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mddak
Dodge Dakota
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11/24/2003
15:26:03
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 Subject: 16 lb radiator cap
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well I did the old mechanic trick of switching out the 16 pound radiator cap to a 7 pound cap with a pressure relief lever. Cost me $ 4 but it will save me a lot of problems.
No it does not affect your temp. Only now instead of boiling at 260 it will boil at 240 but it should not go higher than 190 due to the thermostat.
It saves a lot of leaks and load on the parts.
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steve sharp
Dodge Dakota
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11/24/2003
16:05:23
|  RE: 16 lb radiator cap
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so does this mean your leaking cooant all the time? or does your therm open sooner?
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mddak
Dodge Dakota
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11/24/2003
18:35:20
| RE: 16 lb radiator cap
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you don't see any difference.
Just less stress on the coolant system and a lower top boiling point which you should never reach anyway.
Your therm opens the same time as always at 192 degrees.
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David Mitchel
Dodge Dakota
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11/25/2003
14:11:43
|  RE: 16 lb radiator cap
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Who manufactures it and what is the part number?
Thanks,
Dave
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mddak
Dodge Dakota
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11/25/2003
15:59:06
| RE: 16 lb radiator cap
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at autozone
part number something like 7707
first number 7 = size of hole for Dakota
second number 0 = plain cap 7 = vent lever cap
last two numbers = pressure 07 = 7 lb 16 = 16 lbs
that's pretty much it. for 40 cents more get a lever vent cap
thers ain't that many different choices
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HotRodSRJ
Dodge Dakota
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11/25/2003
19:34:29
|  RE: 16 lb radiator cap
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I wouldn't celebrate yet....and certainly do NOT talk others into what you have done because it's risky to lower your cap specification. Why do you think Dodge has engineers running out the whaaazooo?
I hate to break this to you but just switching to a lower cap pressure does NOT mean your cooling system will generate less pressure necessarily! The cap is only a safety device and plays absolutely no functional role in the cooling ability of the system. Usually the system sits at a constant pressure under normal driving conditions. This is commonly determined by size or capacity, operating temperature, water pump specification and lastly it's location on the radiator (suction side (crossflow) vs pressure side (downflow)). And moreover, the lesser cap is apt to cause more problems because modern systems commonly generate in excess of 10 lbs easily...with 12 lbs a common number. Then all you need is a high rpm romp and all of a sudden you have coolant expelled all over the place due to the insufficient protection at the cap and due to the increase in pressure from the water pump output at higher rpms! YOu have defeated the millions of $$$ of R&D for your truck. Do it several times and voila...you are overheating because you have expelled your coolant. This is the way it usually happens, not the other way around.
Because of capacity and operational temperature points of your system, higher cap pressures are very common and often needed as stated. The parts will not suffer any either whereas most stock systems will bear in excess of 20 lbs easily! I build street rods, muscle cars, classics as well as design custom cooling systems for cars and trucks and I can even put a 16lb cap on an old time copper/brass system from 1957 and do just fine.
Another issue you may have not taken into consideration is "hot spotting". Under high loads your engine may reach high temperatures and pressures in parts of your engine even if just acutely and the lack of "friendly" pressure to keep the coolant from boiling off a head location can be critical. So, I would opt for as much "friendly" pressure as I can get.
For the most part, you have fallen to a myth sir sorry to say. In my professional engineering opinion you are risking coolant expulsion by lowering the OEM specification.
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mddak
Dodge Dakota
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11/25/2003
19:53:00
| RE: 16 lb radiator cap
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I too am an engineering manager.
It is a personal choice as to what lb to use.
It's amazing they still sell 7 pound caps when no OEM puts them in their cars.
Folks I know, when they buy a new car, they throw away their original caps and put 7 lb on and they work for the car manufacturers. Won't mention any names.
Keep it at 16 if you're worried. People been running sevens for years.
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Dave Mitchell
Dodge Dakota
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11/25/2003
20:02:29
| RE: 16 lb radiator cap
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What?
As far as I knew, it was the cooling system volume, the expansion coefficient of the fluid involved, and the temperature said fluid was being subjected to, that would determine the pressure in the system. I really don't think the radiator flow or the water pump flow capacities have anything to do with the pressure upon the cap (that would be internal pressure relative to the external or atmospheric pressure). The water pump, as your professional engineering experience or education should tell you, is not a positive displacement pump.
The pressure rating on the cap will ideally retain the rated pressure. As you submit a heated liquid to said pressure, the boiling point will be raised by some degrees, most likely dependent on the ratio of coolant to water and the type of coolant used in the system (HOAT vs. non-HOAT). So, if your vehicle does not overheat, the pressure rating being less should not matter. The increased pressure should only delay the event of pop-off when the vehicle is already in an overheat condition, or somewhere in a temperature range above 212 degrees fahrenheit, assuming the coolant used boils at a higher temperature than straight water.
I guess what you are saying, is that the Dodge Dakota engines all operate with coolant temperatures well above 212 degrees fahrenheit on a normal basis? Therefore, the increased pressure rating on the cap is necessary.
Are you and the engineers at Dodge also aware of the bursting heater cores that are so common then? I supposed they "designed" them with a pressure rating of less than 18PSI to insure eventual failure and therefore a continual income through a $2,000 repair that will be needed at least once in the vehicle lifetime?
Just what are your engineering credentials and just where did you get them? ITT Tech?
Dave
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Hey
Dodge Dakota
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11/25/2003
21:22:58
| RE: 16 lb radiator cap
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Now, now. Let's all play nice. This forum is best used for a friendly exchange of ideas. BTW, I believe in a lower pressure cap and have used one with no ill effects. So have many people I know. The Dealer sure hates the idea, but they aren't too open to anything other than stock specs.
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GraphiteDak
GenIII
11/25/2003
21:44:46
| RE: 16 lb radiator cap
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Just my .02 cents but the boiling point would not be 212 when under pressure in the system. It would not boil until you reached a higher temp depending on the atmospheric pressure inside the system. On the other hand if you drew the system into a vacuum you could get the water to boil at a temp under 100 degrees!
I'm just playing around. but thought I could thow in my little tid bit there. But I'm no engineer.
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mddak
Dodge Dakota
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11/25/2003
22:06:09
| RE: 16 lb radiator cap
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Dave, you're right. The pressure cap maintains the pressure not the pump. Since it is only a recirculating pump in a closed environment.
A good experiment is to start and run the car to temp with the cap off. All you would see thru the hole is the flowing coolant. The coolant does not blow out of the radiator
Like I said, they sell a lot of 7 pound caps and they've been selling them for years.
And you bring up a good point about the heater core seam leaks.
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HotRodSRJ
Dodge Dakota
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11/26/2003
10:29:38
| RE: 16 lb radiator cap
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Well...I don't know what fluids engineering courses you (DAve etal) took in college, but let me pass some fluid dynamics/engineering facts along to you that I learned there and after designing nuclear vessel cooling systems and hundreds of automotive cooling systems for racing, special vehicles (such as large RVS and towing trucks) and street. This is not about bragging...just calibration for those out there that don't know us and reading our posts. I also write tech articles for automobile magazines, but that doesn't always mean I am right necessarily. This is NOT what this is about. However, I do understand cooling systems to boot and there are behemouth myths out there that I like to bust. This is just one of them. Putting a lower psi cap on your system will take the pressure off the components when in fact it will not under normal circumstances. And in my opinion, you are degrading the design of the system. Read on!
First of all, even tho water pumps are NOT positive displacement machines, as one poster prudently pointed out, they are becoming closer and closer to positive displacement with high efficiency designs being used today. The stock pumps of yesteryear are terrible at pumping and positive displacement should be no where near them in description......but new highflow/volume pumps will perform expotentially better. The Dakota pumps are pretty good in design and output FWIW.
Regardless of type or vintage, water pumps DO INCREASE the pressure at certain points along the system with higher volume PRODUCTION. This is simply because with a fixed volume system, when the pumps volume/output is increased with rpms from idle (10 gpm are typcial) to high rpms (100gpm are typical) the increase in flow thru a fixed space will mean that the pressure goes accordingly...at least in my fluids books they do...and I am sure you all will agree (Coolant flow has a direct relationship to area and an exponential relationship to pressure. Meaning that when you double the area of an orifice and maintain pressure the flow doubles, but when you double the pressure and maintain area the flow is only increased by 1.414 (the square root of 2)). Typical internal pressures in any automotive cooling system can build to over 25psi easily depending on where you measure (top hose, lower hose, block manifold etc..all with differing volume sizes and pressures) and how much flow is present. Now the cap is usually in the lowest pressure point in the system. It's designed that way on purpose. But, that does not mean that the cap can't actually feel increased pressure depending on location and type of system. Crossflow radiators with a fill cap always have the cap on the outlet/suction side. Upright/downflow radiators have the cap in the inlet side and thus subject the filler cap to the pressure drop of the radiator's core in addition to the system pressure. This phenom can lower the effective pressure of a 22 PSI cap to as low as 10 PSI. In other words, on crossflows the cap is located on the suction side of the system which means it will NOT see any appreciable increase in the pressure DUE TO THE PUMP ACTION..you are right on this one. However, upright/downflow models of radiators still have the cap on the "pressure" side of the system and WILL ABSOLUTELY see the pressure increase at higher RPMS due to the increase in volume....physics simply says it has too.
On another point, cooling system capacity and operational temperature range have dramatic affects on typical operational pressures as well. This is obvious since given that you drive temperatures to higher and higher temps, the radiator cap is serving as a safety device to hold that fixed volume of gases and coolant in to a predetermined pressure of the cap. That's why it's rated as it is.
Given that the radiator cap size and location are consistent regardless of capacity and temperature, the increase in coolant volume will have an increase in expansion value of the "pool of coolant" accordingly rising to whatever temperature compared against a smaller capacity system. And accordingly, if the temperature range is 195* ish instead of 180*ish, the expansion goes with too. The normal expansion of coolant and gases under normal conditions will put more pressure on all components of the system. Since the pressure vs pressure drops added throughout the system are a net zero additive in a closed-loop system, the raising of the operational pressures (whether by increase coefficient of coolant volume or temperatures) will indeed put MORE pressure on every component regardless of location. THIS MEANS THE CAP TOO!
You (Dave) inferred that I inferred that Dakota engines commonly can work over 212 degrees. Yes, this is true and happens often especially in high power output situations. I have seen heavy duty situations and towing up long grades easily run systems to over 230 degrees and still maintain the integrity of the cooling system...due to the high cap psi design. I have also seen systems run this hot out in the deserts just motivating down the road so to speak. This can be a common event for some people. This is why anti-freeze helps to raise the boiling point and maximum "friendly" pressure is designed into the system as well. But, if you lower the cap pressure you run the risk of pushing coolant out under these common conditions. This is why it shouldn't be done.
Now, expressing your concern over components that go bad under common pressures is a whole another argument with quality me thinks. I have a friend who has a radiator design and fab shop the designs, repairs, radiators and heater cores. He commonly tests all his replacement cores at 30psi because he wants to make sure that the device is good. This includes DAk heater cores I might add. Usually any issue with heater cores is due to poor workmanship (so blame that great union labor in my opinion) assembling these units. I can't really address that aspect with science facts per se.
And to Mddak, if you take your experiment at operational temperature and romp the throttle hard (stand back) because it will flow coolant all over the place. At least my rides do.
While putting a 7lb on a system designed for 16lb cap can be a personal choice, it also is a dangerous one in my opinion and won't make one ioda of difference in protection of parts under normal circumstances. Your system under normal circumstances may be making only 10lb at the cap all it's life and never see anything less and replacing the cap will not necessarily lower the pressure on any one component under these normal circumstances, but you may experience those normal circumstances where you push the temperature higher and the system will void itself of coolant making for less coolant available to cool. This is not good and can lead to overheating conditions. You want to contain your coolant at just about all expenses and usually your system can/should take the hit. I have tested 50s era systems with a pressure pumper to over 25lbs and nary a whimper. I think your modern systems with better radiators and cores should be able to handle it.
That's all......Happy Turkey Day to everyone and please think of our troops overseas!
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HOTRODSRJ
Dodge Dakota
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11/26/2003
10:37:41
|  RE: 16 lb radiator cap
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ps.......you can go to my cooling site at http://streetrodstuff.com/Articles/Cooling/More_Cooling_Suggestions/ or http://streetrodstuff.com/Articles/Cooling/Cooling_Suggestions/
Another good site (if ya just don't want to take my word for it....corroborating evidence is here) is my friend Howard Stewart's site at Stewart Components (the best cooling site on web for tech information) at http://streetrodstuff.com/Articles/Cooling/Cooling_Suggestions/
Enjoy!
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docfeelgood
Dodge Dakota
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11/26/2003
14:36:24
| RE: 16 lb radiator cap
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hey hotrod.
relax, reduce your pressure or your gonna blow an artery. You need a lower pressure cap, you're runnin high and about to see the white light.
Tho you are a heck of typer or copier.
LOL........Like my daddy used to say:
HEY, WHATEVER
How about K&N filters .....LOL
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HRSRJ
Dodge Dakota
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11/26/2003
16:57:05
| RE: 16 lb radiator cap
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F-you, and your comments about union labor. POS heater cores have nothing to do with union labor, it is about corperate bean counters that figured they could save a couple of dollars by farming out the assembly to some south of the border workers, or maybe even some Chinese workers. ( gee we should would like to sell Chryslers to them people in the Far East.)
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HotRodSRJ
Dodge Dakota
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11/26/2003
23:29:33
| RE: 16 lb radiator cap
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HrSRJ..can't think of your own moniker......and I like your inference to the F word , it always denotes intelligence, education, knowledge and ability to get your point across.
Gee, are we a union member? I drive all union made cars so don't tread on me.
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HRSRJ
Dodge Dakota
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11/27/2003
08:32:11
| RE: 16 lb radiator cap
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I will post under whatever moniker I like, if you dont like it too bad. Am I a union member? you bet, not in the automotive field but in construction.
I like the way you and others, like to bash unions about the problems with your truck. The fact is that in most all cases it has nothing to do with the union final assembler of your truck rather the EDUCATED ENGINEERS who design, ( lets make it good enough to last through the warranty) and the non union sub-assembly workers being paid $ 8.00 an hour in the US. or the $ 8.00 a day Mexican worker to assemble the junk.
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HOTRODSRJ
Dodge Dakota
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11/28/2003
11:12:10
| RE: 16 lb radiator cap
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HRSRJ.....well you may have a good point AND since you made it without aN inferred profanity laced diatribe I will respond in kind. This will be the last on my part however whereas I don't want to "hijack" this thread into another topic.
I generally do not "bash" the union per se and perhaps my off the cuff comment should have read "just blame it on poor workmanship" and left it at that (which means it could be any of the parties involved..management, engineering, whatever). Interesting that I was an ironworker early in life and hated it because I was forced to join even tho I was part time. That got me started off on the wrong foot at the very impressionable age of 18 with the "union" mentality. I wanted to do my own negotiation in life not depend on someone else to do it for me.
I will tell you coming from the midwest that I have a lot of relatives that are union members and some that are not! My father-in-law is a Chrylser employee union guy and my wife's uncle was the union negotiator for the IBEW. So, I know unions well and all their good and bad points alike, but I DO blame both management and unions for the degrading namesakes of our national automotive products.
I see this train coming and powerless to do anything about it! We are losing our national distinction and hold on automotive technology at the speed of light. This is due IN GENERAL (not always) to let's say mundane engineering, quality, assembly and way too high of costs (attributable to high wages and overhead...this is a fact..not my just my opinion). In-so-far as shipping jobs out to less expensive countries, this is something that every manufacturer does to compete effectively. If you don't, you will see the very same thing happen to the automobile industry as the consumer electronics industry in the 70s and 80s. It will completely disappear off the radar screen and take all the jobs with it. The automotive industry needs to be smarter about this and "outsourcing" is one way of controlling costs and offering competitive products. Yes, I know that this takes union jobs but better to take a few union jobs than close the plant! And please don't tell me that parts from Taiwan and China are not as good, they CAN be as good and often are. I have imported parts from all the Pacific rim countries with excellent results meeting higher quality specs (such as MIL and ISOs) than that used in the automotive realm. I had to do it to compete and keep the bulk of my jobs in the factories here in the US....so I know what I am talking about. Not every job that gets "outsourced" is a bad thing from the "twenty-thousand foot" view of the whole picture.
Anecdotal evidence of two close relatives that were UAW memebers for 20 years and now building non-union foreign mark autos here in the midwest that absolutely love the fact that they are treated better, make better money and have a much better attitude than building cars in a hostile union vs management environment. The fault is on both entities, not just the union.
I do continue to support the domestic marks because I do know there are hard working great union members as well. So, I don't lump all the "union" workers in one pile. I also think that there are some great quality products out there as well. My last Dodge Durango never saw a dealership or shop once for a quality issue or problem! I like that! So, I bought the Dakota. I have had a minor problem but for the money and amennities, I think this truck is the best vehicle that I ever owned. Four-passenger, pleanty of torque(4.7), 20mpg on the road, and is comfortable for me to drive long 10 hour trips in! I love it and I have owned GM, Mazdas, Toyotas, Volvos, Acuras, BMWs, etc, so it is measured against a pretty good crowd of marks. Obviously I don't think this stuff is junk in any way! I also like my wife's PT for the money.
But the "union" mentality just rubs me the wrong way....again not necessarily the members that make up the union. If you want to join your union then that is your personal choice and I respect that, however I am nor ever been a fan of the "union" mentality simply because if someone wants to work or cross the picket line they threaten violence to get their way. That is "mob" mentality anyway you look at it and by default disqualifies what ever union and their participants thereof.
Th..tha..tha..that's all folks.
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sleever
Dodge Dakota
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11/28/2003
17:05:08
| RE: 16 lb radiator cap
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thanks man
put a 7 pd cap on and now i don't have to keep adding coolant every week. don't know where it went but it ain't going there now. cheap fix
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alex petrone
Dodge Dakota
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8/09/2013
11:46:26
| RE: 16 lb radiator cap
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Well that escalated quickly...I got a 20
cap on my 04 dak 4.7 .does that matter.(no
problems for over a yr)
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