Civic overheated... why and now what?

I drive a 1998 Civic hatchback. Last night while I was driving I needed some gas. I pulled into a station and the only gas they had available was 93 (highest octane). I only ever fill up with 87 or whatever the lowest grade is, so I put 2 gallons in to get me to my destination and the opportunity to find another gas station. Shortly after, I was back on the highway and the engine starts making a loud rattling pinging noise when I step on the gas. I normally might have a low rattle or ping that I’ve never been able to get rid of, but never loud like this. Then a few things happened– smoke starts coming out the exhaust, the check engine light comes on, and the car starts to overheat. Seems like it was pretty much all at once, although it was in that order that I noticed… I rolled the windows down and turn the heat on high, but the air coming through the system wasn’t at all hot. I got off the highway and as I downshifted, the engine started to smoke a little. I get to the end of the off-ramp and the engine dies. It wouldn’t start back up right away but I managed to start it a couple of times (between it dying) to get it to coast into a parking lot. Under the hood, there was coolant everywhere it seemed, but I couldn’t see anything else apparently wrong– hoses, etc.

In the end I had AAA tow it home. So any idea what happened and what I’m looking at now in terms of repairs? I will need to have it towed again to a mechanic if it is something I can’t figure out myself. Thank you in advance!

If you have coolant all over the engine compartment, you have coolant leak somewhere. It could be a leak in the radiator, or a crack or hole in a radiator or heater hose. I found some pin hole leaks in my '03 Civic 3 years ago, this was in the top radiator hose near the connection to the radiator. I had several hoses replaced at that time since if one goes, others are likely to follow soon.

You may have pushed things too far by continuing to run the engine when you saw it was overheating. Civic’s don’t handle overheating well. Heads warp easily and when the leak is fixed you might find you have an internal leak due to blown head gasket, or worse a warped head.

Find the leak, fix it, but then drive the car carefully and watch your coolant and oil levels closely. If you are lucky all will be well. But, frankly I’d expect at least a blown head gasket due to the overheating scenario.

I would add that I don’t think that the octane of gas that you used had anything to do with the issue. On certain luxury or sports cars that are supposed to use 93 octane it may cause a problem with pinging or knocking if you used 87 octane, but not the other way around.

The damage was definitely not caused by using a higher octane gas. It was due to happen, and it just picked that time to do so.

My guess is that the low rattle or ping that you’ve nnever been able to get rid of has caught up with you. Pinging and rattling are symptoms of mild preignition. Pinging is actually the spark-induced wavefront clashing with a secondary spontaneous-ignition wavefront. Over time this can burn a hole in a piston.

The only way to assess the damage now is by (1) checking the compression, and possibly pulling the head.

I found a leak either in the radiator or a hose (front of the radiator). Water goes in, and then right back out. I just had it towed to my mechanic, so I’ll see what they say. I’ve been trying to figure out the low rattle for the longest time. It had been only firing on 3 cylinders because of carbon buildup, so we fixed that, but it’s still happening.

I hate to say this, but if you only cleared the carbon and changed the plug, you’ve fixed the result of the primary problem but not the problem itself. Carbon buildup is a symptom of either a fuel metering problem (too rich) or prolonged oil burning (which is the one I suspect here).

I’m guessing that you’re working on this yourself. Let me suggest that you pick up an inexpensive compression test kit at the parts store or tool store and start by checking that. You may save yourself a lot of time and aggrevation.