Correct LB radiator cap for 1957 Cadillac

[Cadillac Jack 82]

Should I use the 7 lb or 13 lb cap?  Reason I ask is my car temp gauge normally shows about 3/4s the way to H...sometimes a little bit less.  I've read that this is still within normal operating temperatures based on some articles I've found here.  I'm wondering if the radiator cap may be causing the car to run warm as the water pump and thermostat are brand new in the engine.

[Jon S]

My 1958 used to run between 1/2 and 5/8 (with the original cap). I had the radiator boiled out even though it drained nicely and since then it has been running at 1/4 with the same cap. I had it boiled out 10 years ago.

The cap is a 13 lb RC6:

[Cadillac Jack 82]

Yeah the radiator on this was rebuilt as well so I figure it has to be the cap or not a proper balance of coolant.  I don't worry too much because its not boiling and I don't have any boil over.  It'll get close to 3/4s on the gage and sit there. 

[Coupedeville]

Hello Tim,

I have a 13lb cap on my 57 rad and the temperature gauge sits at 1/4 constantly, unless in heavy traffic.

Joe

[Jon S]

Yes, They should run at 1/4 on the gauge.

[willits]

Both my '58 and '61 sit right at 1/4 on the gauge.  I have 160 degree thermostats in both at 14lb radiator caps.  The needles do creep up at idle if the coolant is low.   
Peter

[Cadillac Jack 82]

I found this on an earlier post.  Mine sits in the middle and slightly to the right.  According to this old add that's fine?

[Jon S]

May well be - When my 1958 was brand new it ran at 1/4 on the hottest of days.  Since boiling out the original radiator, it is back at the 1/4 mark and has never exceeded it.  1/2 may be OK, but 1/4 is cooler.  I have a 180 degree thermostat in the car. 

Remember, the gauge is only an indicator . . . it measures "relative" temperature.

[Dan LeBlanc]

Best thing you can do is take an infrared thermometer and take some readings to see if you're really running hot, have a gauge problem, or a sending unit problem.

[Cadillac Jack 82]

Awesome yeah I've purchased an AC Delco 13 lb radiator cap as the one that's on there looks old.  I'm going to top off the coolant and then test everything out.  Thanks everyone