440 Highway temps

[zombezoo]

Update:
It finally cooled off here (mid 70s) enough to work on the car.

I made two changes:
1) I swapped back to my recurved distributor. Before the head swap, I had trouble fouling plugs and poor running and the engine seemed to like the factory RV distributor better. Now with the fresh heads, the recurve unit works better. This did help slow the creeping temps down significantly. I still had a problem with 30min+ runs over 70mph reaching 220 degrees.

2) I pulled the AC Condenser (currently in-op) and found some leaves and trash between the radiator and the condenser. Maybe blocking the middle/bottom of the radiator, maybe 5% of the area. I blew out the radiator from the engine side, left the condenser out and went for a drive. It now does not get hotter than 206 (Robertshaw 370-180 stat).

For reference: 206 on the CTS has the 73 factory rally gauge just overlapping the right side of the operating temp line on the "C" side of the gauge.

Anyone ever check how much temperature drop they get across their radiator core?

Radiator is a re-cored Factory 3673054 26in radiator, I'm only seeing about a 25 degree (165-140ish after pulling over from highway speeds where engine is 206) drop from top hose to bottom? I'm trying to understand what's happening. When driving around local roads at 45mph and below, temps are 195 on the CTS mounted in one of the plugs near the heater hose connections. When I get on the highway, it very slowly creeps up to 206 over the course of like 30 minutes of driving 70+.

Temps fall back to 195 shortly after exiting the highway. Either idling or slowing down to speeds below 50pmh.

Is this because the thermostat is restricting flow because temps are nearing the opening temp (195 degree temp on a 180 stat)?

This all makes me think the system is barely keeping up with the heat being generated at speed. Engine spins roughly 3000rpm at 70mph.

I still need to gather a bit more data but wanted to get this temp drop question out in case anyone has input here.

 

[68BabyBlue]

I wonder if your clutch fan is pulling enough air at higher rim. My GTX doesn't use a clutch fan and it runs cool . 7 blade fan and factory shroud.

I have an apples to apples comparison. In the 90s, I owned a factory A/C '69 GTX that had a spacer installed at the factory, rather than a clutch fan. Car was special ordered by a guy in Virginia who had previous experience with air conditioned Plymouths. I had maintenance history. The car had the original factory radiator, but it had been rodded out twice. That GTX never ran the temperature gauge past center, under any conditons, but always ran left of center when running under 60 mph.

My current factory A/C '69 GTX is completely OEM, but has the thermal drive fan clutch. It will run the temperature gauge just right of center, when driven 70 mph on a 95 degree day. Below highway speeds, including idling in stop and go traffic, the gauge stays well left of center. Seems to indicate the clutch versus direct drive does make a slight difference at higher rpm,with OEM components.

Although it ran marginally cooler at highway speed, the direct drive fan generated noticeably more noise under the hood.

 

[j-c-c-62]

So common thinking is still, at speed, no fan is actually needed. So is that wrong?

 

[RJRENTON]

So common thinking is still, at speed, no fan is actually needed. So is that wrong?

YES.... that is incorrect. 3x More hp is required to operate a direct drive fan than a thermal drive fan. See #3'fan laws....
BOB RENTON

 

[j-c-c-62]

YES.... that is incorrect. 3x More hp is required to operate a direct drive fan than a thermal drive fan. See #3'fan laws....
BOB RENTON

So the elevated temperature the above reply #62 reports is the Ok result, additionally with the of saving hp?
I wonder if actually then if the poster maybe has too much fan at low speeds and is over cooling, wasting hp?

 

[zombezoo]

So having the CTS brought some actual numbers to the game. I have an IR temp gun too. Temp gun pointed at the water pump housing (where the CTS is mounted) shows roughly the same temp. 195-205 on the CTS has the gauge needle either on the left or right side of the first line above cold.

I have seen the gauge get into the middle of the gauge which is about 235 on the CTS.

Does anyone know what the rough gauge position to temp reading should be? Perhaps I have a faulty (or incorrect) sending unit? I pulled the one from the 318 that came out of the car which is the same unit that has been in the car since the mid 90s when it was purchased.

 

[zombezoo]

Maybe I'm overthinking this and its fine. It's never gone more than 1/2 gauge but once I saw how hot in degrees 1/2 gauge was I started getting worried.