POST CHANGE UPDATE
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Yesterday I did all my planned maintenance on my 'new' Jazz. Here's a little feedback to help other total newbies like myself in the future.
OIL Change
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This was relatively easy and straightforward. With the front end jacked slightly and the engine warmed I managed to get nearly the whole capacity emptied. Only issues were with the Sump plug. With it reversed from front access I was trying to tighten it up at first! Once removed there didn't seem to be a washer installed. The bolt seems to be two part and at first I thought there was a stuck washer but it was part of the sump plug. I replaced the cheap filter with an original Honda filter and added the washer that came with the filter. I used Castrol EDGE 5W-30 LL Fully Synthetic. A little over the top but I thought she should have the best after years of neglect.
Coolant Change
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My engine tray it beaten up and held on by various half broken clips and cable ties. In the end I just left it and only drained from the radiator (and not the engine block drain). I didn't get much fluid out, probably only a litre. I was able to remove and empty the overflow tank. This was tricky with the lower tray in place, but I undid the bolt and lowered it down to the floor, then lifted it up to reinstall. This gave me another 300ml or so of fluid to change. On refilling the coolant I didn't have any issues with air blocks (probably because of how little I changed). It took ages for the engine to warm up enough to get the radiator fan going. Using my OBD reader it was 93 degrees that turned it on. Once mixed round it didn't do much to change the dirty original colour. The dirty blue stuff that came out did however look like the blue Honda Type 2 coolant I added. I assume it was the original factory coolant, so at least I'm not mixing two types.
Spark plugs
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Changed these for orginal NGK BKR6E-11 plugs. Front were easy, the rear ones were tricky. I had to slide the wiring harness out the way and use a rortating elbow joint with my spanner extension. I used the hose pipe trick to remove and start the new plugs. Front plugs looked fresh, rear plugs had carbon build up. Either the rear plugs work harder, or more likely they weren't changed when the fronts were done.
Air Filters
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Cabin was very easy to change, and absolutely disgusting. Obviously had never been changed.
Intake filter was in good shape. I found it a real pain to remove and replace the lid. Not sure why when it looks easy in the videos. I just couldn't get the clearance, a real PITA! Maybe there's a knack I don't know about.