This video is to help guide you on replacing the thermostat on your 1998-2006 Isuzu trooper with the 3.5 liter v6. I hope it does help you.
The following links are for partsgeek’s website, which is where I found the water outlet gaskets the cheapest. Amazon was $14.99 and Advance auto was $12.99. No one else carried them including Rockauto.
Thermostat part number: 1331-07351669
(comes with rubber seal)
https://bit.ly/363Uys9
intake gaskets part number: 1331-05037404
https://bit.ly/37oZ58F
Water outlet gasket part number: W0133-1643981
(will need two of these gaskets)
https://bit.ly/36ooZJq
Assume all links provided are affiliate links and if you click on a link and purchase that item, the channel may get a small commission at no extra cost to you.
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Wow. No reason whatsoever for them to put the thermostat in that location. The "engineers" could have put the thermostat in the metal tube close to where the rubber hose connects.