1968 Coolant overflow issues

[TexAg]

Before I start, I'd like to state that I have scoured the forums and searched for every possible answer. Unfortunately, I haven't found the specific answers that I'm looking for, so here goes.. I did find one very close (forgot who wrote it) that involved a small tear in the head gasket, but I'm not yet ready to start a tear down.

My car consistently pushes coolant out the overflow. Having several Mustangs in the past, I'm familiar with this concept and wasn't overly concerned at first. I've always assumed that it would equalize at the proper level. Never ran hot, and didn't give me any reason to be concerned, other than the constant.. "excuse me sir, but your car is leaking."

That said, last weekend it did run hot. When I pulled in the driveway it was at about 260. I let it cool and topped off the coolant. It was very low. I didn't assume enough coolant would push out to cause a problem, so I wasn't as good as I should have been about checking it.... BAD CAR OWNER!!

Anyway, all seems to be ok and it runs normal and has returned to normal temp. It's amazing what ample coolant will do. I did notice bubbles (frothing) in the coolant when I was refilling it, but I'm assuming that was caused by the low coolant level and air mixture.

What I know so far:

1) No antifreeze in the oil
2) Thermostat appears to be working as it after running for a few minutes I can see coolant start to circulate. Not a great indicator, but something...
3) Other than the bubbles, antifreeze doesn't look "milky", at least not compared to pictures that I've seen. Also, there is no evidence of an oil residue and the coolant dumped on the drive evaporated without leaving a brown film.
4) I haven't checked timing yet, but it runs great and the guy who built it has a pretty good reputation around this site. :icon_wink So, I'm gonna guess that it's at least close to what it should be.

Questions:

1) Did running it at that temp for an unknown amount of time cause damage that I haven't yet discovered?
2) Why is it pushing coolant so bad?
3) Lastly, I've seen some discussion on radiator caps. Mine is a 13lbs, would a 16lbs correct the problem? Is there a disadvantage?
4) Should I just resign myself to a catch can and keep a better eye on the coolant level?

This weekend I'm going to flush and refill the coolant to see if I find anything more, and to make sure that the mix is right, but if I need to be checking anything else, I'm open to suggestions.

Thanks in advance!

 

[CougarCJ]

20 or 24 inch radiator? Do you have a fan shroud?

Fixed or clutch fan?

 

[TexAg]

24" with shroud and clutch fan.

 

[franklinair]

A few recollections & observations:
The radiator is a new 24" with fan shroud & thermal fan clutch and new radiator cap. (The PO had the incorrect/smaller 20" radiator in it) New fan, new hoses. I don't recall if I replaced the thermostat- but after replacing these major cooling components, I would think that I would have. Easy to tell- when I replace a thermostat I always drill a 1/8" hole in the thermostat flange as a mini bypass precaution. Pertronix solid state unit, timing @ 8 degrees, without vacuum advance. Edelbock 500CFM, electric choke carb, good vacuum @ idle RPM.
As you said the engine runs OK, with normal temp indication. My primary suspect would be the radiator. Even though it's new, I've read about faulty Chinese repo parts. (The radiator came from NPD) I'd have a radiator shop check the radiator for proper flow rate. Also, I have no aversions to a coolant recovery bottle. It adds clutter under the hood, but functionally it' not a bad idea.

Neil

 

[rvrtrash]

Have you run the car up to operating temperature with the radiator cap off? Even if the thermostat has been drilled, or has a vent hole, air can get trapped in the top of the intake water passages. When air gets hot it expands since the system is sealed, pops the radiator cap and pushes water out with it. Guess what. Now that you pushed a bunch of water out, you've allowed more air in the top of the passages by dropping the water level so you get to do it all over again when you put more water in. If you let it get to operating temp with the radiator cap off, it doesn't build up pressure, the air bleeds out when the thermostat opens and the water circulates, you add water as needed and then you're ready to go.

Steve

 

[teamlo]

Pertronix solid state unit, timing @ 8 degrees, without vacuum advance.

You could go higher with the initial timing. My slightly modified J-code 302 is running 15 degrees of initial advance, 36 degrees total, also has vacuum advance hooked up (MSD billet distributor). I bet advancing the timing some would help, and engine would likely run cooler as well. I do not have any issues with pinging at all on 92 octane gas. I'm using a Quick Fuel HR-580 VS carburetor. I also suspect a radiator issue, but try the timing.

Terry

 

[dalorzo_f]

260 is way hot! A new cap or recovery tank masks the issue, does not fix it.

Start simple test your cap, if it is not holding correct pressure the coolant can boil and lead to overheating...

Coolant recovery is nice, but as it was never needed from the factory again just masks the real issue.

Could also be a worn out water pump, have seen some with almost no impeller due to age, corrosion and cavitation damage.

 

[TexAg]

Thanks for the input guys! I knew I could count on you. A couple of clarifications..

Neil - do you think setting the car up at NC mountains altitude and then bringing it down here to about 500 feet above sea level would have any impact? I know it can affect the carb performance, but what about boiling points etc? If I can't find a simple solution, I'll have the radiator tested.

rvrtrash - Excellent point. When I flush the old this weekend, I'll make sure to bleed out the air.

teamlo - I think I will probably try to advance it a little more. I wasn't sure where it was originally set. Now that I do, I think a little more might help.

dalorzo_f - I agree! Keep in mind that was only one time when the coolant was too low. I won't let that happen again. It runs at normal temp otherwise. It just keeps pushing coolant.

So, back to 2 of my original questions..

1) Should I expect damage from the one time it hit 260 degrees? Or did I get lucky?
2) Should I go with a 16psi radiator cap to increase the boiling point? Is there a disadvantage?

Thanks again!!

 

[Maine gt/cs]

I have the same problem.My 302 was rebuilt 1500 miles ago back to stock specs. The car would push coolant even though it was not running hot. I took the radiator out, had it flushed and tested for leaks and had 200 degree water flowing through it for 20 minutes. Had great flow and no leaks. Put in 2 new thermostats,new 13 lb. radiator cap. 20 inch radiator, fixed fan and shroud. Took the car for a 150 mile ride and when I got home and parked it, it pushed coolant. Not very much but still a pain. I am going to try what rvrtrash recommended and see how that goes. Great help from a great site.

Tim

 

[dalorzo_f]

No real way to tell if its damaged unless you take it apart. If it "sounds fine" it probably is. Some additional wear maybe, but that's is what it is.

A 15-16lb cap won't really solve why it is happening, but if it works then it treats the symptom. New engines, as yours sounds to be, can run hot for a while.

Retune your carb and see if it helps, altitude changes do impact air/fuel mix. But you would tend to run rich going altitude to lower, which should not really cause overheating. Actually in general, the opposite.

Was the distributor recurved? Do a full timing check, may show something.

 

[whodat]

If you want to try a 24" aluminum radiator I have a Champion never used, but new in the box for sale.

 

[x-codegtcs]

Steve's suggestion is where I would start. Timing maybe, but if the car is running in "normal" range, then the timing is most likely not the issue...

I would change the oil as the hi-temp most likely damaged the oil and you could see more wear due to the damaged oil - and depending on how long it ran at the high temp would change the possibility of damage at the rings/cylinder wall fit.

 

[candycal]

TexAG is there a chance you're overfilling tha radiator? If it's filled to the top (commonly done) the coolant will overflow when it gets hot, every time. The correct level is about an inch from the top of the neck.

 

[Bumblebee]

All of the above and also, make sure the fuel line isn't crimped from a jack, that can make it run lean. Finally, what is the condition of the block? Barn finds that we're left with water in the journals for long enough can corrode the journals and create a partial or complete (happened to my first mustang) blockage. In my case, the radiator and water pump came off and they drilled out the solid journal, oh brother!!!

And one last thing, if someone is doing a cheap engine rebuild, they sometimes punch the welsh plugs into the block and leave them there, and just put new ones in, that definitely can hurt the cooling efficiency too.

All very extreme but actual situations.


Good luck with it!

 

[TexAg]

Thanks, guys! I'm going to start with flushing and refilling the radiator (to the correct level) and check the timing. I'll see where that takes me, but I do feel better, as it doesn't appear to be anything too serious..

 

[Mosesatm]

I had the same problem and it turned out to be nothing more than the vacuum hoses on the vacuum advance being switched front to rear.
The hose from the timed port was hooked to the rear instead of the front, which retarded the timing instead of advancing it.
It ran HOT and belched a lot.

 

[CougarCJ]

Good point, vacuum advance must come from ported vacuum, not direct manifold which is constant.

 

[Maine gt/cs]

I took the radiator cap off, let the car run for 20 minutes until the engine pushed out the air and coolant. Put radiator cap back on and then went to a gathering of cars and bikes that gather every Friday in a parking lot about 75 miles away. Put on well over 150 miles and one good part of it was 70 mph for about 15 miles of interstate. Got the car home and not a drop of coolant pushed out at all. Hope this solves the problem.

Tim

 

[stangfan]

Sounds to me like you have fixed your problem. Air in the cooling system is not a good thing. :smile:

 

[Maine gt/cs]

Yes, Thanks to all the great information and knowledge on this site.