I won't swear my life upon it, but I think the sixes DID come with just a two-row core; I'm pretty sure the OEM rad I just pulled from my '64 Valiant is a two-row, and I know for certain that the '73-'75 Dart/Duster radiator I just installed(new aftermarket replacement) is a two-row; this is one of the reasons this cooling system can't tolerate a lot of junk in it...

The presence of a 7# cap also suggests possible leakage with a 13-15# cap...

The white crud in the top tank and red mud in the over flow tank all suggest a clogged cooling system. You could so a poor-man's flush by pulling one heater hose from the T-stat housing, and connecting the garden hose to the heater hose, using a male hose fitting from your local home center, and flushing bakc through the heater core and block...don't turn the pressure up full until the water starts running pretty clear (so that you don't rupture the heater core on city water pressure...).

Pulling the T-stat out also helps with the flush...

Good Luck...

Frank McMullen

Thought I would give you all an update, but first want to thank you for your informative responses. The radiator shop reported that they were unable to "get through 7 rows on the radiator due to severe corrosion." I've entrusted two race car radiators to them in the past and they do honest and thorough work. They ordered a new core for me, and it should be in today. After I get it installed in the next couple of days, I'll give you more feedback. My club is hosting a Wings and Wheels event in Chesapeake, Virginia this weekend and I hope to take both the 65 "Cruiser" and 66 "Race Car" to to show off.

Put the newly recored radiator on this morning. At the shop got a good chance to see the old core, and it was proably 75% clogged. They couldn't even begin to rod it out. Put the proper coolant in, started car and no leaks. Let it idle for it seems forever, and it took longer than that for the radiator to feel hot to the touch. The gauge moved about slowly and finally settled heat the H. I had left the radiator cap off to see when the termostat opened (new). The water never seemed to get hot enough to open it I guess. Put the 7 lb cap back on hoping that might heat things up faster and it never did. Outside temperature here was about 67 deg. Not enough time this morning to take it for a drive, but another malady developed. The engine ran rough as the dickens, with some black smoke (rich?) coming out the tailpipe. I pulled the air cleaner and the choke was facing straight up. Now, a couple of thoughts: My fuel gauge reads full, when it should be reading about 3/4. Probably have a problem with the voltage limiter (don't like thinking about that). What about installing a 15 lb cap? I think the prior owner put a 7 lb cap on because he was having overheating problems. Now that the system is now, it might be time to put the right cap on. Agree? I hate how things dominoe....

Well, this morning I put a 16 lb Stant Cap on the radiator, fired the engine and life is good. You aren't going to believe this...now the Gas Gauge reads fine and the temp gauge doesn't work! I guess now its a game of eenie, meenie, miney, moe? No more black smoke from the exhaust, and no more blow by. Go figure.

Keep pluggin' away...you're fightin' 40 years of "entropy"...


Wow, seven rows clogged... , no wonder it was running a fever !

I'd suggest driving the beast for a bit; get acouple of good half-hour highway trips on it, and see if the black smoke and "loading-up" go away.

As for your temp gauge, double check the connections at the sending unit and the dash unit.


The radiator pressure cap has no impact on how quickly the enginecomes up to operating temperature: that is solely a function of ambient air temperature and the thermostat.

What the pressure cap does is determine at what temperature the coolant boils. At normal atmospheric pressure @ sea level, water boils at 212 deg F. For every one pound increase in pressure, the boiling point is raised about 2.5 degrees, therefore you reach a higher temperature before coolant starts boiling away. (This is the principle on which Grandma's pressure-cooker operates.)

So, with a 15 # cap, this would raise the boiling point of our coolant to about 250 deg. Fahrenheit.

When radiators get old and clogged (and weak) they sometimes begin to leak when the system reaches full pressure; a common band-aid is to replace the 13 -15# cap with a 7 # cap...instead of leaking from the core, the radiator then just pushes coolant out the overflow, if things get hot enough.

As a bit of historical trivia, pressurized cooling systems didn't come into use until about 1950.

I "solved" my clogged radiator problem, and was immediately confronted with a "rusty gas tank = clogged fuel system left me dead on side of road" issue. The car has been up on jackstands for 2 weeks now, with the gas tank out, waiting to get scrubbed-out and treated with POR-15 gas tank system, then re-installed.

yes, it's always something...

Hang in there !

Couldn't stand it any more. Pulled the gauge cluster out. Didn't find anything alarming but decided to "renew" the gauges. Calibrated all and cleaned all connections on the "plug in". When ready to reinstall, I will add a little dialetric grease to slow down future corrosion. While the gauge is out anyway, I went ahead and bought a new voltage limiter and will keep the old one in the trunk along with all the other junk. I found something that I wasn't expecting though...what is the capaciter-looking item that plugs into the panel (looks like the same thing you might see inside a point-type distributor)? It appears to be something to reduce the old static in radios. Don't need it if that is what it is since I have an aftermarket stereo in the car. Although the speedomter works fine, the mileage numbers were stuck in place. Pulled those out and put in a new set (new old set that is). Once the gauge is back in, I will post my next update.

That cap is there to offset the affects of the "voltage limiter". The limiter acheives its function by turning on and off so many times a second, so the 12v appears as approximately 5v to the gauges. But, every time it turns on and off, it creates a disturbance in the 12v line. Because of this, the dash lights appear to pulsate at the same freqency as the voltage limiter.

In my car, when I was replacing the lights in the dash while it was still in the car, I accidentally knocked that cap wire loose, and if I look closesly enough at say the brake light when I have the e-brake pulled, I can notice it pulsing.

The cap isn't mission critical, but it may throw the water/gas gauges off a slight amount and cause the dash lights to pulse.

Installed the refurbished gauges this morning. Life is good! All gauges work great. I don't know what the final line was, whether a mixture of causes or one specific problem. Each gauge was re-calibrated, cleaned up all plug ins, etc, and installed a new voltage limiter. Bottom line...it all works. Again, thanks for the many post helping me.