How do I replace the heater filters?

Easy job...remove the shroud beneath the spare tire just forward of the windshield.

From your picture, note the air route on each side to find the now obvious black box -26-. Remove the clamp and hose -4- on forward end of the box. Remove the filter -25- by popping loose the box end piece. I removed the box (couple screws). It was unnecessary but made it easier to completely clean out the box.

 

Crap...I didn't even realize there were filters there! One more thing to add to the To Do list.

 

Any idea what filter to put in there?

 

Go to a hardware store and get some aluminum screen. You can cut it with scissors, or tin snips.

 

I dismantled both units last year and did not find any filters!?! or anywhere a filter would fit in for that matter....

 

I replaced the dust that was left of my original filters with pieces I cut out of a foam shop vac filter sleeve from the local hardware store. I tested a bit first in front of a heat lamp to make sure it could take the heat. No problems.

 

Good info - I had no idea there were filters there either until seeing this thread. I checked my 328 manual and there it is: "...change or clean the filters on radiators 9 every 6 months."

As others have noted, I'd bet when I service them later this month it will probably be the first time since the car was in warranty (if it was even done then).

 

speaker foam , too.

 

And the filter goes where?

 

Inside the plastic heater core boxes. You can pop the front plate off the box (though it is a bit tight!) and the filter slips in there. The only reason I even thought of replacing them is that I had the heater cores out of the car to replace all the heater hoses, and when I took the boxes apart I thought, "Hmm, what's all this crumbly stuff falling out mixed with leaves and dirt?"

 

So does the filter sit snug right agains the heater core? There is not a lot of room in those boxes. Does'nt that pretty much stop the air flow? And what about the core temperature... 195 degrees, right on the filter material...

 

This is exactly why:

1) I used shop vac filters. They're designed to filter well while allowing high volume air flow. (The technical name for this stuff is "reticulated foam")

and

2) I tested the foam with a heat lamp. There was no problem after being at 200+ degrees near the heat lamp for 2 hours. They'll likely degrade in the long run, but then so did the OEM ones.

 

Any particular shop vac filters??

 

I just got whatever Home Depot had on the shelf. It comes in a round sleeve, and you can just cut sections out of it to fit. I also suspect viper_driver's register filters will probably work just as well.

 

Looks like all those expert $10,000 major services left something out over the years...

 

From the pics it just looks like standard foam that is used as filters on a lot of small home/marine ac units. Should be easily available at any hardware store.

 

"I can't tell any difference in the amount of airflow now with filters installed vs yesterday with essentially no filters. "

You shouldn't feel any difference at all unless the filters are too restrictive for the application.

 

I was able to use the carbon filters that are over a range vent hood.They cut nicely and are rather rigid.

 

When I bought my car and gave the old bumper to bumper fanatical once over and major engine and chassis service, I got into those heater boxes and one had traces of filter, dirt and leaves, and the other, just dirt and leaves, I explored downstream and found those hoses to be completely filthy dirty! Yuck! So after the exercise of cleaning filters, you're carrying air through 25+ years of dust and crud covered ducts. So I scrubbed them out with damp towels etc.

On one car I replaced those hoses! I found really nice replacement hose from McMaster Carr. IIRC it was FDA approved for cleanliness (no smell), and was even a good - but not exact color.

BTW: After all that cleaning, I didn't put any filter media back in there. It would be nice to get some filter media like BMW etc use with charcoal. I like the idea Viper Driver came up with for the Home Depot vent filter material. Now I may need to go back in there.

 

My 308 had been sitting in an aircraft hangar in Colorado for three years before I bought it. I never opened the vents or turned on the fan when I drove it. Didn't want to take the chance of breaking something. The first time I took my wife for a drive, she wanted some air. When I opened the vents and turned on the fan, spiders blew out. Not just regular spiders, Black Widow Spiders. Spiders blew all over the interior, me, and my wife. I freaked out a lot more than she did. Then I took my car to Eugenio's for a Major Service. During the service he told me, "Your car is in very good mechanical shape but, you have a major spider problem!". He said my heater filters were just dust and really should be changed. That along with bug bombing the car should help keep dust and spiders out when the fan is turned on. I am happy to report that he was right. Since I changed the filters, (an easy job), and bug bombed my car, I have had no further contact with stowaway spiders or blowing dust.