spark plugs

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moparguy

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I'm having trouble with my duster overheating. My question is can different heat range spark plugs significantly alter your engines operating temperature. Havn't really changed anything other than running hotter plugs. 400, mild cam,750 holley,4.10 gears, automatic 727 in a 72 duster. reached 225 degrees when temp was close to 90 degrees outside. Not a problem in winter.
 
Plugs sound like the least of your problems.

How is your cooling system?

mechanical fan?
shrouded?
radiator?
t-stat/temp range?
good cap?
 
The heat range of a plug really doesn't effect how hot or cold a motor runs. When you say you are running hotter plugs, do you mean you are running hotter plugs than stock? As HP goes up you want to run a colder heat range plug not hotter. The general rule is for every 75 to 100hp you add go one step colder plug.


Chuck
 
I have a fairly new looks like a 4 core radiator with 190 thermostat and an 18 inch flex fan no shroud with a good cap also have a 12 inch electiric fan that doesn't seem to help much. I switched to the hotter plugs because it seemed to run better. That was back in the winter. Do you think that having no shroud could cause this kind of severe overheating with a supplemental fan.
 
moparguy said:
I have a fairly new looks like a 4 core radiator with 190 thermostat and an 18 inch flex fan no shroud with a good cap also have a 12 inch electiric fan that doesn't seem to help much. I switched to the hotter plugs because it seemed to run better. That was back in the winter. Do you think that having no shroud could cause this kind of severe overheating with a supplemental fan.
Click to expand...

It's possible. Add a shroud and swap in a 180 degree thermostat.
 
I would ditch the flex fan for the stock fan and see if that helps.A shroud would definately help.
A lean car will run hot,to much advance,plugged heater core are other reasons.
Is your fan a pusher?If it is it could be impeding air flow through the radiator.
 
I got a 160 degree stat in the Duster. With a stock 7 blade
clutch fan. It never gets hot. Go's about half way up the stock
guage in traffic. When I went to the Car Crap Nats this past
july everbody was over heating on the way in. In the slow
traffic. Never had a bit of trouble.
 
Get a shroud and you'll see a big difference. Also, make sure that the rubber seal that attaches to the hood and seals against the radiator core support is in place and in good condition. At 90 degrees, every cooling system is getting taxed.
 
ran flex fan for 200,000 plus miles wiyh stock 340 radiator ac type in 150 mile per day traffic bumper to bumper all day for 5 years wiith shroud never over heat therm was a 190 youll find it good luck:happy11:
 
I high efficiency 3-row core will cool circles around a 4-row. Most 4-row cores are too dense to allow proper air flow in town.

If you are running a flex fan, thats part of your problem. If you are running an electric AND a mechanical fan thats part of your problem (run one or the other, NEVER BOTH).

Thermostat rating will not make any difference, since the engine is getting warm enough to open the thermostat. Once the thermostat is open, it is out of the picture. Now if the engine gets hot and the top tank of the radiator stays cool, you need a new thermostat.

Try this: Turn on the heater full blast when the engine is around 225 degrees or however hot it gets. If the temp goes down, your radiator is the problem, it simply can't shed the heat. Do this at highway speed, that way you have plenty of airflow, (this eliminates the fan as a cause, since the fan is pretty much along for the ride past 30 MPH.)

Mopars were never know for overheating, and in fact they had pretty robust cooling systems. If you are running that hot, something is wrong.

And if it runs better with the hotter plugs, you are either too rich, burning oil, or have a puny ignition system (or you just needed new plugs and thats why it ran better). Hotter plugs tend to "glow" under high loads and will cause pre-ignition. Higher octane will not compensate for this.
 
moparguy said:
I'm having trouble with my duster overheating. My question is can different heat range spark plugs significantly alter your engines operating temperature. Havn't really changed anything other than running hotter plugs. 400, mild cam,750 holley,4.10 gears, automatic 727 in a 72 duster. reached 225 degrees when temp was close to 90 degrees outside. Not a problem in winter.
Click to expand...

Make sure you have all the rubber seals around your engine compartment in place, You want all the air you can get going thru the radiator and not sucking thru the engine openings. Also check your timing, is it set before or after TDC, make a big difference. Just a couple of suggestions.
 
The flex fan is not likely to be part of the problem. When I bought my car it had the original fan with no shroud and ran so hot in traffic I had to fill the cool can (it was a race car when I bought it) in the summer to avoid vapor lock. It was not long before I pulled the stock fan and put on a flex fan. Problem gone.
 
Great info. Appreciate it. I'm on a very tight budget, any suggestion on where to find a CHEAP fan shroud. On the running better with hotter plugs subject. could that 750 holley model 0-3310-2 4160 with 72 main jets stock secondary metering plate and 6.5 Hg power valve be too much gas? Once again 400 bored .040 over, mild cam, dual plane intake, stock manifolds. I was stumbling above 3500 rpm, hotter plugs seemed to help.
 
On the jets, try some 70's and see what happens. What color were the plugs when you pulled them?

Does the engine run hot on the highway? Or as close to highway as you can get with 4.10 gears. Or just in traffic.
 
The plugs were black and sooty. Bosch platinum recommended for a 400 in a 73 charger. These were not but 2 or 3 months old when taken out. As for highway use i try to avoid interstate. Most of my driving is around town. It screams on highway so i guess it would probably run hot, but don't know for sure.

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Since we are kind of working two problems here, two questions,

What ignition system are you running? A hotter plug can help compensate for a weak ignition system.

When does you car get hot? idling in traffic or cruising above 35mph?


Chuck
 
Running stock distributor with no vaccuum advance, reworked slots, stock ECU, MP recurve spring kit. Total timing set around 36 with 14 initial. MSD blaster coil with new taylor wires and new champion plugs. Temperature increase when sitting in traffic and holds steady when cruising but not dropping.
 
If i change the primary jets to 70 are they not just used for cruising. I was having trouble at WOT. Is that the power valve or secondary plate which i cannot change. Havn't tuned any carbs before only rebuilt.
 
ditch the rear metering plate and get a metering block. that way you can jet up or down as needed. a carbed motor doesn't need a platinum plug. use a good ngk, nippon denso plug and you'll be fine. wehat is the vacuum at idle in gear? make sure you find out and go 2 hg lower for the power valve. definitely get a shroud.
 
If i ditch the secondary plate for a metering block. What size jets would i put in it and would i leave the primarys.. ? Should this be easy to tune for my motor or should i save for a 650 double pumper or some other smaller carb?
 
when a power valve is in the calculation, about 8 jet sizes above the primaries. yet at top end you may only need 6 sizes. what is the vacuum in gear at idle? this is necessary to know if your pv is too big or just right.
 
I don't have a vacuum guage. My cam is a comp cam XE 268H-10. .477/.480 with 224/230 duration at 050. Very streetable cam that should have good vacuum. So dropping to a 4.5 Hg power valve should help to lean up the mixture?
 
maybe, maybe not. to tune it properly, you need a vacuum gauge. get a loaner from an auto parts store or just pick one up at sears or auto store. you might be fine with a 6.5, but you need to know for sure. also, if you switch out to a rear metering block, you need to change the dual inlet feed to a 4150 style. after you figure out the power valve, then go to jetting.
 
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