OK, slowly, but surely I am progressing with my quest to sort out thermostat issues on my CRD. Having original and functional OEM thermostat cracked open I have repeated my kitchen sink test to find that the main thermostat valve failed to fully close, letting through quite a flow of coolant through the radiator on the cold engine. Here is the proof:
https://drive.google.com/file/d/1AKkYjE ... sp=sharingSimple modification by deepening the hole in the housing which accepts thermostat plunger/piston results in this:
https://drive.google.com/file/d/1GZM-gm ... sp=sharingQuite a difference, n'est-ce pas? Closer look at the issue reveals the following: while most cars these days are using what are termed "thermostat inserts", some, mostly Audis, some Cadillacs and Saturns - and of course KJ CRD - use what are called "housing" thermostats. The former type are complete devices which simply need to be installed into the housing and sealed around the perimeter. Both the main valve and its seat are within the device and the valve closure is established during the assembly at the factory. All I have seen so far fully close the valve when cold. Here is an example:
https://www.amazon.com/dp/B000EQRH5G/re ... B000C9C00WThe latter (our) type relies on the housing to provide the stop for the piston, the seat for the valve and the attachment for the lower bracket holding the valve spring. Here is the typical one:
https://www.amazon.com/dp/B001FDWCWU/re ... B000C9F5TUMain advantage of the "housing thermostat" is substantially bigger valve diameter which could be as big as the housing permits. Thermostat "insert" fitted in that same diameter housing is going to have a valve roughly twice smaller in diameter - big difference in the coolant flow given the fact, that the amplitude of the piston motion is roughly the same. But that's where the advantages end. With "housing" type the housing becomes an integral part of the design and needs to be machined more precisely. In my case it was machined such that the valve failed to close. Just a little deepening of the piston guide hole in the housing resulted in almost complete seal despite being simply metal-to-metal.
The real question is, whether this is a feature or a flaw? As a feature it could be there to provide at least some minimal cooling in case the thermostat fails in the closed state. I recall reading about something similar on some Fords. As a flaw, well, the flaw is a flaw. Interestingly the mods by Kapalczinsky and TURBO-DIESEL-FREAK both used "insert" (and fully closing!) type thermostats to no ill effect, but did anyone do heavy towing with those? Also interestingly, the Chinese-sourced thermostat I currently have installed behaves in exactly the same way as OEM one - never closes fully. Was that a feature incorporated in the design given the difficulty of procuring and swapping the permanently sealed expensive unit? Somehow I am skeptical on that one ...
Well, now that my OEM unit is "fixed", all is left is to figure out how to reassemble the darn thing without the roll crimping. Wish me luck!
Cheers,
Alex