Every bigblock mopar i,ve ever owned always ran a little hot in traffic no matter what i tried with the cooling system ,timing , jetting etc.

They would never overheat or boil over but would start to run not as well as they did at cooler temps .
But once i switched over to an electric fuel pump with a return line they actually ran better on the hot side .
Nowadays i rarely even look at the temp gauge .

I've ran into the same exact problem a few different times and has always been cured the same way. A 160 degree thermostat, and the installation of an aluminum radiator!! Nothing else has ever worked for me. When an engine builds a bunch of power, the cooling system is the first to show it.

Hey Martin:

I bought a 6 blade 16" solid fan from Flexi-lite and ran it during the hot day on Thanksgiving last year. I purposely got stuck in stop and go traffic and it never got over 185. I took it off to try the same size fan with a clutch. It too worked good.

I'm running a 22" aluminum reproduction Mancini rad. Are you using a 26" rad?

I tried to run an electric fan on my old Charger and I had problems when idling (couldn't pull enough air). It too had an aluminum rad (Be Cool cross flow). It cooled better with a clutch fan.

Timing can be significant, even a few degrees could make a big difference. Try running 38 degrees total timing (without the vacuum advance). Running lean will also cause it to heat up. Try backing out the idle mixture screws a 1/4 turn each.

Think your block passages are pristine ? If you haven't had it hot tanked yet, knock out one of the core plugs and tell us what horrors you see !!

What brand of hi flow tstat are you using?

FWIW I found an interesting experiment about fan blade / shroud placement. This guy found the lowest temp, in his cars case, was with the fan fully inside the shroud compared to partially or wholly out.

http://forums.performanceyears.com/forum...roud+experiment

I'm having a cooling issue too (~215 at idle), I am going to start with the easy stuff (timing, possibly tstat If I can get a hi flow one), water wetter, then maybe go to a more agressive fan.

Others have mentioned this, First I would advance idle timing, at least to 20 deg. initial. Engine will run cooler at idle by doing this.

second I would use a non clutch fan.

Third get rid of pusher fan.

Getting the cooling system to work rite is not rocket science..
An there are no qwikee short cuts..

The original OE Mopar systems were pretty good so thats where you start..
1. Chuck the electric fans
2. Pull the factory radiator, flush it kleen and here increasing the core in size can do wonders go to a 3 or 4 core
3. Flush the block/heads
4. Use the factory shroud but make sure the fan is about 1" back from the radiator, we like to use a clutch fan
5. Refill the system with 50/50 mix
6. Make sure to use a quality thermostadt, 180 degrees is fine

We have been building/racing big block Mopars for almost 40 years and the majority of cooling problems are created by parts mismatch and/or faulty installs. Take it step-by-step and you will be surprised on how well the OE cooling system can work..
Here in So Cal it can easily hit 102-105 degrees and our cars typically run 200-205 degrees in slow stop/go traffic. If the outside temperature is more normal like 75-85 degrees they typically run 180-190 degrees.

We just fixed a friend's 340 Dart GS was running about 210-220 degrees, some wizbang said mount this dual electric fan system..
Current jumped 50 amps on the charging system and no improvement for cooling..

Threw out the dual fans into the dumpster added a shroud and it dropped 15 degrees.

Just my ..

I found the Milodon and Mr Gasket T stats work much better than cheap parts store ones , and a 18 inch HD thermal fan cured my idle heat-up problem .

well here's an update. I installed the rubber seal between the hood and rad support. I installed a 180* deg Mr Gasket high-flow stat. also removed the pusher electric fan. Now everything is stock except the high flow stat. WHAT A HUGE DIFFERENCE. The car used to drive (correction to my old post now that i payed attention to the gauge) 190 when crusin, and creeped from there at a stop, probably reaching 200 then vapor lock symptoms were setting in. Now it cruises at 175-180; it cycles between there, you can see the stat open and close, when it opens it drops instantly to 175, then slowly goes to 180. Last night i put the parking brake on, left it idling in gear for 15 mins, after a 1hr drive, and it stayed rock solid at 180. Plus i can hardly believe how much less engine compartment heat there is now. Also one thing that i thought was stupid when i was doing, but did anyways was wrap the fuel line in tinfoil. to my total amazement the fuel line is cold now, where before it was almost impossible to touch > that one blew me away. Anyways, i still have the milodon high flow pump on order, i'll put that in as well and i'm positive my running hot issues are solved now. thanks for all the help guys, i was really stumped on this one. i could not believe regular old tin foil was so effective at reflecting heat as it does. The part of the fuel line that i didn't wrap with foil was hot, and the part i did was totally cold!!!! i have a new item to add to my tool box as well as the following "must have items": duct tape, electrical tape, zip ties, JB weld, hammer, automotive GOOP, TIN FOIL!!!! i'm convinced that with these items anything can be fixed!!!

OK GUYS, TOTALLY STRIKE MY PREVIOUS POST. THE DAMM THING STILL RUNS HOT.

Who wants to buy a nice charger r/t???

I just don't get it, i went out for a drive, everything was fine, 175-180, then i hit traffic, there she went, 185, 190, 195, 200....then it ran like crap.

I'm totally lost for just about the first time, i just can't see what the problem is, as long as i'm moving, everything is perfect.

HELP....

Check your timing. This happened to my brother and the timing fixed it.

Does it cool down if you put it in neutral and rev the engine to 1000 to 1200 rpm?

what kinda stat are you running? el cheapo wallmart brand or a performance stat?
mabey try replacing the stat with a 2" flatwasher with a 1/2" hole in the center (restriction).
then see what happens.