328 Expansion Tank sender unit

not to hijack the thread..more like "piggyback" Rutlands tells me my resevior tank senders ( I have two, a electric one and a vacum sensor) are NLA. ( I remember a thread about finding a replacement) so very curious to test if mine is working...I just pulled my tank and took it to the rad shop...$30 later they steam cleaned it and sealed tiny holes with solder and sealed the unit....I would also like to know what should be used to "seal the senders into the tank so they hold pressure and don't leak...teflon tape on the threads? silicone sealer? or is the brass washer enough..any idea of torque settings? I will be disconnecting my air pump finally so I figure I don't need the vacum sender.

 

I believe for the 328 the correct coolant temp switch logic is cold=closed and warm=open.

Closed doesn't need to be perfect (i.e., 0 Ohms) -- it would probably be OK if it was a few Ohms. To do a functional cold test (everything plugged in), measure the voltage between the ZN wire leaving the coolant temp switch (or where it enters the injection ECU) and a good chassis ground -- should be near 0 VDC during cold-running (or maybe a few tenths of a volt maximum).

Open shouldn't be a mystery -- infinite Ohms.

 

I'm 99% sure that 4~5 Ohms when closed won't make any operational difference (as a test, you could always just unplug the coolant temp sensor and intentionally jump the two terminals in the harness together simulating a perfectly closed switch when cold).

You can't "follow" the ZN wire. Just measure at the connector of the injection ECU -- you should be able to place your probe onto the metal terminal of the ZN wire there even when the connector is plugged in and the engine is running.

 

Mike -- I should have said "you might be able..." rather than "you should be able..." to make that measurement of the ZN wire at the injection ecu connector. The ZN wire also goes over to a nearby ...101 relay and that might be another place to measure it more easily. But what's the problem? Are you having a specific poor cold-running symptom?

 

I guess you'll need other 328 Owners to speak-up, but I've had previous reports from 2 other 328 Owners confirming that it should be cold = closed and open = warm.

If you can make the voltage measurement of the ZN wire at the injection ecu, and it is no more than a few tenths of a volt during cold-running, IMO that would indicate that the coolant temp switch is not associated with your cold-running problem.

If your air injection system does operate during cold-running (when the engine oil isn't super cold) and shuts off correctly for warm-running, that would be another sign that the coolant temp switch is working OK.

Good hunting...