I was curious why my radiator would overflow from the drain tube (I don't have an overflow resvoir) under normal driving conditions. I didnt top off the radiator recently. Before I drove it the level was about an inch below the fill area. Also, the top hose that goes into the manifold seemed abit swollen near the bracket. Any ideas? Anything bad? Thanks in advance...

The overflow is normal, but just keep an eye on the level cold. My 307's radiator, when cold is about 2 inches below the water fill neck.
As for the swollen hose, this is only a sign of age. Might be a good idea to replace the hose before it burst at the worst possible time, probably the furthest point from a hose/water source. While replacing this hose, I would replace the lower as well. They are most likely the same age. Might want to take a peak at the heater hoses over all too. Check them at the firewall, waterpump, intake and over all. Even where they are held by the bracket on the inner well.

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Better Late than Never Fred
Team Chevelle #400
Madness takes it's toll, please have exact change.
www.geocities.com/motorcity/shop/9385/1970Chevelle.html (http://www.geocities.com/motorcity/shop/9385/1970Chevelle.html)

Hey 70,
Rif is right. Water and coolant expand when they get hot and since they are not compressable, it has to go somewhere. Advice I get is to replace the old hoses and belts at the same time. Consider installing an overflow tank it's pretty easy. mgg

[This message has been edited by Manny Gomez (edited 11-04-99).]

and a new radiator cap

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Leo Paugh
Maryland Chevelle Club #017

My over flow tank is a 900ml Miller beer can,a real attention getter at car shows...FRED

OK guys, I drove her to work this morning and more fluid is overflowing. That makes two times in a row that it has overflowed. Is the radiator clogged? Recall, I just flushed the radiator a few weeks ago, found a small heater core leak, added Prestones version of Bars Leak. No more heater core leak. I have driven the car 5 - 10 times since the Leak fix was added. Last two time driven (at least 20 min drive), it has overflowed. Just seems to me that if overflow was a natural occurance, then eventually it would come to a point where fluid would have to be added. Any clues out there?

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D Smith
ALABAMA
1970 Chevelle 350


[This message has been edited by 70Chevelle 350 (edited 11-05-99).]

[This message has been edited by 70Chevelle 350 (edited 11-05-99).]

It shouldn't be overflowing. The cap is supposed to maintain 15 lbs. of pressure in the radiator. If it's weak it will overflow. Try a new cap.

Maybe you are overfilling your radiator. It should be filled to just cover the trans oil cooler. Look at the aft side of the radiator; there may be a "fill" line stamped into it. Some have it and some do not.

Trans oil cooler? What's that got to do with a radiator?

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Tom Parsons

I am wondering if the stop leak REALLY worked: if it stops leaks outside the radiator, what makes you think it won't stop them INSIDE the radiator?? I think you plugged up some of your radiator.

OR; blown head gasket??

Did you change/do anything else ??anything??
eg:timing, etc??

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Gotta have a Chevy !In Durham N.C.
Why is there never enough time or money to do it right the first time, but ALWAYS enough to do it over?
Make it look the way you like it, forget what the other guys say!

Only flushed the radiator and added the stop leak. No other work was done on the cooling system. I had the level about 2" below the overflow line, now about 3" below. Is there any way I can tell if the radiator is clogged, or how to tell if the thermostat is bad? Just wanting to know why it would overflow 2 times in a row...????

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D Smith
ALABAMA
1970 Chevelle 350

I would take the radiator out and have a shop boil it out. It sounds like you may have an old corroded radiator that just doesn't cool enough anymore. I had a similar problem where the cooling was just on the border. Boiled it out and it was still really clogged up. New radiator fixed the problem. Maybe a head gasket also.

Doesn't the oil look milky if the head gasket goes out? Also, where can I get a new radiator and how much does one cost?

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D Smith
ALABAMA
1970 Chevelle 350

With the motor cool take off the radiator cap then start the car. Get it warmed up, rev above idle if you have to. Get it warm enough so the thermostat opens. When it opens you should see the coolant flowing pretty good. Take a flashlight and shine it in the radiator and take a look at the fins. Do they look clogged? Is your thermostat opening at the right time, ie not late or at all. Take it out and boil it in a pan of water on the stove with a thermometer. At what temperature does it open? Also you should never use stop leak in anything. Nothing good has come from stop leak. Only use it for short term motors, like in a demo car. Don't use things that are made to clog small passages in things that have small passages. You owe it to your Chevelle

How do I tell if and when the thermostat opens? That is, without removing the thermostat from the vehicle. Thanks...

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D Smith
ALABAMA
1970 Chevelle 350

68SS gave a good idea what to look for when the thermostat opens with the thermostat still in the car. You can see the coolant flowing when the thermostat opens. It may start and stop when the thermostat first starts to open but should run pretty good once it warms up.

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Dave Knapp
TC #388
'70 SS 396

You can't miss the difference. Before the thermostat opens when the car is cold the coolant just sits there. Basically it doesn't look any different from when the car is off. As the car warms up and the thermostat begins to open you will see movement of the coolant pick up in the radiator. When its finally open the coolant will be flowing out of the fins inside the radiator at a good rate of speed. There is no mistaking the difference. If you do this and you can't tell if its flowing or not then its not. If your watching and the coolant starts to flow you'll know it, trust me. Once you see you will understand. There is a big difference between still coolant and coolant that is flowing properly. Its not going to come out at the force of Niagra Falls but you will know.

OK, great. I will check. Now, if it is not flowing, then the thermostat is broken? So, a broken thermostat could be causing the overflow problem?

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D Smith
ALABAMA
1970 Chevelle 350

Yes, if its not flowing then the thermostat is no good. At this point you can pull it out and check it in a pan. This is of coarse assuming that the inside of your radiator looks ok and its totally clogged, but I doubt it is that bad. Yes it will overflow. The water pump makes the water flow but the coolant in the radiator is still linked to the coolant in the engine via the bottom hose. If the thermostat doesn't open the coolant in the radiator will still get as hot as the coolant in the motor and overflow. Don't rule out a bad cap as mentioned earlier. If the cap is no good it will also overflow. My day is over and I only have this at work. I will check on Monday to see how you made out.
DZ-I can tell you have a standard trans like me. Remember those weird automatic radiators have that cheesy trans cooler inside. When the coolant level is down you can see it. I think thats what JWagner was talking about. Although thats seems to be too low a level as the top of those seem to be more than a couple inches down.

By the way don't you have a temperature guage? If so what does it read when the radiator overflows etc. Is it overheating or just overflowing? If you don't have a guage get one. If its overheating most likely its the thermostat. If its running at a good temp and overflowing its either overfull or a bad cap. The level shouldn't be down more than a couple inches

GREAT. Thanks for your input 68! I will stop by and get a new cap. Should be only a few bucks. Will check the flow when I get home. I have the idiot lights. It is just overflowing, not overheating, that is the light is not coming on.

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D Smith
ALABAMA
1970 Chevelle 350

Over flow is normal. Get an overflow bottle. That is why they started putting these on cars. http://www.chevelles.com/forum/smile.gif :0
Had the same problem on my 70 ss454. Put on an overflow bottle. It would leak into the bottle. Then when it cooled off, it recovered it back into the system. http://www.chevelles.com/forum/smile.gif Problem solved. http://www.chevelles.com/forum/smile.gif http://www.chevelles.com/forum/wink.gif

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Mr. D
72 454 El Camino
68 RS/SS Camaro
73 RS/LT/Z28 Camaro
99 Firebird TA WS-6 A4

i'm too lazy for the overflow bottle, or broke, but I know NOT to fill my radiator on my '70 anywhere near the top or it will spill out. Standard.