Slant Six Forum :: overheating problem

A few years ago I created a simple model of a cooling system so I could tell quantitatively what would help, rather than just try things randomly. It assumes all the internal passages and thermostat are open so the engine/radiator system is in equilibrium.

A short form is to measure the air going into the radiator's temperature (T2), the temperature of the air leaving the radiator (T1), then define Ta=(T1+T2)/2, and define a dimensionless flow
v=1/ln((T2-Ta)/(T1-Ta)). The function r(v)=(T2-Ta)/m where m is a constant containing a description of the system gives how what temperature rise you'd get for a given flow r(v)=(1/v) /( 1- e^(-1/v) ). (ln=natural log, e=2.7.18...., ^=to the power)

If your flow v>3, you'll gain very little by increasing the flow changing nothing else; if v<1 you'll gain much. Water wetter, water vs antifreeze, changing radiators, etc. changes m. Once you measure one point on the curve (and hence m), you can predict what will happen.

This should serve as a guide to tell you whether you have increasing the flow would help and by how much.

Good luck!

Author:	Slanted Opinion [ Mon Jun 15, 2009 5:16 pm ]
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The additives might have a small effect on the temp, but additives don't solve problems, only mask them. Do you have a shroud? Most of the cars with AC have a fan shroud. Pulling air through both a radiator and a condensor takes work! How many blades on the fan? -Mac

Author:	wjajr [ Mon Jun 15, 2009 5:53 pm ]
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emsvitil Quote: Straight water actually has the highest specific heat......... Perhaps I misspoke. crash922108, What I intended to convey was that a 50/50 mixture of water & antifreeze will increase the boiling point which will suppress formation of steam bubbles on the hot castings. Eliminating the bubbles increases the casting surface area coolant is in constant contact with, and will allow the coolant to rise to a higher temperature over water, enabling it to carry more BTU's to the radiator. A higher temperature coolant entering the radiator causes a larger "delta T" with ambient air temperature which increases the efficacy of the radiator. In other words the larger the difference in temperature between the out side air & coolant, the faster the radiator can shed the heat. I'm not a thermal dynamics guy, but I can tell you 50/50 mix beats the hell out of plane old water every time at every temperature above freezing when used in conjunction with the proper heat range thermostat. Additionally, antifreeze has corrosion inhibiters that will slow the formation of scale in one's water jacket, as well as lubricants to extend water pump life. Get that lower block drain plug near the oil filter removed & flush that baby out. If you find the block is full of rust & crud, you may need to remove the side freeze plugs as well to gain access to more of the lower water jacket to aid the cleaning process. Don't forget to flush the heater core, it may be old & weak, so be careful not to burst it with too much pressure.

Author:	crash922108 [ Mon Jun 15, 2009 7:09 pm ]
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wjajr, what you said makes sense, I remember reading up on "delta t" and heat transfer several years ago. That old engine sat up for 17 yrs, so I know deep down that its full of crud, from looking in the water jackets at the water pump everything was good but futher back I bet its clogged up. Thats why the temps climbing. Heck I bet thats why I cant get it to purr like a kitten like I used to, back cylinders are running too hot. This weekend I'll get that plug out and start poking around. Of course I'll have to dissconnect the radiator first, dont wanna plug that up again!! Kinda hard to hotrod a slant when it wont keep its cool!!

Author:	RustyRamcharger [ Mon Jun 15, 2009 8:12 pm ]
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Quote: Guess I need to put some antifreeze in it, that might just get me over the hump! Anybody using the "other" coolant additives (cant name any of them right now)? I hear the some of them will lower your temp by up to 20% Actually, the antifreeze solution has a lower specific heat than plain water. (it can't carry as much heat per unit volume, so the cooling system has to be derated) It has a higher boiling point though. Everything is an engineering tradeoff. In this case, the "break even" point is somewhere between 50% and 60% antifreeze concentration. 50/50 is about the best for coolant performance and longevity. http://www.engineeringtoolbox.com/ethyl ... d_146.html btw if the cooling system has a lot of crud, solder bloom, etc, clean it using Prestone Heavy Duty Cooling System Cleaner. Its the yellow cardboard cylinder; one end contains oxalic acid, the other is sodium carbonate. Dissolve the acid in hot water in a plastic pail. pour it into the radiator and top off with water. Drive the car for 3-4 hours with the heater on. Drain the radiator and block. Fill with plain water and use a bsckflushing adapter (uses water and compresed air) to blow out the loose crud. Dissolve the heutralizer in warm or hot water and pour into the radiator. run the engien with the heater on for a few minutes, then drain. I usually fill and drain the system using plain water twice after this. At this point the cooling system will be shiny clean. Fill with 50/50 antifreeze/water. There's nothing wrong with using HOAT antifreee instead of silicate base (the water pump seal will last longer). Just don't mix with different type or brand. Don't use DexCool or other OAT antifreeze if there's any brass or copper in contact with the coolant anywhere in the system! Long life antifreeze does work, but it will not tolerate any neglect of maintenance. Be sure you have an overflow bottle on the system. It is the air that gets into the radiator and then dissolves into the coolant that causes corrosion. Keep out the dissolved oxygen and maintain the pH above ~8.0, and the system will stay clean.

Author:	66aCUDA [ Tue Jun 16, 2009 5:31 am ]
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A warning about that back block drain plug. Its REAL easy to break that plug and still not get it out. Remember that it has rust welded to the block. Its probally better to just drill it or LEAVE it alone. Just my 02. Frank

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overheating problem https://slantsix.org/forum/viewtopic.php?t=35825	Page 2 of 2

Author:	crash922108 [ Tue Jun 16, 2009 5:43 pm ]
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Thanks for the warning Frank! Thanks everyone for all your help. My son is driving the car now, This weekend we are gonna attempt to clean out the coolant passages some more and maybe take a little timing out of it.

Author:	RustyRamcharger [ Wed Jun 17, 2009 7:08 am ]
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Use a 6-point box end wrench or a 6-point socket on the plug. Apply torque while tapping the wrench with a hammer. The plug will loosen without breaking or stripping. DO NOT use a 12-point wrench...there's a good chance that you will round the plug and have to drill and tap. Applying heat with an oxy-acetylene torch to the block immediatly surrounding the plug will also help loosen it. If you replace the plug, use steel. The same goes for core plugs. Installing brass will cause internal corrosion. The copper in the brass will cause galvanic corrosion of the iron. Ken

Author:	KBB_of_TMC [ Wed Jun 17, 2009 9:23 am ]
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A few years ago I created a simple model of a cooling system so I could tell quantitatively what would help, rather than just try things randomly. It assumes all the internal passages and thermostat are open so the engine/radiator system is in equilibrium. A short form is to measure the air going into the radiator's temperature (T2), the temperature of the air leaving the radiator (T1), then define Ta=(T1+T2)/2, and define a dimensionless flow v=1/ln((T2-Ta)/(T1-Ta)). The function r(v)=(T2-Ta)/m where m is a constant containing a description of the system gives how what temperature rise you'd get for a given flow r(v)=(1/v) /( 1- e^(-1/v) ). (ln=natural log, e=2.7.18...., ^=to the power) If your flow v>3, you'll gain very little by increasing the flow changing nothing else; if v<1 you'll gain much. Water wetter, water vs antifreeze, changing radiators, etc. changes m. Once you measure one point on the curve (and hence m), you can predict what will happen. This should serve as a guide to tell you whether you have increasing the flow would help and by how much. Good luck!

Author:	crash922108 [ Wed Jun 17, 2009 5:27 pm ]
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Dang I thought I was a fairly smart person but KBB_of_TMC just blew me out of the water and went right over my head Maybe a little plain english for a layman?? lol. Rusty ramcharger I've already messed up the plug, thats why I need a pipe wrench and you must own a radiator shop or something with what you know or have been through this before . Thanks for all the help guys

Author:	emsvitil [ Wed Jun 17, 2009 7:37 pm ]
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Quote: A few years ago I created a simple model of a cooling system so I could tell quantitatively what would help, rather than just try things randomly. It assumes all the internal passages and thermostat are open so the engine/radiator system is in equilibrium. A short form is to measure the air going into the radiator's temperature (T2), the temperature of the air leaving the radiator (T1), then define Ta=(T1+T2)/2, and define a dimensionless flow v=1/ln((T2-Ta)/(T1-Ta)). The function r(v)=(T2-Ta)/m where m is a constant containing a description of the system gives how what temperature rise you'd get for a given flow r(v)=(1/v) /( 1- e^(-1/v) ). (ln=natural log, e=2.7.18...., ^=to the power) If your flow v>3, you'll gain very little by increasing the flow changing nothing else; if v<1 you'll gain much. Water wetter, water vs antifreeze, changing radiators, etc. changes m. Once you measure one point on the curve (and hence m), you can predict what will happen. This should serve as a guide to tell you whether you have increasing the flow would help and by how much. Good luck! How about an example...............

Author:	KBB_of_TMC [ Thu Jun 18, 2009 9:49 am ]
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Let me apologize for accidentally corrupted the formulas when I posted them before. I've gone back to my notes and tried to cut & paste them here. You need 4 temperatures, not 2, the air temp entering & leaving the radiator and the coolant entering and leaving the radiator; the thermostat must be fully open and there must proper flow in the engine. An infrared thermometer works well for the coolant (measure the hose at the radiator), the air exiting is a little harder and a card in the airstream is what I've been using. mean air temp at radiator Ta== (Tentering+Texiting)/2 T2==temperature of coolant leaving engine and entering radiator T1==temperature of coolant leaving radiator and entering engine. Then the equations ought to be: coolant flow(dimensionless units): v=1/ln((T2-Ta)/(T1-Ta)) temperature near the gauge: T2=m r(v)+Ta a function of flow: r(v)=(1/v)/(1- e^(-1/v)) (ln==natural logarithm, sometimes called log-sub-e, and e^ is its inverse function, sometimes called exp, and is 2.718... raised to the power) m is a constant summarizing the volume of the system, the specific heat and density of the coolant, and the efficiency of the radiator. Example 1: Say we measured a nearly stock 1970s Plymouth 383ci V8 on a rather cool fall day and found Tentering=60F, Texiting=100F, T2=180F and T1=150F. We can calculate what we need to know: Ta = (60F+100F)/2 = 80F v= 1/ln((180F-80F)/(150F-80F)) = 1/ln(1.429) = 1/0.3567 = 2.804 r(2.804) = (1/2.804)/(1- exp(-1/2.804)) =0.3567/(1-exp(-0.3567)) = 0.3567/(1- 0.7) = 1.189 m = (T2-Ta)/r = (180F-80F)/1.189 = 84.1F If we doubled the flow, T2 could drop to 172F: T2 = m r(22.804) + Ta = 84.1F * 1.09 + 80F = 172F No matter much we increased the coolant flow (take v->infinity), r(v->infinity) -> 1, so the lowest T2 we can get is: T2 = m r(v->infinity) + Ta = 84.1F * 1 + 80F = 164F Example#2 In contrast, let us consider a 1950s DeSoto 392ci Hemi that's running hot. If we measured Tentering=80F, Texiting=120F, T1=150F, and T2=230F, we would find that Ta=100F and that v=1.047, r=1.554, and m= 83.7F. Doubling the flow would give: T2 = m r(v) + Ta = 83.7F * r(2 1.047) + 100F = 205F If we could double that flow again: T2 = m r(v) + Ta = 83.7F r(221.047) + 100F = 194F You can also derive a formula for m and predict the temperature rise for water vs. other coolants and so forth, but I'll leave that for a the full article. Good Luck!

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Author:	RustyRamcharger [ Wed Jun 17, 2009 7:41 pm ]
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You need to read the saga of the stuck oil pan drainplug on the Mopar Mailing List. LOL! www.moparmailinglist.com Goeff 'Drainplug' Gariepy told the story of how he finally prevailed over the drainplug from hell. Post a request on the MML; I'm sure someone saved his posts, otherwise the MML archive can be searched...but its tedious. Do you have a welder (either stick or MIG)? As for heat transfer, it can be modelled as an electric circuit. I'd be curious to see the derivation of the equations. Ken (forensic engineer by day)