Which monovalve failure mode is this?
 

I expected to open this up and see a totally rotten bit of rubber. But, the diaphram seems to be just fine.

However, the screen is buckeled into an uneven, eliptical shape and there is what looks like aluminum corrosion deposit on the washers/spring. Most of the corrosion seems to be sticking to the copper (?) flat spring.

I've already ordered a monovalve repair kit from Fastlane (should have done it weeks ago so I had it.), but, I was wondering.

Does this deposit signify anything about my cooling system? I've got the recommended coolant in there, but I have no clue what the previous owner had in. It might have been whatever was cheapest and, as he lived in No. Carolina, probably didn't need to worry about freezing in his lines like I do.

Acidic
 

Hello sohj
At some time the system has gone Acidic.
Neutralize the system, flush, then refill.
Hope for the best.
Have a great day.

Litmus papers and draining , flushing and replacing?

I assumed the coolant was neutral. Is it neutral or is is it alkali? If alkali, do I put in vinegar until neutral?

I don't think that running a chemical analysis is really neccessary. It sounds like your coolant is in need of changing, that's all. Coolant doesn't last forever and I'm sure that MB has a recommended changing schedule. Coolant goes through breakdown and also absorbs the various metallic and other elements that are present in the cooling system as well as create calcium/mineral deposits based on the minerals present in the water you use when mixing it.

You should mix the coolant with distilled water.

VeeDubTDI, I just noticed in your signature, "2000 Volkswagen New Beetle TDI (RIP)" What happened that the TDI got a RIP? Did I miss something?

I totalled it in January, 2003. It is sitting in my friend's garage in Stafford County, VA. It still runs... er... it will if a new instrument cluster is installed. I've been selling pieces off of it for a while, and the cluster was one of the first things to go. The cluster contains an electronic engine immobilizer, so without it, the computerized injection pump will not allow the engine to continue to run for more than one second. I have cranked it for 15 seconds or so every few months to keep oil in the head and valvetrain.

Anybody want a 1.9 TDI engine and 5-speed transmission with ECU? All you need is a cluster, which can be found at a junk yard, on eBay, or at the dealer. It has 55,558 miles on it. Oh yeah, the ECU is chipped (~115 hp/210 lb-ft).

VeeDubTDI, sorry to hear about your misfortune. It sounds like you made it out OK. That's what matters most.

Yeah, my friend and I were both okay. The impact was such that it caused the driver's seat airbag to deploy. I was just shaken up a bit, with no bumps, bruises, or scratches. The New Beetle is a very safe car in a collision... because it's designed to absorb all of the impact. Unfortunately, the car usually doesn't survive.

That's one of the reasons why I have my 300D as I've heard are very safe in a crash as well.
Well its always better that a car gives up its "life" than you lose yours and the car survives instead.
:) Keep driving safely!:)

Got another question about the coolant.

Will drain and flush and replace next weekend, now that I've found this deposit. I was planning on doing it in mid-March.

What do I need to know to look for on a regular basis? Should I periodically pull the monovalve and look to see if there is more deposit? And, if so, on what schedule? And, was this deposit indeed aluminum corrosion?

Should I flush with distilled water? or something slightly acidic or alkali? If it is regular tap water it will be very slightly alkali, I think.

Or am I being too fussy?

If you plan to inspect/replace/or do anything with the thermostat, ber very easy on the housing bolts. I did a flush on thursday, BTW completely solved my overheating problem, and snaped one bolt and found one bolt hole in the housing was cracked from the PO using the wrong size replacement bolt. :mad:

It seals and does not leak despite having 2 of 3 bolts holding the thermostst in.

You do NOT want acidic or alkali coolant.
 

Hello sohj
There seems to be an error in communication.
When I say acidic, this is a generic statement meaning acidic or alkali.
The system needs to be neutralized with the chemical equivalent of baking soda.
You do NOT want acidic or alkali coolant.
Here are some links that may help you with the task you face.

http://www.advanceautoparts.com/howtos_tips/automedia_html/ccr/ccr20010501rm/index.html?page=/howtos_tips/automedia_html/ccr/ccr20010501rm/ccr20010501rm.htm
http://www.wynns.be/
http://www.valvoline.com/pages/products/category.asp?cid=2
http://www.sierraantifreeze.com/
http://www.prestone.com/
http://www.justicebrothers.com/theproducts.htm
http://www.gunk.com/
http://www.peakantifreeze.com/whychange.html

Have a great day.

Heck yeah I want it to put in my Samuri. I just cant afford it.

What is affordable to you?