ericgrau

iTrader: (1)

I did some calculations and posted this in another thread, but that thread was not cooling specific. I thought the results were interesting enough to show. Basically, your coolant is less likely to boil (and therefore less likely to form hot spots or overheat) from using more antifreeze, not less: raising the boiling point is easier than lowering coolant temps. This is the basic logic behind Evan's NPG, btw. It's also why racers use high pressure coolant caps, to raise the boiling point even more.

As for me... I'm going to keep running 50:50.

ASSUMPTIONS

• I assumed the outside temperature was 30C (86F) - a nice hot day.
• I assumed excellent conductivity between the engine & coolant and the coolant & outside air. In reality the first assumption is reasonable, but conductivity to the outside air (through the radiator) will increase with temperature, favoring coolant with a higher boiling point.
• I pulled boiling points and density off a table from one of my mechanical engineering lab classes.
• The specific heat of antifreeze at various concentrations came from the web.

CALCULATIONS
I calculated the heat transfer at the boiling point - the limit of the system's cooling capacity:

Q = M * c * dT

dT = (boiling point) - 30C
c = specific heat of the ethylene glycol: water mix
M = mass flow rate of coolant

The cooling capacity climbed from 0% to 35%, then dipped until 50%, then climbed again until 95%. 35% ethylene glycol is only 2% better than 50:50 or straight water. Past 65% the cooling capacity gets a lot better. I uploaded the results to:
http://www.geocities.com/ericjgrau/EGcooling.xls


CONCLUSIONS
A 2% difference between 35:65 and 50:50 or pure water is small enough to be negligible. If you consider the underlined statement in the assumptions section, using more antifreeze is better. Especially since most people must upgrade their radiators when they need to handle more heat. Your temps will be hotter, but it will be harder for your coolant to boil. That means it will be harder for your car to overheat and harder for "hot spots" (localized boiling) to form - these are the very 2 things the cooling system is supposed to prevent.

Carzy Driver

and what's wrong with 50/50 mix?

gus5891

does an rx7 require antifreeze to keep it from boilin over

Sideways7

iTrader: (7)

You should use antifreeze in ALL street driven cars, if for nothing else than the anit-corrosion agents it contains. It also raises the boiling temperature to help reduce isolated hotspots where a water pocket starts boiling.

ericgrau

iTrader: (1)

Nothing.

Here's some more general information, if anyone is curious:
http://auto.howstuffworks.com/cooling-system.htm

gus5891

i personaly agree to always use antifreeze but at this present moment i'm right at broke in funds an everybody is callin askin for money. so i dont have any in my car i'm hoping this wont hurt anything short turm wise

Sideways7

iTrader: (7)

Honestly, you cant afford less than 5 bucks of antifreeze at walmart? As long as it isn't for very long, then you can run straight water, just keep a close eye on temps, and add antifreeze asap.

ericgrau

iTrader: (1)

Yeah, you're asking for rust... at least add a little antifreeze; siphon a pint from a neighbor or something . Or buy a bottle of anti-corossion additives.

gus5891

No i cant afford 5 dollars of antifreeze. I got like a dollar on me an 29 cents in my bank account. I'm strait up broke Dont ever think you got it bad till you see how bad someone else has it But i continue to live as do we all

I got a bottle of barr's stop leak in it i think it helps a little

Sideways7

iTrader: (7)

Trust me, I know where you're coming from. The only reason I have any money at all is because my mom lends me money occasionally to pay bills. I've currently got over 400 backs in late bills already, because I hate asking her for more money.
Anyway, maybe you can use a friend's anti-freeze, or something. Surely you know someone with a spare bottle.

gus5891

yeah my dad but he is pretty mad at me right now.

he helped me buy this car an i already kinda screwed it up

Sideways7

iTrader: (7)

The only reason my mom is still lending me money is because of my daughter...

gus5891

how old are you

Sideways7

iTrader: (7)

23, daughter is 15 months.

ericgrau

iTrader: (1)

Wow... I'm 24. Scary thought. Feel bad for ya.

Tell him you don't want to screw it up more... at least get a little antifreeze to hold the cooling system until you get a full gallon.

gus5891

well congrats on your daughter. i kinda though you were older than that being you seem to know so much about these rx7's.

but i do notice we younger generation really arent ready the live completely on our own well not me anyway

Sideways7

iTrader: (7)

Thanks. And we would have been fine, but the Chiropractor (sp) my wife worked for as a massage therapist went out of business, and she hasn't been able to find a new job that pays nearly as well. I'm still in school so that hurts my job chances.
As for knowing a lot about rx-7's, I just spend way too much time on these forums I get on here and read pretty much everything posted and absorb the knowledge, plus I've done a crapload of stuff on my car, too.

gus5891

thats part of the problem though he helped me buy the car an i ran it hot bein stupid an i'm pretty sure i blew the coolant seals thats why its got barr's stop leak in it. I know it wont fix this type of thing but if it will just slow it down a bit it would be nice

Yeah i read an study alot to just cant remember all of it specialy when i need to anyway

Sideways7

iTrader: (7)

Wow, sounds real similar to me. My dad had to help me a bit with buying my car, then it started having coolant seal problems and I overheated it, so it needed a rebuild. He had to pay for most of the rebuild, but I have repayed him since then. I mainly paid him through work and fixing his computer. I estimate I saved him at least 2k in computer repair fees in the past few years. He still starts ranting if I say anything about spending money on my car, even though I have an entirely seperate account for my money I can spend on my car (I get the money from parting out a car I have.) It really pissed him off when I said that my car has had fewer problems than his WRX, even though its true.

gus5891

yeah that does sound really familiar. But i lost my job an still owe my dad like 400 on the car not to mention 1500 from before that. an yeah i got a parts car when i bought my car so now i'm startin to strip it down to get some money. Plus i found another RX7 around the corner from my house that has exactly 50,000 miles on it an it dont run i think the apex seals are bad on it. an then i know a guy that has a twin turbo for sale that only wants like a grand for it an it runs

its killin me buy one of these cars an now i want them all an i'm findin them all over

ericgrau

iTrader: (1)

Congrats on your daughter, Sideways7. Sorry, I assumed worse. Now I'm thinking I need to get myself hitched. Hope your wife finds a good paying job.

I've been collecting notes myself from reading a great deal on these forums & elsewhere. When I finally finish school I can get working on my car. It's funny the things I get involved in here when so far I've only had time to swap out the fluids on my '7 (bought 11 months ago). OTOH I have a pretty good idea of what I will get and how much it will cost.

I'm actually on my 2nd '7. My 1st one met a slippery road. It was from a tow auction. It ran great but it looked awful. My dad screwed up just about everything on it trying to "fix" it (it wasn't broken, except aeschetically) and I had to undo/redo his work. The grey paint varied in degrees of faded-ness. Replaced a smashed up passenger window. Partly flattened out a huge dent. Patched an exhaust leak that used to make it so you could hear it from a mile away. After I crashed it I went into withdrawl for about a week before I found a much nicer RX-7.

gus5891

I Have Been In Withdraws Not Bein Able To Drive Mine An Its Only Been 2 Weeks