ace_cobra

I used to deny it, but now I don't. I have a frankenstein. I have a 350 and up until now the cooling system 'worked', but I started trying to make it work better. I have a 1970 with a Dewitts aluminum rad, but I also have the aluminum expansion tank. I have a 15# rad cap on both. My expansion tank has 2 hoses on the bottom coming and going from the heater core, and 2 lines, one coming in from the rad and one oerflow. When I open the rad cap you can hear the air rush in and the water gurgle down. My expansion tank gets HOT, boiling hot very quickly while the rad doesnt seem to get even warm at all. Again I have 2 rad caps, one on the radiator and one on the expansion tank, both 15#. Lately when I run the engine coolant is gushing out of the overflow on the expansion tank, or I hea a loud hissing from the expansion tank. Thoughts?

noonie

You shouldn't have 2 radiator caps, but if you must, then the one on the radiator should be a simple "block off" cap. It seals just the top lip, no springs or anything in it.

Big2Bird

Noonie. How the h*** are you?

C6_Racer_X

Pressure in the system when you first start it cold = blown head gasket.

If the rad never gets warm, that's usually a stuck thermostat, or possibly blockage in the radiator core. Either one can lead to overheating and cause the blown head gasket.

C6_Racer_X

To be clear, when the expansion (overflow) tank has a pressure cap, the ideal cap at the radiator seals the opening, but allows free flow into the "overflow" hose that leads to the pressurized expansion tank.

If you can't find a cap that fits that spec, you can use a cap with a much lower pressure rating than the one on the expansion tank. You can also cut/remove the spring from the cap on the radiator.

ADDITIONAL INFO: Stant 10203 is the part number for a Stant "0 psi" block off cap.

noonie

Stayin very busy, little girl starts college in less than a month, tryin hard to help her get her life set up.

ace_cobra

OK I will try installing just a block off cap on the rad and a spring cap on the expansion tank. I will report back when I get it running and hot enough to see if it worked.

Eddie 70

Just to add, the expansion tank is not to be full of coolant either. If it is full, it will bleed itself to the correct level when you turn the car off.

carriljc

I gutted an old radiator cap on my radiator to just use it as "block off" cap and the "real" cap is on the pressurized expansion tank. It's been working great for like 10+ years.

ace_cobra

I ended up gutting a rad cap, and putting a 15# on the expansion tank. It ran much better and much cooler. Almost too cool... I ran it in 30*C weather (85*F) for about 4 hours and it never even hit the increment between the 100 and 210 on the gauge. I'm not complaining though, I know it will stay cool now!

carriljc

FYI--Ensure that the hose, and clamps, from the radiator to the expansion tank is in good shape. It is now functioning as part of the pressurized system.

ace_cobra

All are fairly new gear clamps. I filled the expansion tank to half full, ran it, it dumped what it didnt need and it seems its happy place is no fluid in the expansion tank. I have filled it 3 times, and it always dumps it, but stays cool . Maybe the Dewitts rad is expanding and containing a lot of it.