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The search for a thermocouple

posted 20 Oct 2012, 17:40 by Robert Crane   [ updated 20 Oct 2012, 19:51 ]
Turns out that picking up a thermocouple for a 355 isn't that straight forward. They aren't as common as parts for other cars unsurprisingly. A contact referred me to Forza Automative who indicated they have a number of used thermocouples available. After checking a few other contacts this seemed to be the best option.

So early Saturday morning I dropped by Forza in hope that I could purchase a replacement and change it out this weekend. When we had a look at the thermocouples that were available the nut that locks one end into the catalytic converter was too small. It seems like these used thermocouples were from another model. Damm.

It was in fact lucky that I checked the size of this nut beforehand. It is about 14mm in size (or fits a 9/16 spanner), if you ever needed to know.


The only option now appears to be to purchase one from US. This one seems to fit the bill - 157501 Thermocouple.


Looking at this though, two things appear wrong. Firstly the bolt at the end that connects into the thermocouple to the catalytic converter seems small (like the parts at Forza) and secondly the length seems too short.


Looking at a thermcouple that is on Ebay (above) you at least see that the length of the thermocouple is much longer. Still also appears that the bolt on these appears smaller that what is on the car but that may be an optical illusion after staring at picture of them on the Internet for so long!

Looking at the connection to the car noticed a significant amount of thread still unused. Could it possibly be that the faulty thermocouple was from a 360 rather than a 355? That might explain why the nut was larger perhaps? However, after checking the thermocouple on the other side of the car it would appear that theory doesn't hold any water as it is exactly the same as shown below.


So the only real option now is to order a new thermocouple from the US and see what arrives. 


According to the parts diagram (above) item 35 is replacement part 157501 - Thermocouple, which is what is needed so.... Hi ho, Hi ho it's off to the Internet with credit card in hand we go.


Here's another example of a new thermocouple I found on the Internet


This seems to check all the boxes that it is the correct part given the bolt looks to be in the right proportion, the length is right and the part number (157501) is on the bag. Phew.

The car had a brief run to keep it active but continued to experience the "1-4 Slow Down" warning on the dash after about 10 minutes of driving. The light continued to flash intermittently but luckily the engine never went into limp mode. Hopefully, the replacement part can be ordered and delivered before the next potential run.

All this has taught another unseen lesson of owning a car like this. Parts for exotic cars are rare. Parts for old exotic cars are even rarer. You need to find a good source for obtaining replacement components and you will probably have to live with the fact that they will take a while to obtain as they aren't exactly off the shelf items.

The other things that you learn is that the information you pick up from those who already have, work with, are involved with these sort of cars is invaluable. You have to of course sort the wheat from the chaff, even in this field, but those people are certainly out there and seeking them out is going to be the best investment you ever make when it comes to owning these sorts of cars.
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