Rep Power: 0

1995 Civic EX coupe, EJ1 chassis, D16Z6 engine.

Recently, I've been going on 4 hour drives to and from the town I'm going to college in to get things set up. This means I take the 4 hour trip down, do stuff for ~4 hours, and take the 4 hour trip back. Roughly 8 hours of highway driving. I've done this twice now.

The first time, all was well until I got off the freeway coming home. I noticed that (a) the temperature was slightly sporadic when I'd sit at a stoplight and (b) it would return to normal after accelerating. When I got home, I popped the hood and noticed that (a) the radiator cap was hissing, probably indicating a pressure loss and (b) the coolant overflow tank was overflowing; full to the brim.

I kept an eye on it for the next 6 weeks. It would regularly be low and I would fill it, though the temperature wouldn't fluctuate as I drove it. I replaced the radiator cap, the thermostat, and drained, flushed, replaced, and bled the cooling system.

During the second trip, when I got off the highway, I parked and let her idle for a few minutes, and the temperature started to fluctuate again. I shut her off as soon as I noticed and let her cool down for 10 minutes or so. Upon inspection, the coolant in the overflow tank was above the max line, though no pressure was leaking that I could hear. I turned the engine back on and carefully revved it up. I noticed that when the temperature was high, revving it would bring it down. After I left the parking lot I was in, the temperature remained constantly where it should have been.

When I returned, I popped the hood and found that (a) the coolant was too high in the overflow tank but too low in the radiator and (b) the dipstick brought up no oil. I turned over the engine for just a second to see if there was *any* oil at all, and some splashed onto the dipstick. I poured in about a quart-and-a-half to get it back to an acceptable level. Also, (c) I assume it had to have been burned since I couldn't see any leaks under the car. Another thing to note is that the oil level was fine the week before I went on the trip.

TL;DR: Coolant overflowing & oil loss after long roadtrip.

Any help is appreciated. Thank you so much!

 
Rep Power: 244

Could be a possible head gasket leak.

Can you do a compression test?

How many miles was this road trip?

 
Rep Power: 222

Probably the head gasket, and while the head is off you should pull the pistons out and replace the rings

 
Rep Power: 0

I think I can do a compression test. I've never done one, but I've got the manufacturers' manual and I'm sure I could rent a compression tester at Autozone or something, if not just buy one from Harbor Freight.
The trip was a little less than 400 miles round trip.
EDIT: added an apostrophe after manfuacturers.

 
Rep Power: 518

Sounds like it has a blown head gasket.

And it probably has an oil consumption issue, although you didn't say how long ago the last oil change was.



Compression test would be a good thing to do, but it isn't likely to prove it has a head gasket problem.

 
Rep Power: 244

I asked about mileage because you can burn up to a quart of oil per 1000 miles and it be ok. This is assuming it was full before your trip.

It can pass a compression test and still have a head gasket issue so it could be a waste of a test. Like ezone said it most likely won't prove a HG issue.

 
Rep Power: 0

Last oil change was at 140k, currently at 143,400.

 
Rep Power: 0

What *will* prove a head gasket issue?

 
Rep Power: 518

Test for why it's doing what it's doing.




A compression test is a good idea though. At least you'd have some sort of baseline..... If you have a low cylinder then you will need to figure out why (valve job?)