Cooling Issues with My 72 Challenger

[ghjedi]

Hi All,

I've been battling intermittent cooling issues with my '72 Challenger for awhile now and I am running out of ideas.  I have a 440 engine in the car and I've replaced the obvious stuff like the water pump, radiator cap, thermostat, and hoses.  I've also disconnected the heater core hoses, as they were leaking.  I thought the leaky heater core was the last bug to work out, but I was wrong after this weekend's drive! 

When I last took the car out, the temp was steady, but started to creep up to 220 and stay there, after driving around town for 20 minutes or so.  I made it home, opened the hood and heard bubbling in the radiator.  The radiator did not leak oroverflow, and after cooling down, I checked the fluid level and it is completely full to the top.  I have an infrared heat sensor, so I'm 99% sure that my aftermarket temp gauge is accurate.

The only part left to replace is my radiator itself and I am wondering if it is undersized for the big block engine.  It meausres 28" wide by 2" deep.  It also has the fan shroud and there is no A/C on the car.  I don't know how many rows the radiator has.  It seems big enough and looks fairly new outside and inside (i.e. no obvious rust).  I didn't install it, so I don't know what type it is.

I'd appreciate your advice on what else I should do or consider.  I'm thinking about swapping out the radiator for an aluminum one, but I'm not sure if that will fix the problem.  I also don't know what size radiator or how many "rows" a radiator should have for a big block engine.

Any thoughts?

[burdar]

When does it get hot?  Does it get hot at low speeds and idleing or when you're at highway speed?  Is there a spring in the lower rad hose?  What's your timing set at.  An engine that isn't tuned right will run hot.

You can use your temp gun to take readings all across the rad.  Any hot spots would mean there is a restriction there.

[brads70]

To see how many "row's" your rad has take off the rad cap and look inside and you should see the rows of tubes?  Have a look at the condition of the tubes as well? Like are they plugged or restricted with "crap" ?
I have an aluminum rad in mine, but I had it from the get go. (Mine is a 26")So I can't say it was a huge improvement or not ? I know aluminum rads cool better than the old style.

What's your engine timming at? That can cause heat too.  What kind of fan are you running? If it's a clutch fan it might be wore out?

[MEK-Dangerfield]

Anything blocking the air-flow to the radiator, like a transmission cooler? 

If it's not your timing, then I would look at air-flow or anti-freeze flow thru the radiator.

[dodj]

You can use your temp gun to take readings all across the rad.  Any hot spots would mean there is a restriction there.

And then you would know if a new rad would fix you up.

[ghjedi]

Thank you guys for the helpful suggestions.  You've given me several things to check out before taking the plunge on a new radiator.

Here are a couple of additional updates in response to the questions posted:
-My timing is adjusted to what the manual recommends for a 440.  I don't recall off the top of my head what it is, but I know that it is not overly advanced or retarded
-The heating issue is not consistent.  It seems to ocurr the most when I am driving around town in stop and go conditions.  The most recent case happened after 20 minutes of winding the car up in between lights/stops in city driving.  I have also taken it on longer highway drives and not had issues previously, so it does not happen immediately after startup.
-I have not yet replaced the upper and lower radiator hoses, so I will check them out more carefully.  There are no cracks and I know there are no leaks at all in the entire cooling system.  My radiator fluid is full to the brim and this continues to be the case even after my last overheating experience.
-The heater core hoses have been completely disconnected, as the hoses were old and leaking, along with the heater core itself.  I don't plan to fix this, as I really don't need the heater where I live.  I thought this was the last gremlin to stamp out, but I was wrong 

I will provide another update after I've had a chance to look into this some more this coming weekend.

Thanks!

[ksierens]

Does it have a shroud and a clutch fan?  Having them can make a big difference.

[Chryco Psycho]

 
 Also a coil in the lower rad hose to prevent it collapsing .
 180* thermostat

[MEK-Dangerfield]

Is the 440 bone stock?

The manual is nowhere near where I have my timing. You might try 12* to 16* BTDC and see what happens.

I use Chryco's method for timing. Set your idle to 2500 RPM's. You will notice your ears hurt at this point     , so some ears plugs can be used. Slowly rotate the distributor to see where it is most happy. Then retard it a few degrees from there, otherwise you will have pinging. 

[burdar]

You need to double check your timing.  I wouldn't go by what the manual says.  The factory initial timing is usually very low.  You more than likely need more initial timing.   There have been a lot of post on timing for improved driveability.  Depending on your engine specs, you may need 18 degrees of initial timing.  Basically if engine vacuum continues to increase with the added timing, the engine wants it.

Make sure your tune is adjusted correctly.  That will affect everything else. 

[moparmaniac59]

It sounds like from your description, that the overheating is basically occuring in stop/go traffic and not so much when the vehicle is moving. This problem is usually due to not enough air flow across the radiator and not in the radiator itself (but could be a combination of both). So how far is your fan away from the radiator? And I don't think you responded about whether or not you have a fan shroud? Have you checked out your fan clutch to see if it might be worn out? What type fan are you using, such as a 5 blade or 7 blade? I had a similar problem and went with a larger aluminum radiator. I sealed air gaps in my fan shroud. Installed a new fan clutch and 7 blade fan and finally went with an added electric fan for sitting in trafffic jams on 95 degree days. There are also some water pumps available that will move a little more water than the factory water pump. You have to first figure out why it's not cooling well. 

                                                                        Matt B.

[ghjedi]

Hi Guys,

These are all great questions and I will definitely double check my timing this weekend and report back the exact number.  I will say that the engine runs smoothly with a nice idle and definitely doesn't knock/ping or backfire under either light or heavy acceleration.  The engine is not original.

To the other questions, yes I have a fan shroud that is snug up against the radiator and I have a 7 blade fan with a fan clutch.  The fan sits about 2.5 inches away from the radiator.  I don't know how to test if the fan clutch is worn or not, but I can spin the fan blades freely in either direction while the car is off and parked in gear (I have a 4 speed manual transmission).

I just checked my upper and lower rad hoses and though they aren't cracked or leaking, they are both "squeezable".  They are not very stiff and neither seems to have a metal spring in it to keep its shape.  I have not yet replaced these after buying the car 2 years ago.  I have replaced the water pump and the thermostat is a new 180 degree one.

[Chryco Psycho]

the clutch should spin somewhat freely cold but should be tight hot , sounds like that my be bad .
 I would advance the timing up & disconnect the vacuum advance . it should run better & cooler

[ghjedi]

the clutch should spin somewhat freely cold but should be tight hot , sounds like that my be bad .
 I would advance the timing up & disconnect the vacuum advance . it should run better & cooler

Good point Chryco.  I was able to spin the clutch freely (there is some minor resistance) with the car cold.  I will fire it up later today and try it again after the engine is warmed up.

You also got me thinking about the rad hoses.  I will replace those, as neither hose is very stiff and that lower hose could be collapsing in a bit when heated.  I've not observed it, but then again, I've not been really looking for that either.

Regarding disconnecting vacuum advance, do you have yours permanently disconnected?  Is it capped off at both the distributor and the carb?

[moparmaniac59]

Another thing you can do is start the car up with the radiator cap off. Check the flow across the radiator with the engine running and warmed up. There should be a good bit of turbidity/flow at idle. If the flow appears reduced or restricted, it may be a clogged radiator and/or a worn water pump. I've seen a lot of people that buy an older car and the coolant is 25 years old and never been changed & they wonder why the car overheats!  Good luck with yours! 


                                                                              Matt B.