car overheats

[Wizard]

A bad thermostat only causes 2 things:

Overheat due to lack of flow (stuck closed or opens late)
Over cooling due to stuck open thermostat.

The water level going up and down when you rev it is a great indicator of a working water pump.

Air bubbles can only get from the headgasket. And other place where coolant would leak would be an external coolant leak. Not bubbles in the coolant.

Rad. cap is a possibility, BUT you said that you had the cap off and then started seeing bubbles. Kinda obvious in my book. A bad rad cap will cause the high overflow/low rad neck situation. Try that first, but I would expect a "blown" headgasket.

I call the other hg failure a "leaking" headgasket. That is where coolant is sucked into the cylinders and then burned. Hence, white smoke and miss. It also slips by the rings into the oil pan.

Wiz

[MATCHBX]

Originally Posted by Wizard

Air bubbles can only get from the headgasket. And other place where coolant would leak would be an external coolant leak. Not bubbles in the coolant.

Wiz

This is not the only way air is introduced into the system. Granted he has a new waterpump on it, but if the seal goes out in the waterpump it will introduce all kinds of air into it with very minimal external leakage. The only leakage seen when the seal is bad (or the shaft of the pump is grooved) is after it's shutdown. And then it sometimes is only a tiny bit that doesn't make it all the way to the ground.

And it's not recommended to rev the engine with the cap off. The radiator cap is a two-way valve for that purpose. The system will push coolant past it at a set pressure. But when the thermostat opens, it draws coolant back into the system via the little poppet in the center. You can let it idle with the cap off, but use the techniques that Shane and those were talking about with the funnel to keep the level always above the engine so it is never starved for coolant.

I agree with Jet, eliminate the easy stuff first. Take out the thermostat and run it to see if it does the same thing. It could be that the thermostat sticks a little and then opens up, thus creating erratic readings. But it would probably be pushing the excess coolant out into the overflow. It could be just enough that it doesn't overflow out of the bottle before it gets sucked back in.