1958 overheats at idle

[Kenny Madden]

Overheats only while idling, going down road temp. stays around 170. Newly rebuilt engine with less than 500 miles. Radiator, water pump, hoses, coolant all OK. Pressure tested system and all checked out fine. Replaced temp. sending unit with NOS and put resistor in line and verified temp. at thermostat housing
with IR gun to verify reading at gauge is right-it is. Also installed new 180 thermostat. Still puked antifreeze after idling for few minutes. Replaced 7#
radiator cap with 13# cap, ran 30 minutes and temp. stayed at 170. Will the higher pressure cap cause me any problems if this appears to correct the problem?

[Duke W.]

Re: 1958 overheats at idle

I don't think the 13 pound cap is going to blow anything out, but I'm confused by your report. The higher pressure cap should not affect the actual coolant temp, but will increase the temperature at which the coolant overflows.

The way I interpret your post you say that at idle the car quickly heats and coolant overflows with the seven psi cap, but it doesn't heat up at all with the 13 psi cap(?).

Duke

[Kenny Madden]

Re: 1958 overheats at idle

That's correct. I have only ran the car once since changing to the 13psi cap and it did not overheat and I didn't loose any coolant after 30 minutes. It would overheat and loose antifreeze with the 7psi cap after running about 20 minutes. What's odd is the temp. gauge read about 185-190 when it overheated with the 7psi cap. I don't understand how it can puke antifreeze at 185-190 degrees, which is accurate after checking with an IR gun. That's not near the
boiling point.

[Duke W.]

Re: 1958 overheats at idle

Interesting, but inexplicable. Keep the 13 psi cap installed and continue to monitor the cooling system behavior.

Duke

[Duke W.]

Re: 1958 overheats at idle PS

Check whether the 7 psi cap holds pressure. Auto part stores usually have cap testers you could use.

It's possible that you are experiencing some localized internal boiling at idle that expands the coolant. If you have a dual point distributor without vacuum advance, localized internal boiling would be more likely than if you have a properly set up vacuum advance distributor for the installed cam.

Duke

[Clem Z.]

Re: 1958 overheats at idle

i have found the there are different depths to rad cap bungs and some do not put enought pressure if you use a short cap on a deep rad bung.

[Joe C.]

Re: 1958 overheats at idle

Kenny:

What is the ambient temp for the test? How long does it idle before it overheates (boils over)? Is the hood open or closed? Is the car stationary or moving? Most of these old timers can not idle for long periods without boiling over, unless moving. Heat exchanger technology left much to be desired back in the "good ole days".

Joe

[Kenny Madden]

Re: 1958 overheats at idle

Joe,ambient temp was approximately 50-55 degrees. Prior to changing cap to 13psi, would boil over after about 20 minutes with hood closed. Car only overheats at idle, is fine moving. One item I omitted, there is an electric fan
which I turn on while idling or stopped in traffic or at a light. Don't need to
run this fan while moving only while sitting. Also standard 4 blade fan has been
replaced with a 6 blade for more air flow.Thanks.

Kenny

[Joe C.]

Re: 1958 overheats at idle

Kenny:

Seems like the old cars had no margin for overheat without copious airflow through the heat exchanger. It would be interesting to see if there would be anyone else who would report the same findings within the same parameters.

Joe

[Clem Z.]

Re: 1958 overheats at idle

does your car have a fan shroud and does the edge of the fan shroud split the fan blade,one half of the fan blade inside the shroud and the other half outside the edge of the fan shroud. i my racing i found out that sometime more blades on the fan caused the air not to flow a good thru the rad because of the number of blades blocked the air movement.

[Kenny Madden]

Re: 1958 overheats at idle

Clem, yes car has a fan shroud and the blade is positioned half in and half out.

Kenny

[Joe Pennington]

Re: 1958 overheats at idle

Have you replaced the 13# cap back to the 7#cap to see if the problem re-appears?

[Kenny Madden]

Re: 1958 overheats at idle

Joe, no I've not put the 7psi cap back on. I was so glad it didn't overheat with
the 13psi cap, I left it on. Guess I could switch them to see if the problem
returns.

Kenny

[Tom B.]

Re: 1958 overheats at idle

Did it just puke out a certain amount and then stay there or did it purge every time it was idled? These systems without overflow tanks can't run filled to the top. It will expand and purge some out but should be OK from then on. They run a couple inches down in the tank.

Tom

[Kenny Madden]

Re: 1958 overheats at idle

Tom, it pukes every time. It not too full of coolant.

Kenny