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ttiiggy
Premium Member
join:2001-03-27
Bozeman, MT

ttiiggy

Premium Member

Check for plugged heater core. How?

Working on a ~1995 GMC Yukon. I get very little heat from the heater.
Do I need to pull the heater hoses loose and see if water will flow through?

I has been freezy cold here and I don't have a garage to work in.
Spraying water around wasn't high on the list of desires.

I did put in a new thermostat because the temperature guage was low. Fixed that.

There was a leak around the actuator valve, so that got replaced.
I didn't think about it at the time to verify that the vacuum controller line actually cycles the actuator.

I do get good airflow from the dash vents.
I haven't checked the fan for actual air flow through the heater.
I expect the fan is before the heater.

I haven't checked to see how hard it could be to tear the dash apart if I had to replace the core.

cowspotter
join:2000-09-11
Ashburn, VA

cowspotter

Member

Try warming the engine up to operating temp and feel the hoses that feed into the heater core. If one is cold and the other is hot then the core is plugged. If both are hot then you have a blend door problem.
HarryH3
Premium Member
join:2005-02-21

1 edit

HarryH3 to ttiiggy

Premium Member

to ttiiggy
The blend door is very likely the problem. They're moved by small electric motors that use plastic drive gears. When the gears strip, the door stops moving. The good news is that you can buy aftermarket motors for about $35 at O'Reilly Auto Parts instead of paying the GM dealer $100+.
dipweed23
join:2009-07-21
Ypsilanti, MI

dipweed23 to ttiiggy

Member

to ttiiggy
»www.rockauto.com/catalog ··· pe=10721

That part is likely the problem if the heater hoses are hot when the engine is hot. Cheap part, probably one hell of a fix!

If the heater hoses are cold, trace them back towards the engine. Your vehicle likley contains a heater bypass valve to shut off the flow of coolant to the heater core when the A/C is running. Look for a box or odd shaped valve looking device on one of the heater hoses, and any loose vacuum lines or electrical connectors going to that device. If you have the device and all hoses and connections are fine, replace that device. If the hoses go straight to the water pump and intake manifold, you don't have the bypass installed, and you are looking at a blocked heater core or coolant passage.

ttiiggy
Premium Member
join:2001-03-27
Bozeman, MT

ttiiggy

Premium Member

Checked heater hoses. One hose cold, the other barely warmer.
Took the hoses off of the new actuator valve. (Hmmm...? ---> Later)
Water flowed easily from a garden hose through one hose and out the other hose. Water flowed fine the other direction.
= Heater core not plugged.

{Later} Flow was not actually verified through the actuator valve. I did check the function of the actuator valve when it was installed ~a month ago. Vacuum line makes the actuator valve function. I know that I put the hoses back on the same as they were, but I guess they could be wrong. Maybe a plugged hose before the actuator valve? Is there a check valve in here anywhere?

Is it possible the water pump is somehow not correct?
The engine doesn't overheat.
Water pump Broke? Not pumping enough? Spin impeller on shaft?
Wrong water pump? May not have the passage open to the heater?
I didn't look at where the heater hose takes off, YET.
dipweed23
join:2009-07-21
Ypsilanti, MI

1 recommendation

dipweed23

Member

Is the valve installed the right way around? Some will allow flow in one direction and not the other (My jeep was like that). You could always bypass the valve by splicing the heater hoses (about $1 part) for a short drive. If it heats up, the valve is bad or on the wrong way. Verify it's opening when heat is turned on.

Hope it all works out for ya.

TheHarvester
Premium Member
join:2006-08-25
Dana Point, CA

TheHarvester to ttiiggy

Premium Member

to ttiiggy
If your truck has the quick connect fitting on the intake manifold for the heater hose, I have seen those plug up. I would not unscrew it from the manifold without the proper tools and knowledge at hand. Most of the pot metal fittings will break when you try to remove them. I have done something like this in the past.
»www.angelfire.com/mech/p ··· ose.html

I now use this tool and is much faster and easier.
»www.schucks.com/ProductD ··· ode=2093

rob_in_chatt
Premium Member
join:2004-09-17
Chattanooga, TN

rob_in_chatt to ttiiggy

Premium Member

to ttiiggy
the mid 90's GM vehicles had awful problems with that dexcool shit breaking down and turning to mud. i recall seeing hundreds like this in the garage i used to work at with the same problem.

the dexcool was marked do not service till 100000 or 150000 miles, and by 80k miles, it was nothing but mud and rust in the entire cooling system.

start the vehicle, and when it is up to operating temperature, reach under the hood and feel both hoses going through the firewall. one should be really hot and the other a little cooler. if they are cool and the upper radiator hose is hot, you have a blockage and will probably need to have the system professionally flushed out.
jastinne
join:2010-02-05

jastinne to ttiiggy

Member

to ttiiggy
If your heater isn't working properly it is best to look at the passenger-side floorboard for signs of anti-freeze leakage. Since anti-freeze plays a crucial part in the function of the heater core. A leaking heater core may also cause a greasy film on the inside of the windows. It may be due to rust or blockage in the heater hoses. Well, to replace the latter, this link might be useful - heater hose.

Anyway, if it isn't getting enough heat, the problem might be specifically due to a faulty thermostat.
18172841 (banned)
join:2001-10-06
Lagrangeville, NY

18172841 (banned)

Member

said by jastinne:

If your heater isn't working properly it is best to look at the passenger-side floorboard for signs of anti-freeze leakage. Since anti-freeze plays a crucial part in the function of the heater core. A leaking heater core may also cause a greasy film on the inside of the windows. It may be due to rust or blockage in the heater hoses. Well, to replace the latter, this link might be useful - heater hose.

Anyway, if it isn't getting enough heat, the problem might be specifically due to a faulty thermostat.
If it has leaked to the point of no heat, you won't be driving far...

The heat again, is before the thermo. OP said temp is right now, so it's not that. Should be blend door or so, or plugged core (op said it's not)...

Hoses also do not rust from the inside, would have a leak before a rust plug I sure would hope.

Donno why a 1month old topic would be bumped either :S

ErRoR0
Premium Member
join:2002-10-26
Tullahoma, TN

1 edit

ErRoR0 to ttiiggy

Premium Member

to ttiiggy
Turn it on full heat and reach under the dash and tap on the heater box. I've had many stuck actuators move that way...will tell you if it's going bad or not. Now if the gears are broke, then this won't work, but it's worth a shot.

Eric

Edit:
Does your GMC have cables for the temp control? I don't see an actuator for that model?
jastinne
join:2010-02-05

jastinne to ttiiggy

Member

to ttiiggy
What I am implying is that the rust could have clogged inside the hoses. I didn't say that the hose itself had rust from the inside. am sorry to bump in this 1 month over thread. but I believe it would be more useful than to to create new threads with the same topics over and over again. That will just be plain redundancy.:(

ErRoR0
Premium Member
join:2002-10-26
Tullahoma, TN

1 edit

ErRoR0

Premium Member

said by jastinne:

What I am implying is that the rust could have clogged inside the hoses. I didn't say that the hose itself had rust from the inside. am sorry to bump in this 1 month over thread. but I believe it would be more useful than to to create new threads with the same topics over and over again. That will just be plain redundancy.:(
Does your GMC have cables for the temp control? Would help to know this information. Slide it from hot to cold rather quick and see if you can hear the blend door open and close.

Eric

Steve
I know your IP address

join:2001-03-10
Tustin, CA

Steve to 18172841

to 18172841
said by 18172841:

Donno why a 1month old topic would be bumped either :S
It's not a bump, it's a helpful reply.
18172841 (banned)
join:2001-10-06
Lagrangeville, NY

18172841 (banned) to jastinne

Member

to jastinne
Always nice to try to help however, nothing in the cooling system rusts so, pretty much you can not get rust in the cooling system so long as anti-freeze is being used.

Sludge, oil, etc yes (for a number of reasons) but pretty much rust wont happen unless straight water is run and even then, the pump is likely to fail before you get rust to the point of clogging anything to do with the heater.

PSWired
join:2006-03-26
Annapolis, MD

PSWired to ttiiggy

Member

to ttiiggy
1995 Yukons do not use Dexcool- that was introduced in 1996. I would suspect the quick disconnect fitting at the intake manifold. It will certainly break when you try to remove it. You will need to extract the pieces using a hacksaw and a small screwdriver, an easy-out, etc.