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Duane in Indy View Drop Down
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    Posted: February-01-2016 at 9:32pm
Does anyone know what the water pressure should be with a 302 1978 ford engine. Thinking of installing a gauge to show pressure just after the RWP. Would rather see a difference in pressure BEFORE the temp gauge takes off. Couple lakes I plan to go to have a weed problem and thought this might be of value Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-01-2016 at 10:59pm
Duane,
I don't feel reading pressure off the RWPor any other place in the system is the way read flow. I don't feel you understand you can have pressure with NO flow!! There are some externally mounted ultrasonic flow meters out there .but I feel you are overestimating a problem. The simple way to make sure you're getting water is to monitor your temp gauge. You do have one correct?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 9:31am
Hi Duane

I don't know what the pressure would be but I'm rather amazed at what Pete can determine about your understanding of pumps and fluid flow from one simple question.

Plenty of pressure gauges for outboards that could be used.

With both a pressure gauge and a temp gauge you would have the best indication of whats going on., but I feel you probably know that already.

I'm sure the pressure would vary with speed and you would get used to knowing the readings at any given speed.and if you sucked up some weeds and lost pressure that would be your first indication of problems before the temp gauge even thought about responding, but I feel you know that already too..

A friend has a pressure gauge on his speedy go fast bass boat that he swears by.

KenO

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 10:03am
Originally posted by KENO KENO wrote:


I don't know what the pressure would be but I'm rather amazed at what Pete can determine about your understanding of pumps and fluid flow from one simple question.
KenO

I've handled a few fluid dynamics projects in my life    so here was my first thought. Cap the discharge of any type of pump. You get pressure and no flow!! A pressure gauge is not a good method of determining flow. Here's just one example I ran into. It was the installation of 5 water cooled compressed air dryers. These were cooled off a cooling tower but even if city water was used the same would apply. The contractor installed pressure switches on all 5 dryers. The idea was to shut down the refrigeration when water flow wasn't enough to prevent a high head trip. It didn't work since as explained there were times when there was pressure with no water flow. I retrofitted all 5 dryers with flow switches. I still feel monitoring the temp gauge is the best method.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Duane in Indy Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 10:12am
Thanks Ken, I have a pressure gauge on both my Ranger bass boat and my Bass Tracker. Big Mercury on one and 30 hp Johnson on other. One utilizes a 30 psi and the other a 10 psi. I am just trying to narrow down what pressure I would use. On both boats I get a loss of pressure before the temps go up. I prefer to catch it before it gets hot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 10:20am
Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by KENO KENO wrote:


I don't know what the pressure would be but I'm rather amazed at what Pete can determine about your understanding of pumps and fluid flow from one simple question.
KenO

I've handled a few fluid dynamics projects in my life    so here was my first thought. Cap the discharge of any type of pump. You get pressure and no flow!!


Hi Pete

Take away the water supply to that pump which is Duane's scenario and what happens to pump discharge pressure?

KenO
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 11:26am
Ken,
You are correct. I'm sure thinking backwards!

Duane,
Are you thinking about a remote gauge so you can read pressure at the dash? Maybe a pressure switch triggering ether an audible or visual alarm?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 11:34am
Aw hell Pete, It's one of them age things

That's coming from another guy the same age

KenO
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Duane in Indy Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 11:52am
Pete, Thanks for your reply. And yes to all the above. Dash mounted gauge if feasible. If I knew the normal operating pressure then I could pick the correct pressure switch if an audible device was utilized. (ie. piezo buzzer)
I thought you were confusing an open versus closed outlet system.
Anyway, back to the original question, short of just hooking up a 30 psi gauge and checking pressure, do you know what range I would be dealing with? I am rebuilding my dash now and all thoughts would be welcome.
Either poplar or cherry and stain it to closely resemble the vinyl original. I have plenty of poplar, cherry, and oak of the width required. I have both a 12" Powermatic and an old 24" Cresent planer. Some boards in stock are 26" wide. Also using boards to replace my "ski locker" boards. Thanks in advance
Also thanks to KenO
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Post Options Post Options   Thanks (0) Thanks(0)   Quote backfoot100 Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 12:26pm
What's the difference if you use a 10 or a 30 PSI gauge? In Ken's loss of intake water scenario, both guages will drop to 0. So if the 10# guage is pegged under normal operating conditions what does that hurt?
Personally, seeing a guage such as this being either pegged high (good) or pegged low (bad) is going to be much more effective then trying to read a specific PSI number. I think even an audible alarm would be much more sufficient under the circumstances. The actual engine temp is far more important and your ultimate goal anyway.
When people run down to the lake to see what's making that noise, you've succeeded.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 12:32pm
Duane,
If you do go with a gauge, I'd go for a 0 to 15 psi. With the cooling being an open system, I don't feel you will see anything close to the 15 psi plus, you will get some pressure drop up to the dash. Poly 1/4" tubing would be my choice for the run.

So, you're one of the non original guys!!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 74Wind Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 12:34pm
Just a thought, but if you are indeed able to install an audible alarm, then a viewable Guage would seem unnecessary, and you could avoid another hole in the dash.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 12:35pm
Duane,
I'll suggest it again and also agree with Eddie that an audible alarm is a better choice. Plus, a pressure gauge in the dash sure isn't very original!

EDIT: plus Jeff with the alarm!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 12:43pm
Am I missing something,I thought a pressure gauge on an outboard was merely for when your jacking up the motor and running on that ragged edge trying to get that 1 last mph. Seems to take the fun out if your worried about everything IMOH-----
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Gary likes to give his HM a rest sometimes and let other boats parade him around the lake.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote desertskier Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 1:16pm
During our ProTec replacement discussions it occurred to me that the ProTec temp switch could still be used to interrupt the ignition voltage and turn off the motor. If it is possible to install the switch in your engine cooling system it could be used to turn off the motor when it reaches 210 degrees. Route the ignition voltage through a normally closed relay, the control line goes to 12V and the ground goes to the switch. When the temp switch activates it closes and connects ground and opens the relay and turns off the motor. The only downside I see to this is a possible safety issue. But in the rare instance that your engine is overheating I think it is worth the risk. Just another idea to consider.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Duane in Indy Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 1:29pm
Originally posted by 8122pbrainard 8122pbrainard wrote:


So, you're one of the non original guys!!


Not really Pete.
But if one 2" dia. gauge can save my engine then I don't feel that I have broken any laws. And if I knew the answer to my question then I would not even have to install the gauge, but it would give me an idea of what range pressure switch to use. Since my engine is out of the boat I cannot check it myself.
Thanks again, Duane
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 2:50pm
Originally posted by Duane in Indy Duane in Indy wrote:

Originally posted by 8122pbrainard 8122pbrainard wrote:


So, you're one of the non original guys!!


Not really Pete.
But if one 2" dia. gauge can save my engine then I don't feel that I have broken any laws.

Didn't I read you were talking about wood for the dash panel? Faux wood grain vinyl is available.
Originally posted by Duane in Indy Duane in Indy wrote:

And if I knew the answer to my question then I would not even have to install the gauge, but it would give me an idea of what range pressure switch to use. Since my engine is out of the boat I cannot check it myself.
Thanks again, Duane

Since what is really needed is alarm to be triggered at a very low or zero psi, the pressure switch can have a low range. I'd say 0 to 60 or lower. If you find one, do check the on/off hysteresis as that will affect the trip point.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Duane in Indy Quote  Post ReplyReply Direct Link To This Post Posted: February-02-2016 at 5:47pm
[/QUOTE]
Didn't I read you were talking about wood for the dash panel? Faux wood grain vinyl is available.QUOTE]
Yea, I know and in my opinion it looks like cheap faux vinyl too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DrCC Quote  Post ReplyReply Direct Link To This Post Posted: February-03-2016 at 9:41pm
      I have water pressure, but it seems it works better with volume.

.

because it's wired to the stereo.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: April-17-2016 at 10:34pm
Hi Duane

I built my low tech redneck rig to measure water pressure at the discharge of the RWP. and also at the suction( actually between the hull suction and the trans oil cooler)
It's on a 351 but that shouldn't really make any appreciable difference.

The short answer is that you better get a 0-30 pound gauge.

The longer answer is below

RPM                           Suction Vacuum               Disch Press
1000                           1" hg                                    1 psig
2000                           5"hg                                    4 psig
3000                           7"hg                                    9 psig
4000                           8"hg                                    pegged the gage but had 15 psig at 3700                  

If you do the math for 5000 rpm you would have about 25 psig. It seems your engine should have no trouble hitting 5000 rpm.

This is with the pump running at the same speed as the engine, that's how my PCM is, not sure how your commander is but I'd guess it's the same or awful close.

Hope this helps.

KenO

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Duane in Indy Quote  Post ReplyReply Direct Link To This Post Posted: April-17-2016 at 10:38pm
Thanks for the reply Ken, that is what I was looking for. Duane
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 10:25am
Glad to help Duane.

I was a little surprised at the numbers but didn't really know what to expect.

Checked twice with 2 different gauges too, just to be sure

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 10:42am
I was surprise too - at the high end!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 10:54am
I guess the pump laws for centrifugal pumps really do work for these little pumps.

You might say the impeller in there was well seasoned too, but it was in good shape with no pieces parts missing
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shierh Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 12:43pm
engine temp and water flow, pressure is no issue.   Only place that will block flow is your risers and you should be pulling every couple of years and acid washing. Replace them every 5 years or so.   

If you want to completely clean your block of rust you can try to circulate Evapo-Rust through it.   Get 5 gallon bucket from Northern tools, less than 100 and put a bilge pump in it and circulate through block with thermostat removed. let run 24 hours.   Will need to put return from exhaust back to the bucket.   I plan to do this once i change it over to heat exchange.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 1:22pm
Originally posted by KENO KENO wrote:

I guess the pump laws for centrifugal pumps really do work for these little pumps.

Ken,
My comment on the high pressure at the high RPM wasn't based on a centrifugal. I've engineered quite a few rubber flex impeller pumps so the comment was based from pump performance charts. Typically as the pressure increases with RPM, the max head is reached and that's when the impeller blades bend to a point where they are no longer in complete contact with the cam.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: April-18-2016 at 11:01pm
Found some info that says this pump (Sherwood g21) puts out about 22 gpm at 4000 rpm and tails off very slightly from that point upwards probably due to impeller blade bending as Pete said..

It's really more of a positive displacement pump till the blades bend over like Pete mentions  

No pressure info other than my results but that makes me think it won't go much over 15 or 16 psig

With a 30# gauge, I'll know the answer.

KenO

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