# The 'radiator cap mod,' what's that about?



## Centurion (Sep 5, 2002)

I see a couple of ppl using a 13lb. radiator cap, how in the world does that improve performance?


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## V i V i D 200sx (Sep 17, 2002)

it has something to do w/ it keeping a higher pressure in the radiator, increasing cooling efficiency


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## javierb14 (Jul 9, 2002)

Radiator Cap


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## zeno (Sep 17, 2002)

Interesting....I never knew about this, and I laughed at the $40 Nismo radiator cap at Mossy.


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## Centurion (Sep 5, 2002)

Dammit, I was hoping this 'mod' added 50HP or something like that!


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## sethwas (Apr 30, 2002)

Well,
The fastest cheapest way to add like 150 HP to your car is to pay a truck driver around $20 to get him to rear end you at 60 MPH at the exact time you want to launch your car vs. your buddy. That should give you a crazy hole shot and easily will get you into the 10's.

Seth


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## johnand (Apr 30, 2002)

I have the NISMO cap and it helped on hot days w/ the A/C on in stop and go traffic to keep the temps down. 

The higher pressure had me nervous about leaks, but none so far!


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## zeno (Sep 17, 2002)

The cap alone produces a gain???

I thought this would only be the case if you upgraded you cooling system.


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## javierb14 (Jul 9, 2002)

yes, the cap by itself will work, but it doesnt hurt to upgrade the cooling system.


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## bahearn (Jul 15, 2002)

The central issue that the higher pressure cap solves and wasn't explained is that coolant only works well when it's liquid. Liquids have two properties called specific heat and latent heat of vaporization. Specific heat is the amount of heat needed to raise the temperature of, in this case, a liquid one degree per unit mass. You'll typically see BTU per pound per ºF or kilojoule per kilogram per ºC . 

An interesting property of liquids is that temperature rises as heat input rises until boiling point is reached. Then, temperature remains constant until all liquid is vaporized, regardless of heat input. More heat per unit time just increases boiling RATE, not liquid TEMPERATURE. The amount of heat needed to vaporize a unit mass of liquid is called latent heat of vaporization. Only after all liquid has been turned to vapor does temperature begin to rise again.

Boiling point is dependent upon pressure. As you raise pressure, boiling point increases. Pure water at atmospheric condition boils at 212 ºF/100 ºC. Raising the pressure of the cooling system forces boiling point up (as does the addition of anti-freeze, which we'll ignore for this discussion). The higher the pressure, the higher the boiling point.

Latent heat of vaporization of water is quite a bit greater than specific heat of liquid water or steam. When you heat coolant to boiling, you get steam, which has low specific heat. It won't absorb heat the way liquid coolant can. You then get hot spots that overheat gaskets and fasteners and causes long, torsionally soft things to bend, like the head.

Raising system pressure raises boiling point of the coolant. If your cooling system is marginal, upgrading to the 300ZX cap can make a significant difference in your car's longevity.

The SE-R suffers both a marginal radiator AND water pump cavitation. Cavitation is simply vaporization caused by mechanical means instead of thermal stress. Raising the system pressure makes these bubbles more difficult to form and keeps them smaller.


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## myoung (Apr 15, 2002)

EXACTLY!.........Very well put Bruce 


http://www.nissanperformancemag.com/september01/radcap.shtml


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## javierb14 (Jul 9, 2002)

hmm, someone knows their thermodynamics

a liquid is also much easier to pump than a gas/vapor.


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## NismoPC (Jul 28, 2002)

Centurion said:


> *I see a couple of ppl using a 13lb. radiator cap, how in the world does that improve performance? *


13 Psi is stock. You meant 16 or 17 Psi.

Unless you are going for show and have the money, it is not worth it to spend $40 on the NISMO cap when you can get the 300ZX TT cap for much less. It is around $10 or so.

Only difference is that the NISMO cap has approx. 1 Psi more pressure than the 300ZX TT


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## LIUSPEED (May 29, 2002)

so the nismo radiator cap is 0.13 and the 300zx TT radiator cap is 1.2 ?

i still not getting this can someone explain it better for me?


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## B11sleeper (Oct 15, 2003)

will putting a 16 lb cap help cooling any if you rarely get up to 200 degrees?


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## azkicker0027 (May 31, 2002)

that cavitation issue at higher rpm's kinda makes me want that nismo cap.


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## azkicker0027 (May 31, 2002)

ok, i bought that nismo cap, one thing i noticed is that the car heats up faster in the mornings, which is good for me cause it's getting colder down here, so i'm happy with it eventhough it set me back $83 with the oil filler cap. :thumbup:


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## Sethticlees (May 30, 2002)

azkicker0027 said:


> ok, i bought that nismo cap, one thing i noticed is that the car heats up faster in the mornings, which is good for me cause it's getting colder down here, so i'm happy with it eventhough it set me back $83 with the oil filler cap. :thumbup:


83 bux, Damn! 
i just got one from my local auto parts store. 5.99 only it don't have that really cool NISMO sticker. I was thinking of buying just the NISMO sticker and putting it on my cap.


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## Gsolo (Sep 11, 2003)

this may be a dumb question....but would the 300zx cap fit a radiator for an E16? only ones ive heard this done for are ga's and sr's. not that an e16 needs it but would be interesting to try out.


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## Gsolo (Sep 11, 2003)

and whats the point of a heavier radiator cap? i mean if you never have problems of running to hot then why bother?


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## azkicker0027 (May 31, 2002)

to some, like myself, it's really a matter of personal preference, i went for it first because of higher pressures, and the fear of a possible cavitation at higher rpm's, faster warm-up times, and it spruces up the engine bay with the oil filler cap.


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## Gsolo (Sep 11, 2003)

azkicker0027 said:


> to some, like myself, it's really a matter of personal preference, i went for it first because of higher pressures, and the fear of a possible cavitation at higher rpm's, faster warm-up times, and it spruces up the engine bay with the oil filler cap.


shouldn't affect warm up time cause water in the radiator doesn't even circulate until the thermostat starts opening up....even then the cap just lets the water get warmer so you would have warmer heater


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## azkicker0027 (May 31, 2002)

okay, i think i got confused :fluffy: 
i noticed it warmed up faster in the mornings cause i always warm the car up before rolling for work, after i installed the cap. And since it's cooler down here now.


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## Gsolo (Sep 11, 2003)

azkicker0027 said:


> okay, i think i got confused :fluffy:
> i noticed it warmed up faster in the mornings cause i always warm the car up before rolling for work, after i installed the cap. And since it's cooler down here now.


might just feel like it cause it gets hotter from the water being able to go over 180...or 210 whatever car you have.


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## Spelchy (Jun 24, 1987)

yuck.. 83 bucks!

i sure could go for a faster warmup though.. it's -20C here right now...

do you think this cap would fit on a ca16de?


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## azkicker0027 (May 31, 2002)

that was $26 for the rad cap and the rest for the oil filler cap, not just the rad cap.


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