Running hot - need some help

[dave73chally]

73 challenger is running really hot. Not sure what temp, my gauge only shows a C and H but it's almost maxing out to the hottest temp on the gauge. It reaches this level within minutes of driving. I changed the thermostat from a 195 to 180, installed a new coolant thermostat sensor, gauge gradually increases and decreases so it seems to be working properly, there are no radiator leaks that I can find. What should I try next?

I read that once it starts to run hot, turn on the heater and it should cool down the engine by drawing heat into the cabin and away from the engine itself? I'll try this tomorrow. Is this a tell tale sign that I need a larger radiator? I have a stock 18" with a stock 318.

[brads70]

I'd install a quality mechanical  temp gauge. Stock ones sometimes are not accurate.

[Bullitt-]

Read this article in Hot Rod recently....lots of causes for overheating covered
http://www.hotrod.com/techarticles/1401_1965_chevy_el_camino_overheating_fix/
I'd start with ignition timing & carb tune to make sure your not running lean.

One not covered that I picked up on in another article that I had never heard was week valve springs.
Valves don't close quick enough...More a problem with high lift cams but who'd a thunk it. 

[hooD]

-maybe your radiator is clogged up and not flowing efficiently.  Has it been flushed out recently? 
-do you have a clutch fan?  it could be at fault if it isn't engaging.
-is your radiator cap holding pressure on the hoses? (it should be)

[dave73chally]

Replaced the radiator cap in hope of a cheap fix plus it was the original, figured maybe had a bad seal. Took the car out, still ran hot, turned on the heat and it stabilized but still hotter than it should be.

So far I have a new temp sensor, 180 thermostat, radiator cap, heat turns on and is hot, not losing coolant, radiator was fully flushed and pressure tested a month or so ago, clutch fan is working properly. What are my next steps? Heat gun/new gauge to figure out how hot it actually is running?

[Chryco Psycho]

Tuning, retarded timing , lean fuel mix etc make sure you can see water flow inside the rad , water pump could be bad , shroud , make sure the lower rad hose is not collapsing

[dave73chally]

Lower hose is not collapsing, I don't have a shroud. How do I test to see if it's the water pump? Seems like this issue started once the outdoor temperature reached 80+, was running cool all spring..

[Chryco Psycho]

Shroud will make a huge difference
 Removing the rad cap you should see significant flow inside the rad with the cap off

[unotre]

Before you go through all the trouble, first check if the coolant temp is actually hotter than 180-190F. If it's not, could be bad gauge or temp sensor.

[dutch]

get a shroud 

[tman]

Once you get a shroud, make sure the fan is partly in it.  Don't know how close your fan is to the radiator, but a shroud helps the fan draw cool air through the radiator.  Without a shroud, all you are doing is circulating air behind the radiator instead of drawing cool air from the front of it.  Basically right now, you are getting cooling when driving, but at idle, just agitating hot air in the engine compartment, thus temps go up.  Been through this experience a long time ago.

[dave73chally]

Once you get a shroud, make sure the fan is partly in it.  Don't know how close your fan is to the radiator, but a shroud helps the fan draw cool air through the radiator.  Without a shroud, all you are doing is circulating air behind the radiator instead of drawing cool air from the front of it.  Basically right now, you are getting cooling when driving, but at idle, just agitating hot air in the engine compartment, thus temps go up.  Been through this experience a long time ago.

Temp rises fast when accelerating/driving. When I let off the gas it cools, when idling it's cool. That's the confusion on my end.

I'll try to get my hands on a temp gun to test true temp

[Chryco Psycho]

opposite of most cooling problems so you either have a flow problem , you are sure the lower hose is not collapsing , you can put a spring inside , is the timing right , jetting too lean >

[Strawdawg]

Sounds like a plugged up radiator core to me. Take the cap off and look at the end of the tunes to see if they are fully open and not stopped up.  If this a new car to you and it's your first summer,  it definitely needs a shroud.

Steve

[dave73chally]

I revved the engine yesterday and didn't see the lower hose collapsing. Should I sustain a higher rpm rather than short revs to fully test the collapsing theory?

Timing was just set a few months back and as far as I know it was done correctly.

I have a 440 for this car in the near future and would rather not buy a shroud for the tiny 18" radiator that is currently in there, when a 26" is in the near future. Should I just jump the gun and buy a 26" with shroud and mount it up to the 318 for the time being if this happens to be the issue?

Also, realized the alternator belt is looser than it should be. Looks like it's the wrong size as the bracket is to it's max position. I'm going to replace with the correct one. Would a loose belt cause an overheating issue at higher RPM's due to the belt being loose, potentially slipping and causing the water pump to run slower than it should be?