Advanced heat problem!

abrasumente

abrasumente

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Whats up guys, I just purchased a 97 m8 with 109k on the clock, in fairly decent shape (interior is immaculate, clear coat is rough) a couple weeks ago. I’ve been searching for one of these that isn’t beat to death for a while and lucked out.

Here’s the issue I can’t figure out- I have VERY minimal heat. I pulled the dash out to replace the blend door actuator- it was NOT cracked or damaged in any way but I replaced it regardless. Putting the EATC in either auto or manual changes nothing. I can see the gray arm moving when commanded to different temperatures. I can feel the air getting slightly warmer (by maybe 5 degrees, if that) when I set it on 90 but it simply doesn’t crank out the heat like I would expect, period. All other functions of the climate system work properly. I even removed the metal shaft from the gray arm and pulled it down like in the “emergency fix” I’ve seen described and gotten nothing.

Both heater core hoses are hot. I have followed the proper bleeding procedure via the coolant crossover cap. What else can I check? I do my own wrenching and have no qualms tearing into anything, especially when it comes to not freezing to death this winter!

Thanks for any help!!!
 
Gee. This is a tough one. What I would do at this point, and though both heater hoses are hot, maybe only a minimal amount is getting through the heater core, which could still cause a hot hose. I'd try a major coolant and heater flush, just blow the shit out of it and see what happens.
 
I’ll do that as my next move.

What about the actual blend door(s) in the airbox themselves? The one attached to the gray arm I know is still operational (I’ve manually moved it myself and it thuds at both ends), but isn’t there another one attached to that little sleeve that the actuator’s shaft fits into? If the coolant flush doesn’t work I’m going to pull the dash completely out and tear into the plenum, but that doesn’t really sound like a fun job...
 
Yes, there is another door attached to the upper sleeve. Accessing that I believe will require pulling out the dash.
 
I’m assuming one door controls outside air and the other splits between the evap coil and the heater core. Hmm. My service manual can’t get here fast enough lol

I ran the EATC diagnostic and got back only code 155. From the limited info I’ve found online about EATC codes this is related to blower motor operation (no issues).

I will drain the coolant and refill this weekend, and report back.
 
Update:

I guess I didn’t burp the system properly! I drained and flushed the system this morning (didn’t see anything funky come out), changed the thermostat and o ring with Motorcraft parts, and have been working the air out all day. I parked the car uphill so the crossover tube was the highest part of the system and following proper air bleeding procedure. Heat is warmer than its ever been (about 110 by the infrared thermometer exiting the center vent) which is way better than it was. My diagnostic tool reports ECT cycling between 200-210 degrees.
 
Well, my heat problem is back. I'm still seeing idle temps at 212ish and coolant level hasn't dropped any but I have no heat again. Blend door still works. Guess I'm yanking the dash this weekend and tearing into the plenum... It's too damn cold to not have heat.

Anything I should do while I have the dash out??
 
Are you getting any heat at all, like a little warm, but just not hot? If so, don't just flush the system, but maybe go to a pro center for a full back flush with cleaning solvent. Maybe the heater core is just plugged up a little where a simple flush fixed it for a bit, but not enough to not plug up again.
 
It's 33 outside and the temp gun says the back of the vent is 47 degrees, so it's barely getting anything. Temp gun also says that the heater core hoses are within 5 degrees of each other and they're around 180. At the coolant temp sensor the crossover pipe sits at roughly 212 at idle. I don't have any symptoms of head gasket problems, the car doesn't overheat- although it does drop down to around 190* while driving. I don't have any vacuum leaks that I can tell, my vacuum tester showed a steady 19" at idle. Maybe one of the vacuum cans in the dash are bad, that's about the only thing I can think of.

This is a real head scratcher. I'm a pretty experienced shade tree mechanic, all the cars I've owned have been GM products except for a little ranger I had (most reliable vehicle I've ever owned, might I add), so I'm new to the mod motor but this crossover system isn't that complicated. I'm hoping I'm just missing something obvious.

I will add I did a pressure test on the cooling system, my crossover cap was leaking so I replaced it with a stainless cap I found from a dude on eBay. No more leaks. My overflow and cap are also brand new Motorcraft parts (the old overflow leaked).
 
What about a bad water pump? Like I said it isn't overheating but the radiator hoses are easily squeezed by hand when the car is running- they should be hard from pressure, right?
 
If water pump I can't imagine it wouldn't overheat, though compressibilty of hose is odd. Yes, your issue is a real head-scratcher. I'm at a loss. Post to the LvC facebook page, its more active than this forum. You may get better feedback.
 
I had a clogged heater core years ago that had similar symptoms, a real pain in the rear. I "flushed" it with the hose on real low pressure and got some gunk out but it was only once i let that heater core have it did the garbage really start flowing. I got heat then a year later had to replace the heater core as it was corroded. As these cars sit and have relatively few miles on them the heater cores corroded and gum up/leak.

Beast of luck
 
whtwhale said:
I had a clogged heater core years ago that had similar symptoms, a real pain in the rear. I "flushed" it with the hose on real low pressure and got some gunk out but it was only once i let that heater core have it did the garbage really start flowing. I got heat then a year later had to replace the heater core as it was corroded. As these cars sit and have relatively few miles on them the heater cores corroded and gum up/leak.

Beast of luck
Click to expand...


You may be right. I would think that with both hoses being within 5-10 degrees of each other that would indicate flow BUT I guess it all depends on how the heater core is positioned in the plenum box. I also own a 93 Cadillac sixty special (a DeVille with rear fender skirts basically) and the way the heater core is set up in that car, the driver side will get cold air but the passenger side will get warm air if it's plugged. This is because the ducting for the driver side of the plenum gets air from the bottom, and the passenger from the top- so it can totally be clogged at the bottom of the core but still put out heat. I remember I had to flush it several times with cleaning vinegar to get it to heat properly.

I've had a couple things suggested- apparently drilling a hole in the stat aids greatly in purging air from the system, so I'm gonna try that next. If that doesn't work, I'm gonna yank the dash, inspect the heater doors, and if theyre working like they should I'm gonna pull the core.

I'll keep you guys posted. Appreciate the tips.
 
whtwhale said:
I had a clogged heater core years ago that had similar symptoms, a real pain in the rear. I "flushed" it with the hose on real low pressure and got some gunk out but it was only once i let that heater core have it did the garbage really start flowing. I got heat then a year later had to replace the heater core as it was corroded. As these cars sit and have relatively few miles on them the heater cores corroded and gum up/leak.

Beast of luck
Click to expand...
Can you tell me exactly how to "flush" the heater core? Are there detailed instructions somewhere?
 
MobyDick said:
Can you tell me exactly how to "flush" the heater core? Are there detailed instructions somewhere?
Click to expand...

Disconnect the heater core hoses. You can then use a regular hose with one of those adjustable nozzles on them and spray in one end of the heater core , and let it flow out the other. Alternate between both hoses. I wouldn't recommend using any type of chemical flush beyond cleaning vinegar- and make damn sure if you do use vinegar you flush it ALL out because it will eat the aluminum.

I ended up fixing the door. Turns out the upper temperature door slot was stripped out enough where the shaft of the actuator couldn't turn the upper door- I made the actuator a two part job by cutting the shaft off flush with the actuator arm, running a VERY small piece of threaded rod through the middle of the whole thing, and putting lock nuts on both ends, and liquid epoxying the shaft end. I had some epoxy putty laying around, so I stuffed a small piece inside the upper temp door slot and shoved the shaft into that. Let it cure 24 hours and now the whole thing works as it should- I have 140 degree air consistently now

If the new actuator ever breaks, all I have to do is take the lock nuts off the back side of the actuator assembly, cut the shaft off the new actuator, slide the new actuator over the threaded rod, and put the new lock nuts on.
 
Ok thanks. I'm pretty sure my BDA is ok since the air moves from the dash vents to the lower vents just fine, so I will try the flush.
 
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