Heater Core Challenge

So with the extra measure of cold this winter I was again freezing my butt.
Last year I tried all kinds of possible solutions non of which effectively worked and then it got Springy again and it became a minor issue.

This year, once again I was too busy to be without my service van due to workload.
Anyhow I finally bit the bullet and scheduled a day in the shop to get the heater core replaced. I requested the old core be left in the van so I could perform an autopsy with my saws-all.

After cutting the core into a few segments I observed what looked like a warm beeswax substance. Needless to say it insulated the flow of antifreeze from transference of heat to the air mass passing the fins but not enough to make a decreased flow of fluid even after a number of prior flushings.

My questions are as follows:

  1. What causes this “beeswax” to form??
  2. What could or should have been used to clean it out??
  3. Is the same stuff in the radiator that will cause replacement to it??
  4. If the same is in the radiator will it migrate to the heater core starting all over again??
  5. Should I consider replacing the radiator or what is the best way to clean it to remove the junk??

I know that is a load of questions. If whomever would like to contribute an answer or comment, take your choice of question(s).

Oh, forgot to mention. My butt does not freeze anymore.

Thanks in advance.


The beeswax substance is formed when a too high of concentration of antifreeze to water ratio is used.


Is there a way to reduce it after forms such as when the weather is warm to remove antifreeze and install just water or something else??

You flush the cooling system, while at the same time introduce a fresh blend of 50/50 coolant.

Here’s the machine I use.


So the machine has a cleaning solution and/or super heat to clean the junk out??

Based on what I typed do you think that my radiator has potential issues??

I use no cleaning solutions.

I run new coolant into the cooling system that exceeds 10% of the cooling systems capacity. So all the coolant is replaced.


Confused here. Exceeds 10% of volume, concentration, or something else??

10% volume.


So what would happen if I drained and replaced with 50/50 plus 10% and just ran that, would it clean the beeswax out or is the machine still needed??

If you’ve had the heater core replaced , I’ll bet the coolant mixture is correct.


I was told that it was. However, I do have a concern based upon your first comment.
I never added coolant to the system it was always my shop. Just trying to understand
why this happened in the first place. Will be difficult trying to figure it out with all the time that has passed. Really trying to understand.

I have no idea what the buildup is, but if your van’s engine temp is OK on the hottest days, there’s little chance of this buildup in the radiator.

Ok so the non flow through the heater core during the summer is the cause??

Assume you meant through the heater core, and yes, that would contribute to the buildup.

Yes, I fixed it. So, then having a constant slow flow through the heater core could be a good solution for future thinking??

Yes, most vehicles have gone to constant flow through the heater core. (The more flow, the better.)

Makes sense as well as the concentration being high.
I am guessing a combination of both.

Thanks for the input.