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Thread: overheating issue and steam pipe using factory rad in 94 gmc z71 6.0/4l80e swap

  1. #1
    Join Date
    Jan 2017

    Question overheating issue and steam pipe using factory rad in 94 gmc z71 6.0/4l80e swap

    Im having overheating problems with my newly swapped truck. 1994 gmc 4x4 sierra z71 with 2004 gmc 2x4 2500hd 6.0/4l80e. I used the factory rad and connected the steam hose off the tb too the expansion/overflow bottle about 6 inches away from where it comes in the top of tank fitting(not the vent). Is that not a good place to put it? I'm thinking it might need to be basically under the top fluid level so that when it burps air the air goes up and escapes, and when it cools down it sucks water into the heads. It may be sucking air into the heads the way i have it now causing an air bubble to form everytime it cools down. And in regards to the horizontal seam at the middle of expansion tank, can someone please tell me when theirs is in relation to the top of the rad? I can see a problem occuring if i had it too high or low.

  2. #2
    Join Date
    Sep 2011
    There's a extra port on my radiator just below the filler cap.. that's where I ran my steam port hose... Have you driven your truck much?? I like to fill the engine with coolAnt thru the upper radiator hose.. after that attach the hose to the radiator and finish filling the system... Then warm engine.. after that I remove the radiator cap and park on a angle or use a floor jack to raise the pass side.. I'll let it sit overnight this way.. Easiest way I have found to purge air

  3. #3
    Join Date
    Mar 2016
    BC Canada
    I also hooked my steam line to the extra port below my filler cap. And plugged the coolant ports that are on the throttle body.
    1995 rcsb c1500, 4/6 drop, 5.3 L33, 5spd, 219/228 112LSA cam, LS6 springs, 799 heads, long tubes, magnaflow mufflers

  4. #4
    Join Date
    Feb 2017
    Haven't yet finished my ls to 95 obs swap (work in progress). I was bound and determined to use the donor truck (01 Silverado) radiator and expansion tank so that it work as designed for the 01. Well after a week or two fighting it and trying every expansion tank I could find in salvage yards I gave up. I reused my 95 radiator, and after some research found a web site (jags that run) that makes an upper radiator hose adapter with provisions for a bleed valve and steam vent hook up. I have only been running truck in garage so far but seems to work very well at burping the system, only had to relocate upper hose so that it runs across the radiator shroud at a point lower than the filler neck of the 95 radiator. Opened the bleed valve and pour in coolant and voila, no air bubbles in system. Here is a link to the adapter I installed:


    It costs $33 including shipping, they also have same set up with a built in sight glass for I think $58. Hopes this helps you out!
    Last edited by westofb; 03-27-2017 at 06:41 PM.

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