Car leaking coolant and over heating. Then stops leaking?

[73super-steph]

So my moms mazda 626 started over heating in the parking lot. So she drove to the nearest parking space and stopped it, steady stream of coolant on the ground behind her. So she asked me to take a look at it, so I let it cool a little then pooped the hood and the burp tank cap, let it steam for a few minutes then put some anti-freeze in it.
Well after cooling for a bit I started it, not leakimg any more and seems to be running fine. But coolant sprayed all over the engine compartment. No water in the oil. What the hell?
I can't tell where it was leaking from.

[Da TOW'D]

pressure test the cooling system with the engine off
special tools needed
maybe it is a split hose our water pump
good luck
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[73super-steph]

[jmartin7]

If it is anything like my 626 then a coolant line is split somewhere. On my car there was a very small line that circulated antifreeze through the throttlebody that split and would only dump coolant after the car had been driven for a while.

[Cusser]

Drive it 20 minutes, then park it. 10 minutes later go lookin' for the leak; the coolant actually gets hotter for a few minutes after stopping.

Autozone has free loaner tool pressure checker, you pump in air into radiator neck, to force out any coolant from a small leak.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[73super-steph]

[73super-steph]

[iowegian]

[73super-steph]

[jmartin7]

[73super-steph]

[drscope]

First thing to remember is that overheating is extremely BAD for the engine! So you need to make sure the cooling system is topped up and full before you try to move it AND keep your eye on the temps as you go!

Plus antifreeze won’t always show up as water in the oil on the dip stick. And if antifreeze is sucked up by the oil pump, it usually takes the bearings right out as the antifreeze moves the oil away from the bearing surfaces.

A cracked head or blown head gasket won’t necessarily put water in the oil or oil in the water. It has to be leaking from water chamber to oil chamber for that to happen. Many times they just crack from water chamber to outside or into the combustion chamber.

A crack in the combustion chamber can sometimes go a long time before it starts problems that you can see. But often those cracks open when things get hot and this causes the combustion pressure to go into the cooling system. That makes the coolant spew out and the temps go way up.

Let it cool, fill the system and all can seem to be well for a while. Sometimes weeks and hundreds or thousands of miles can go by before you get a repeat of the overheat and spitting coolant out.

Many GOOD auto parts stores (the ones who supply garages) sell what is called a block checker. You need one of these! Or take it to a shop that has one! They sell for about $35. It’s a glass tube with a bubble stone and a rubber ball that you fill with a magic liquid.

You then start the car, remove the radiator cap, place the rubber end of the tube over the hole and pump the rubber ball. This pulls air off the coolant up through the bubble stone and through the magic liquid. If exhaust gas is present in the coolant, the magic liquid will change colors.

These things WORK! But most folks are not aware they exist. I know NAPA has them.

Another thing to be aware of is that you should NEVER open the system until it is 100% COLD! Think about what they taught you in physics class. Water boils at 212 degrees at atmospheric pressure. Most cooling systems have a 12 to 16 pound pressure cap so the pressure in the system is much higher then atmospheric pressure and as such the coolant can go way higher in temperature before it starts to boil.

When you open the system, you release the pressure and as soon as you do that the coolant in the system goes to atmospheric pressure. If it is above the 212 mark, it will INSTANTLY start to violently boil.

This usually results in a volcano effect with some poor chap getting the crap burnt out of his hands as he tries desperately to put the cap back on so he isn’t showered with boiling coolant.
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Mother Nature is a Mean Evil Bitch!

[drscope]

I also forgot to mention that cracked head won't always show up on a pressure test. Many times they will hold pressure until the system comes up to high temps and the crack opens up. So just because you had it pressure tested and it held pressure, doesn't mean it isn't cracked.
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Mother Nature is a Mean Evil Bitch!

[VOLKSWAGNUT]

Sounds simply like a bad radiator cap to me..
If it wont hold the proper pressure, it will boil out when hot, and seem fine when cool.
It can also cause an undetectable leak.. ..

Step 1 for me.. test system for any leaks and replace the cap, Refill with a proper mixture antifreeze, (which is also anti boil) and water..
See what happens.
.
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[notchback]

[busdaddy]

[skills@eurocarsplus]

^^^^yep

I have also seen them have a green tint on the insulator.
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[iowegian]