If fhe overflow tank is overflowing, you may a have a problem besides the filler neck. The coolant should never expand to where it overfills the catch bottle. Try running the engine with the radiator cap off and the radiator filled about 1/2" below the radiator neck. Everything working properly, you should notice the coolant start to flow across the radiator as the t'stat opens. Open both vent valaves to alllow air out of the system. Close vent valves when coolant comes out without bubbling. Some big air bubbles may come out the radiator neck, and the coolant may overflow slghtly. The t'stat should atart to open at around 190 deg. Watch the temp gauge & don't let the coolant temp go over the boiling point. Shut engine down and let things cool till rediator level drops, repeat procedure several times. The problem with these cars is that the radiator sits lower than the top of the engine making it hard to get the air out.
If air bubbles are present the t'stat is not going to respond properly because it needs water to flow around it in order to sense the coolant temp. In this case when the t'stat finally opens the metal in the water jackets is going to be much hotter thsn normal, and when the coolant finally gets to touch it, it is going to turn into steam and blow the coolant out of the radiator.
A bad head gasket leaking from the combustion chamber into the water jacket will not show any contamination of the engine oil, but will blow combustion gases into the cooling system and cause violent overflow. I realize a bad gasket is the last thing you want to hear about, but a simple test for combustion gases in the coolant will let you know for sure.

 

I don't have a tool to check for gases in the radiator. When I start my car the coolant gets to the neck and will overflow before the thermostat opens. I can't run the car long with the rad cap off. However, the bleed screws were closed so I will try it again with the bleed screws open.


Here's what I have done:
1. My overflow was way too full. I syphoned out the overflow so not it sits between full cold and full hot.
2. When I replaced the water pump, I did fill it with coolant through the thermostat housing before I started the car with the new pump. As I understand it's not good to run these dry.
3. The overflow metal pipe had a crack in it and was leaking. I fixed it.
4. When I started the car with the cap on after I put the coolant level in the overflow where it's supposed to be, the coolant still leaked out from the cap. I have tried 3 caps.

*** IMPORTANT NOTE: When the car is running with the cap off, I see a stream of coolant going in the rad from the hose below the overflow hose.

I was thinking about double gasket on the cap, but I'm not sure if it's a good idea.
How can I tell if it's the head gasket? What tool do I need to check for gasses in the coolant?

 

Most part stores sell the kit, and most repair shops can do the testing, some may even do it for free in hope of making some money later on. Check this link out for more info: Head Gasket or Combustion Leak Test Procedure (Gasoline Engines Only)

 

I did an oil test and it doesn't show any coolant in my oil:











so if the head gasket is blown, then it's out of the combustion chamber.

 

On our cars pressurized oil does not flow through our head gaskets. If you have oil in your coolant it would be from your intake gasket. Oil in the coolant is a head gasket issue with over head cam cars.

If you want to check for a blown head gasket just borrow a coolant pressure tester from a chain parts store. Hook it up cold don't pump it up, start the motor and watch the needle. If it starts building pressure right away and the needle is jumping then you have a blown head gasket. If the head gasket is not blown you can get some movement from the water pump but it should not build pressure until 3-5 minutes.

This will not detect the early stages of a blown head gasket like the kit Pete linked but if you think the car is pushing coolant out because of a blow head gasket you are well past the early stages.

 

I'm going to do a proper bleed of the cooling system one last time tomorrow. Hopefully it's just airlocked. I asked a bunch of part stores today to see if I could rent a pressure tester but no one does up here in Canada. To buy one is $95.00 with tax, which is our price here in Canada for the exact kit at NAPA that Pete linked.

 

Well, I did the following procedure:


1. run car with rad cap off and both bleeder screws open
2. Put heat on high and full.


The coolant level in the rad was going up and down like someone was rocking the car. The car ran without coolant spilling over the neck until the thermostat kicked in. I closed both bleeder screws when coolant was streaming out.


I shut the car off and the coolant level went back down. The level in the overflow only went up a little as the engine got hotter. I dover the car around the block and no coolant was leaking from the cap! Everything stayed dry!


I'll let the car cool down for a few hours and add some coolant to the rad since it's down some and repeat the procedure. So far so good, looks like it was airlocked. Prior to changing the water pump and thermostat I had a feeling the thermostat was sticking. Could it of just been a bad thermostat and airlocked cooling system? I hope so!

 

theres a spot at the back of the heads that holds air sometimes. causes a hot spot the creates steam and makes the system overflow. usually comes out but sometimes you have to park the car on a hill with the front of the car up and do the bleed thing. i do mine while on the jack stands or ramps.

 

Thanks for the tip craby!


I bled the system again and wow this engine really is hard to bleed. I hopefully got all the air out but no leaks from the cap after driving the car and it's cooling as it's supposed to. I'm glad I can drive it again! I can't believe the amount of air that bled out of the cooling system. I heard these were hard to bleed but wow! Tomorrow I'll just open the bleeder valves and let any air out that might still be there.

 

Glad you fixed it. If there is air in the system the t'stat can't work properly.