Cold start valve, what is the difference between the revisions?

[crewcab1964]

I have a 1970 Squareback and has a 311906171A, can a 311906171B be used instead?

[KTPhil]

Where do you live? I ask because unless you are often starting near zero degrees, the cold start valve is not in operation regardless of the part number, so it may not matter anyway.

[Bobnotch]

[KTPhil]

I think I read somewhere here that the change was in operating temperature. One was near 32F, the other was much lower, maybe 10-12F.

Also, it only works during cranking, not during running.

So you can appreciate that there are rare instances where it ever worked at all!

[Tram]

[crewcab1964]

Thank you for all the response. I have only had issues with starting the vehicle near freezing temperatures and will run into a few instances where the vehicle would flood. I was reading through a troubleshooting guide and it mentioned flooding can be caused by a leaking cold start valve.

[Bobnotch]

[KTPhil]

Actually, I took his question to be about the thermo-time switch, not the jet, but I see it wasn't, sorry!

The reports of flooding came from two causes... a leaky injector that either bled down after shutoff, or dripped when it should be closed. Or it could be forced on by putting the wire on the solenoid on the wrong contact.

Your '70 has the middle-vintage TVS that added the ten "access pump" firings as you press the throttle. So you can use this like a cold start valve when it's really cold by pumping the throttle during cranking, or even turning the key on, flooring it, letting up, then moving the key to start. This will give extra gas during the first rotations.

So I really think you can do without the CSV setup, unless you are stationed in Point Barrow or similar.

[Tram]

Actually, the whole cold start system thing has way more to do with 1960s/ early 70s battery and lubricant technology than actual temperature. Remember, the original A/B systems had cold start as an option

When the temperature gets really cold, the old paraffin based motor oils got the consistency of molasses, and batteries of that era would lose 50% plus of their cold cranking capacity. Lots of people ran single weight oils in those days too.

When you were at 0 degrees with sludgy oil and a diminished capacity battery, your FI car wouldn't start because there wasn't enough juice for the FI system, so VW developed the cold start system as a band- aid. A shot of gas got the engine- and generator- spinning so that the FI would kick in.

With today's modern motor oils and better batteries you really shouldn't need the CSV system at all as actual enrichment is done via the temp sensors and the AAR compensates for the cold enrichment.
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[Donnie strickland]

Yep. Mine is disconnected, but it starts in single digit temperatures.
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71 Elm Green FI A/T Squareback

[crewcab1964]

Good to know that the cold start valve is not that critical. I have a new one coming. in the future, disconnecting the valve could be an option.

[KTPhil]

Found a reference for the operating temps:

This is for the sensor, not the jet.

It remains to determine if the difference in the jet part number matters. I haven't found any cross references or tables to distinguish them.