My AAV is failing

My hot idle RPM has been increasing over the last year, so today I had a closer look.

When cold I could see that it was fully open but when hot it was only half closed.



As a temporary measure I have blocked the output air port of the valve. It will be interesting to see how the next cold start works out.





I will look for a replacement in the mean time or refurbish the existing one when I replace the coolant next spring.

Is these a "How to" refurbish the AAV here? I had a quick look but did not see one.

Hey Jim,

are you looking for something like this youtu.be/hbQcWBykjbc ? He made a whole series on the idle issues of his 560 SEL.

Personally I find his videos excellent. Is a German guy that used to work for Bosch or Mercedes and is in the US now. I like his deep knowledge on KE but also his accent!

Success,
Maurice

Thanks Maurice, the 560 AAV is a bit different to the 450, it's electronically controlled Vs temp controlled. I have thought about using an electronically controlled AAV and using a small microcontroller to sense the engine temp and RPM to adjust the idle RPM. It would be fairly easy for me to do but difficult to make it look OEM.

I did try rebuilding a spare AAV that I had a few years ago but managed to break it, hence now looking for a good "how to".

Jim,

I didn't realize but it makes sense!

Cheers!
Maurice

D Jet and K Jet Aux Air valves are fairly simple things and I've refurbished a few.

The basics.

62 degrees Celsius is the hot temp

The AAV is never fully shut

Adjusting the "Idle" with the screw only buggers your base idle settings (Common mistake)

Cleaning is the number one step, carby cleaner, lots of it.
A white container will aid this and tell you when you are clean.

Between cleaning run the AAV through heat cycles a pyrex jug and a kettle works well observing how its open/closing.

The open/close temp is controlled by a wax oil bulb in the manifold jacket, in older D jet cars this needs testing for operating temp (62 to 68c) although its the same value for K jet.
Once you are sure the AAV is clean you may have to crimp the bulb as over time they can drop in pressure, this takes a lot of force so be gentle.

I had a Stroke 2 weeks ago so im not 100% on typing but thats the nuts and bolts of it, AAV are difficult to get, Bosch does a reman every so often but its a core return.

Good luck

Tony the Dirty D jet guy

Hi Jim,

there are various issues why an cooling water based AAV fails. It is dirt / coke in manifold. But it is also waekening thermo expansion element or leaks from cooling system that creates condensate inside. Last effect is most annying as it makes piston completely stuck and it can be really hard to get it out in one piece. Trouble overall is that the hosuing is cast aluminium and can brake easily. But you need well dosed force to pull expansion element out. In other words this part is common to fail and needs overhaul after 40 years. It is designed to be replaced as a whole and therefore overhaul is tricky.

I have created tools to do that job and made new expansion elements with housing and sealing and for the fitting you have there. I do not know where Tony learned that 62°C is the correct temperature. I slightly disagree.

Hi and I also disagree that AAV is never fully shut. Opel versions first close and open at high temperatures again to improve engine fan cooling if it gets too hot.

62 to 68c

Australian thermostat (Tropical)

107, 116 both D jet and K jet.

As these are now 50 years old the Wax/oil thermostat temps are imprecise.

As tested in my 72 350SLC, 73 350 SE, 74 450 SEL and 77 450 SE.


I'd love to hear your temp setting as it may be climate dependant and worth noting.

Weirdly I've only had 1 K jet AAV jam in actuation and no D jet.
Granted I usually dealt with D jet but Bosch was super high quality of manufacture in the 1970's.

Tony The Dirty D jet guy.

Hi Toni,

there is no tropical version of this AAV. And it was never specified to close at a definite temperature.

I said "Australian thermostat (Tropical)" as in tropical/Arid region cooling system not AAV.

And you still haven't mentioned the Open/Shut temps for the AAV?

If my information is incorrect it would be nice to know.

What I do know is that my settings work with both D and K jet from 0c to 40 ish c