Does Anyone Run Lower Radiator cap Pressure ?

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I was at an engine rebuilding meeting and found out that some engine shops replace radiator caps on most rebuilds and replace them with lower pressure caps such as 13 lbs instead of say 16 lbs and in some cases 7 lbs.
We don't replace radiator caps unless they are defective and then only purchase Stant or oem..

I don't think a 13 lb. cap would hurt anything but a 7 lb. seems to low pressure. My ocd keeps me from cutting certain corners My top rebuilder does not think cap pressure makes such a difference... What does my fellow Bitogers think?
 
Originally Posted By: DoubleWasp
I think it lowers the boiling point of the coolant, which sounds like a bad thing to me.
+1 No doubt there is some crazy explanation.
 
~3° Farhenheight delta water boiling point per PSI. Clapeyron’s equation.
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Lower pressure might be easier on marginal hoses and whatnot though.
 
Don't. Pressure isn't just there for boil over protection. It's also there to stave off cavitation. In fact Kestas was saying that a decrease of just a couple of pounds can allow it in some applications.
 
Originally Posted By: Chris142
We do occasionally. Many older cars had 16 or more psi caps and the old metal rads can't take that much pressure and they don't want to fix it right.


Yeah; it's a shortcut which will result in faster water pump wear and easier overheating. Higher OEM pressure should be kept for optimum cooling.
 
I agree with the 'situational' use, but perhaps only 2 or 3 PSI at most unless it's 'really bad' and just needs to get you by with a bigger drop. At that point, the radiator cap really won't matter if dropping the pressure that much is actually needed.

Otherwise? Just stick with OE pressure requirements/recommendations.
 
Originally Posted By: andyd
Because stuff wears out faster under higher pressure.


What "stuff" wears out faster?
 
Originally Posted By: The_Eric
Don't. Pressure isn't just there for boil over protection. It's also there to stave off cavitation. In fact Kestas was saying that a decrease of just a couple of pounds can allow it in some applications.


Now that's actually a good reason and basis. I was going to say that since I've never seen much above 200 degrees on some of my cars, 7 psi vs 16 is probably ok. Especially if the glycol prevents boiling somewhat. But if this is the case, then the story is a little different.
 
Can someone please explain the logic in having a lower 'ultimate' coolant pressure?

There were also thoughts some time back on Reverse flow coolant systems.
The flow was from the Rad to the Head, through the block and back to the Rad.
As I understand it, this could result in smaller Rads and more uniform block temps.
 
I think anyone who attends 'engine rebuilding meetings' would already know the answer to this question. If you don't want to 'cut corners' and only buy Stant or OEM... When you do in fact change the cap, then why wouldn't you replace the cap with the original spec?
 
Those rebuilders do not have much confidence in their work if they believe six pounds less pressure will have an effect on an engine. It simply raises the boiling point of the coolant, no more no less.
 
Originally Posted By: ltslimjim
^Ooops, go to 17:30 on the first video.
smile.gif


As soon as I saw the "block tester" (in the first video) that uses the blue fluid to test for combustion leaks, I had a Ford 3.8 flashback. I actually smelled/tasted antifreeze.
 
Originally Posted By: Kuato
Originally Posted By: Chris142
We do occasionally. Many older cars had 16 or more psi caps and the old metal rads can't take that much pressure and they don't want to fix it right.


Yeah; it's a shortcut which will result in faster water pump wear and easier overheating. Higher OEM pressure should be kept for optimum cooling.

You want to explain that one??? The pump is going to wear out faster at 7 psi vs 16??? Baloney... If any thing the shaft seal has a easier life at the lower pressure as does hoses, radiator, heater core etc...

I ran my '88 T-Bird with a 7Lb cap from '99 till '09 and never had ANY issue... It does have aftermarket temp gauge and good radiator, never saw temps above 230*F but I never let it idle for long periods with A/C blasting... My beater '96 F-150 also has a 7Lb cap, that's because of radiator tank seepage(every hose and water pump is new)... I replaced radiator last year but that 7Lb is still in place, on there for 2½ years now(yes it's idled in traffic for half hour or more with ambient at 95F and A/C blasting, no problem)...

I've run a '93 Grand marquis with cap totally loose(screw on type), for a couple years because of a weeping radiator tank... No pressure, no leak(finally sold it to a friend who needed a car and knew it had issues)... I did same for over FOUR years on a '98 because of the POS plastic intake... I knew if it did crack, without pressure it wouldn't instantly blow out all the coolant... Intake finally did crack and has been replaced, now 16Lb cap is tightly in place with no issues, still has orig water pump...
 
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