Question...what is the normal running temp for a 1972 340

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John Morrow

John Morrow

Mopars and Harleys
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what is the normal running temp for a 1972 340 at Highway speed, say ......65 mph .....323 gears .... 14 inch tires.. on a 75-80 deg. day ?
 
I would think 185+/- a few degrees. What temperature is your thermostat set for, 195*??
 
190* i believe ....... my problem is when I get out on the highway it starts to run hot .....like all the way over to the hotline after only 10-15 min at 65-70 mph .......soon has I slow down it immediately starts cooling down ....like in the first mile at 30 mph .....i added a aftermarket gauge and it confirmed what the stock gause was doing ...... new pump ( flowkooler ) new lower hose ( with spring ), clutch fan, temp sending unit, Radiator rodded out ( questionable of the guy that done the job) checked motor in different areas with a laser temp gun seems to be consistent with the 230 deg the gauge reading at the time
 
Keep "the radiator" in the back of your mind. I had a 360, now a 318, similar problems with the original 67 273 rad, and the "rad guy" claimed it should cool

A couple weekends ago I decided I'd had enough, threw an unknown SLANT SIX rad in the car out of a 73/4. Hell, the thing is night and day. The needle "runs" as far below 1/2 scale as it used to above (I have a 180 stat in the car).

Oldmanmopar posted something a few weeks ago, a theory that something (heat cool cycles?) eventually cracks the fins loose from the tubes, reducing heat radiation. In other words it can flow lots of water and still not cool.
 
Thanks, I agree ..Ill have to look back at his thread...Everything seems to keeps pointing back to the Radiator, I'm just not understanding how it can cool off so quickly as soon as I slow down, but then I,m not even close to being an expert on anything I'm more of a remove and replace kinda guy. lol
Any thoughts on who or where to buy a new Radiator ......maybe a 3 core ? Its an air conditioned car , it has the 2 core radiator in it now.
 
Radiator, water pump, bottom hose collapse, lots of crap in the system. Something is causing it to lose flow at highway speed. Might even check to see if the outside of the radiator is stopped up with dirt and dead bugs.
 
Yeah, you might try diagnosis. It seems to work rather well.
 
Do you have a fan shroud? How well is it sealed? Air may be going around your radiator at highway speeds instead of through it.
 
What is Diagnosis ?
Everyone keeps saying ...Bigger Radiator ....If I buy one I plan on at least trying to get a bigger 3 core, but I keep asking myself ......surely it was not running hot in 1972 with the original 2 core. I have had the car for 16 years used to drive it to the Nationals 10 + years ago .. about 4 hours from my house, 55-60 mph on highway, after about 3 hours would always notice it leaning to the hotter side.... nothing to scare me, I just blamed it on the 391 gears. I started trailering to Columbus, the short 30-40 minutes from hotel to show never noticed anything.
Last year I drove it back to Indy for a Good Guys show and the following weekend to Monster Mopar again 55-60 with 323, gears took my time ....again it ran a little on the hot side enough to make me a little nervous this time .......now I cannot seem to drive 45 min. at 55 and driving 65 70 for 10-15 min puts the temp gauge up to 230-240 before I get off the highway and it starts cooling down. Looks like Radiator is next ......after that I guess Ill pull the motor knock out all freeze plugs and have a look around.
 
Remove upper and lower radiator hose, hold your hand over low radiator outlet, fill with water, remove your hand, water should dump out like a toilet flush.
Next even though you replaced the fan clutch check it. Your running cool at lower rpms so low speed operation of the fan is probably working. At higher rpm on the highway the fan may be turning to slow.
High flow water pumps sometimes cause cooling problems due to coolant moving to fast thru the radiator. ie not enough time for heat transfer.
 
mderoy340 said:
Remove upper and lower radiator hose, hold your hand over low radiator outlet, fill with water, remove your hand, water should dump out like a toilet flush.
Next even though you replaced the fan clutch check it. Your running cool at lower rpms so low speed operation of the fan is probably working. At higher rpm on the highway the fan may be turning to slow.
High flow water pumps sometimes cause cooling problems due to coolant moving to fast thru the radiator. ie not enough time for heat transfer.
Click to expand...

Thanks for the Reply .....I will try that, i'm kind thinking i did that when I first took everything apart .....not for that reason ,,,just to drain the motor and radiator when I started ...but I will check that out again .
After changing all that I have changed I still have the very same problem .......so I'm just guessing I did all that for nothing ......except having a lot of new parts.
 
X2 on this

"Your running cool at lower rpms so low speed operation of the fan is probably working. At higher rpm on the highway the fan may be turning to slow.
High flow water pumps sometimes cause cooling problems due to coolant moving to fast thru the radiator. ie not enough time for heat transfer. "

When you shut motor off that fan should stop rotating within 2 or 3 turns.....If it keeps spinning the clutch is shot.....replace....could be slipping......that is the only thing bad about clutch fans versus direct drive fan.....

Do you have an 8 blade fan on there already?
 
You do not need a fan or shroud at 65 mph so it's not the fan. At 65 mph air is being rammed through that radiator just from the car traveling through the atmosphere.
 
1968FormulaS340 said:
You do not need a fan or shroud at 65 mph so it's not the fan. At 65 mph air is being rammed through that radiator just from the car traveling through the atmosphere.
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If the air is going around the radiator instead of through it....

Yes, they have a good point that your radiator is capable of cooling the engine at slower speeds, just not at highway speeds.
 
1968FormulaS340 said:
That's just not going to happen at 65+ mph unless he has some big air diverter mounted to the front of his car.
Click to expand...

exactly the car in my avatar hasn't had a fan shroud for 10+ years, cheap aluminum flex fan and it never runs over 200 degrees on the hottest day

although when I've done core plugs in most mopar v8's there filled nearly up past the core plugs with sludge and dirt, a good washing out with a pressure washer when the engine is out is a must

when the engine isn't out I recommend a cooling system flush
 
1968FormulaS340 said:
That's just not going to happen at 65+ mph unless he has some big air diverter mounted to the front of his car.
Click to expand...


it happens on new cars. that's why they pack the cooling modules with seals to keep the air from going around the radiator and condenser.

If the fan is spinning too slow, it can block the airflow at highway speeds also.
 
Next time it gets hot,, use your heat gun to measure the temps all across the rad., you're looking for cool areas,, I know it's been rodded, humor me...

I'm also curious about the temp difference between upper and lower hose, while hot and running..
 
John Morrow said:
Thanks for the Reply .....I will try that, i'm kind thinking i did that when I first took everything apart .....not for that reason ,,,just to drain the motor and radiator when I started ...but I will check that out again .
After changing all that I have changed I still have the very same problem .......so I'm just guessing I did all that for nothing ......except having a lot of new parts.
Click to expand...


BINGO..... Moving to fast thru the radiator. ie not enough time for heat transfer.

So many times this gets over looked... Just like running no thermostat.

" The coolest i could get is a "185 so i didn't use any" How many times have we heard that. Bad move.
 
inertia said:
Next time it gets hot,, use your heat gun to measure the temps all across the rad., you're looking for cool areas,, I know it's been rodded, humor me...

I'm also curious about the temp difference between upper and lower hose, while hot and running..
Click to expand...

I will try that today ......if the wife has nothing going on for us
 
68-GTS said:
BINGO..... Moving to fast thru the radiator. ie not enough time for heat transfer.

So many times this gets over looked... Just like running no thermostat.

" The coolest i could get is a "185 so i didn't use any" How many times have we heard that. Bad move.
Click to expand...

I agree with this ....... only I had the same problem before changing water pump.
 
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