Another "Hot" problem

I have a 70 Dart, 318, auto, with AC. It has a 22" inch 2 row radiator , 19 inch HD clutch fan, 180" thermostat, 50/50 mix. The other day, about 85 degrees, going down the interstate at 70 mph and 2500 rpm I was running about 215 degrees. At 75 mph it went to 225-230. At 55-60 it runs about 200-205. Temperature has been verified with a new mechanical gauge. I took the rad cap off and dropped the sensor in the radiator and the thermostat opened right on 180. I let the car idle and there seemed to be plenty of flow through the radiator, the clutch fan seemed to working, and the temp continued to climb till I shut it off at 215. Outside temp was about 75. Running the aftermarket AC only seems to make a little difference. I know I need to find a shroud but I would think even my setup shouldn't be running this hot. Any ideas? Thanks in advance.

Not enough radiator, collapsing lower hose, or DEFECTIVE radiator. "Oldmanmopar" posted this idea some time ago, and it turned out to exactly what I believe to wrong with my car. He claims the finds can crack loose from the tubes over time, with multiple thermal cycling, showing the radiator to be clean and having good flow, yet actually unable to reject heat.

My own car (at the time) a mild 360, was overheating on the highway, the faster the more heat. I swapped in a "junk" late model SLANT rad. Both rads were two core, the original old 67, and the slant, a 73--74 car.

INSTANTLY the temp dropped like a rock, no other changes.

PlumCrazyJay said:

I have a 70 Dart, 318, auto, with AC. It has a 22" inch 2 row radiator , 19 inch HD clutch fan, 180" thermostat, 50/50 mix. The other day, about 85 degrees, going down the interstate at 70 mph and 2500 rpm I was running about 215 degrees. At 75 mph it went to 225-230. At 55-60 it runs about 200-205. Temperature has been verified with a new mechanical gauge. I took the rad cap off and dropped the sensor in the radiator and the thermostat opened right on 180. I let the car idle and there seemed to be plenty of flow through the radiator, the clutch fan seemed to working, and the temp continued to climb till I shut it off at 215. Outside temp was about 75. Running the aftermarket AC only seems to make a little difference. I know I need to find a shroud but I would think even my setup shouldn't be running this hot. Any ideas? Thanks in advance.

Click to expand...

I was running an unsealed hoodscoop, on the hiway it would heat up, air was pressuring the engine compartment, and not letting air flow in through the rad.

famous bob said:

I was running an unsealed hoodscoop, on the hiway it would heat up, air was pressuring the engine compartment, and not letting air flow in through the rad.

Click to expand...

Can I squeeze a 26" radiator in without to much trouble? I can borrow a 26" and want to experiment with it before I go shopping. I figure 26" is better than 22" if it isn't to much hassle to get to fit. Any ideas or thoughts? Thanks again.

I just went through the overheating with two different 64 Belvedere. One 318 the other 225 /6. Both had new 50/50 antifreeze and cooled fine when I first drove them. Then after a 100 miles of driving they both started to heat. Both cars had very dirty coolant. Dirty coolant will not cool like clean coolant. I ran a water hose in radiator top and opened the bottom plug. After 45 min coolant started to look cleaner. I drove both for 50 miles and redid the water flush. This time it ran clean after 20 min. I did the flush one more time then added fresh 50/50 coolant. Now both run cool with 180 thermostat. This might try this if you think it will help. Hope you get it running cool.

Many posts. My rough summary from reading others woes is:

Changing the thermostat won't help, since once full-open it doesn't affect it. A 195 F will give better mileage, w/o causing over-heating. Avoid "fail-safe" ones since they lock open if ever overheated, then your car will run cold in the winter.

Best way to verify your dash gage is to watch it in the winter. Once heated, if it holds a steady position, that mark should correspond to your T-stat setting, so any numerical marks on your gage should "calibrate" to that. This assumes you know your T-stat opens at the stamped mark (tested in hot pot w/ thermometer).

Most who installed a new aluminum radiator had their cooling issues disappear. Don't recall results for a new copper radiator, but as post #2 says, even if an old radiator flows fine, the fins may have detached from the tubes on the outside.

Shrouds and sealing the radiator to hood helps a lot.

A larger area radiator helps. You don't need to cut the opening larger to get most of the benefit.

More rows doesn't always help, especially w/ new aluminum radiators.

the clutch fan seemed to working

Click to expand...

is not good enough.
Shut the engine off at 200 or so. grab the fan and try to turn it. It should be quite difficult and the belt must not slip. A thermostatic clutch is the best,IMO.
I run an anti-cavitation plate on the back of my 8 vane waterpump. My rad is a stock A/C teener from 1973, and ASAIK,has never been touched. I have owned that old-timer since the mid to late 70s.I did cut out the core support to take advantage of the 26 inches.
If you are overheating at over 50mph and over 2500rpm, then there is a real good chance your rad done, or your teener has problems and is creating more heat than it outta be.
If you are also overheating at idle, then the entire cooling system is suspect, and again, the teener may be creating excessive heat.
Since the engine and the rad are both suspect at this point, I would be verifying that the timing is close,doing a blow-by test
and finally,a compression test,in that order.
Oh yeah, and blowing the mud out of the rad fins. Stuck behind the A/C condenser, they both have a tendency to accumulate a lot of dirt.I'd do this first, for obvious reasons. I usually take the rad out, so I can clean the condenser out first.