Heat Residue on Windshield

[Davarron]

Was wondering if any of you have had this happen before...Whenever I have the heat on in the airplane, the front windshield on the inside develops this haze near the defrost vent. It is usually worse on the pilots side than the right side and if I open the defrost knob it becomes very hazy by the end of the flight  (which forces all the air to the defrost vents as opposed to half to the defrost and half to the floor when the defrost knob is off).

The windshield was replaced about a couple hundred hours ago with 1/4 inch GLAP Solar control gray tint. Not sure if that has anything to do with it but was wondering if anyone knew anything more. The air is generally pretty warm when it exits the vents.

In the photo, the specks aren't actually there, but you can see some of the haze which extends further up than what I have circled. I usually just wipe it off with the cleaning product that I use on the outside of the window. Thanks for your help as to what is causing it. 

[Skates97]

I don't get that on my plane but I get similar haze on the inside of the windshield in my cars. Not sure what causes it. 

[Hank]

Just now, Skates97 said:

I don't get that on my plane but I get similar haze on the inside of the windshield in my cars. Not sure what causes it. 

It's usually outgassing from the plastic dash. 

In your Mooney, are you running full hot defrost? My Owners Manual says to mix in some cooler air to prevent damaging the windshield.

[LANCECASPER]

I had my glareshield covered 18 months ago with black Ultraleather and I still get some outgassing. 

[Davarron]

11 hours ago, Hank said:

It's usually outgassing from the plastic dash. 

In your Mooney, are you running full hot defrost? My Owners Manual says to mix in some cooler air to prevent damaging the windshield.

What does the outgassing mean? 

And no I usually just have the heater knob pulled out some and the defrost knob closed. But with the Mooney system, defrost air still comes out even with the defrost knob off. Hmmm maybe I should be mixing in some cooler air like you suggested. 

[RobertE]

I have the same thing on mine.  It's permanently discolored in that area.  I attribute it to the previously owner who lived in Denver really cranking up the heat on a consistent basis.  I suspect I'd have done the same.

[Hank]

18 minutes ago, Davarron said:

What does the outgassing mean? 

And no I usually just have the heater knob pulled out some and the defrost knob closed. But with the Mooney system, defrost air still comes out even with the defrost knob off. Hmmm maybe I should be mixing in some cooler air like you suggested. 

Chemicals called plasticizers are mixed into the plastic used to make your panel, to increase its flexibility and to make it feel softer. These "evaporate" over time, but must go somewhere; running high heat will accelerate it, as will parking in the strong summer sun. Sometimes what you clean or treat the surface with can contribute to the effect.

 

[Davarron]

54 minutes ago, Hank said:

Chemicals called plasticizers are mixed into the plastic used to make your panel, to increase its flexibility and to make it feel softer. These "evaporate" over time, but must go somewhere; running high heat will accelerate it, as will parking in the strong summer sun. Sometimes what you clean or treat the surface with can contribute to the effect.

 

Ahhh ok. Thanks for explaining that. I can usually just rub it off for now but I hope it doesn't get worse as that's a new windshield. 

[carusoam]

Hank hit the nail on the head regarding PVC plasticizers... if it washes off, that is what it was...

The windshield is made of acrilic and has a realitivly low softening and melting point... lower than the boiling point of water.

http://www.bayplastics.co.uk/acrylicsheet_faq.htm

Use caution with high heat settings.  Heat off the exhaust muff can be quite hot (1650°F EGT based) compared to automotive equivalents that are limited by the boiling point of glycol and water... (350°F?)

PP thoughts only, not a mechanic...

Best regards,

-a-

[Davarron]

1 hour ago, carusoam said:

Hank hit the nail on the head regarding PVC plasticizers... if it washes off, that is what it was...

The windshield is made of acrilic and has a realitivly low softening and melting point... lower than the boiling point of water.

http://www.bayplastics.co.uk/acrylicsheet_faq.htm

Use caution with high heat settings.  Heat off the exhaust muff can be quite hot (1650°F EGT based) compared to automotive equivalents that are limited by the boiling point of glycol and water... (350°F?)

PP thoughts only, not a mechanic...

Best regards,

-a-

Even if it washes off, is it still bad for the windshield? Or only if it isn't cleaned off?

[N201MKTurbo]

If you are only getting it when you run the heater, it is most likely stuff from the heater air box or scat tubing. If you were to take off all the scat tubing and wash it all out with soap and water until it was clean and then washed down the air box with solvent and then lube it with some low volatility lube vary sparingly. It would probably take care of the problem. But that is a lot more work then cleaning the windshield once in a while.

[carusoam]

8 hours ago, Davarron said:

Even if it washes off, is it still bad for the windshield? Or only if it isn't cleaned off?

That is an interesting question... in the auto world, the plasticizer deposits on a glass surface which is mostly impervious to everything...

We would probably need a chemist to answer this question.  We have a couple of chemists on MS...

The chemistry has changed over the years, with plasticizers used with PVC.  It had Health concerns related to food contact and young children.

Overall, I doubt that the windshield would look so good, for so long, if it were sensitive to the plasticizers... if it got absorbed, it probably wouldn't wash off very well...

PP thoughts only...

Best regards,

-a-

[jrwilson]

11 hours ago, Hank said:

Chemicals called plasticizers are mixed into the plastic used to make your panel, to increase its flexibility and to make it feel softer. These "evaporate" over time, but must go somewhere; running high heat will accelerate it, as will parking in the strong summer sun. Sometimes what you clean or treat the surface with can contribute to the effect.

 

Now that was a good answer!  Answer his next question about long term damage...I'm wondering too

[Hank]

28 minutes ago, jrwilson said:

Now that was a good answer!  Answer his next question about long term damage...I'm wondering too

Sorry, I'm a Mechanical Engineer who likes a clean car and plane. Like Anthony said above, you need a Chemist, and I barely made it through freshman chemistry (thankfully only one semester was required!).