Big GMC truck
Registered Member
What could cause coolant to leak inside the cab? How difficult to fix?
CK5
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coolant inside cab
- Thread starter Big GMC truck
- Start date
y5mgisi
1 ton status
Leaky heater core... not to bad.
Good article on the home page under tech
koldsimer said:
replaced it in my truck in 1 hr.... in my '86 z-28 took 8 hrs... had to take EVERYTHING out including the fricken dash!!!! and I mean.. UNBOLT THE BOLTS THAT HOLD THE DASH METAL TO THE FIREWALL!!!
our 1996 GMC Jimmy 4 door was in need of a heater core.... $850 for a shop to do it
traded dat sum bish in
2005 TrailBlazer EXT now....I dont know why they make newer vehicles so hard to get to.... I love my '78.. nice and easy
Yep. Heater core is leaking. 
I have a new one to go into my '90 Sub right now. It was leaking so bad that coolant was dripping out from under the front passenger door. 
The good news is that the part costs $23 at Autozone. 
The bad news is that you need to be a contortionist to swap it. 
I have a new one to go into my '90 Sub right now. It was leaking so bad that coolant was dripping out from under the front passenger door. The good news is that the part costs $23 at Autozone. The bad news is that you need to be a contortionist to swap it. 
Leper
1/2 ton status
If you don't need the heat, get a coupler from AZ to put the 2 size hoses together.
88Silverado
1/2 ton status
On mine it was easier to remove the inner fender well to get to the two lower nuts that are below the blower assy in the engine compartment. I think I had more problems removing the core from the inner duct but its not bad. Just be careful that you dont break any of the vacuum hoses that attach to it. The tech article is real good. If your vehicle has a ECM located above the inner duct, check your connections when your done. I somehow knocked one of my plugs loose and after three months it worked its way out and the socket. It would figure it was the one that powered the fuel pump and only took 3 weeks to find it
Big GMC truck
Registered Member
Do you think old, worn heater hoses could cause coolant to leak inside the truck?
Maybe, if it was leaking right at the firewall. But as others have posted, I'm 99% sure it's the core. And there's no two ways about it, that job sucks.
snoman87
Registered Member
Big GMC truck said:
It's possible ... I mangled the pipe on the small end of the heater core when I swapped motors. The hose wouldn't seal properly and it started to leak into the cab which made the appearance of being a heater core. If you think it might be hoses, replace them. Probably want to do that anyway when you do the heater core.
broc944
1/2 ton status
My vote is the heater core, have fun replacing it, I would say it is one of the most miserable repairs that you can do. While you are at it clean the blower wheel, mine was really packed with crap and made a major difference in the amount of air that was moved, plus the fact the heater core was really plugged also.
snoman87
Registered Member
I have also been told that putting a blower from a 92' extended cab will move more are ... don't know the truth to that or not.
BTW: I had to pull the inner fender down to get at the lower bolts because of the diesel sound sheilding that I had.
BTW: I had to pull the inner fender down to get at the lower bolts because of the diesel sound sheilding that I had.
tx_sub
1/2 ton status
I had coolant smell in my cab and the hose clamps were just loose. Try that before tearing into the dash, at least for a few days to see if the smell will dissapate.
Big GMC truck
Registered Member
Thanks for the info. I think it's the hoses becauses a week earlier I had tightened them at the firewall and the leak went away for a while. By the way, it only leaks about 2 tablespoons a day. If it were the core, wouldn't it leak a lot more?
k20
3/4 ton status
I just got done changing my heater core, still waiting on the carpet padding to dry 
. Off and on total work was ~3hrs. Probably an hour was spent trying to figure out how to get the actual heater box apart to get the core out. Gm likes to hide screws under weather stripping.
It apparently started as a small leak cause I had been having problems with my windshield fogging, and just chalked it up to our screwy weather. Then one bright & sunny day it fogged up, reaked of coolant, steam out the vents, and a puddle in the passenger floor. Watching coolant drip out of the box sitting at redlights.
. Off and on total work was ~3hrs. Probably an hour was spent trying to figure out how to get the actual heater box apart to get the core out. Gm likes to hide screws under weather stripping. It apparently started as a small leak cause I had been having problems with my windshield fogging, and just chalked it up to our screwy weather. Then one bright & sunny day it fogged up, reaked of coolant, steam out the vents, and a puddle in the passenger floor. Watching coolant drip out of the box sitting at redlights.
It all depends. I've seen them only drip a little as you are describing and I've seen them puddle up the passenger area in a few minutes after the engine warmed up. It's basically just like the radiator. It can start as a small leak and grow from there, or it can fail big-time all of the sudden. I've seen one rupture where the inlet/outlet pipes meet the core and it emptied half the cooling system in a few minutes.
