>>28551509
Oh yeah, definitely pull the oil filler cap and look in there.
>>28551334 (OP)
Also OP, if you can get your hands on a borescope, pull the sparkplugs and check the pistons. Normally you'd expect to see a bit of carbon/grime on there in an older car, but water basically steam cleans the pistons so if one is suspiciously clean there's a good chance you've got a blown headgasket leaking into that cylinder.