Replaced heater core in a 2018

[DimensionTheory]

Not sure if this is the right section. Also going to be kinda long, sorry guys.

Just had to put a heater core in my 2018 ES 5sp with 61k miles. I lived in FL until 2021, so never needed heat.

Winter of 2021/22 in South Dakota, the car was warm (just warm). I assumed just had poor insulation and a small engine. I never have passengers. I also hadn't lived in a cold place in about a decade so my memory of cabin temp was fuzzy.

Winter of 2022/23 it was much worse, glass was refreezing with my breath unless I'd been driving like 30min, passenger side was very hard to get/keep defrosted. It was also a polar vortex and I was working nights, so I assumed the car just couldn't handle the cold..bought a block heater but thought it strange it didn't seem to do much for the inside.

Towards the end of that winter, the passenger side wouldn't defrost and I realized something wasn't right. I started feeling around and noticed the passenger side felt only barely warmer than outside air. If it was 20 outside, the vents felt about 40.

Sort of confirmed it by reazling the car got way, way, warmer on recirc. Obviously not a solution. Didn't temp probe it. Car was also 1 month beyond warranty when I realized it, so hard numbers didn't matter. All signs pointed to the core, core was getting yanked.

That was an absolute nightmare to install working with an untreated fractured right hand! That being said, I got it done and the car felt immediately warmer on the passenger side.

**Also, DO NOT reuse the coolant drain bolt gasket if possible.

I had it off twice, the initial drain to do the core, and, then a second drain of distilled water.. I was driving 10 miles home (highway speeds) from where I did the work, and began smelling coolant about 2 miles from home, there's no real place to stop so I just cranked the heater and didn't stop. No lights came on the dash, Torque showed coolant temp climb from 195 to 201 and sort of slowly go between the two..

When I got home I Noticed the carpet where the core tubes come through was damp and assumed I buggered something up and started looking for leaks on the lines and core.. then I popped the hood and noticed the entire insulation along the firewall was soaked, as well as the lower crossmember area. I have to wait for someone to give me a ride tomorrow, but I couldn't see any other place it could have came from. Guessing it sorta made a squirt jet out of it.. Block was near empty and the radiator cap was ice cold. Hope that little bit of abuse didn't do anything bad. It wasn't leaking for the 30 minutes it idled with the cap on before I left, so it must've needed some RPMs to get it to start spraying.

Don't know if anyone else has had a 2018 with a core issue yet, but here's one. And sorry I umm don't have the old core, long story.😅

[foama]

There are plenty of heater core stories and how-to's in this forum. Use the search function and you shall see.

My replaced heater core was clogged with lime scale. A very tiny amount was enough for all that trouble. Other heater cores were plugged with silicate from the wrong or from mixed-brands coolant. Make very sure you only have one brand of coolant in the car, and that is absolutely the correct sort in the correct strength, otherwise the problem may likely come again.

[Eggman]

Heater core problems are a pain.

My Mirage would never really warm up in winter. Even with a grill block and block heater, the engine temps would get up to around ~155℉. My commute was only about 10, 15 minutes max, so I would try whatever easy trick to get it to warm up sooner in cold weather. At some point I was looking into an engine blanket to insulate the little aluminum block.

Moved this thread from General Discussion to Technical Discussion. It's looking like heater core problems could use a sub-forum of its own haha.

[foama]

Just for the record, a proper working thermostat is very important for proper fuel economy and cabin heating. Thermostats can remain open and can also remain partly open. With a partly open thermostat, warm-up takes much longer and it may not warm up at all. Cabin heat will not be enough.
Replacement is cheap and easy and can be done without needing to remove anything else if you are experienced, although the space is tight.

[Top_Fuel]

...the passenger side wouldn't defrost
...noticed the passenger side felt only barely warmer than outside air.

I'm going to put this out there for anyone in the future who may read this thread...

The easy way to test your heat output is to direct all air out of the instrument panel vents. If your heater core has no internal restrictions, the air temperature coming from each vent should be the same (within a few degrees). If your passenger side is significantly cooler than the driver's side, that is the #1 symptom of an internally restricted Mirage heater core. Go to THIS post and read the PDF file attached. It explains the problem with pictures. If you have low heat output and/or the heat is uneven from side to side, this may be your issue.

There are some potential solutions for cleaning out the heater core (instead of replacing it). The few bad heater cores (in North America) that have been cut apart have been caused by some sort of goo that collects on the passenger side of the core (reducing coolant flow on that side...which causes the passenger side of the car to have low/no heat output). So if you have these symptoms, it's worth trying to clean the heater core out to restore the coolant flow (and heat).

If you decide to replace your heater core, the entire dash has to come out. This is probably an entire day/weekend job for the average Joe. A much better solution is to install a replacement heater core with removable inlet/outlet tubes. This can be done without removing the dash from the car. Here's a pic of this type of heater core...



You aren't going to find a heater core like this at AutoZone or Rockauto. If you're in North America, you may have to get this from an overseas supplier. HERE is one suggestion.

[DimensionTheory]

I'm sorry if my original post wasn't completely clear but I did just finish up replacing the core yesterday.

I used the Thermotec core to avoid removing the dash, as I live in an apartment and can't do that level of work at my storage unit... It took me a few days. Those clips to hold the tubes on are beyond frustrating. I had to "install" the tubes off the car at different angles with my eyes closed for an hour or so to get the muscle memory down.

I don't know if I was unlucky but my tubes did not fit well. There was some plastic pieces that protrude under, and on the firewall side of the heater box that wouldn't allow the tubes to sit flush.

With the temps rapidly dropping and snow being an issue, I couldn't go coreless so I made a last ditch decision and cut the tubes in half on the long runs and slid them into 5/8th heater hose to get about 1/2" of space around of of the obstacles and the other tube was able to flex a little right there and go in. I absolutely do not like having fail points or doing backyard fixes on good cars but I simply ran out of time and patience. Also to add, even with the tubes cut, you cannot clear the steering rack. Rack joint keeps the core a couple degrees off from being able to go straight in.

I had broke my hand working on a friends car a few weeks prior, so trying to do all of that under the dash with my dominant pinky/ring finger dangling also didn't help 😅😅😅

I know heater core issues have plagued mirages. I hadn't seen or heard of anyone with a 17+ having the issue yet, and I thought i read there was some assumptions they may have corrected the problem. Id never touched my cooling system other than to add maybe a couple ounces of distilled water in FL. I planned to save the core and cut it open, but I was so tired I tossed it during clean up. Tried to recover it a few hours later dumpster had already been emptied (at 9pm apparently)

Also, I am using red Prestone Heavy Duty Command NF. It meets all the same specs as Asian blue. I had 4 or 5 gallons I got free laying around. Might cause issues, but its an OAT, silicate/nitrite/borate free, has phosphorus, and is compatible with all males/models/coolant.

[Top_Fuel]

...I used the Thermotec core
...tubes did not fit well
...some plastic pieces...wouldn't allow the tubes to sit flush
...made a last ditch decision and cut the tubes in half
...slid them into 5/8th heater hose to get about 1/2" of space around the obstacles

Thanks for the details on the Thermotec heater core install. Sounds like it might be more challenging to install one of these things than it appears.

Just curious... Where did you buy the Thermotec heater core and was it model # D65003TT?


Foama... If you are reading this, did you ever install the Thermotec heater core you purchased?


There is another brand of replacement heater core (Nissens) with removable tubes. Maybe it uses a different design?!? I pulled this quote from a Foama post...

The new core was branded Thermotec, type D65003TT.
The Thermotec core starts around €50.- (US $50.-)
A different and well reputed brand is Nissens.
The Nissens core type 707183 costs around €123.- (US$123.-)

[MetroMPG]

Sounds like a nightmare job, DimensionTheory. Thanks for posting the details.

I have nothing useful to add. I'm glad my 2014 is generating lots of cabin heat. I'm on my 3rd 2014, and haven't encountered any heater core probs in any of them... touch wood.

[Fummins]

The fleet Mirages have put on millions of miles(combined) over the last 9 years and no heater issues to report, though they never carry passengers.

[MetroMPG]

I wonder if the Canuckistani Mirages have a secret sauce in the coolant to keep us alive in the winter. (Based on my questionable memory of no Canadian core gum-ups.)