe 1/2 closed, out of caution so that the engine wouldn't get too hot. Maybe I'll open it up and see what happens.
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Old 03-05-2012, 03:57 PM
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Now that I have joined the "no thermostat" group I observe that the engine runs about 10 degrees cooler at WOT. It seems that the thermostat itself had become the most restrictive component (MRC) or bottleneck in the system. I start the engine with the bypass wide open and the engine will get up to around 145 degrees at 1000 rpm. Only when I go to cruise rpm is it necessary to start closing the valve. I run 2000 rpm at 165 with valve fully closed.
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Old 03-05-2012, 04:50 PM
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Quote:
Originally Posted by ILikeRust View Post
I think you meant ball valve.

I'll have to try this next time I'm motoring anywhere. I think I turned it so it was maybe 1/2 closed, out of caution so that the engine wouldn't get too hot. Maybe I'll open it up and see what happens.
Yeah, I "meant" ball valve
I was trying to think of the wording opposite of the check valve, and ball was on the brain, but gate on the fingertips, and fingers won...
Either way the valve that controls the flow is set to a non restriction at this point.

Just one more thing...
to pull off the last 100-200 max rpms I can see,,,,, the engine has to be warmed up alot.
When she is cold 2,400 rpms wot, after hot(well warmer rather) 2,600 rpms if barometer, and humidity are willing..
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Old 03-05-2012, 05:15 PM
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I think several posts here highlight one of the benefits of the recirculating loop. With the loop you have some control over the temp of the coolant entering the engine and from that you can gain more control over the operating temp. FWC or RWC the affect of the temperature of the water the boat is sitting in can be minimized.
I also think that the higher the temp of the incoming coolant is, as long as it still can cool the engine, the better. There would be less difference between entrance and exit temps and that would add to more even temps thru out the system. Dan S/V Marian Claire

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Old 03-05-2012, 07:04 PM
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Quote:
Originally Posted by ndutton View Post
How does solely running coolant faster lower its temperature? Does running hot coolant faster make it cooler? Using another thought experiment of an extreme example, could we run the coolant fast enough to eliminate the need for a heat exchanger??
Probably a bad choice of words. Running coolant (either raw water or antifreeze) through the block faster results in it being in the block a shorter amount of time, hence, as you have pointed out, it doesn't have as much time to absorb heat, and doesn't reach as high a temperature. Hence, faster corresponds to cooler.

Quote:
Originally Posted by ndutton View Post
...Without consideration of the variables of exchange efficiency, heat exchanger capacity, raw water temperature and raw water flow rate, inside the heat exchanger the longer the coolant remains there the more heat is extracted...
I know it intuitively seems that way, but it's just not so. True, the longer a particular cubic inch of coolant remains in the heat exchanger, the more heat is extracted from that cubic inch and the lower it's temperature gets; however, this also means that fewer cubic inches per second are going through the heat exchanger, reducing the total heat transfer. In addition, those cubic inches are now cooling to a lower temperature while inside the heat exchanger , decreasing the delta-T between the hot coolant and the colder seawater. This greatly decreases the heat energy transferred, because the total heat energy transferred is a function of the square of the temperature difference, much as electrical power (watts) is a function of the square of the voltage.

I know we'd like to ignore "...the variables of exchange efficiency, heat exchanger capacity, raw water temperature and raw water flow rate...", but in a dual heat transfer problem (block cooling jacket and heat exchanger), you have to deal with them. A static solution is not going to yield correct answers, as this is a dynamic problem that will eventually settle into a steady state. The two exchangers (block & HX) interact with each other and with each other's temperatures, every time something perturbs the system.

So lets try another thought experiment. Assume we have a FWC system where the coolant is running at some flow rate, and the raw water section is running at another rate, and everything is sized such that the system is in equlibrium and the HX is extracting all the waste heat the engine is generating. The temperature on the "hot" section of the coolant loop from the engine to the HX is higher than the temperature on the "cold" section from the HX back to the engine.

Keeping the engine (heat production) and raw water rate (heat removal) the same, lets increase the flow rate in the coolant loop. Each unit of coolant now spends less time inside the engine, and so does not absorb as much heat and its temperature increase is less. At the same time, this lower temperature allows a higher heat transfer rate, and the engine temperature falls reducing the heat transfer rate back to what it was.

Similarly, in the HX, each unit of coolant spends less time there, and does not loose as much heat there, and thus it's temperature does not fall as much. This higher temperature drives a greater heat transfer into the seawater side, until it also adjusts into equlibrium.

So it seems that the faster flow in the coolant loop causes the temperature difference between the "hot" and "cold" side of the coolant loop to be less.

We can convince ourselves that this is so by carrying the experiment to extremes. If we increase the coolant flow rate to infinity, each unit of coolant spends an infinitely small amount of time in the block, and so it's temperature does not rise. Similarly, each unit of coolant spends an infinitely small amount of time in the HX, and its temperature does not fall. So, for an infinite coolant flow rate, the temperature is uniform around the whole coolant loop. But the cooling system still works, as the engine sees it's coolant jacket filled with coolant at a uniform temperature that is lower than the engine's , and the HX sees its coolant side filled with coolant at a uniform temperature that is higher than the seawater's. The engine is still running at the same load, and producing the same amount of waste heat energy, it's now just running at a little lower temperature.

So the conclusion of all this is that running the FWC coolant loop faster results in less temperature extremes in the coolant, and lowers the engine temp.

And we see evidence supporting this in the real world. FWC systems remove the same amount of heat energy as RWC systems, they just tend to do it at a higher temperature. I suspect that the "equlibrium temprerature" of the engine in our infinite flow rate thought experiment is theoretically equal to that of RWC system at the same engine load and seawater flow rate. Since real-world FWC systems operate with a coolant flow rate somewhere below infinity , they should run a little bit above that of a RWC system.

MAN! I feel like I just completed a final exam word problem in a Thermodynamics class!
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Old 03-05-2012, 07:32 PM
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Thumbs up Stunning!

Ed - Thank you for that clear and logical discourse which will be of enormous value to this forum. And you did it without resorting to differential equations and integral calculus. This should be maintained as a link of very particular interest.
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Old 03-05-2012, 07:46 PM
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Oh crap! I'm having flashbacks to Chem 31. I still remember the name of that class: "Chemical Equilibria in Aqueous Systems." I remember only a teeny, tiny fraction of what we covered, let alone what I "learned" - I do recall we spent a fair amount of time on thermodynamics.

Now I think I need a beer...
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Old 03-05-2012, 08:09 PM
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Quote:
Originally Posted by ILikeRust View Post
Oh crap! I'm having flashbacks to Chem 31. I still remember the name of that class: "Chemical Equilibria in Aqueous Systems." I remember only a teeny, tiny fraction of what we covered, let alone what I "learned" - I do recall we spent a fair amount of time on thermodynamics.

Now I think I need a beer...
I think I need two!

Yeah, this does invoke flashbacks. And everywhere you look, chemistry, physics, thermodynamics, electronics, mechanics, biology, the same few equations keep popping up over and over again!
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Old 03-05-2012, 08:25 PM
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Faster flow = more cooling for another very cool reason, on top of what Ed mentioned. Liquid flowing through a tube exhibits "laminar flow", where the wall of the tube cause a drag. The liquid in the center flows faster, and there is a small dead zone along the tube walls with little flow. The dead zone acts as a sort of insulator between the tube wall and the flowing water. Increasing the flow velocity decreases the size of the dead zone, which increases thermal transfer efficiency more than than the simple factor of more flow (up to point). This is especially important for tubing walls which may have minor imperfections. Or in the case of most A4s, somewhat larger imperfections.
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