Holy moly, temp temp temp

[Chryco Psycho]

Retarded timing adds more heat than anything .
That seems more like a water flow problem if it would not cool on the highway

[kawahonda]

I'll check timing again, but 4 days ago she's at 17 degrees initial....

I will check vacuum advance connection too.

[Chryco Psycho]

Timing rarely moves unless the dist is loose , I doubt timing is the issue .
The fan should be tight when it is warm but on the highway is hould freewheel & get out of the way of the incoming airflow .
more likely to be a plugged rad , bad thermostat or a collapsing lower hose restricting flow

[Cudakiller70]

Test your radiator cap for holding pressure. Test system to verify no leaks and also holds pressure .
Autozone and O'reillys has free loaners

[kawahonda]

What's a good cap that you guys would recommend for this ride?

[Chryco Psycho]

16 Lb Stant , you can order both from Rock auto

[chargerdon]

Look, if you haven't changed anything, then the most likely culprit is the thermostat has gone bad.   

Simple test...remove the thermostat and take car for a ride and see if that fixes...if yes then buy new thermostat...If no then keep looking. 

[70 Challenger Lover]

The timing can be a pain on certain engines depending on the vacuum source. You can have it connected but not working as well as it could. In a perfect world, it will apply maximum vacuum when not under load (idle and cruising on freeway) and cut all vacuum when under heavy load. It helps to have a vacuum gauge and also a hand held vacuum pump. The pump checks that the advance can isn't leaking vacuum and also tells you how many inches of vacuum it needs to start working and how many it needs to reach maximum advance.

On the car I just picked up, it was hooked up but at idle, it had zero vacuum so it wasn't getting any vacuum advance at idle. The initial advance was 15 which wasn't bad but the vacuum advance was adding nothing. After switching to a better vacuum source, the vacuum advance at idle added 20+ so I had to back off the initial to 5 degrees. At idle, I'm now running 25 degrees but the engine likes it. So much in fact that the temp needle dropped to 1/3 within minutes. Going down the road with higher rpms, the centrifugal advance adds more but again the engine responded well to it under all conditions and the needle never went higher than 1/3. If advancing the timing speeds it up at idle, than it's because the engine runs more efficiently like this which will result in cooler operating temperatures. The vacuum advance can is simply a way to do this on an intermittent basis.

I found that the lowest vacuum nipple on my 2 barrel carb provided 15 inches of vacuum at idle, zero when under load, and 15 inches at higher rpms while cruising. If you're running a hot cam, the engine may not produce enough vacuum in most driving conditions to properly operate the vacuum advance.

Your problem may not be linked to timing but it costs nothing to verify all of this before you spend any money replacing parts (which is a lot more work). Most of my overheating issues over the years with lots of different cars have been caused by timing problems. Only once was it a thermostat and only once a worn out fan clutch.

[kawahonda]

I believe that this is not a timing related issue. My timing is dialed in. Even if something was wonky with my brand new vacuum advance, it shouldn't drive up temperatures. I know this because a long time ago, I drove it with vacuum advance plugged up and didn't run into over heating.

When I replaced the rad cap about 8 months ago, the one that came off was crusty and causing the hoses to kink. It basically wasn't venting. My cap is still somewhat new, although I've kinda "bent" the pressure lift-off arm on it.

It seems it would be a good idea to replace the t-stat as the next course of action.I remember when I pulled in the garage about 4 days ago, I was messing around on the work bench, then I heard some water movement in the engine. Probably related to the stat behavior?

How much water do I need to drain to get to the T-stat?

[JS29]

You could get it to operating temperature and shut it off and check for cold spots on the radiator core. 

[70 Challenger Lover]

Your first post indicates it was running pretty warm before. Halfway up is on the warm side. You can get away with that forever but it gives you no safety margin for those days when it's super hot or you get stuck in traffic. I think it was always close to overheating and some small thing changed that tipped the scales. That's why I mentioned getting back to basics first. You can get a thermo gun to manually check temperature and they are super cheap. It's probably a good idea to know the exact temperature a halfway needle means. I'd bet it's about 200.

As far as the cap, a stronger cap will allow you to run at a higher temp without boiling over. It will not make the engine run cooler. Moroso makes a 22 lb cap and I used it on a GM car that always ran on the warm side. It worked great but the car still ran warm. It just didn't boil over anymore. And a 22 lb cap shouldn't hurt anything if the whole cooling system is in good order.

[kawahonda]

I actually have a thermo-gun. Engine temp is probably best gathered by shooting the intake manifold?

Good idea about shooting areas of the radiator as well.

I can do this very soon just by having it idle in the garage.

Good advice that being half-way up is considered a little hot. I should treat that not as a "happy medium" anymore, but should really try to be 1/4" up on the scale.

I have a 180F t-stat on the way from Mopar Dave. If my old cap was corroded and crusty, It's probably going to mean that my t-stat is corroded and crusty.

[70 Challenger Lover]

I actually have a thermo-gun. Engine temp is probably best gathered by shooting the intake manifold?

Good idea about shooting areas of the radiator as well.

I can do this very soon just by having it idle in the garage.

Good advice that being half-way up is considered a little hot. I should treat that not as a "happy medium" anymore, but should really try to be 1/4" up on the scale.

I have a 180F t-stat on the way from Mopar Dave. If my old cap was corroded and crusty, It's probably going to mean that my t-stat is corroded and crusty.

I like to shoot areas all over just to show that water is actually flowing through the water pump and radiator as it should. I'm a bit compulsive on things at times so I check the temp at various points so that I know 1/2 up is 200, 1/3 is around 180, and so on. You are used to 1/2 now as your normal but if you knew it was 200 degrees, it might compel you to shoot for better.

You won't get it to 1/4 unless you run a 160 thermostat and 160 isn't a very good temp to run your high performance motor. You really want a 180. With the 180 thermostat working properly and everything else in good shape, you should be able to maintain about 185 or so and I'm guessing that will put your needle around 1/3.

If you go to the trouble of draining fluid to change thermostats, I'd drain it completely and flush the whole system out. Then you can fill with the correct mix of coolant and later if you pull the manifold, you can just catch save and reuse the clean stuff that you pull out. Maybe you will get lucky and flush out some sediment from the radiator.

By the way, I used one of the super duper water pumps before and I saw no difference. In my opinion, the stock one worked well so I'm thinking it's hard to improve something that is already more than adequate. I am a big fan (pun intended) of the heavy duty Hayden fan clutches. Sometimes the old stock ones fail slowly over time so you don't realize how wimpy it is until the new heavy duty one goes on.

Hopefully the thermostat will be a quick fix for you. It seems to me though that if it stuck closed, it would overheat within minutes and the gauge would peg out until the motor failed. I'm no small block expert though so perhaps the bypass hose allows enough coolant flow to prevent this situation from happening.

[kawahonda]

Over the winter I did a 3-phase flush. Flushed it completely. So it's recently been flushed!

Yeah, I'm curious to know what temp t-stat is in there now. Probably not a 180F....maybe the stock 195F or whatever it is.

I'll post some info later today with my heat gun.

Yep, I'm going with a 180F Stant t-stat.

I can also run the engine while cold without the radiator cap on there and measure the temp when the water starts moving....

[Chryco Psycho]

I would run it with the cap off & see what kind of flow you are getting ,
Check the lower rad hose , if it is soft it could be collapsing on the suction side , It is good to have a wire coil in there , you can bend up a welding rod or coathanger
You only need to drain a qt or 2 to get below the thermostat , it is at the top of the engine
I never run vacuum advance , it will not cause heating issues