I have been having trouble with my coolant running out. When I drive the car after I fill up the coolant, as soon as I turn off the car half the coolant will get forced out the over flow hose on the radiator and on to the ground. I took off the radiator cap with the car running and coolant is moving all around so I think my water pump is good. I replace my thermostat also. Still the same problem the coolant just gets force out of the overflow hose and I bet it does it a little also when I am driving it. Let me know what you guys think. Oh by the way its a 72 240z.

Thanks Frankenstein Z

First off, have you tried a new radiator cap? It might be building up too much pressure and forcing the coolant out. Make sure it is a 12-14lb cap, if it is higher that may be your problem right there.

Second thing that comes to mind is a leaking head gasket that is causing the pressure to build up.

What to do first? Try a new cap, if that fails have the radiator pressure tested, if it loses pressure, you possibly have a leaking headgasket (barring any other leaks, but they wouldn't cause the coolant to be forced out). You could also do a cylinder leakdown test to find out for sure if the headgasket is leaking. If you find a cylinder that is losing pressure, turn the engine over until it is starting up on the compression stroke(both valve closed) and then pressurize the cylinder, if the gasket is leaking you will see bubbles in the radiator. While you are at it, you can also check your valve seat to see if they are leaking, if you have to pull the head for a gasket, it's a good time for a valve job while it's off.

There is a third possibility, but hopefully it won't be a cracked head... If the engine has been overheated, it is a possibility.:disappoin

Okay I will try the cap, but it looks like the original. Then I will go from there.

Thanks Frankenstein Z

I looked at the radiator cap and it says 14. So how do I do a cyclinder leakdown test, and what do I need to do it?

Cap pressure sounds OK, but you did say it looks original so I am assuming it has not been changed in a while?

I'd get a new one just to be sure the old one isn't the problem. They will go bad over time so for 10 bucks (more or less)a new one isn't a bad idea....

You should be able to get a shop to do the radiator pressure check and leakdown test for a small charge if you don't have the tools to do it. You can usually pick up the tools needed at most any good auto parts store, however, buying tools to diagnose one problem and then never having a use for them is a waste of money.

The tools for the leakdown test are usually fairly reasonably priced, but you will need and air compressor or a large air tank to do it and the radiator tester is fairly high priced.

By any chance have you noticed steam coming out of your exhaust after the car has warmed up? If it is a bad head gasket, coolant will leak into the cylinder and end up as steam out the tail pipe. And vice versa pressure will build up in the radiator from the cylinder causing your coolant pressure to get too high and leaking out the overflow.

Old rad. caps will get weak - not holding 12-14 psi. That will

cause the cap to allow it to "overflow" early. Try the new cap 1st.

That should be changed every 3-4 years antway.

- Jeff

Are radiator caps generic and anyone will work? Napa, hires, etc.

12-14 lbs

Most brands will work fine.

- Jeff

Had no problem finding the cap 13 #. Will give it a try as soon as my dash is back in this week.

Frankenstein Z