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  #1  
Old 06-26-2003, 01:12 AM
waggin'ear waggin'ear is offline
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I have been experiencing marginal cooling in my '82 for several weeks. Seems to do OK around town (gauge usually stays in the lower 1/4 of the green) when i cruise around town for more than 30min it will get up to the 1/2. After about 15 min on the highway it creeps up to about 3/4 then it nevers cools down again.

Fan shroud in place
replaced fan clutch some improvement, but minimal

To completely rule out the thermostat is just took it out. I didn't know what temp had been in there before (160, 180, and 195 available, and this thing always runs alot cooler than my 79) I am now running without one and the temp is staying just below the green or never more than 1/4 of the way in the green.

Can I run too cool? I know that it will take longer to warm up, I know that the oil viscosity will be higher (my PSI seems a little higher, how can this be bad in a GW?). It's in the 90's here and i might not put it back in until October. opinions?
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Old 06-26-2003, 01:29 AM
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Too cold? Absolutely. Running an engine below 180° causes faster wearing of parts (besides loosing power and other things, but that is small %). I always run a Robert Shaw 180° stat. Allows the best flow while still controlling the heat range.
To note, if you happen to start running hot without a stat, it is an easy easy way to overheat as the water doesn't spend enough time in the radiator to actually cool down any.
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Old 06-26-2003, 01:46 AM
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My 82 wag ran too hot when I got it years ago. Rad was clogged. As long as you have the thermostat out, take the cap off and make sure you have good flow through the radiator. If you have to, drain a little off so you can see it pumping through the fins. You should see it squirting through it well. Make sure you have a good radiator cap. If you loose pressure it could heat up too. Put in at least a 180 thermostat.
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Old 06-26-2003, 02:23 AM
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Quote:
Originally posted by Hammer:
... To note, if you happen to start running hot without a stat, it is an easy easy way to overheat as the water doesn't spend enough time in the radiator to actually cool down any.
Edited 7/13/03 - Bottom line is to install a 180 or 195 degF hi-flow thermostat such as the Robert Shaw referenced by Hammer.

Wes

[ July 13, 2003, 05:30 PM: Message edited by: Wesdog ]
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Old 06-26-2003, 02:51 AM
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Wesdog,
I think this really depends on the components of the system. At a number of points in time I had take the stat out of a few vehicles, and had completely different results in them. Noting that AMC typically had the tendency to overdrive the water pump, so most AMC engines will not heat up without the stat.
But one thing on temp is that most engine parts will not have expanded to what they were designed for due to lower heat. Thus many things fall out of tolerance. This really cuts down on engine life, not to mention other metal wearing out faster.

As for the restriction, you are very much correct there. Even racers use a restrictor plate to keep this from happening while still keeping the best flow.
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Old 06-26-2003, 03:17 AM
PhilSine PhilSine is offline
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Here's what you gotta do.....

Get a candy thermometer and duct tape it to the big radiator hose on top. Drive around for awhile, stop, and check the temp. This is an accurate method of determining the approximate temperature of your cooling system. My sending unit is not right so therefore my gauge reads way too cool. But, according to the thermometer trick I'm right where I need to be. So, normal for me is when the needle is right at the bottom of the green mark.
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Old 06-26-2003, 04:48 AM
HeepofaJeep HeepofaJeep is offline
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Another thing you can do is install say a 180* thermostat, and drill a small hole or two in it.
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Old 06-26-2003, 07:35 AM
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Robert shaw stats come with the holes in them. Others come with a trapped bearing over the hole.
This is to relieve any air that builds up under the stat. Cause if the air builds up, it will not heat the stat spring enough for it to open, and you can overheat the motor easy this way (not common in these motors as there is usually plenty of ways for air/water to get around this).
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Old 06-28-2003, 03:50 AM
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Just a point of clarity, the water pump does not produce pressure in the cooling system. The expanded hot coolant does that, with a typical 15psi cap on the system, a pressure check anywhere in the system will show a reading of 15psi. The water pump's purpose is to move the coolant throughout the system, the mention of restrictor plates, they are just for that, to limit and restrict the flow, NOT to reduce the pressure. The liquid needs time to absorb the heat from the engine as well as time to release it through the radiator.
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Old 06-28-2003, 07:55 AM
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Anybody who calls himself "steamer" must know something about cooling system pressures.

He makes one good point not mentioned - a functioning radiator cap. They wear out, which prevents the buildup of pressure. Pressure increases the boiling point of the coolant. In other words, with proper pressure within the cooling system, you could run 215-220 without boiling.
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Old 06-28-2003, 10:35 AM
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Quote:
Originally posted by steamer:
Just a point of clarity, the water pump does not produce pressure in the cooling system. The expanded hot coolant does that, with a typical 15psi cap on the system, a pressure check anywhere in the system will show a reading of 15psi. The water pump's purpose is to move the coolant throughout the system, the mention of restrictor plates, they are just for that, to limit and restrict the flow, NOT to reduce the pressure. The liquid needs time to absorb the heat from the engine as well as time to release it through the radiator.
Edited: 7/13/03- I have done some research and I believe Steamer is correct. The waterpump moves the coolant through the cooling system and it's the heating and expansion of the coolant that pressurizes the cooling system. Good point Steamer, sorry for my error. I don't however agree with the last statement about slowing down the coolant to absorb/release heat.

The thing that confused me is the difference between how a gas and a fluid behaves in a closed system. Coolant is not compressible in it's liquid state and so is under a constant pressure throughout the cooling system. The exception is if areas of the liquid become separated from each other by multiple vapor pockets. So here is my revised info. Thanks Steamer for getting me to consider that I could have this wrong.

The coolant moving through the cooling system ALWAYS has time to absorb and release thermal energy. It is true in a very simple sense that the slower any specific gallon of coolant flows through the system the more heat it absorbs in the engine and the more it releases in the radiator, but the key is gals per minute of flow and btu's per minute of absorbed/released thermal energy. When viewed as a system a higher flow rate absorbs and releases more energy. Also, once the coolant exceeds it's boiling point and vaporizes in the engine cooling passages it stops absorbing more heat and no cooling is provided in the area where the vapor pockets are located. Moving the coolant through the engine and radiator faster does not in any way slow the transfer of heat to/from the coolant and helps to preventing coolant vaporization due to localized area heating in the heads. A higher flow rate also increases the turbulance inside the cooling system which is another key factor in absorbing and releasing heat. A higher flow rate is better because any given gallon of the coolant doesn't absorb as much energy in it's trip through the engine and thus doesn't have as much potential to reach it's boiling/vapor point. Removing the thermostat can affect the max system pressure in the engine developed by the pump at higher rpm because of less restriction to flow in the system. A lower max pressure in the engine lowers the boiling point of the coolant in the engine. Removing the thermostat also increases the system pressure in the upper radiator tank which pushes coolant out of the pressure relief valve on the cap at higher rpms. These are the main reasons for the myth of the need to slow down the coolant flow to allow the engine heat to be absorbed/released:

hmmmm.. remove the thermostat and the cooling system doesn't cool the engine as well...hmmm, must be that the coolant is now flowing too fast to absorb heat and release it in the radiator.....wrong! Remove the thermostat and the boiling point of the coolant goes down in the engine because the system pressure drops and the coolant boils at a lower temp, as the coolant boils the extra system pump pressure now present in the radiator upper tank at higher rpms the pressure cap relief valve to open and expel coolant which lowers the cooling capacity of the system which causes the system to get hotter which causes more coolant to vaporize which causes the system to get hotter increasing the overall pressure pushing more coolant out the cap and ... eventually meltdown/overheating.

The pressure in the system results from the heating and vapourization of the coolant. The vaporization of the coolant is only part of the overall system pressure in the engine cooling system and you want to avoid boiling/vaporizing the coolant if possible. Removing air from the system (critical) and preventing the lower hose from collasping is important.
There are FSJ cooling system design limitations for waterpump inlet/outlet flowrate and exceeding those by turning the pump too fast or changing the impeller design can cause the waterpump to cavitate if the system can't handle it. The higher the system pressure the faster the impeller can turn without cavitating. It will also potentially draw air into the system through the pump bearings/seal and weep hole. When air gets trapped or sucked into the cooling system even the stock waterpump in a stock cooling system may not function correctly. There are ways to improve the flow rate potential such as changing to a different radiator design and plugging the weep hole to prevent air leaks into the pump. A thermostat controls the engine temperature by increasing/decreasing the coolant flow through the radiator up to it's limits of fully closed or fully open. It's fully open restriction to flow is designed with the full waterpump rpm/volume in mind as well as the relief value pressure rating and the radiator surface area and flow rate capacity. A hi-flow thermostat is a sort of compromise improvement. It potentially allows more total coolant flow through the system by providing a larger thermostat opening. This changes the system design but only slghtly when compared to removing the thermostat altogether. The hiflow thermostats are also much higher in quality and a better design and are less prone to failures. When coupled with a higher flowrate waterpump it increases the system flowrate. The hiflow waterpump and thermostat raises the max system flow capability. Now the radiator becomes the potential weak link if it can't handle the increased coolant flowrate and restricts the flow of coolant to the pump inlet. What you don't want is the radiator upper tank to core interface area to be the place that most of flow restiction takes place in because it exposes the pressure relief valve in the cap to higher pressure and causes coolant loss to the system.
Now if a coolant with a higher boiling point is used and a "low pressure drop/hiflow crossflow radiator" with the pressure cap in the return tank is used it is then possible to remove the thermostat/restrictor without the negative consequences previously mentioned but now you have to consider controlling the minimum operating temp and possibly not getting the engine up to operating temperature. I have made the mods mentioned and I still use a thermostat to maintain a minimum engine temp even though I could remove mine. I also use a 7psi cap.

Respectfully, Wes

[ July 13, 2003, 04:55 PM: Message edited by: Wesdog ]
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  #12  
Old 06-29-2003, 01:51 AM
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Wes,
I agree with your statements on the cooling effects and pressure and flow. I have only one thing to add about the open stat issue. Especially for people with stock systems. The flow through the block is NOT even. Some racers would put a water outlet on the backside of each bank on the intake rather then just one that goes to the heater. And run these lines forward. Flow through our blocks is not that good when talking about pushing the limits, and it isn't impossible to create an air pocket at the back of the driver side head. Keeping the stat, or at least a restrictor of some sorts truly helps out with this issue (although most people will not put their engines in this area of usage to worry about).

And it's hard to throw away older trains of thought. Sorry about that one. (I should and do know better).
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Old 06-29-2003, 02:30 AM
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Hammer, as usual you show your good depth of knowledge in this area and I thank you for keeping an open mind to new info. If someone can show me where I am wrong in my thinking and experience I will also be happy to learn. Here is my current intake and you can see the implementation of the cooling lines you described for the reasons you mentioned. The lines from the rear help balance the coolant flow through the engine and provide a path for the removal/escape of vapor. This is a case where a little is good but more is not better. You wouldn't want to make those lines too large because it would reduce the flow of coolant to the front and also critical center exhaust twin area of the heads that get the hottest.

Regards,
Wes



[ June 29, 2003, 08:49 AM: Message edited by: Wesdog ]
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Old 06-29-2003, 02:34 AM
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Waggin'ear,

Sorry for sort of hijackin your thread! I hope the info I provided was helpful to your basic questions.

Wes

[ June 29, 2003, 08:35 AM: Message edited by: Wesdog ]
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Old 07-13-2003, 11:26 AM
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I came across this post recently on another site and it shed some light on why there are inconsistancies between various explainations of how liquid cooling systems function. I edited my post above based on this info and some other stuff I also found. I appologize to Steamer for questioning the info he posted about cooling system pressure and how it is formed. There is an outlet/pressure side and inlet/suction side of the waterpump but the system pressure differential is apparantly not significant. I may do some tests to satisfy my own curiosity in this area. I still don't believe the 'slow down the flow "myth"' but I'm willing to consider any reasoning on why that is true. Here's the post that got me thinkin':

**************
Post:......The old wives tale that removing the thermostat runs the water too fast through the engine to pick up heat always makes me laugh. The pressure the impeller is spinning in is reduced and it cavitates......

Response: from my background as a Physics major and as a submariner, the pressure in water does indeed determine the velocity at which a given propeller (or water pump) blade will cavitate. Higher pressure allows greater blade speed without cavitation. But the notion that obstructions in the flow of water cause variations in the water pressure within the cooling system is erroneous because water is not compressible like air is. Within the accuracy of a mechanic's measuring equipment, all of the water in a cooling system is at the same pressure, whether it's in front of the pump or behind it. The fact that there may be bubbles in the liquid is irrelevant, and long as you don't have two complete vapor locks that isolate one section of liquid from another. If you want to reduce cavitation, you either have to reduce the pump speed or increase the overall pressure. This has a lot to do with why the Evans NPG low-pressure coolant requires special pump and radiator.
*******************

So this adds a few more important pieces to the whole cooling system operation, at least in my mind. It's hard to diagnose problems unless it is clear how something is supposed to work. So this means I need to re-think some of the key things I've been recommending to others. In the words of Maxwell Sharp - "sorry about that Chief"!

Wesdog



[ July 13, 2003, 08:23 PM: Message edited by: Wesdog ]
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Old 07-13-2003, 05:22 PM
Jeepadilly Jeepadilly is offline
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Thats smart!
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