In addition to the good advice you've already received, let me suggest you pressure check the system and the radiator cap. Many of the hard-to-find overheating problems I've seen ended up being associated with a relatively small pressure leak, and I've seen several radiator caps go bad after one good overheating.

Also, I've gotten enough bad parts along the way that I always test a thermostat before I install it.

Thanks again for all the help, guys.

No problem with the bottom hose. I'm back running at 12 before, and it's definitely better. But still a little hot.

Wouldn't be such an issue if I didn't have a 300 mile trip back to San Diego through the desert on Thurs.

For reference, on hot 90+ degree days at 60 to 65 mph my temp gauge reads straight up at max.
The engine wiring harness is new and sender is about a year old. I also run a high-flow Milidon/Robert Shaw style 195 degree stat. I also use a 16 pound all silver Stant radiator cap.

At speed the air 6" dam under the car seems to force enough air up and through the radiator to keep the fans from turning on and temps read at about 1/3 on the stock temp gauge. On cooler days the temp needle stays at 1/4 at freeway speeds. During the winter months I run a 205 degree Robert Shaw thermostat Summit Racing part #330-205 to keep the mileage up.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Thanks for chiming in, Ted. I was wondering what kind of temps you see, as you were the originator of the setup I'm now running.

I would expect that the fans would be much better at cooling than a stock mechanical fan (it certainly feels like it's dragging a lot more air through), but the temp thing certainly surprised me.

The plug color is either the additives in the gas or you are running on the extremely lean side.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

63valconvert,

Some other thoughts........I am running a total of 52 degrees total timing at cruise and also took SL6 Dan's suggestion and dropped down a few heat ranges on the plugs. I installed NGK UR6 plugs gaped at .035 this summer and they stay nice and clean with no ping on 87 octane with 10% ethanol from CENEX.

Every year I add a bottle of water wetter just to keep the corrosion down and heat transfer up.
By keeping engine temps around 1/3 to 1/2 (a little below to straight up) on the stock gauge, I get the best mileage.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Hey Ted,

I have NGK Z5FRNs running, and I'm not sure if they're too hot. I looked up the UR6s, but they don't seem to have the same design. I like the "extended tip" idea of the form as SSD mentioned that it works well with the older heads.

Is there another Z5FRN plug design-style plug that is cooler? Anyone?

I am mostly in the "it's the cooling system" camp now. I'll do a reverse flush when I'm back on the West Coast.

Those should be fine. Mine is a 74 head which use the Chevy peanut plug design. They are one step colder than yours. The 4's are hotter 6's colder.

Every time some scale comes loose it comes out through the thermostat into the top of the radiator. Over time the loose scale can clog the radiator tubes.
Turn the radiator upside down when your flushing it out. Hopefully gravity will be on your side and the debris will come out.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Was there a change over midyear in the heads? My 74 Dart has the drool plugs.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

'74 heads have plug tubes and use gasket-seat plugs. '75-up heads don't, and use taper-seat plugs. No midyear changeover.

You don't need cooler-than-#5 spark plugs, you need to find and fix whatever is causing the lean/hot running. I'm thinking your overly-hot (lean) combustion is causing your overly-hot cooling system temps -- not the other way round.

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

Well, I made it back, but it wasn't exactly good fun.

Had to run the heat (for extra cooling) the whole way, and got an ungodly 15MPG at about 70-80MPH. Still remained at the top of the range.

Plus, a lot of pinging at high RPM, even at 8BTDC. Clearly, I have some carb problems, too.

I will definitely be flushing this thing. Ugh. I may even be looking for a new carb. I spotted an NOS Economaster 1920 on ebay, but I don't know if my linkage is right. Are there any easy adapters for a 63 to put on a 77 economaster?

Thanks.

I don’t think this fuel consumption is too out of line at 70 to 80 mph. Remember you are pushing a brick through the air, and wind resistance increases by the square of the speed. No mention of grade change. Were you climbing in elevation from start of trip to end, or going down hill?

40 x 40 mph = 1600
50 x 50 = 2500
60 x 60 = 3600
70 x 70 = 4900
80 x 80 = 6400

If you graph this there won’t be a straight line, so at 80 mph one is pushing four times the air compared to at 40 mph.

Additionally there are more efficient throttle openings (just what that magic percentage opening is escapes my head at the moment), than others. Your rear end gear ratio will dictate cruse throttle opening to a great extent. Once out of the optimum throttle opening zone, fuel consumption will increase.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Some up hill, but oddly a lot of downhill action. The Las Vegas to San Diego highway journey seems crazy with the downhill. From basically Baker-San Diego, very little uphill, mostly down.

I'm probably assuming too much, and "seeming" isn't actually the truth.

That last statement was to avoid any potential SlantSixDan wrath.

Poor mileage…
…pinging…
…hot running…

Have we checked for exhaust restriction, including a stuck manifold heat control valve?

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

63valconvert,

Out of curiosity, what #jet are you running in the carb? Dan touched on this a few posts back. You may be running too lean. If you have a #56 or #57 jet that is very lean......
When I run a #58 to a #62 the high speed temperature comes way down.

Since most of my driving is near sea level and short hops locally I can get away with a #57. If i was making that trip through the dessert I would bump up the jet size. You may even get better mileage by staying out of the power valve. I drive by a vacuum gauge and try to keep it above 16" to 20" most of the time.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG