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.

 

[RJRENTON]

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.

YES.....you are overthinking the situation.......you are comparing an UNCALIBRATED, UNDOCUMENTED instrument panel display against ????....or are you just surmiseing or hoping everything is ok??.......
BOB RENTON

 

[zombezoo]

YES.....you are overthinking the situation.......you are comparing an UNCALIBRATED, UNDOCUMENTED instrument panel display against ????....or are you just surmiseing or hoping everything is ok??.......
BOB RENTON

Ok, so to recap why I'm asking:

I have read countless posts where people talk about running hot and people referencing specific temps. I have read many posts with people saying their vehicle runs cool essentially never gets hotter than the thermostat rating. Perhaps this is all completely unsubstantiated statements based on the assumption that a position on the uncalibrated gauge = some temp.

Seeing that my temp gauge used to run into the middle of the range, and prior to my big block swap it was pretty stable around that first line after cold, I knew I had a problem.

The addition of a CTS gave me an actual temperature, one that I could roughly confirm with an IR temp gun pointed at the water pump housing (where the CTS and gauge sender are installed)

I was seeing temps creep into the 230s which when reading other posts on the forums it seemed the consensus was that was too hot.

I have gotten my highway temps down to around 206 which if I'm to believe other posts I have read is still hotter than others claim to run.

My last few posts were an attempt to get responses from others who have actually compared real temps to where their gauge sits. Perhaps everyone is really running a little over 200 degrees and have just relied on the gauge to see that it's at something they think represents their thermostat open temp?

Given that the uncalibrated gauge is now behaving as it did with my 318, perhaps I'm done. I was just concerned I have a system that is right on the edge of keeping up with temperature management which once its above 80 degrees (and I add the AC back to the car) I will be back to a hot running situation.

 

[Some Car Guy]

The gauge in my car has very little variance in what it displays at 175 from what is displays at 205. It’s discernible by knowing what it looks like after jumping out and putting the temp gun in the same exact spot to get something of a useful bit of data.

I was a bit surprised at this outcome after doing my cooling system resto this summer. I thought it might not be much cooler based on the gauge, but the temp gun shows I’m getting a consistent 10-20 degree drop on average, while this weekend it was cool out and I did windows down instead of ac and that netted more like 25-30 degrees.

My car was running 205 at times before I did the work, radiator tanked, new edelbrock pump, new hoses everywhere, and new belts to go with an oem type pulley setup on my 69 440. They were running a three belt arrangement in place of the factory 4. All this stuff was to my estimation 20 years old and was time for it to go.

 

[Geoff 2]

......and then......there is.....the rad cap. Everybody assumes that their 16 lb cap is going give them a overheating 48* cushion. When the cap may be leaking/not holding pressure..

 

[zombezoo]

......and then......there is.....the rad cap. Everybody assumes that their 16 lb cap is going give them a overheating 48* cushion. When the cap may be leaking/not holding pressure..

New cap, of course new parts dont necessarily = working...

But let's see if I understand how this works...

The cap raises pressure which would raise the boiling point of the liquid but what does that mean for temperature?

Assuming everything else remains the same except the pressure in the system, would a 0psi system show a hotter temperature than one at 16lbs?

My understanding was the cap just allowed the liquid in the system to get hotter without boiling so raising the heat capacity of the system but that capacity goes "unused" as long as the system temps remain below the liquids 0psi boiling point?

I should add, I see the system holds pressure but I dont have a cap tester so I cant confirm how much. I should also add that at 235 I was not boiling over the system so I believe there is at least enough pressure to raise the system protection to there. But since I dont go above 206 now, if my logic above holds correct, it seems that the cap isnt a place I should be looking.

 

[zombezoo]

The gauge in my car has very little variance in what it displays at 175 from what is displays at 205. It’s discernible by knowing what it looks like after jumping out and putting the temp gun in the same exact spot to get something of a useful bit of data.

I was a bit surprised at this outcome after doing my cooling system resto this summer. I thought it might not be much cooler based on the gauge, but the temp gun shows I’m getting a consistent 10-20 degree drop on average, while this weekend it was cool out and I did windows down instead of ac and that netted more like 25-30 degrees.

My car was running 205 at times before I did the work, radiator tanked, new edelbrock pump, new hoses everywhere, and new belts to go with an oem type pulley setup on my 69 440. They were running a three belt arrangement in place of the factory 4. All this stuff was to my estimation 20 years old and was time for it to go.

That helps, so after a system refresh, you think you're running in the 185 range (no AC) no matter what your driving condition is? This is the core of my concern; I think I have a system that is just on the edge of its capacity. Around town the temps are locked in at 194-195, getting on the highway and running 70+ mph, they creep up to 206 over the course of 30 min. That just doesn't seem right to me.