OK WELL I HAVE MY D16Z6 JUST GOT DONE REBUILDING THE WHOLE ENGINE RAN IT FOR ABOUT HALF A MONTH AND STARTED NOTICING THAT THE UPPER COOLANT HOSE GETS BIGGER THAN NORMAL ALL BULGE OUT. IT THOSE THIS AFTER I DRIVE ABOUT 20 MILES OR SO ON THE FREEWAY!! THERMOSTAT WAS REPLACED WHEN THE ENGINE WAS DONE AND NOW I REPLACED THE UPPER HOSE TOO AND IT STILL DOES THE SAME THING. I WOULD TAKE THE RADIATOR CAP OFF REALLY SLOW AND ALOT OF STEAM COMES OUT LIKE IF IT HAVE A HUGE AIR POCKET OR SOMETHING. I NEED SOME HELP TRYING TO FIGURE THIS OUT. IF ANYONE HAS AN IDEA I WOULD LIKE TO HEAR IT THANKS!!

 

overheat issues?
does the bottom hose get hot?

 

It sounds like a blockage in the system, possibly in the radiator as the upper should be your return hose. That should come with overheating problems

 

Have you flushed your radiator and added new coolent?

 

the highest temp it gets to is about 200 which its normal range...and yeah the bottom one is hot and gets really hard.

 

naa the radiator gets got also the lower hose i know theres flow through the system

 

yup already flushed out system.

 

also when the engine is running and the radiator cao is off little bubbles come out...it'll stop for a bit then keeps bubbling!!

 

ok my radiator cap is rated 0.9 it came with my new aluminum radiator..the old one had a 1.1 cap and never had a problem....you think if i switch caps it will make a diff!

 

Could be air in the system....does the car ever surge at all (i.e. idle)? Take the cap off and run the motor until you don't see any bubbles then put the cap back on.

 

just used a spill-free funnel and run the system for about 20 mins to get all the car out.

 

naa for sure theres no air in it! and just got back form the zone and bought me a new cap..ima drive it tomoro and ill see what happens!

 

ok i founded out what it was..it was the head gasket.exhaust gases were escaping into the coolant passage ways creating lots of pressure in the coolant system!!

 

on my old z6, the coolant bypass hose let go cruising with the the radio up, no temp guage= cooked motor, put a hose on it, and drove it for a week with a blown headgasket, after my 20 minute drive to work, all of my tiny hoses were ready to blow off, the upper and lower hoses were pretty ballooned, and it was going through about a gallon of water for a day....

it was really kind of funny... **** was beat when i got it, and it just killed it lol

 

i was about to say if there are bubbles in the radiator, its a head gasket issue, after you bleed the system and **** if its still there def a head gasket.