For any long trip I make sure to have lots of fluids (engine oil, diff oil (80/90EP, pre-mixed coolant, DOT3 brake fluid), plus a full spare gasket set. Last year I had a head gasket fail -- easy enough to fix, but not if you don't have the required bits and they're not locally available. I tend to bring many spare parts that I have on hand waiting for future services, but I don't like to be stranded for a few days waiting for stuff. I also bring a low jacking lift, jackstands, a full, full toolkit plus torque wrenches, breaker bar, etc. My car also has a fire extinguisher mounted to the transmission tunnel in the passenger footwell area so it's within easy reach. If you're travelling south of the border varied vendors can ship stuff to a shop quickly if need be if you have a breakdown.
AriK just drove from Montreal (Laval) to Wisconson and back for FFO in his '79 and was fine. 1800 mile round trip. But he really knows his car. (He did have some exhaust work done when there). He drove mainly on the Canadian side to Sarnia, then took a ferry across Lake Michigan.
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Last year I drove Ottawa to Detroit (1000 miles round trip) in my '74 and AriK a bit more since he starts further east. The year before 4uall (in an '80) and I drove Ottawa to Pittsburgh (1100 miles round trip), plus AriK a few more miles. That time 4uall lost a wiper and had a nail in a tire; AriK had oil pool in the spark plug holes due to a leaking cam cover. These cars can really go if you look after them, but it's best to know them already so you know what to look/listen for. Mine purrs on the highway - at about 3800k rpm at 70mph and it really pulls up to and beyond 80mph (about 4,400 rpm). Mine breathes well with a bigger carb, exhaust, etc so it's happy to just cruise -- much happier than in stop and go downtown traffic. Yours may have a different diff than mine (did they switch in mid '78?) so gearing may be altered.
On the other hand, my water pump had a catastrophic failure two days ago in town; main seal blew and it was only two years old. Totally didn't see it coming and the only fix was a new pump. Luckily 4uall had a spare on hand or I would have been off the road for days. Glad it didn't happen two weeks ago when I was driving to Montreal and back or it would have meant a tow truck. On about the same day 4uall's 1980 FI started spraying fuel all over the engine as a hose cracked; lucky he didn't have an engine fire. Meanwhile, Spiderdan's 1968 just had its clutch let go with no warning (I saw it apart and four of the six springs in the clutch pack were shot - though I suspect once one or two go the rest go, too). Bad luck comes in threes so maybe we got rid of the Spider bad luck in Ottawa for you.
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Who owns the car you're buying? We might know it...
If you discover you desperately need spare parts when you arrive in Ottawa I might have some on hand or 4uall might. We also know a guy that knows a guy that has everything Fiat and can fix almost anything.
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Addendum: just read your other post. Is the car a carbed '79? If so it may be totally plugged with anti-pollution equipment. When you get safely back home start looking at getting rid of that stuff if it hasn't been removed already, assuming it will still allow it to pass BC emmissions laws. All that stuff really hampers performance.
Before your huge trip just make a few test runs on the highway. Sometimes stuff only turns up when things are hot after running for a while at speed (e.g. dragging rear brake, axle seals that only leak when diff oil gets really heated). The car can be rock-solid reliable around town if that is what it was used to with the previous owner and issues only creep up when going balls-to-the-wall for hours. Don't ask me how I know.
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On your trip check fluid levels often to see what gets used up.
Have a blast!! Get in touch when you're in town!
Cheers,
phaetn