question about questioning a mechanic

[darkred87T]

Hi,
A coworker has a 96 Chevy Blazer and his mechanic told him it needs a heater core. I offered to change it for him to save him some cash but I don't want dive into a project like that until I'm sure that's the problem. Is there a sure fire way of determining if it's clogged? I thought they leaked when they were bad. Iv'e never heard of one clogging.
Thanks,
Mike

 

[mhogan6]

Take the outlet heater hose off and see if it's flowing. Or take both off and use a garden hose to see if it's clogged. But first check coolant level, could be low due to leak at passenger side rear hose fitting on intake manifold.
What's the coolant look like, old and dirty?
HTH

 

[darkred87T]

Thanks for the quick response

I haven't looked at it yet. He claims the heat is not hot enough.
My Regal had the same problem and it turns out the door in the heater box wasn't opening the whole way. A thermostat stuck open can cause this symptom too right?

I guess the only way to tell is to pull the line off and run water throught it. Kind of a grey area though. I guess it could still flow but might be still clogged enough to cause poor heat.

 

[chopped39]

If it has eletric control .Open glove box and look at top of box . The blend door motor is on top of heater box. Move temp from hot to cold and see if motor moves,if it does not move or it looks like it is jumping replace it.you do have to pull dash but not box.It is a little tight but you can get it out with 1/4 drive ratchet with 5.5 mm socket I have the dash out of one right now that someone replaced core in and the controller is bad.Have you ever done one of these heater cores?There is some short cuts that will save you a bunch of time. You do not have to pull hood and fender like service book says. Before you do anything pull both hoses off and take garden hose and flush both ways.Make sure you have no coolant leaks. look at front corners of intake and look at rear of intake also.I have had alot of these trucks come in and it sounds like water rushing under dash.I flush system and flush core by itself . then airlift system and so far i have done 10 of them with out replacing core. i have replaced alot of the controllers on the eletronic dashes. good luck

 

[darkred87T]

Thanks. I figured I'd try to find a Haynes book for it. What a pain with the electric motor. I wonder why they couldn't just keep them vacume. If book says to pull fender and hood then I guess the heater core isn't inside under the dash? Also, how do you arilift the system?
Thanks in advance.

 

[2QUIK6]

The heater core in my '95 TA clogs up about every 2 years, so it can clog up depending on the design of it.
I just take the input and output hoses off the heater core at the fire wall... Take a garden hose that already had the end cut off and hose clamp it to the input, turn on the water faucet and blast it out, then reverse the connection connecting it to the output and blast it again and it all works fine then for another 2 years or so.

 

[jcj53115]

Thanks. I figured I'd try to find a Haynes book for it. What a pain with the electric motor. I wonder why they couldn't just keep them vacume. If book says to pull fender and hood then I guess the heater core isn't inside under the dash? Also, how do you arilift the system?
Thanks in advance.

The core is inside the car, you gotta remove the dash to get to it. Book time for laabor is 5.9 hrs to R&R heater core. Ive replaced many that were plugged but also saved alot of my customers alot of money by just flushing out the existing one while still in the car. This is fairly dangerous for the mechanic butto flush it i disconnect both heater hosesand pour a small amount of meratic acid into the core heavily dilluted with water. let it sit about 5 minutes flush with water and repeat till clean. just be sure not to get anything on you or the paint!!!! This works 7/10 times for me and I do this at least 4-5 a month in the winter

 

[Dave Levey]

My own over the counter diagnosis would be a leaking intake gasket that let air into the cooling system causing the dex cool to turn to mud. You should be able to flush and back flush the heater core to get it flowing again.

 

[darkred87T]

Thanks. He said his mechanic flushed it once already and the heat is cold again.

Funny thing, he had it over here today for me to take a closer look at it. He asked me if I could remove the runners that were rotted aong the bottom of the doors. They are attached to the body mounts underneath. Apparently I tore the nut loose up inside the front left front body mount and the bolt just spins and won't tighten now. I really have my hands full now. The guy at the local auto parts store told me I'll need to cut a hole in the floor to get at it. I don't think this backyard mechanic stuff is worth it. Just a freind form work I was trying to help out and now I'm in knee deep.

 

[mhogan6]

I don't think this backyard mechanic stuff is worth it. Just a freind form work I was trying to help out and now I'm in knee deep.

No good deed goes unpunished.

 

[darkred87T]

Take the outlet heater hose off and see if it's flowing. Or take both off and use a garden hose to see if it's clogged. But first check coolant level, could be low due to leak at passenger side rear hose fitting on intake manifold.
What's the coolant look like, old and dirty?
HTH

I looked in the overlflow tank today and noticed it was a little low and the fluid looked dark brown (dirty). He said he recently had the radiator and thermostat replaced. Maybe it's leaking somewhere. Could a leak contaminate the fluid and clog the heater core?

 

[darkred87T]

. You do not have to pull hood and fender like service book says. Before you do anything pull both hoses off and take garden hose and flush both ways.Make sure you have no coolant leaks. look at front corners of intake and look at rear of intake also.I have had alot of these trucks come in and it sounds like water rushing under dash.I flush system and flush core by itself . then airlift system and so far i have done 10 of them with out replacing core. i have replaced alot of the controllers on the eletronic dashes. good luck

Looks like I gotta pull the fender off. The box is in two sperate peices. The top peice won't separate from the bottom unless the whole box comes out. the haynes manula that I just spent $20 on shows a completely different set up. Oh well, I have to decide if I want to go further with this or pack it in and put it back together.

 

[darkred87T]

Actually there is a section in the shop manual for 1998 and newer models and the only difference is with the later models you have to remove the HVAC and unfortunaltely I don't have time to get into that. I got it back together and working though. Thanks for the help,
Mike

 

[chopped39]

My bad . I thought you were working on a 99. the 96 is a lot easier to due then the 99 you dont have to mess with anything under the hood except hoses. As for the nut that broke loose in floor. get a hole saw .I think its about 1 1/2 just pull nut out of hole. Put back together with nut and bolt. I have broken my share of them when doing fuel pumps:biggrin: .

 

[darkred87T]

That's alright/ 1998-2004 is when they changed. I don't know why they would do that but who knows it probably saved them money somehow.

I cut a small hole in the floor and put a new nut on it. Good as new.

I flushed the core out with water and the heat is hot again so maybe it's not a total loss. I feel kinda bad though I might have been able to tackle it if I had another day. Problem is, I don't. Thanks again