20 lb radiator cap? 5.3 ls swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

robert_63 · 10-23-2013, 07:12 PM

I have a question, I'm using my stock radiator for my 85. I bought a new cap. A 13 pr 16 lb I believe, and it wouldn't seal to the radiator it wouldn't pressure up just blow out . I stepped up to a 20 lp cap just to try it and it sealed like it supposed to, what I'm asking is. Is this too much? I don't know anything about the lb rating of a radiator cap or the system pressures required, all I know is the 13 lb cap wouldn't seal off and I figured it wouldn't work

**Clyde65** · 10-23-2013, 07:32 PM

Hmm, I had that issue with the 13lb but went to the 16lb and all was good

whitels1 · 10-23-2013, 07:59 PM

How is your cooling system plumbed?

cdowns · 10-23-2013, 08:32 PM

a 20lb cap is a great way to blow out your heater core

robert_63 · 10-23-2013, 08:41 PM

It's plumbed with factory 85 radiator steam line tapped into top of water pump . The lower pressure cap wouldn't seal off think it was a 13 lb one from autozone

solidaxel · 10-24-2013, 08:13 AM

Is the neck of the rad in good shape, no nicks or erosion, hav it checked.
Like he said 20# on the heater core is bad news!

robert_63 · 10-24-2013, 08:29 AM

The radiator is in good shape. I probably just got a cheap part that didn't fit right. Going to go to napa and get a different brand of cap and see

ls1nova71 · 10-24-2013, 09:13 AM

Are you using any kind of overflow bottle? 16lb with overflow bottle is what it would have been stock if I remember correctly and should work fine.

BR3W CITY · 10-24-2013, 02:43 PM

I run an overflow on a sbc rad, with a 16lb cap. No problems whether coolant or water.

Robznob11 · 10-25-2013, 04:06 PM

Its also good to know that the higher the pressure the higher the boiling point of the coolant. If you do boil over with a 20 lb cap the coolant will be so hot that there will be more carnage with the motor

10-23-2013, 07:12 PM	#1
robert_63 Registered User Join Date: Jul 2011 Location: mexia texas Posts: 35	20 lb radiator cap? 5.3 ls swap I have a question, I'm using my stock radiator for my 85. I bought a new cap. A 13 pr 16 lb I believe, and it wouldn't seal to the radiator it wouldn't pressure up just blow out . I stepped up to a 20 lp cap just to try it and it sealed like it supposed to, what I'm asking is. Is this too much? I don't know anything about the lb rating of a radiator cap or the system pressures required, all I know is the 13 lb cap wouldn't seal off and I figured it wouldn't work

10-23-2013, 07:32 PM	#2
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,546	Re: 20 lb radiator cap? 5.3 ls swap Hmm, I had that issue with the 13lb but went to the 16lb and all was good __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!*

10-23-2013, 07:59 PM	#3
whitels1 Registered User Join Date: Apr 2012 Location: Vegas Posts: 617	Re: 20 lb radiator cap? 5.3 ls swap How is your cooling system plumbed? __________________ GoldyLS1 K20 Build My K10 Rock Crawler -Dave

10-23-2013, 08:32 PM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 20 lb radiator cap? 5.3 ls swap a 20lb cap is a great way to blow out your heater core __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-23-2013, 08:41 PM	#5
robert_63 Registered User Join Date: Jul 2011 Location: mexia texas Posts: 35	Re: 20 lb radiator cap? 5.3 ls swap It's plumbed with factory 85 radiator steam line tapped into top of water pump . The lower pressure cap wouldn't seal off think it was a 13 lb one from autozone

10-24-2013, 08:13 AM	#6
solidaxel Registered User Join Date: Dec 2002 Location: Cactus Patch So. Az Posts: 4,749	Re: 20 lb radiator cap? 5.3 ls swap Is the neck of the rad in good shape, no nicks or erosion, hav it checked. Like he said 20# on the heater core is bad news! __________________ 53 TuTone Extended Cab 350 4-Spd 3:08 (SOLD) 53 Chevy Moldy pearl green ZZ-4 4L60E 9" 3:25 55 GMC 1st Black Mll (ZZ4) ZZ6 TKO 600 5 sp 3:73 62 Solidaxle Corvette Roman Red (327 340hp 4spd 3:36) C4 & C5 suspension tube chassis LS 3 4L70E 65 Corvette Coupe 327 350hp 4spd 4:11 78 Black Silverado SWB (350/350) 5.3 & 4L60E 3:42 2000 S-Type 3.0 (wife cruiser) 2003 GMC SCSB 5.3 4L60E 3:42

10-24-2013, 08:29 AM	#7
robert_63 Registered User Join Date: Jul 2011 Location: mexia texas Posts: 35	Re: 20 lb radiator cap? 5.3 ls swap The radiator is in good shape. I probably just got a cheap part that didn't fit right. Going to go to napa and get a different brand of cap and see

10-24-2013, 09:13 AM	#8
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: 20 lb radiator cap? 5.3 ls swap Are you using any kind of overflow bottle? 16lb with overflow bottle is what it would have been stock if I remember correctly and should work fine. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

10-24-2013, 02:43 PM	#9
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: 20 lb radiator cap? 5.3 ls swap I run an overflow on a sbc rad, with a 16lb cap. No problems whether coolant or water. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

10-25-2013, 04:06 PM	#10
Robznob11 Registered User Join Date: Feb 2004 Location: brownfield texas (west texas) Posts: 1,936	Re: 20 lb radiator cap? 5.3 ls swap Its also good to know that the higher the pressure the higher the boiling point of the coolant. If you do boil over with a 20 lb cap the coolant will be so hot that there will be more carnage with the motor __________________ The Ghost 67 short wide full custom. 550 hp LSX, 4l80E, narrowed 9". Body dropped w/air ride! ........................ ___ .........________//__{\_____ ,,,,,,,/__(⊙)___//___/__(O)_/ @disciple2.rc 💪instagram💪 LED TAILS



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