ok, here's the deal.
I will try to cover everything I did to keep questions to a minimal. Had a clutch go on my 86 the other day, body was hit by hail storm last year. Car looked like hell, so I didnt want to replace clutch in that car.
I swapped motor ( S4 Street Ported N/A ) from my 86 to my 88, which has a pretty clean body except for some sun fade on the hood. Everything was ok when motor was in 86, but when i swapped into 88, I was boiling coolant. I am using motor, hoses, radiator, cap, water pump(which was not disturbed from front cover) and a few things which dont involve coolant from 86. Heater core i did not change, that didnt work in the 86. So I am using heater core from 88.
Now the baffling part here is it all worked fine before, none of which got ruined during swap. I filled some 50/50 mix in the fill neck, then I started car and let warm up a bit till t-stat opened, and bled the system as should be done. With overflow at full line. Ran the car no more than 4000rmp for 20minutes, pulled into driveway, opened hood, and I'm boiling over from the overflow. You can here the boiling everywhere, but the gauge (stock) did not go above half way. I'm not overheating, according to the gauge, but im boiling all my fluid, and the buzzer starts.
I let her cool down then I filled and bled and filled then tried again this time with the heater running. Same thing, steady 3500-4000 in third gear for 20-25 minutes. This time overflow was at low line and i pulled over every 6 minutes to look under hood, each time i looked the overflow tank was about 2 inches higher. Heater running whole time here, and working good. After 20-25 minutes im back in driveway and im boiling over again, and buzzer starts.

T-stat was replaced, system was flushed, and compressed air blown into one heatercore hose, came out good from other hose morning of said day. Rad and water pump worked fine in other car, engine was out Thursay and in Saturday.

I'm stuck here. I think I covered everything. Please help

 

ah ****..I has some Posting on this awhile ago..I'm just lazy( I just got in from doing my Coilovers)..look into One of my Posts....What I am wondering is When you filled the Rad,IF you had the Heater On,Full BLAST..this would allow coolant to Circulate through the Heater core when the thermostat opens up..it sounds like air..Another thing is Wehn teh car is Running,with the cap off,do you get Air Bubbles in the Coolant?..DO a Compression check.also do a pressure test on your Cooling system IF you can..that will Show you IF your Cooling system is Faulty(by that I mean a bad seal)...oh how is your rad cap?..and is the thermostat NEW,and is it OEM?

 

the heater was not on for the first run. before, during , or after fillup.
No bubbles.
As stated in first post all worked fine in other car, cap is good, t-stat is oem and coolant seals are good ( for now) im sure if keep boiling over they wont be good for long, so im not intending on running till i get some informative advice.

Engine has only about 40,000 since rebuild and porting ( done by Atkins )

 

someone must have some intput on this

I also did entire emissions removal last night, capping and blocking all off, following Kevins write up.
The only hoses left are the heaterhoses, upper and lower rad hoses, which check out to be ok.
I am still boiling coolant.

 

Did you use the right caps in the right places? did you put the belts on right with the correct tension?

 

Try bypassing the heater real quick just to rule it out. It won't take long and from what you say is the only thing different so thats the problem then. Bypass see if it works then report back and we'll take another crack at it.

 

just got in
already did the heater bypass and that didnt help,
and just for the hell of it put in a new water pump, that didnt help
I only have 2 belts both going to alt. dbl. pulley, so u cant mess them up they are same size. NO AC, PS, or Air Pump
The problem was there before i did emission removal, (which by the way is a X write up by Kevin)
I just did it to eliminate possibilities, was going to do it anyway, just not for a fews weeks.
Im convinced it must be a blockage internal, that coincidently happened during the 2 days engine was out of car.]

Or the DEVIL!

 

did u ever compression check the cooling system to see if its leakin? when mine did this i kept bleeding the system over and over and it would get a little better each time, sometimes those air bubbles are great hiders,