Scottie-GNZ Posted August 31, 2004 Share Posted August 31, 2004 What effect does the preesure rating of a cap have on cooling temps? For example, if an engine runs at 198*F with a 13# cap, what effect would a 10# or 16# cap have on the cooling temp, if any? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted August 31, 2004 Share Posted August 31, 2004 As far as I know (which isn't too much), the cap is like a safety valve for the cooling system. The OEM manufacturer designs the system to run at a certain pressure, then the cap is 'sized' appropriately. IF you use a cap that is lower rated, then it will puke, if higher, then it may blow out another portion of the cooling system.....well that's my story anyways..... Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted August 31, 2004 Share Posted August 31, 2004 Also the higher pressure rating will keep the combintation from boiling over until a higher temp. Another thing is that it will help to prevent localised boiling in the head and such. Quote Link to comment Share on other sites More sharing options...
Chaparral2f Posted September 1, 2004 Share Posted September 1, 2004 The higher the pressure in the cooling system, the higher the boiling point of the coolant. For instance the boiling temp of water is several degrees lower in Denver than it is at sea level. It all has to do with atmospheric pressure, and closing the system allows a higher pressure on the coolant ergo, a higher temp. Does this make any sense?? Joe Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted September 1, 2004 Share Posted September 1, 2004 If your engine cools well with your current 13 pound cap, raising the pressure will make no difference. The car will still run at 198 degrees. Higher pressure caps allow higher cooling system temperatures to be seen without boiling over. The higher the pressure, the hotter things can run and still avoid disaster. If the system is adequately sized and has sufficient airflow, the thermostat determines operating temperature. Given your example, the 10 pound cap should have no effect either (with luck and no hot spots) as the coolant is below its boiling point. I looked for a site with a temperature vs. pressure chart and found this... http://www.are.com.au/techtalk/coolants.htm Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted September 1, 2004 Share Posted September 1, 2004 I found this interesting..... http://www.stewartcomponents.com/html/tech_support/techtip2.asp LARRY Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted September 1, 2004 Share Posted September 1, 2004 I havent read the link Larry gave, but the pressure cap on the coolant system assists the coolant system in altering the boiling point of the medium under pressure. The boiling point of the coolant is increased when put under pressure. When coolant is put under pressure, each psi will alter the boiling point 3 degrees. So if your car has a 16 lbs cap then, providing your system is w/out leaks, it will have altered the boiling point 16 x 3 = 48 degrees. The cap is not the only outer force that alters the boiling point. Altitude also effects pressure. Every 1000 ft change in elevation alters the boiling point by 1 psi...which effects the coolant system by 3 degrees. So if you begin a road trip at sea level w/a 16 lbs cap and travel to Denver Co (approx 6000ft higher) you will have lowered your cap's efficiency by 6 psi...which translates into a deduction of 18 degrees in which the boiling point of your coolant system has been lowered. ...and this is why many bottom dwellers experience over heating prob's when they decide to vacation to the mountains. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted September 1, 2004 Author Share Posted September 1, 2004 Thanks guys. Quote Link to comment Share on other sites More sharing options...
clint78z Posted September 1, 2004 Share Posted September 1, 2004 Yes everyone is correct, it increases the boiling point just like a pressure cooker. A note for you florida boys, running glycol with water increases the boiling point and heat transfer on your cooling system. It also is anticorrosion agent. Having water boiling over isn't just a mess, it traps air pockets in the system and causes hot spots and detonation and thermal fatigue. Keys to keeping it healthy, Flush the system to get the scale out Run glycol and water wetter from redline, use distilled water Some shops can pressure test a cap Quote Link to comment Share on other sites More sharing options...
johnc Posted September 1, 2004 Share Posted September 1, 2004 Another point... Higher cooling system pressures also reduce nucleate boiling which reduces the gas buildup in the cooling system. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 3, 2004 Share Posted September 3, 2004 So uh... yea or nay, would it be "BETTER" to run a higher pressure cap? Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted September 3, 2004 Share Posted September 3, 2004 It is "Best" to run the pressure for which the system was designed. If a stock system is not doing the job, raising pressure is only a band-aid to cover the true problem (plugged radiator, bad pump, head gasket etc.). Raising the pressure causes more flexing in the radiator tanks due to heat cycling (shortened fatigue life/eventual cracks), and higher stresses on hoses. It may help short term, but it could also cause an old system/radiator to develop leaks. Since this is a hybrid site, design pressure will probably depend on the radiator manufacturer's specs. If a range of pressures is shown, I would prefer to try the lower end first. But then, I've never run a 'nucleate' coolant ... maybe John can expand on that racer's tip. Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 3, 2004 Share Posted September 3, 2004 ...design pressure will probably depend on the radiator manufacturer's specs. If a range of pressures is shown, I would prefer to try the lower end first. Yes, but don't forget you have another radiator in the system too, the heater core. If you still have the stock Z heater I would recommend sticking with the original pressure spec. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted September 3, 2004 Share Posted September 3, 2004 ...design pressure will probably depend on the radiator manufacturer's specs. If a range of pressures is shown' date=' I would prefer to try the lower end first.[/quote'] Yes, but don't forget you have another radiator in the system too, the heater core. If you still have the stock Z heater I would recommend sticking with the original pressure spec. Nah....only Gurlie men run heaters Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted September 3, 2004 Share Posted September 3, 2004 Nah....only Gurlie men run heaters And those who actually drive there Z's. I'm surprized you don't have a heater in your Z, Tim. I've heard that older people get cold easily. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted September 3, 2004 Share Posted September 3, 2004 Pot calling the kettle black, old man!! I think that you're old enough to be mah daddy..... Quote Link to comment Share on other sites More sharing options...
johnc Posted September 3, 2004 Share Posted September 3, 2004 Nucleate boiling is boiling that occurs at a very small level (smaller then the bubbles in the head of your beer) on the walls of the cooling passages. When this type of boiling occurs at larger scales the coolant boils off and gas pockets develop in the cooling system. This can lead to hot spots in combustion chamber and detonation, blowing coolant out the overflow tube, overheating, and other engine damage. I know, cost me $5,000 because I didn't install a 25 psi cap as my engine builder instructed. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 4, 2004 Share Posted September 4, 2004 *doesn't run a heater* One less thing to worry about for me... and I drive to work late at night and come home very early in the morning, AND I've always got my windows down. And I"m not old Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted September 5, 2004 Share Posted September 5, 2004 $5k... Ouch! Thanks for the explanation John; always nice to acquire knowledge without the original cost. (My assumption is that this caused the heating at Thunder Hill)?. Sounds like your engine runs so hot with a normal cap that the tiny bubbles can't shed their heat of vaporization & things cascade. Cooling system wasn't designed for your kind of power . Quote Link to comment Share on other sites More sharing options...
johnc Posted September 5, 2004 Share Posted September 5, 2004 No, the basic problem surfaced in 2003 when an intake valve fell into the combustion chamber. Fixing the engine cost me $5K (although Sunbelt didn't charge me for any of their labor). At OTC when I saw you guys I was still trying to solve the bleed off of the inevitable outgassing (and get the blown Penske shock fixed). Because of the engine repositioning, the lowered C&R radiator, and other changes I had to move the bleed to the top of the thermostat outlet and then run it to the top of the tank back on the firewall. Once I did that and bypassed the additional inlet bleed I had no more cooling problems. We figured that out at the Sears Point stop during the event. Since then, the engine coolant and oil temps stay happily at 190 to 210 degrees all day long - even in 100 degree Buttonwillow weather. Quote Link to comment Share on other sites More sharing options...
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