Chevy Nova Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
9,964 Posts
You want a pressure cap that is within the limits of your radiator, too much pressure can deform the tubes. The pressure cap doesn't directly affect the temperature other than that it allows the coolant to absorb heat at a higher temperature by raising the pressure corrected boiling point. Each pound of pressure raises the boiling point by about 3°.
 

·
Premium Member
Joined
·
5,318 Posts
Discussion Starter #4
Here is a quote from Steward Components

"Radiator Caps
In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

The coolant will typically only build to 16-18 PSI, due to expansion up to 200°F. However, if the engine does overheat due to external factors, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a "safety valve", so always use the highest pressure radiator cap that the radiator will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating pressure."

If I read this correctly, cap pressure directly effects coolant temp.
 

·
Registered
Joined
·
9,964 Posts
FunkyNova66 said:
If I read this correctly, cap pressure directly effects coolant temp.
Let's put your red sentence in series with part of mine from the first post:

Higher coolant pressures also transfer heat from the cylinder heads more efficiently by raising the pressure corrected boiling point. As the coolant approaches its PCBP its ability to absorb heat is diminished. If you don't approach the boiling point with the coolant, it will absorb the heat just fine. If you replace a working 10# cap with a 20# cap, your engine won't get any cooler because it won't get to 20#. If your engine runs all day at 190°, putting a 20# cap will make no difference. If you've been boiling water out at 10#, a 20# cap will result in a much cooler motor.
 

·
Premium Member
Joined
·
5,318 Posts
Discussion Starter #6
Mike Goble said:
Let's put your red sentence in series with part of mine from the first post:

Higher coolant pressures also transfer heat from the cylinder heads more efficiently by raising the pressure corrected boiling point. As the coolant approaches its PCBP its ability to absorb heat is diminished. If you don't approach the boiling point with the coolant, it will absorb the heat just fine. If you replace a working 10# cap with a 20# cap, your engine won't get any cooler because it won't get to 20#. If your engine runs all day at 190°, putting a 20# cap will make no difference. If you've been boiling water out at 10#, a 20# cap will result in a much cooler motor.
Ahhh....this is what I was wanting to hear.:D I had a 7 lb cap on my radiator. Don't ask...lol...It was on there when I bought my last car. :rolleyes: I just replaced it with a factory replacement 16 lb cap (this was the specs for a 327 replacement). I was constantly boiling water out with a 7 lb cap. Again...the car didn't overheat sitting in my driveway idling for 40 min. But the minute I hit the highway it would creep to 195...200....210...215.....and I couldn't get the temp back under control at lower speeds again. I would have to shut the car down at the nearest exit and let it cool. I will be very curious to know if this will help. My friend's Camaro had the same problem and he said all he did was put the correct PSI cap on his radiator and it solved it 7 PSI to a 13PSI. I won't count my chickens before the hatch though.:rolleyes:

Thanks again Mike for the replies. I really do appreciate it. Either way....I'll let you know how much difference it has made in my car when I take it for a test drive tomorrow.
 

·
Registered
Joined
·
576 Posts
ALWAYS LEARN SOMETHING FROM STEVESNOVASITE.COM

I just got back from a a long drive and it was about 97 deg outside. I filled my overflow to halfway before I left. It ran a little warmer than usual but not hot. I also recently put on a 7 lb cap to help stop my head bolts from leaking and noticed it boiled some out of my overflow can tonight, will have to wait for it to cool to see if it goes way low or not. I dont want to go back to 13lb cap because of the head bolt leak, so not sure whats next- guess I'll wait to see how much really boiled out.
 

·
Premium Member
Joined
·
11,072 Posts
If your headbolts are leaking, use some Ceramic block sealer
Talk to your local pharmacist, have him order some sodium silicate. Pour about a pint of it in the radiator, run it a half hour or so to get fully warmed and circulated--No more leaks! It's the same ingredient in some stop-leak products, as well as Moroso Ceramic sealer, but a lot cheaper.
 

·
Registered
Joined
·
11 Posts
This is all great info. Currently my Chevy has a 7 LB cap (Car was given to me like that) and it boils every time I take if for a drive. I just placed an order in amazon for a 13 LB cap (that's what the owner manual said came with it) It is funny that I would have never thought of looking in the manual! google has ruined me ... :awkward:

thanks for all the great info
 

·
Premium Member
Joined
·
2,495 Posts
#4 post said "Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off.
I don't think that is true. I used to have the same problem with a 7 lb. cap on my previous Nova. Once it started to heat up on the highway and vented I would get on surface streets and slow down the temp would come down.
 
1 - 15 of 15 Posts
Top