Over the weekend I took the duster out on the highway to see what it would do, and the temp gauge rose to about 3/4 of the way after about 15 minutes. The temp has never been that high even when sitting in traffic. Around town it is just over the second left mark.
Idle is not affected by the heat readings however when the temp gauge starts to get toward 1/3 it will backfire through the intake when taking a left turn. None of the driving was done with the A/C on and the temp did cool back down when I got back into town

The only things that are different are STP fuel additive and the autolite 985's that I put in just before the trip.

So my choices are:
1. Hotter plugs + fuel additive are causing the engine to run really hot.
2. Temp gauge just started working. ( unlikely )
3. Timing is too advanced. ( currently is 8*BDC at idle )
4. way lean at top end

or I have a combination of issues.

(current setup:
stock 73 225 65,000 since rebuild
fuel line mod
timing 8*BDC
Carter bbd super six from 78 volare
Remflex intake/exhaust gasket
cap, rotor, fuel pump, filter are 3 months old
Plugs Autolite 985
180* thermostat.
Engine turns about 3k RPM at 70MPH
Engine idle in N = 750/800
Engine idle in D with A/C on = 600/650 )

Whew ..Thanks

Is the thermostat in good working order? Is the radiator partially plugged-up? (drain it by 1/4 and look at the tops of the cores with a flashlight)
Is the fan belt tight?
DD

Oops forgot to mention that the cooling system was flushed and water pump, thermostat were replaced back in December. The radiator looks nice and clean inside, and the temps have been fine up until this weekend. The strange thing is that today while driving around at lunch, the temp gauge is reading about 1/3 which is about 2-3 needles width more than normal.
My plan is to get the car up to operating temp and use a thermometer to see the "actual" temp, because even when I tested the thermostat when I installed it the gauge never read above the second left line but actual temp was 180.2 when the t-stat opened, so based on the gauge being 120 at the bottom and 250 at the top of the scale, 180 should be closer to what the gauge is reading now at operating temp, maybe I'm worried for nothing.. but still doesn't explain the backfire issue. I'll have to check on the fan belt.

my thought would be the hotter plugs... im not as in the "know" as doc is on engines so take what i say with a grain of salt.

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1976 Plymouth Feather Duster
2002 Dodge Dakota 4.7l v8

even if the top of the core looks clean this type of a radiator liked to plug up, towards the bottom where it can't be seen thru the fill hole. A typical "flush" won't break it loose either. Ive had a few that temps rise as speed increases because of lack of flow; fine in town but get out on the road and up go the temps. I'd pull it and take it into a good rad shop, see what they say about it. with the age of the car don't be surprised if they tell you that it's plugged.

There is a very good chance that the radiator is having problems with flow. When they get this way they will flow enough for town driving but highway driving will heat up.



Also it may just be as simple as you running to lean. When it gets hotter it will want more fuel and with it backfiring on a left turn this sounds like it leans out. If you have a choke try wiring it slightly closed, jjust a little because you dont want to choke it out, but enough to make it run richer and test drive and see if it quits backfiring and if the temp goes down. Its possible the lean mix could make it run hot at highway speeds. When running lean, they want more timing. But this can get you into spark knock to unless you just dont have enough timing to begine with.


With the heated intake when your running lean, then the exhaust gets hotter which inturn heats the intake more. After a piont it will evaperate the fuel so much in the intake it gets lean becuase it no longer has fuel sticking to the intake runner walls which adds to the fuel mix.. I know we think of needing extra fuel when they are cold, and rightfully so but when the intake starts vaperizing the fuel you get into this. Be sure you have enough timing to begin with though. Not enough timing on a lean mix can cause the whole problem to.


Jess

Not very much to update, but I was able to determine that when the temp gauge reads dead center the thermometer at the radiator is reading 200-203 degrees, and the flow past the rad cap seems fast ( not sure if that means anything). So it seems as though the radiator isn't cooling enough to close the t-stat, but still what could be causing it? it does run much hotter around town in the last couple of days.
I'm not so keen on the radiator as a problem just yet because when I went to melbourne back in January it wasn't running hot. I'm trying to focus on the things that were changed: Plugs, fuel.

At this point I'm ready to switch back to the stock plugs and deal with some of the starting issues.
When I switched over to the long nose plugs should I have tuned the carb to run more fuel?

If your problem is being caused by the cooling system, this indicates a water-flow problem. High-speed heatup means the water isn't being cooled down enough as it flows through the radiator (because at high speeds, there's plenty of airflow through the rad by dint of the car's forward motion), while low-speed/idle/stuck-in-traffic heatup means an airflow problem (because you're relying on the fan to pull what air it can through the core, and the car's not moving fast enough to push significant air through).

I say "if" because there are other factors that can cause heatup — retarded ignition timing, lean fuel mixture, excessive exhaust restriction, and improper cam timing chief amongst them.
This is likely being caused or aggravated by improper float adjustment and/or other problems with your carburetor. Holley 1920s, with their side-hung float, are much more prone to this kind of left-turn problem than BBDs with their front-hung floats; it takes a pretty serious problem with float adjustment to cause it in a BBD. How carefully did you set the float height?
Neither the fuel additive nor the spark plugs are causing your overheating, but the STP stuff was not necessary.
No. Not only are the 985s not hotter than the standard plug — they are the same heat range, only the tip configuration is different — but hotter/colder in reference to spark plugs does not refer to (or affect) the running temperature of the engine. It refers only to the operating temperature of the spark plug itself.
Overheat is more likely to be caused by insufficiently advanced spark. Have you checked your vacuum and centrifugal advance mechanisms to make sure they're working?
Could easily be, given that you are also experiencing other carburetion-related issues (left turns as discussed above).

Could also be that your lower radiator hose is collapsing at high speeds.
Probably not the cam timing, then.

You mention it's running hotter around town...this suggests that the problem, whatever it might be, is worsening. Check your timing advance mechanisms, and if they check out OK, the next things to check are the radiator and other cooling system parts (hoses, thermostat), and exhaust restriction.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, As always thanks for the detailed break down.
Advancing mechanisms have been checked, and the rotor is springing back, but the vacuum advance pod will not hold vacuum. The local parts place has 2 different pods listed, one for manual trans and one for auto trans. My car has a 904, what would be the difference in the pods?
The whole recurving the dist thing really hurts my head, but if it is a huge benefit I'll give it a shot while I have it apart. Can the vacuum pod be changed while the distributor is still in the car?

The float level was set dry with the carb upside down from the sheet in the carb rebuild kit. 1/4 inch at the center of the floats.
Thanks
Matt

Mmm. Retarded spark and a vacuum leak.
See this post; any of the listed units will work in your distributor (you can use an early advance in the double-drilled plate of a late-type distributor).
No, remove it.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Like with alot of things that "will work" which one would work best with my setup? The parts place doesn't have any in stock so I'll have to wait a day.

So yes, lean condition and not enough advance. = huge amount of heat
I was hoping you wouldn't say that.

Tough call. Check with Doctor Dodge and some of the others who've done extensive testing with different distributor configurations. You might make a post saying "Which vacuum can should I use?", describing your engine and car, and linking to the list I linked you to. Are you running EGR, or is that blocked off?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

EGR got blocked off before I got the car.. That's my story..

In that case, you shouldn't run a vacuum can that puts in a whole whackload of advance, or you'll have pinging issues. So that knocks out VC-208 (the Feather Duster/Dart Lite can). One down, rest of the list to go!

Did you (er, did the previous owner) also bypass the OSAC?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yep the vac can goes right to the side of the BBD, Should I be using the OSAC (of potatoes)?

I just thought it would be easier to get the thing running with all of the weird emissions stuff blocked off, than have to trace through a mile of vac lines to find the leaks. However it does seem to run just fine without most of it.