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Smooth72

I'm needing help finding out why my radiator is acting up. I have a 1972 Pontiac LeMans Sport 350 4bbl and when it runs for any length of time the radiator overflows out of the overflow. I have no idea why. I have the radiator restored a couple years ago and recently put a new thermostat and radiator cap on it and it still does this. Any ideas?

Oldcar_Mechanic

What does "any length of time" mean? A couple of minutes? An hour?

Does the water spill out of the overflow for a long time? In other words, is the car overheating, or is it just seeking it's own level? You can't fill the radiator to the top on these cars. There needs to be some room for expansion so just fill the radiator so that the cores are covered by a small amount.

If it's over heating, then I would check that the thermostat is in correctly (this can happen very easily). You also could have a bad new thermostat. Once it starts to heat up you can try to feel the radiator in various spots (high and low, side to side) to see if you have any cool spots. That will tell you that the radiator is blocked and not allowing the coolant to circulate well.

Overheating can be due to the coolant not able to circulate and remove the heat from the engine, so it can be something in the block also that does not allow the circulation to happen like it should.

It can also be due to improper timing, or an excessive lean condition (something like a vacuum leak).

You have to look at the entire picture to diagnose any one particular problem.

Hope some of this helps

Ron

d2_willys

There can be several causes to overheating if that is what is really going on.

The first thing I would do is to check obvious things as you have done.

Next I would take the car down to a radiator shop and have them do a BLOCK test. They simply remove some of the coolant and install a big syringe type thing that is filled with a blue fluid. While the engine is warmed up they simply squeeze the bulb on the tester to draw any gases into the blue fluid. If it turns green or yellow you have exhaust gases in the cooling system and probably have head issues such as bad head gasket or warpage. :mad:

If it stays blue then the probable cause is some sort of blockage that is not allowing coolant to flow properly.

One other thing that sounds stupid, but is a culprit alot of time is the fan clutch. You may want to check that too.:eek:

Twitch

Wait! For sure that car originally had a closed system overflow jug. If it doesn't have it and the radiator is filled up to the lip when you shut off the engine it will puke out of the overflow tube even when it isn't hot.

In an old car you should fill a rdaiator about 3 inches from the opening. If you try that an an closed sytem radiatior you can see that you aren't even covering all the cooling tubes. The newer radiadors have a different head shape than the old ones that aren't made to accomodate expansion. In an overflow system you should fill the radiator to the max with the proper amount in the overflow jug. That's usually like a pint. That leaves nearly a gallon for expansion.

As the engine warms and the radiator pushes expanded coolant out it spilss to the overflow when the engine is shut off. When restarted the cooler radiator will black flow without the heat expansion and use all the coolant in the radiator from the overslow. Note- there are no bubbles or air pockets in the closed system.

Also the "new" radiator cap. Did you get the proper poundage for pressure? If you got one just a few pound too weak you may get over heating boil over.

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