Hello,

Vehicle: 68 Dart 270 w/225/A904

History: Had overheating problem on long trips or high speeds (sustained highway) for quite a while. Engine would run up into the top 1/4 of the gauge, occasionally letting off a little steam. Replaced radiator with a used one... helped some, but problem slowly returned over last year.

Problem now: Just installed a nice AFCO aluminum radiator. Very nice unit. But right from the installation I can now no longer drive 10 minutes in town without overheating. Same or worse at highway speeds.

Hoses are not kinked. No steam from tailpipe. Upper radiator hose gets hot, so I don't believe I put the thermostat in backwards (although I will check that tomorrow). Heater blows very hot air.

Running the factory 4 blade fan, about an inch to 1.5 inches from the radiator.

I'm really stumped. Could I have a bad head gasket without the tailpipe steam? Last I checked compression (a couple of months ago) I was 120-135 on all cylinders.

Ideas, please. This is my daily driver Dart!

Thanks in advance.

-Mac

How wide of a radiator did you use? (19 or 22 inch)

Check to make sure the thermostat is in correctly, but also make sure it doesn't "stick"... when you remove it, dump it into a bucket of boiling water and see if it opens...then remove with a set of BBQ tongs and see if it shuts or stays half shut (I have had to return two Stant Super Stats because the copper 'pill' would bind up on the outer spring coil and stick the stat partially open (enough to keep thing cold in the winter, and not enough to allow good flow off coolant in the summer...)

When was the last time you flushed the cooling system?

Also what color are your spark plugs/ hows the carb tuned? (running a very lean mix can cause some temp problems in an engine...)


You might think about running a 7 blade fan too, eventually if everything checks out...

Technically every mopar I've driven always sits at the 3/4 mark if everything is in tune and the insturment cluster is in good condition...(have you verified the temp using a thermometer to make sure the cluster isn't just 'having some fun'?)

-D.Idiot

180 or 195 degree thermostat?

I think a 68 should have the 180 (my 64 uses a 180, and tends to stay in the middle of the gauge)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

If you have cooling issues at high speeds you have a water flow problem not air flow problem.

If you replaced the radiator then the rest is up to the block and water pump. Pull out your freeze plugs or the water drain plug on the block and dig around with a coat hanger or other stiff wire. Chances are if you pull the drain plug your block may be so crudded up nothing will come out until you clean it up.

simple as this put a lower thermostat in or a new water pump mine did the same thing when i first bought the car replaced the water pump has never come close to overheating again.

Kevin

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PROBLEM SOLVED!

The thermostat was sticking. Before replacing the radiator I had run it for a month or so without the thermostat, just as a test. It still ran almost up to the "H". When I replaced the radiator I reinstalled the old thermostat.

Took the thermostat out, now can barely get gauge off the "C".

Thanks all. My clue should have been the "radically different operation" after replacing just a couple of parts.

I'll put a new 180 back in tomorrow.

BTW- Now running with original 4 blade fan.

-Mac

Wait a minute, your telling me you replaced radiators before replacing a thermostat?

I'm not 100% sure about the thermodynamics, but, with everything in working order, an engine with a thermostat will run hotter then an engine without one right?