Okay I swaped in a b16 in my eg, Now the overflow tank on the rad is boiling. I replaced the termostat, There are no leaks, and the car doesn't over heat.
Whats going on?

 

get a new radiator cap..

 

Already replaced. Problem still occurs

 

Could the head-gasket be leaking? there seems to be no external leaks at all.
It only does this if I drive on the freeway or get on the gas.

 

headgasket, mine did the same thing when the gasket blew. the gasket is allowing air into the coolant which is pushing coolant outta the rad into the reservoir and outta it too.

 

don't tell me that 30k mile engine is giving you problems, a friend of mine bought one of those so called 30k mile(12 yr old) engines and was overheating came to a conclusion that the water pump blades where completely gone. so what I would do is take out the pump and checked it my friend. btw the guy swore that all engines come with 30k or so. what crock of $hit. to me it's more like 130k miles but some peeps still believe that, they even tell that a 1985 civic engine has 30k when you look at it its covered with oil that you can see the engine number. this is before they degrese them and make them look shiny with armoall.

 

Well I guess I know know why this motor didnt cut it in japan. damn but the oil and spark plugs look fine. Also the temp gauge stays normal. Fan turns on too.

When I come to a stop light. The rpms stay above 1 then about 5sec it goes back down. Sound like headgasket to you guys?

 

the up and down idle is either tps, iacv or a vacuum leak

 

It does'nt go up and down. It just stayes up for like 5sec then goes back to normal.
This happens everytime im out of gear.

 

Mine was doing the same thing, pushing coolant into the overflow tank. I replaced the stock radiator with a fluidyne. Car doesn't overheat anymore, but I don't have any heat in stop and go traffic. When I start driving at a constant speed the temp drops and heat comes back. It also retains pressure in the system after 12hrs of sitting.

 

you prob need a larger radiator, that stock is probably old too

 

Im going to get everything checked this Thursday. I have'nt been driving it for like a 2 weeks.

It was not getting hot at all. Didn't want to damage anything so I just parked it.
lets see what happens.

 

Hey sounds like you should just sell your car