needin' some heat!

Hello all, I know the "no heat" threads are tired and old but I am really hoping to avoid the heater core replacement project. If y'all would be willing to look this over and give me your thoughts I'd be most grateful. I just want to make sure there isn't something left to try before I go tearing into a core replacement. Thank you!

STUFF I'VE TRIED
-flushed/backflushed 3 times now. I switch between backflush and flush for about 20 minutes. Mostly backflushing, just alternating every now and then. For the last flush I filled with a 50% CLR solution, soaked for awhile then backflushed/flushed again.

-performed bleed procedure as outlined in [You must be registered and logged in to see this link.].

-pulled junk drawer/ashtray and glovebox, verified that actuator controlling the flap inside the box is responding to control module. It has about a 90° range of motion. I also removed the actuator and turned the knob manually, I can feel the flap hitting its stop at both ends so I don't think it is stripped. With heat set to 90° and manually activating the flap, my heat is still just barely warm.

-cleaned reservoir tank/replaced inline flow restrictor

-battery disconnected, waited 10 minutes and reconnected.


SYMPTOMS/CHARACTERISTICS
-Set on 90° my heat is just barely warm with motor fully warmed up.

-both core hoses get hot, inlet being just a hair hotter than outlet. Upper radiator hose gets hot, motor seems to run at normal operating temperature. Don't know what thermostat is installed.

-when flushing/backflushing, water runs freely and runs clear.

-with control module set to 90°, AC cycles on at 15 second intervals for 10 seconds. (not sure this is related, just seems weird)

Is a thermostat in place and working?What is the actual water temp?
Jim

The a/c compressor is supposed to cycle, so you have hot dry air...not hot humid air.

Just for fun, push the Vent button to shut the compressor off and see if that gives you more heat.

Too bad the battery trick didn't fix ya! Good luck!

-Mike

Like someone asked Mike did you check the in and out hoses to see if there is water at least circulating thru the heatercore?
Jim

Flasheroo wrote:

Is a thermostat in place and working?What is the actual water temp?
Jim

Previous owner states there is a thermostat of some kind in place. I can't say what the actual temp is- although I do have a baking thermometer I could stick in the reservoir tank. It sure seems like the motor is coming up to normal temp.

81X11 wrote:

The a/c compressor is supposed to cycle, so you have hot dry air...not hot humid air.
Just for fun, push the Vent button to shut the compressor off and see if that gives you more heat.
Too bad the battery trick didn't fix ya! Good luck!
-Mike

THANK YOU for letting me know about the AC cycling on/off. Wasn't sure if that was normal or not. Switching to vent doesn't seem to make much difference.

Flasheroo wrote:

Like someone asked Mike did you check the in and out hoses to see if there is water at least circulating thru the heatercore?
Jim

Not sure how to check that- the hoses are not full of crud, and both core hoses get hot. Coolant comes out of the core when I unplug it for flushing. When flushing with the garden hose, water flows nice and free through the core.

NEW DEVELOPMENT:
So before when I would test the heat after flushing, I would just leave it on 90° and let it idle up to temperature. As stated, it just blew barely warm air.

I have now discovered that if I let the motor get up to temperature and THEN turn the heat on, I get nice hot air- for about 20 seconds. It gradually goes from hot to barely warm over those 20 seconds. I can turn the heat off and let the motor continue to run for a few minutes, and when I turn the heat on- once again I get ~20 seconds worth of heat before it gradually goes back to lukewarm. Seems like I can repeat this ad infinitum.

Maybe coolant is only flowing through a small portion of the core???

Wow thats different and I have not messed with LT-1 cooling systems.Maybe something in the climate control that is recirculating the air rapidly.I am sure one of the cold weather guys has way more expierience with this.
Jim

More data: I stopped on the way home from work and borrowed(begged) a laser thermometer. Fully warmed up, readings were about 175° on both the input and output hose. 160° on the upper radiator hose. Then I turned on the heat to 90° fan on full and the output dropped to about 135° in 15-20 seconds.

Please help me make sure I understand this system- are the following statements correct?

1. there is no heater control valve on LT1 vehicles. Coolant flows through the core at all times. Heat on/off is controlled by a diverter flap inside the box.
2. There is only one flap/diverter that controls heat versus cold- the one controlled by a little electric actuator about the size of a pack of smokes located behind and just to the right of the ashtray/junkdrawer. There are no other flaps/diverters to investigate.

nowhereman wrote:

More data: I stopped on the way home from work and borrowed(begged) a laser thermometer. Fully warmed up, readings were about 175° on both the input and output hose. 160° on the upper radiator hose. Then I turned on the heat to 90° fan on full and the output dropped to about 135° in 15-20 seconds.

Please help me make sure I understand this system- are the following statements correct?

1. there is no heater control valve on LT1 vehicles. Coolant flows through the core at all times. Heat on/off is controlled by a diverter flap inside the box.
2. There is only one flap/diverter that controls heat versus cold- the one controlled by a little electric actuator about the size of a pack of smokes located behind and just to the right of the ashtray/junkdrawer. There are no other flaps/diverters to investigate.

It sounds right to me.

Sounds like the issue you are having is a plugged core. I had the same issues with all 3 of my LT1 wagons I've owned. By letting the car warm up first, then turning on the heat, the small amount of heat built up in the core from the little bit of coolant going through the core gives you nice warm heat for a few seconds then back to cold again. You will have to flush the core again..... and again..... and again..... and again..... My last winter car was the worst, I flushed the whole system 8-10 times, and the heat would still go away with-in 15 miles of driving. Last ditch was installing 2 brass Y strainers (filter), one in the inlet side heater hose, and one in the upper radiator hose (in let to the rad.) to filter out the scale and junk in the cooling system. I got half way home (about 10 miles) and the temp gauge was spiking, pulled into a gas station and pulled the strainer out of the Y stainer and emptied out a good 1/2 cup of scale/stuff that had been floating around the cooling system for who knows how long. This happened 4 or 5 times before I got enough stuff out of the system so it wouldn't clog up the heater core. I finally got the heat to work good by the end of February. It was a cold winter last year too. Long story short.... Flush the system, for a long time, multiple times, remove the knock sensors from the engine block and then run more water through it. I also ran some stuff called "Boiler Buster" through it for a few minutes too, that helped a lot, but don't smell it.... fair warning.

Mike

Air in the system - Make sure its bleed correctly

200OZ wrote:

nowhereman wrote:

More data: I stopped on the way home from work and borrowed(begged) a laser thermometer. Fully warmed up, readings were about 175° on both the input and output hose. 160° on the upper radiator hose. Then I turned on the heat to 90° fan on full and the output dropped to about 135° in 15-20 seconds.

Please help me make sure I understand this system- are the following statements correct?

1. there is no heater control valve on LT1 vehicles. Coolant flows through the core at all times. Heat on/off is controlled by a diverter flap inside the box.
2. There is only one flap/diverter that controls heat versus cold- the one controlled by a little electric actuator about the size of a pack of smokes located behind and just to the right of the ashtray/junkdrawer. There are no other flaps/diverters to investigate.

It sounds right to me.

Sounds like the issue you are having is a plugged core. I had the same issues with all 3 of my LT1 wagons I've owned. By letting the car warm up first, then turning on the heat, the small amount of heat built up in the core from the little bit of coolant going through the core gives you nice warm heat for a few seconds then back to cold again. You will have to flush the core again..... and again..... and again..... and again..... My last winter car was the worst, I flushed the whole system 8-10 times, and the heat would still go away with-in 15 miles of driving. Last ditch was installing 2 brass Y strainers (filter), one in the inlet side heater hose, and one in the upper radiator hose (in let to the rad.) to filter out the scale and junk in the cooling system. I got half way home (about 10 miles) and the temp gauge was spiking, pulled into a gas station and pulled the strainer out of the Y stainer and emptied out a good 1/2 cup of scale/stuff that had been floating around the cooling system for who knows how long. This happened 4 or 5 times before I got enough stuff out of the system so it wouldn't clog up the heater core. I finally got the heat to work good by the end of February. It was a cold winter last year too. Long story short.... Flush the system, for a long time, multiple times, remove the knock sensors from the engine block and then run more water through it. I also ran some stuff called "Boiler Buster" through it for a few minutes too, that helped a lot, but don't smell it.... fair warning.

Mike

Thanks Mike. I appreciate the verification. I don't own any printed documentation other than the Haynes manual so that helps a lot.

Sounds like you have been where I'm at. I really have verified everything else, I think I probably do have the same situation as what you describe. I will flush the entire system next since I have flushed the core several times now. Maybe there's enough crud floating around to re-clog my core as soon as I flush it. What's the procedure for a system flush? Just drain/fill/run/drain/fill/run? I've never heard of Boiler Buster, maybe I'll flush with water and then use some Prestone radiator cleaner or something.

1phastsswagon wrote:

Air in the system - Make sure its bleed correctly

Well, it seems to be bled. I performed [You must be registered and logged in to see this link.] several times.

Sounds to me as if the coolent flow is correct. I would verify the location of the heat control door. This is an electronic temperature control system with the primary input being the interior temp sensor (located under the dash in front of the glove box) and the sunload sensor (under the defrost dust vent on top of dashboard). If either is fubarred, it may be telling the control head that the interior is up to temp and closing the door on you. At max temp, the heater door should be at full deflection.

If it still turns out to be a plugged core, remove both hoses at the engine and blow out any coolent with air. WIth both hoses above the heater core, fill system with straight CLR, or if you feel lucky, drain cleaner. Allow whatever you use the time to work (CLR-overnight, drain cleaner no more than 15 minutes). Flush out completely in both directions. Also a good idea to do the knock sensor thing and flush out the block.

Bill

Thanks for your reply, Bill. What you are saying makes a lot of sense but I think the door is in the proper location - I had previously removed the actuator that controls that door and held the door towards the heat manually. With the car fully warmed up and manually holding the door all the way to the heat side, the "heat" was still poor.

I also tried the CLR trick in the core, although I didn't have the balls to use it full strength or overnight. I used a 50% solution and soaked for about 10-15 minutes. Too scared of causing a leak and being forced to do a emergency core swap.

When flushing the block, where do you input? The knock sensor hole? Please, tell me what hole to put my hose in!

Well, I backflushed the core again this evening- this time I drained the
radiator and flushed it out from the upper hose. Coolant didn't look
dirty. I backflushed for about 30 minutes, then I filled the core with some
50% CLR solution I had left over from last time and let it soak for about 30 minutes. Then backflushed again for 10 minutes or
so to clear out the CLR, then bled the system.

I think I am making progress- before when I turned the heat on full, it would
be hot for 5 seconds or so, but would peter out almost completely in 20
seconds. Now it doesn't peter out quite so much. I'd say before it
would lose 90% of its heat in 20 seconds, now it loses maybe 30% of its
heat, and it takes longer to peter out. Who-hoo! I guess the 4th time is the charm. I think I'll drive it
a bit and then do this again. Might avoid that core replacement after
all.

Thanks everyone- I am cautiously optimistic about being on the right track... It's 65° here right now so I'll wait and see what tomorrow morning feels like.

With all the time and water you have used you could have already replaced the heater core.
Hope this does the trick for ya!
Jim

Boiler Buster is made for cleaning cast iron boilers in a home up to a large facility. I poured it in the heater core and let it sit for about 5 min., then flushed the core and some small dark chunks, and lots and lots of small white particles cam out. I used a small drain pipe camera to take a look in the core and it was quite a bit cleaner than when I started. If I remember Boiler Buster was mostly muriatic acid.

The knock sensors are located on both sides of the bottom of the engine block just behind the engine mounts in what used to be called block drains. They are kind of a pain to remove, but I got lots of crud out of those two holes for a long time when putting water in the upper radiator hose with a garden hose. I use an old t-stat with the guts cut out of it when flushing the cooling system.

Well, the fun didn't last long. The heat lasted only a few days. Time to flush yet again. If it weren't for my kick-ass Buick seat heaters I'd be chilly.

Mike, I'm curious about this "Y-strainer" you used as a filter - can you elaborate a bit on what it is, where to get it?

I'm also wondering if replacement cores are cursed with the same small passages? You guys who have replaced the core - do you still have to flush every season?

Doug:

The issue about the cores is that we are addressing the symptoms and not the cause. If you flush the block correctly, than all the core problems disappear. You really have to do the knock sensor thing after filling the block with something like the Boiler Buster stuff or strong acid base cleaner. The CLR is nothing more than concentrated acidic acid (vinagar). Not strong enough to melt aluminum but vinagar none the less.

Acid base cleaners will not attack cast iron so it should be safe for your block. You have to clean out the block first, than the heater core problem goes away. The only way your going to get rid of the acid wash from the block is to drain and flush through the knock sensors.

Hope this helps.

Bill

so if I remove both knock sensors, do I fill and flush using those holes or from somewhere else?

Alot of crud / setitment settles at the bottom of these blocks, when removing the sensors, you get a chance to remove alot of junk that build up in them, remove the sensors, and flush out the block using your standard procedures, once you get constant clean water, reinstall the sensors, or while they are out replace them with new units.

Well I have now drained the radiator and reservoir tank, filled with some Prestone flush and am driving the recommended 3-6 hours to hopefully clean the system. Planning on a full drain and water flush when this stage is over.

At this time I would like to state that the plastic draincocks on these radiators SUCK. Opening it requires enough force to risk breaking the plastic, and when I do get it open, it trickles out very slowly. Is it only supposed to turn about 45°?

I might have stressed the draincock out since now it leaks a little when it is closed. From now on I'm draining the radiator using the lower hose.

A Y strainer is basically a filter that removes particles from liquid or stem. I used them to keep all the crap from getting into the heater core. It worked ok, I also used a blow off valve (ball valve) on the strainer for cleaning it out quickly. This set up worked ok, but removing the knock sensors is a must. I removed my sensors in the car I put the strainers on and noting came out at first, I had to poke a screw driver in the hole then came the chunks. I still had a lot of stuff floating around the cooling system, that's why I put the strainers on.

[You must be registered and logged in to see this image.]

Here's a link that talks about strainers in more detail if any one cares.
[You must be registered and logged in to see this link.]

Thanks, now I understand how your heater core filter works. I may resort to that, we'll see.

I have a question about the knock sensors - I read somewhere that it was important when reinstalling the sensors to torque them to a specific range- too loose and it wouldn't sense, too tight would cause problems too...anyone know what ft/lb to tighten to?

Just a thought . . .

Someone on the ISSF driving a Roadmaster had a problem with his heat which sounds something like what you're describing. It turned out to be a bad output from the controller. It was opening the cold air inlet flap and the wintery air overpowered the warm air from his heater core. I don't remember the resolution.

Thanks Nick. I thought about that at one point, makes sense.

However, I can now say for sure the actuator is turning the flap both ways lock to lock. I was able to see it when I removed the cover to replace the heater core this afternoon ;-). I have flushed and flushed and flushed (entire system), coolant was crystal clear and still my heat only lasted a day or two. So, we'll see what happens now. Thanks to everyone for your help.

I saw you said "some sort of t-stat". I had a no heat issue last year. Come to find out my car only had a 160F t-sta where the stock is a 192F one. I replaced the stat with a 192 and I had heat again. Something to look into at least.

Just did mine as well - Replaced the T Stat with a 192, adding new 50/50 mix, and now the heat kicks you out of it