So just very generally, what stuff should I check for before making a cross-country trip from SoCal to DC--especially going through the rocky mountains and traveling at 11+k feet?

I'm sort of wondering as I've got a 92 Civic DX with just over 200k miles. I've already done the trip, having gone out and back by the same way last summer. Unfortunately, in the middle of the trip, I had an exhaust valve burn out, so afterward I had the cylinder head rebuilt by a shop and put it back on myself. That's been the only major repair I've done on the car--got it last year, before the trip. Haven't had any other major issues. That said, I'm just wondering whether it'd be good replacing anything or not, other than typical air filter replacement/oil change/etc stuff to do, and whether it'd seem like it could generally hold up for another long trip out. Thanks, appreciate the help.

 

For high altitude driving, you should consider replacing the coolant, thermostat, and radiator cap. Are the tires and brakes in good shape? When was the last basic tune up (plugs, wires, cap and rotor)? Is the CEL ON? If you have an automatic transmission, also consider replacing the ATF.

 

Well I just recently did a coolant flush; reinstalled the thermostat last fall--actually, funny enough, discovered I didn't even have a thermostat before then; no recent CEL issues, already fixed some CEL issues last fall; also had the spark plug and spark plug wires replaced; got a stick-shift, although is there oil to replace there too?; I probably could use a new radiator cap, although so far it's done it's job; brakes seem to have been alright, although I notice if I'm braking medium-hard going highway speeds, it's been vibrating--which would be a sign to replace the pads soon or something?

Actually, on that note, is it normal if, driving high altitude, the coolant starts boiling out of the overflow reservoir?

And is there a basic tune-up guide?

 

It's so cheap and important. Just replace it.

Sounds like you may need to replace the brake rotors.

This is definitely not normal. The radiator cap should prevent this from happening. Again, just replace the cap.

Basic tune up = replace the plugs, wires, cap, and rotor.

 

Actually that is normal at higher altitudes. The air-pressure at sea-level is 14.7PSI, and it decreases as you increase altitude. At higher altitudes with this decrease in air pressure IT ALSO LOWERS THE BOILING TEMP. That is why high altitude military pilots, and astronauts wear pressurized suits (because blood boils at body temperature (98.6*F) up in the ionosphere and space), and why jetliners 'pressurize' the cabin for cruising at 30,000ft. A Honda cooling system is pressurized at 1.1 bar (16.2PSI) which RAISES the boiling temp above 212*F/100*C so it doesn't boil under normal driving conditions. I would recommend a new radiator cap (if yours is old and cannot hold pressure of 1.1 bar 16lbs), but the hot coolant in the overflow tank IS GOING TO BOIL when the engine is shut off at operating temperature (195*F) at a high altitude because of this decreased air pressure. Another thing to consider is your Air/Fuel ratio runs rich at higher altitudes (because of the thinner air). In fact the gas at high altitudes is mixed differently because of this, but most OBDII cars' ECUs are able to compensate.

 

Water/coolant does in fact boil at a lower temperature at high altitude. Nonetheless, the radiator cap allows controlled pressurization of the closed cooling system, and therefore the lower water boiling point at reduced high-altitude pressures is not particularly relevant.

In addition, the OP asked "Actually, on that note, is it normal if, driving high altitude, the coolant starts boiling out of the overflow reservoir?". I maintain that it is not normal for the coolant to boil and OVERFLOW from the reservoir while driving at high altitude. If this occurs, then you likely overheated the engine by driving it too hard on the mountain roads. This typically happens because there is less air available for heat exchange with the radiator. In summary, while driving at high altitude, drive moderately and keep your eye on the dash temperature gauge. I recommend that you pull over and let the engine cool if the gauge reading rises above the halfway mark.

 

About the cap, yeah I'm definitely gonna get a new one. Confirms why my mechanic cousin thought it was weird the coolant didn't spew out when he was (cautiously) opening the radiator cap to check out the water pump in action, make sure it was working. Apparently it's not been pressurized like it should, I've noticed myself.

But yeah, the weird thing was, at the time, when I was driving through the mountains, the temperature gauge stayed stuck at the barely below mid-range point, didn't butch. Surprised me, even when I was going up 6-7% grades in 90-100 heat, stayed normal. I kept checking and refilling the reservoir every couple hours, at the time, so maybe that's why it didn't overheat.

 

For a cross country drive, I would consider to get a full size spare tire to replace the useless donut tire.

 

Full-size eh? Yeah that's a good idea. Would it fit where the spare is, bottom of the trunk?

 

I was trying to explain why the coolant in the overflow tank would boil at high altitudes. When you shut off the engine at operating temp some coolant will exit the radiator through the radiator cap's overflow into the overflow tank heating up the coolant already in there and cause it to boil.