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10/12/10 8:41am - Original Message: 'Is changing the heater core on a C4 really that bad?'
LT1*C4
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, - Canada

Vette(s):
1992 Corvette Black on Black ZF6 6-speed LT1 EM headers/Corsa exhaust

Joined: 3/22/2009
Posts: 34
YES IT IS!!!  

For month's now, I've known that my heater core's day's were numbered.  What started off as just an occasional smell of anti-freeze every now and again, over time, gradually turned into fogged up windshields every morning  and eventually, over the past month or two, ended up turning into "steam" pouring out of my dash vent every time the car came to a stop at an intersections/stop sign.

I'd been putting off replacing the heater core for the longest time due in no small part, to all the horror stories I'd read on this forum in regards to removing them. 

Last  week, while vacuuming my car, I discovered my passenger-side floor mat was completely soaked with anti-freeze. Needless to say,  I was NOT a happy camper and knew I couldn't put it off any longer.

Looking back, I guess it was probably a good thing I did the work now, since summer is quickly coming to an end and before you know it, the weather's gonna get colder. I hate working on my car in the cold and I NEED to have my heater working in the colder month's.  Better that I did the work now while it's still warm...

I didn't bother to look through a repair manual as in my experience, they usually only add to the confusion and make matters worse.  I don't know who writes those things, but more often then not, they usually make things appear to be much harder than they really are and generally only succeed in confusing the hell out of you. LOL



I started off loosening the 2 screws and two bolts holding the surge tank in place.  Then I carefully moved it over so I had access to the 2 heater hoses underneath leading to the heater core through the firewall.  



The hoses were caked on pretty bad so I had to slice them down the side about 3/4" with a box-cutter knife in order to pull them off.



Because there was still some antifreeze in the lines, I made sure I slid a tray underneath the car to catch any if it spilled.  With the two lines pulled out, I simply wedged them off to the side pointing upwards so no more coolant would spill out of them.


(Though the picture doesn't show it because I took it later on, the heater core ends stick out about 1" from the firewall)


Now that all the outside work was done, I made my way inside of the car.

I removed the 2 screws holding the hush panel into place, then gently disconnected the wire that runs to the small light that's attached to panel.  I squeezed my head into the foot well and peered into the dark void behind my dash.  This was definitely NOT going to be a walk in the park....

Aside from being darker than ape sh*t in there, it was cramped, hot and there was about a million wires all over the place making access to the heater core and housing screws all the more difficult.


***I suppose if I could give anyone looking to tackle this job just one piece of advice, it would be this***

DO YOURSELF A FAVOR AND REMOVE THE PASSENGER SEAT!!!

I didn't because I'm a moron and like making things difficult for myself.  By the time this little project was over, I had twisted and contorted myself into positions I never knew the human body was capable of.  


(Just to give  you an idea how cramped and uncomfortable it is in there with the seat still in place, go out and open your passenger side door and look inside.  Not very much space in that foot well is there?)

Now imagine having to stick your head way up in that foot well so that the top of your head is right up against the fire wall.  All those wires back there are going to be hanging just low enough to be resting on your FACE. Now picture your lower back/@ss  arched up and leaning off the very edge of the seat and your legs/feet sticking out the roof-line.  This is NOT a natural position for the human body to be in.  LOL

Do yourself a favor and learn from my mistake.  Take out the darn seat!!  It will make a world of difference.  


Once I'd finally positioned myself in there, 3 of the bottom screws were immediately visible and relatively accessible.  I used a 1/4" wrench and socket with a flexible extension to get at the screws.  I believe they were 9/32".   You also have to unhook a bunch of clips GM decided to use to hold a bunch of wiring to the plastic shell that covers the heater core.  They all have to come out before you can pull off the cover.

Next, I took out the glove box lid.  I was really hoping I'd have access to the top screws this way, as I didn't want to remove the entire dash like most others have had to do.

There are 6 screws holding the hinge/door in place.  Remove them and carefully pull away the door and set it aside.



Next you will find two philips screws holding the latch in place.  They also happen to hold the entire tray in place as well.

Remove them and pull out the tray.

Right away I saw that at least one of the top screws was visible and accessible using a wobble extension.  Good stuff.  4 screws down, one to go.

The 5th and final perimeter screw is way in the back on the right side just below the windshield.  I was totally blind on this one, but after finding it with my fingertips, I used a 1/4" wrench with an adjustable extension and amazingly enough, found the head of the screw the first time in.  So far, things were going pretty darn good...

Before the cover can be pulled out, there are 3 small plastic hose's that direct air to the various vents  behind the dash that need to be disconnected. They just pull right out and can be slid back into place later.

Unfortunately, as I found out later, not only are there the 5 perimeter bolts to remove, but there's a hard plastic hose screwed into the middle of the plastic cover with two screws holding it in place.  

You can see in the picture below the hole in the cover.  That's where the hose goes into.  Just above and below it, are two screws holding it in place.



The bottom one, I got from underneath.  The top one was a MAJOR pain in the butt and probably added about 1.5 hours to the job.

This one single screw was a real head ache, but eventually, I was able to get the little b@stard out!  :lol:
With that out of the way, I now had the joy of trying to pull out the cover through the foot well. A job easier said than done. All the wiring back there is in the way so I had to take my time and move the wiring around as I pulled out the cover .

With that done, I finally had access to the heater core.  You'll notice right away there a thin metal "strap" along the bottom of the core with a screw on one end of it.  This little arm/strap basically just holds the heater core in place.  Remove the screw and swing out the arm and pull out the core.

There will still be some anti-freeze inside, so if your floor isn't already soaked like mine was, you may want to put a plastic bag on the floor so your carpet wont get wet.




Looking at the old core, it was obvious it was leaking from the top corner...




I could also see that a few of the rows of "fins" were  bent/crushed for whatever reason.  It was probably put in that way 18 years ago from the factory so I guess I can't really complain since its lasted this long...


Before I installed the new one, I made sure the new core matched the old...







Then went about putting everything back together.

I noticed afterwords while trying to install the new core, that there was another little bracket at the top of  the inner housing which I'm assuming was there to hold the heater core into place just like the little arm/strap at the bottom.

As hard as I tried, I was not able to slide the new core back into place with this "hold-down" bracket in place.  I decided just to remove it.  With that out of the way.  The core went right in.  I tried to re-install the upper bracket but couldn't. I couldn't see it and couldn't even reach it if I did.

I ended up leaving it off since there's really no need for it.  The core is held in place by the bottom strap and the inlet/outlet pipes extending out of the firewall towards the engine also keep the core in place.  Then there's the plastic front cover which also helps keep the core in place as well.  Bottom line is, that upper bracket is totally over kill and NOT necessary.  Good riddance. 

Once the core was put back in, I started up the car and let it idle to reach normal operating temperature.  Turned on the heater and inspected the outside lines as well as the core itself, for any leaks.  

All was well.  Clap

Put the plastic cover back on (another major pain in the butt with all those wires in the way) re-attached the 3 plastic vent-hoses on the inside and once again started the car.  I cycled through each of the vent settings to make sure all the vents were working the way they were supposed to.

Again, all was well and each "mode" worked as it should.   I finally re-attached the glove box liner and installed the door again.




Note:

The top right screw just below the windshield (the one totally hidden away, unfortunately, I was not able to put back but there doesn't appear to be any sealing issues with the box as I did not feel any leaks from that area even with the heater on full blast.  The 4 remaining screws hold the two haves of the box together tight enough and there's a "ridge" between the two haves that basically locks them into place when the perimeter screws are tightened.  No air leaks, no problem.  Haven't given it a second thought since.

The whole job probably took me about 5-6 hours but I know I could have done it in less time had I removed the seat and been allowed to work a little more comfortably but hey, live and learn I guess.




My heater is now working again, no more anti-freeze smell, no more fogged up windshield, I can go back to enjoying the car again.

In a nut shell, yes, it's a time consuming project.  Patience is definitely a MUST and thin arms really go along way in helping you reach some of the screws but this project IS doable in a garage with some basic hand-tools in an afternoon.  Any reports of HAVING to remove the entire dash are not entirely true.  I didn't, and everything turned out alright!

Just remember, take your time, be patient and don't forget to remove the seat.
LT1*C42010-10-12 06:42:46
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10/12/10 6:13pm - Reply: 'Is changing the heater core on a C4 really that bad?'
eddie20890
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lanoka harbor, NJ - USA

Vette(s):
1990 L-98 white/ red/black leather interior targa top auto 1975 L48 blue/black leather interior t tops auto

Joined: 3/22/2009
Posts: 1363
thanks for the write up. i found an easier way to do this job.  I'LL LET YOU DO IT FOR MERolling On The Floor Laughing. hope you had a case of beer to help things along. there are somethings in a shop manual that are useful. know what you mean when you say they confuse you. glad you got it fixed.

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10/13/10 7:43am - Reply: 'Is changing the heater core on a C4 really that bad?'
ThinBlue
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Bowling Green, OH - USA

Vette(s):
1984 Light Bronze/Dark Bronze Z51 Coupe 2002 Magnetic red convertible

Joined: 10/3/2009
Posts: 30
Nice write-up.

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11/20/10 12:26pm - Reply: 'Is changing the heater core on a C4 really that bad?'
helphos
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Olney, MD - USA

Vette(s):
93 Polo Green Convertible with Bilstein Shocks, Autopower RollBar, Simpson 5 point harness, Grand Sport wheels, bald tires and dirty air filter!

Joined: 10/20/2010
Posts: 37
Are you familiar with the notorious and infamous "Blend Door?"  I'm wondering if what you did would give better access to that blend door motor so that it could  be replaced.  My heater core is OK for now (after all, it's only 18 years old) but if I had to go through t he steps you went through, I'd replace my broken motor and replace the heater core at the same time.  
If they can do arthroscopic surgery, why can't they do arthroscopic blend-door replacement, or heater core replacement???
Inquiring minds want to know!!


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11/24/10 10:54am - Reply: 'Is changing the heater core on a C4 really that bad?'
jrzvette
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woodland park, NJ - USA

Vette(s):
1993 black/black zf6 coupe

Joined: 12/5/2009
Posts: 9
Nice write-up.  I'm going to save this one just in case.
 
It's been said that when the C4s were in production the heater core came down the assembly line first, then the rest of the car was assembled around it.


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11/27/10 3:43pm - Reply: 'Is changing the heater core on a C4 really that bad?'
BATaylorEsq
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San Tan Valley, AZ - USA

Vette(s):
87 Red Coupe, not as pretty, had 213G miles, great running engine; got 20-21 around town, 27-28 on hwy; I got to drive a Vette, every day for 6 yrs. It was my first; so now I know what the fuss is all about. (Sold it 2015 for $3000, still ran great.)

Joined: 11/29/2009
Posts: 90
Great article and pics.  You are a hero to heaters!   However, I am not that  brave, nor mechanical, so if anyone knows of a repair man/shop in the Phoenix/Mesa/Tempe/East Valley area where I could get work done on my heater, I'd be interested in having someone fix mine.  
 
(The temperature slide on my dash unit won't move from the Cold side to the Warm side, it's just stuck.  I could use the AC in the summer, but can't use the heater now that it's cold in the AM, what Arizonans call "the winter." 45-50 degrees isn't much to whine about, but it would be nice....  BTW, I have an 87 coupe.)


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10/1/13 4:33pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
DeanC4
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San Pablo, CA - USA

Vette(s):
1993 coupe

Joined: 10/1/2013
Posts: 1
This is a great write up. However, I have a questions, before pulling the heater core, don't you have to drain the coolant system first?
 
Thanks,


|UPDATED|10/1/2013 2:33:11 PM (AZT)|/UPDATED|
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10/8/13 3:30pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
cco
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, - Canada

Vette(s):
1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191
I would guess that that might be adviseable; if not necessary. But you already knew that didn't you. Smile

I've heard of this job and it's no fun at all. I sure hope mine stays intact for as long as I have it.

C.

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12/15/13 9:58pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
Big J's 90 vette
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Joined: 12/15/2013
Posts: 1
what year was the vette u did the core on
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12/18/13 8:55pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
corvetteguru
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San Pedro, CA - USA

Vette(s):
1992 Polo Green Coupe 1987 Bright Red Coupe

Joined: 6/20/2013
Posts: 7
nice write up...

and it's a bitch on a good day... It took me 8 hrs to get it apart, I got the core in, then figured, "eh, I'll put it back together tomorrow (Sunday)." Yea... I got the flu and it took me another month before I got the time to put the rest of the dash back together. 



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12/25/13 10:34pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
BATaylorEsq
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San Tan Valley, AZ - USA

Vette(s):
87 Red Coupe, not as pretty, had 213G miles, great running engine; got 20-21 around town, 27-28 on hwy; I got to drive a Vette, every day for 6 yrs. It was my first; so now I know what the fuss is all about. (Sold it 2015 for $3000, still ran great.)

Joined: 11/29/2009
Posts: 90

Well, mine finally died and I had my mechanic replace the heater core.  Three years ago, (see above), I posted a wish that mine never would, but, even then, I couldn't slide my control from Cold to Hot, so I didn't have heat, anyway.  After they did the new heater core, half the dash out and all, for $575, it would have been another 3 hours to take out the rest of the dash to feed the tubes and wires from the used Heater/AC control unit I bought, so I had a new heater core that didn't leak, but still no heat.  Then I noticed the anti-freeze smell, again, but not as strong.  Back to the shop, where they found a leak in one of the conduits and were going to try to solder or weld it in place inside the firewall/dash.  However, since I haven't had heat for 3 winters, and winter is only 2 months long anyway, we skipped further surgery and went with a by-pass, so the system doesn't even go to my new heater core, but I have no leaks, the car's AC still works, the anti-freeze is stable and keeping the car at 185 degrees on the road and 200 at stop lights or heavy traffic. 

If someone buys the car, someday, I've got them a new H/AC control panel for the dash, a new heater core to un-by-pass and run it to, and a great running old Vette to drive around in.  For now, I'll drive it without heat (not so bad in Arizona) and enjoy the ride. 

BTW, Happy Holidays, Merry Christmas, Happy New Year, and thanks, as always, for all the help, sympathy, solutions, and good wishes shared on this forum all year long.

Bruce Taylor



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1/7/14 8:40pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
Crouchley
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Pasadena, MD - USA

Vette(s):
69 big block & 90 L98 6 speed

Joined: 1/7/2014
Posts: 12

Hi Folks!  I donít usually post but changing the heater core in my 90 was worth writing up.  I just completed my job and it took me 2 long days and I did take the seat out.  The fellow above did a nice write up but I could not do it quite like he did.  Not sure why, but I think he did a 92 whereas mine is a 90.  I just thought it was worth pointing out the difference in the two approaches.  After taking the seat out I looked up into the box area and I just could see no way at all to work anything in the area.  I am 54 now and I canít see that close either so I took a new approach.  I took off the upper trim first.  This is the piece that runs the whole width of the car on top of the dash.  Only 5 screws hold this piece in but to get to them you must remove the cover for the gear shift (4 screws) then the cover for the HVAC (3 screws) and you must also pop the cover for the defrost vent (0 screws).  Take all the vent covers off and you will have access to all the upper trim screws.  Once this upper trim is out of the way things brighten up a lot!  It allows removal of the brace (RH side) at your knees (4 bolts).  Then you can cut lose the RH brace that holds the whole dash on the right side.  It doesnít need to come out but gives you just enough maneuverability to get the job done.  I also had to unhook about 5 electric plugs and also remove the Bose Delco radio box(not the radio) (5 plugs).  With the glove box out this will give you pretty fair access to the Heater box.  Here is another problem :  That hole in the front of the box not only has a flange on it but the pipe sticks into the box about 3 inches.   Folks this was a show stopper except for the fact that pipe that sticks into the box simply slips onto the flange.  With some creative fingers you can push it off and get the box out.  Whew!  The only problem is that I could not figure a way to get it back in once the box is in place.  So I left it out as its purpose seems to be an ever so slight adjustment to the flow of air in that port.  I could not find any adverse affect at all.  In my case I was able to replace all box and core screws pretty easily.  It did seem worth the extra effort.  I ended up with an aluminum core replacement.  I was very concerned about this.  This core was even less area than the brass one so I was worried about the performance.  I did a lot of research and found nothing definitive-all antidotal evidence at best.  Bottom line I got 140 degree F on low fan (3) and 122 degree F on high speed (10)( 40 degrees outside).  So I am happy with the core performance.  Sorry I didnít get any data with the old core as it had a big hole in it.  The whole job did take 2 days but I donít think this is something you want to rush through.  There is too much to go wrong like forgetting screws, plugs, vacuum lines, hoses etc.  All with big consequences.

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1/7/14 10:02pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
cco
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, - Canada

Vette(s):
1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191
After reading about you guys slugging it out, I'll get a shop to do mine should it need a replacement. I'd love to tackle it just to say I did it, but my back won't stand up to that abuse any more.
Fingers crossed that mine stays intact.

Kudos to you guys who did it yourselves.

C.

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2/21/14 2:04pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
Smokey
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Wills Point, TX - USA

Vette(s):
1992 C4 Pure 100% stock

Joined: 2/20/2014
Posts: 6
I'm the poster above and am a good wrench. BUT at 64 years old now things just don't move like they did 20 years ago much less 5-10 years ago so To the shop it will go when and if it decides it wants out. Just a question here though. Who made these heaters core's? Was it Harrison? It seems like that not only Corvette had this heater core problem but Chevrolet had a bad run of heater cores in all their model line...

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2/22/14 8:32am - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
Crouchley
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Pasadena, MD - USA

Vette(s):
69 big block & 90 L98 6 speed

Joined: 1/7/2014
Posts: 12
All I can say is 24 years on a core isnt all that bad.  People say you should change the coolant regularly, but I never did in the 18 years that I owned the car.  And I am not convinced if I did change the coolant I would have got any more life out of it.  This could be a new topic of discussion.  I would like to hear some actual data from the "not broke dont fix it" vs. "change the coolant every year" folks.  Any data out there?
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11/3/14 10:58pm - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
vetster90
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Joined: 11/3/2014
Posts: 2
I have the same problem and do u wnat to come up and change mine.  lol.  Maybe I could call u to get a bit more information such as how long did it take ?.  Is this possible??  

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11/7/14 12:52am - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
vetster90
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Joined: 11/3/2014
Posts: 2
I notice in your pix that u replaced the stock radio.  How did u get around the issue of system error on the speedometer?  I might be easier if I could call u.  Could you send me your number and I can save you the long distance call.

B


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9/27/17 12:09am - Reply: 'Re: Is changing the heater core on a C4 really that bad?'
Merlin49
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Fresno, CA - USA

Vette(s):
1990 C4 coupe, Bright Red, L98, auto (stock)

Joined: 6/12/2017
Posts: 3
Hey Crouchley, I have the same model C4 as you do and I am just now in the middle of a heater core change. So far I am into it for over 3-workdays on the heater alone, but I've had many other items to attend to along the way. I am fully restoring a 1990 coupe and this is my first Corvette, so the learning curve seems straight up. I have studied every post on here and have learned a LOT about the differences in various C4 Vet models. I have also studied ALL the factory service manuals from 88 to 94 on the subject, and made friends with a couple of old GM dealer techs that worked on these things. The C4 models are certainly NOT all the same. The 84 - 89 models don't have the glove compartment in the way, and as such have a completely different (and simpler) dash system. The 1990 model is the first year of the new dash design with glove compartment, and I think GM assembled those any way they could, just to get them out of the production plant. On the 90-91s they did some really stupid design work in the heating/AC system, especially putting the temp-control door motor on the "top" of the heater case (where it is totally inaccessible). At the urging of the GM dealers the factory redesigned the system in the mid-year 1992 models and at least moved the temp-control-motor to the "bottom" of the case where it was accessible. The 92-96 models were again redesigned and somewhat easier to access for repair. But the 90 and 91 models are the worst you can get. I bought my 1990 cheap because it had a heater core leak. Not being a GM guy I thought "gee how hard could it be to change a heater core". That quickly proved to be a really stupid mistake. As of now, I have now completely removed all my seats, center console, instrument panel and control panels, ALL dash trim and most of the right side of the dash frame up to the fuse box. Because I suspected problems with my temp-control-motor, I also had to remove the entire heater housing to access the motor on the top of the case (there is absolutely no way to get to it in the car). But in order to fully remove the entire heater case I also had to fully remove all the AC case on the engine-side of the firewall too (the stupid screws for the heater case were underneath the AC evaporator case from the engine side of the firewall). So now, I am just starting to reassemble the entire system, BUT I am having absolute fits trying to find new parts that fit correctly. I have tried 4 new heater cores (from 3 different sources) that do not fit correctly. The water tubes are 1/4" to long to correctly line up with the holes in my firewall. I finally just hogged out the holes to get the clearance I needed. Then on the temp-control motor, I got curious about the Chinese replacement I bought. So I disassembled it to find that it was full of cheap plastic gears and plastic shafts and a cheaper motor. I compared it to my original OEM motor that had brass bushings, metal shafts and mostly metal gears, and decided to re-lube it and reinstall my original. My gears and bearings were in like-new condition. It also tested perfect anyway. I sent the Chinese junk back for a refund. My next big problem is that I can't find a correctly made AC evaporator core. I have ordered 3 of those now from 3 different sources and they ALL come with the pressure switch sensor port welded in the wrong position. My original sensor was toward the engine. The 1990 evap. core I first bought had the port pointing down so the switch hits the AC evap. case. The 1989 core. I just received had the port pointing away from the engine toward the coolant expansion tank, (and the picture in their catalog showed it toward the engine, but that's not what they delivered). At least I can install this with only a slight extension of the connecting wires. So overall I have been delayed about 4 weeks in just trying to find the correct parts to get my system reassembled. By the time I finally get my Corvette heater/AC system all back in operating shape, I will have over 6-weeks of time wasted and mountains of frustrating disappointments. . . . SO as to the question of "Is changing the heater core on a C4 really that bad", my answer is simply WORSE. Much worse on a 1990. . . .

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Corvette (Vette) Model Years on this site: 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 30