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Username Post: Radiator cap        (Topic#366007)
Johnny468 
"13th Year" Silver Supporting Member
Posts: 851
Johnny468
Loc: Richmond, Va.
Reg: 10-24-08
08-04-21 07:57 AM - Post#2824463    

I recently had the brass and copper radiator from the Impala repaired by a local radiator shop. When I told the owner I was running a 16 lb cap, he said that switching to a 10 lb cap would help to reduce wear and tear and would increase the long term service life of the radiator. Any thoughts?

Thanks,

Johnny

1965 Impala SS
505/4-speed/3.90


 


Shepherd 
Frequent Contributor
Posts: 2305

Loc: Lake George, NY
Reg: 11-11-15
08-04-21 10:19 AM - Post#2824473    
    In response to Johnny468

Anytime you reduce the pressure in a cooling system you extend the life of hoses and radiator, this assumes the overall condition of the cooling system is good, of course the boiling point has now been lowered.



 
Johnny468 
"13th Year" Silver Supporting Member
Posts: 851
Johnny468
Loc: Richmond, Va.
Reg: 10-24-08
08-04-21 11:54 AM - Post#2824481    
    In response to Shepherd

Cooling system is excellent, temperature never goes over 190 even sitting in traffic in 100 degree weather. Can I safely run a lower pressure cap?

1965 Impala SS
505/4-speed/3.90


 
IgnitionMan 
Valued Contributor
Posts: 3903

Reg: 04-15-05
08-04-21 04:42 PM - Post#2824503    
    In response to Johnny468

Run the 16 PSI cap, leave the high tech dyno tune stuff out of it.



 
Rick_L 
Member #409
Posts: 27907
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
08-04-21 04:46 PM - Post#2824504    
    In response to Johnny468

You are lowering the boiling point significantly by going from a 16 psi cap to a 10 psi cap. Maybe 30-40 degrees. Once the coolant starts to boil, it's all over - the temperature will run away and you'll risk engine damage.

Ask yourself if you want that risk starting right now and continuing, or if you want to postpone that risk until you have some significant time and miles on the radiator and hoses. At that time the difference in risk starts to equalize.



 
Johnny468 
"13th Year" Silver Supporting Member
Posts: 851
Johnny468
Loc: Richmond, Va.
Reg: 10-24-08
08-05-21 03:26 AM - Post#2824528    
    In response to Rick_L

Thanks gents, I will keep the 16 lb cap.

1965 Impala SS
505/4-speed/3.90


 
65_Impala 
Very Senior Member
Posts: 4797

Reg: 12-29-02
08-05-21 04:53 AM - Post#2824533    
    In response to Johnny468

Have you adding an overflow tank so any coolant released when hot gets pulled back into the radiator when it cools again?



 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-05-21 06:23 AM - Post#2824536    
    In response to Johnny468

Here's a link for some useful info:

https://durathermfluids.com/pdf/techpapers/pressu r...

Before there were external expansion/recovery tanks, expansion of the coolant was accommodated internally to the radiator. One needed to not over fill (fill to just above the 'fins'). That left enough expansion space for 'normal' conditions (including getting somewhat 'hot'). When it did not (or the radiator was over filled) the coolant could 'spill' out the expansion tube onto the ground upon sufficient expansion.

Such a 'closed' system is environmentally friendly. I never 'added' one to a car, and never had any cooling problems because I did not. But I also do not over fill the radiator.

Just info.

Pete




Edited by japete92 on 08-05-21 06:25 AM. Reason for edit: No reason given.

 
someotherguy 
Senior Moderator
Posts: 29476
someotherguy
Loc: Texas
Reg: 08-01-03
08-05-21 06:51 PM - Post#2824593    
    In response to Rick_L

  • Rick_L Said:
You are lowering the boiling point significantly by going from a 16 psi cap to a 10 psi cap. Maybe 30-40 degrees. Once the coolant starts to boil, it's all over - the temperature will run away and you'll risk engine damage.

Ask yourself if you want that risk starting right now and continuing, or if you want to postpone that risk until you have some significant time and miles on the radiator and hoses. At that time the difference in risk starts to equalize.


100% agreed - you might prolong the life of the radiator, hoses, etc. with that lower pressure cap, at the risk of damaging the engine. It sounds a lot like cutting off your foot to save yourself the pain of an ingrown toenail. :/

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5251
Mel Foye
Reg: 09-29-00
08-05-21 07:55 PM - Post#2824595    
    In response to Johnny468

A ten pound cap will increase the boiling point of water from 212 to 242.



 
65_Impala 
Very Senior Member
Posts: 4797

Reg: 12-29-02
08-06-21 04:09 AM - Post#2824611    
    In response to Mel Foye

You can't count on the straight pressure increase. A 65 Impala rad is downflow with the cap on the inlet side. The pump pushing coolant through the engine adds pressure to the upper tank. The pressure the pump adds to the upper tank reduces the boiling point increase the rad cap pressure rating adds.




 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-06-21 06:46 AM - Post#2824628    
    In response to Mel Foye

  • Mel Foye Said:
A ten pound cap will increase the boiling point of water from 212 to 242.



Correct.

AND, a 50/50 antifreeze/water mix boils at 222F @ 0 pressure; 252F @ 10 psi; and 267F @ 15 psi. A 16 psi cap will be approx 270F.

The '63 full size Chevy's used a radiator pressure relief valve setting of 13 psi.

'Later' engines were tuned to run hotter (to help meet 'new' smog requirements). I do not have any data, but It would not surprise me if those engines' did not 'up' the coolant pressure (15/16 psi?).

just info.

Pete










 
dgstarr 
"4th Year" Silver Supporting Member
Posts: 264
dgstarr
Loc: Portland, OR
Reg: 04-16-13
08-06-21 01:25 PM - Post#2824655    
    In response to japete92

63 cars with A/C had 15 lb caps. I have a 62 with factory A/C. I changed my (correct) 13 lb cap to a 15 and I developed a small leak on the passenger floor matt, from ether the heater core, or the thermostatic heater valve. I added a small bottle of K-Seal and went back to the 13 lb cap. The leak stopped.



 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-06-21 02:38 PM - Post#2824658    
    In response to dgstarr

  • dgstarr Said:
63 cars with A/C had 15 lb caps. I have a 62 with factory A/C. I changed my (correct) 13 lb cap to a 15 and I developed a small leak on the passenger floor matt, from ether the heater core, or the thermostatic heater valve. I added a small bottle of K-Seal and went back to the 13 lb cap. The leak stopped.




I've never owned an a/c 63 Chevy, but the only pressure cap rating specified in the Shop Manual is 13 psi (for all power trains). I can not find any mention of an exception/difference for a/c in the manual.

A loooong time ago (1968 'ish') my 1963 Impala convertible 'sprung' a leak in the radiator. I had NO $ to fix. I found the leak point, 'plugged' it with some bubble gum, loosened the radiator cap. It held for a while; when it started leaking again, I replaced the bubble gum. I drove like that for about a year (until it was stolen and I never saw it again). I hope that thief got stuck somewhere REALLY bad

Just info and a story.

Pete





 
65_Impala 
Very Senior Member
Posts: 4797

Reg: 12-29-02
08-06-21 05:56 PM - Post#2824662    
    In response to japete92

Newer cars (compared to a 65) moved to crossflow rads with the cap on the outlet side of the radiator so they didn't need to up the cap pressure because the system pressure caused by the pump was no longer trying to push open the cap.



 
dgstarr 
"4th Year" Silver Supporting Member
Posts: 264
dgstarr
Loc: Portland, OR
Reg: 04-16-13
08-07-21 09:24 AM - Post#2824686    
    In response to japete92

The 1963 owners guide only shows the 13 lb cap, but the assembly manual shows different part numbers for the A/C cars radiator caps, but does not give pressure rating. My source of info on the 15 lb cap was the 1938-1964 Chassis parts catalog:

1.203 CAP Radiator filler, with gasket
Pressure type 63-64 Pass w/all air cond (RC15) (15 lb) 861050



Edited by dgstarr on 08-07-21 09:25 AM. Reason for edit: No reason given.

 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-07-21 12:26 PM - Post#2824690    
    In response to dgstarr

  • dgstarr Said:
The 1963 owners guide only shows the 13 lb cap, but the assembly manual shows different part numbers for the A/C cars radiator caps, but does not give pressure rating. My source of info on the 15 lb cap was the 1938-1964 Chassis parts catalog:

1.203 CAP Radiator filler, with gasket
Pressure type 63-64 Pass w/all air cond (RC15) (15 lb) 861050



I am NOT disputing you, or your source regarding the 15 psi cap.

I looked in my copy of the 63 Assembly Manual (sect 11-13; sheet 14.00) and it has 3 part numbers listed for the cap. The first one is 850559 which is a 13 psi cap.

The next two are 3748424 and 3748425; both are listed as 'OPT.' I do not have any documentation that IDs those number. Perhaps one (or both) are 15 psi.

I also scanned (rather quickly) the A/C section of the 63 Assembly Manual. I did not see any reference to the radiator cap (I may have missed it).

Did you find the different part numbers for the A/C car's radiator caps?

Because the 63 Shop Manual is a 'Supplement' to the 61 Shop Manual, I quickly scanned thru that manual too. I found nothing on a different radiator cap for A/C. Again, I amy have missed it.

Personally, I think using a 15 psi (or even 16 psi) cap on a car with A/C is good idea. I'm simply curious about OEM caps.

Pete




 
dgstarr 
"4th Year" Silver Supporting Member
Posts: 264
dgstarr
Loc: Portland, OR
Reg: 04-16-13
08-07-21 02:37 PM - Post#2824694    
    In response to japete92

Pete,

In the assy manual go to section C60, sheet 21:

3827008 cap asm.-radiator filler
861042 opt

According to the GM parts wiki, these two part numbers were superseded by 861050 (RC-15) (15 lb) which I had found in my parts manual.

Dave



 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-07-21 04:36 PM - Post#2824700    
    In response to dgstarr

Dave,

Thanks.

I'm glad it was not obvious. I'm not embarrassed that I missed the cap difference for A/C when I visually scanned that page.

The rev '8' notation that changed to the 861042 is dated 11-1-62. Perhaps some early production A/C system cars were delivered with the 13 psi caps. That would explain why some of the other documentation/manuals don't mention it. But that is pure conjecture.

Pete





 
G. Baker 
Poster
Posts: 54

Loc: Ontario Canada
Reg: 12-18-15
08-09-21 05:11 AM - Post#2824779    
    In response to Johnny468

Some good and bad info here, but ALL Cooling Systems from at least 1960 were Pressurized. There is pressure throughout the entire system unless there was a shut off valve for the heater core.
At one time all GM Rad Caps were made in India.
Depending on your driving/traffic expectations, keep the 13/15 lb cap.
At one atmosphere, the boiling point for water is 212°F or 100°C. A 10 psi pressure cooker will bring the boiling point to 240°F, but a 15 psi pressure cooker will top at 250°F. In other words, the boiling point increases at a decreasing rate against increasing pressure. This applies to Cooling systems as well.



Edited by G. Baker on 08-09-21 05:49 AM. Reason for edit: No reason given.

 
454cid 
Valued Contributor
Posts: 3230

Age: 48
Loc: West Michigan
Reg: 02-18-12
08-09-21 02:07 PM - Post#2824826    
    In response to G. Baker

  • G. Baker Said:

At one time all GM Rad Caps were made in India.



What time frame?



99 K3500 RCLB


 
nicholes 
Newbie
Posts: 7
nicholes
Reg: 11-11-20
08-12-21 04:02 AM - Post#2824987    
    In response to Johnny468

I always went to a lower temp cap ,not 10 but from a 16 to a 13, never had problems



 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5251
Mel Foye
Reg: 09-29-00
08-16-21 04:36 PM - Post#2825313    
    In response to G. Baker

Back when I suggested a 10# cap which would give a boiling point near 240 I felt as folks with old cars many to most would be passing water on themselves at 190. 200 equals the side of the road. Higher temps can take some time to get used to as when we bought a new 1993 Vette. First fan did not come on till 227. That is where I learned about passing water.
Why run more pressure?




Edited by Mel Foye on 08-16-21 04:37 PM. Reason for edit: No reason given.

 
japete92 
"7th Year" Silver Supporting Member
Posts: 1749
japete92
Loc: No. Virginia
Reg: 01-18-13
08-17-21 06:20 AM - Post#2825365    
    In response to Mel Foye

  • Mel Foye Said:
Back when I suggested a 10# cap which would give a boiling point near 240 I felt as folks with old cars many to most would be passing water on themselves at 190. 200 equals the side of the road. Higher temps can take some time to get used to as when we bought a new 1993 Vette. First fan did not come on till 227. That is where I learned about passing water.
Why run more pressure?





I agree; especially about the over-reaction to observed slightly higher coolant temps (which actually help the oil flow).

I learned via this discussion, that GM used 15 psi on the A/C cars. Perhaps because of the added heat load. AND because 'idiot lights' were standard.

I have those lights, BUT I have added a mechanical temp gauge. I read in an old vintage Chevy manual of some sort (I do not remember the title) that the idiot lights did not begin to illuminate until around 235F (or so, my memory is not reliable enough to say that is exactly the temp).

I think the choice (10 psi vs 15 psi, for example) is more a choice of how much 'safety factor' (prior to boiling) does an owner wish. Is 'more' better? I guess that depends on the owner's tendency to pay attention to their 'indicators' AND their pucker factor.

Pete





 


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