Hey guys, this is still driving me nuts 4 weeks in. 98 Honda civic, recent radiator, hoses, thermostat (2), plugs & wires. CEL code P0420, but I don't care. Still overheating after about 30 miles of freeway/city. Engine sounds fantastic, hasn't run this great in years. Replaced the thermostat again yesterday and did a coolant flush (no shortcuts, took about 4 hours to do it completely). Refilled with coolant, bled properly (jacked the f*ck out of the front, engine was level with my chest and I'm 5'2"). Test drive--fine on the freeway, came back on back roads, about 1/2 mile from the house the temp gauge started to rise again. Normally sits about halfway. Went down again, when I parked in the driveway it went all the way to redline. Popped hood, fan is running (runs intermittently during driving, I can hear it). Bubbles going into reservoir, smelled end of hose but just good old stinky antifreeze. Just went out again this morning, opened radiator, level was fine (covering top of fins). Added a bit more and started up. Got to operating temp, there are still bubbles coming to the neck of the radiator, sometimes a bit foamy but still no exhaust smell. This has me completely stumped. There is still no oil in the coolant, oil looks fine (2 months brown, I call it, just what it looks like when it's about 500 miles before an oil change). Big cloud of white smoke when I revved it this morning, but it smelled like gas and no condensation to speak of, after about 5 seconds the smoke went away and have clean exhaust. Also I did the jump test on the temp switch on the thermo housing, fan runs all the time when jumped (by the way, 1/2" staple gun staples work great for this), when it was on I checked the gauge and it was going down slightly. Doesn't seem to be losing coolant anywhere, sometimes it won't go back from the reservoir.

Sorry for the long post, but I like details. Any ideas? Anyone? Bueller?

 

I wonder if there is a physical blockage in the line somewhere.

Did you have the heater on full blast when you were bleeding the thing?

 

With the system well-purged and you still have a steady stream of bubbles in the radiator when you rev the engine, the head gasket is probably leaking. It only takes a small leak to displace the coolant out of the engine and cause overheating. The only symptom of such a small leak may be the coolant being displaced. There might not be any white smoke from the tailpipe, water in the oil, etc.

 

Yep, heater on full blast, cap off, let it go until the fan ran 4 times (overkill I know, but what the hell). I'm fairly sure now it's a very small leak in the gasket, I say fairly small because it will sometimes go a couple of days before it overheats. On occasion the cooling system does exactly what it is supposed to, throw coolant into the reservoir when hot, then suck it back in again after cooling down...but then again it will overheat after driving 20+ miles. I just came home from work (17 mile drive) and it didn't even think about overheating. I know I shouldn't even be driving it, but with two jobs and a crappy public transportation system I HAVE to. I can't take a full day off that it would take to do the head gasket (2 days if I need to get it machined) so I am stuck between a rock and a hard place, with no gasket in between (pun intended). I'm tired of this sh*t.

One thing I thought of, could it be a blockage in one of the heater hoses? I haven't checked them out thoroughly although I know they aren't leaking. Also, I noticed yesterday when it overheated that once the rad fan came on, the temp got even higher. I jumped the fan to see if it would cool it down and temp stayed the same, engine off and key on. Bad ECT switch? Temp sensor? WTF? I don't get it. I know I should just bite the bullet and take it somewhere to get it checked out, but it's at least $100 for them to just look at the damn thing and I hate getting screwed by mechanics (maybe someday I'll post the story of my Geo Metro with bad valves to illustrate).

 

Ok guys, here's some more info:

1. Checked all four spark plugs today, all are fine (no deposits, slight combustion smell but no oil, fuel, or coolant smell/residue).
2. Finally replaced hose from rad to reservoir--reservoir still filling up after driving and not draining back into rad.
3. I don't SEEM to be losing any coolant (after cooldown I dump the reservoir back into the rad, levels equal back out as when I started), there is still no funky exhaust and no oil in the coolant or vice versa.

Goofy guy I work with had an idea, and I want to bounce it off you--when I replaced the plugs (NGK) I didn't gap them (pause for horrified gasps). He thinks that may be making the engine run too hot? Grabbing at straws I know, but I want to make sure I cover ALL my bases before killing myself with a head gasket replacement. Any ideas welcome.

 

I fully empathize.

95 Civic D16Z6.

I finally did a leakdown test to prove that the HG was blown at cylinder #2.

I did a compression test first to point me towards the correct cylinder(s) then backed off on the valve adjusters for #1 and #2 to keep the valves from opening with #1 at TDC on the compression stroke.

Next, I fitted the compression tester hose to cylinder #1 and essentially connected it to my air compressor with a regulator set to 100 psi and watched for bubbles at the radiator. #1 was negative but #2 was positive for air bubbles. The leakdown was about 5% for both #1 and #2 so watching the coolant was the difference.

If you do this, make sure the transmission is out of gear and that you removed the wrench that you rotated the crank with because otherwise you will have an air powered car for 1/2 a crank rotation and/or a wrench slamming into something when the piston is pushed to the bottom of its stroke. (You could of course avoid it entirely by starting with a cylinder whose piston is at the bottom.)

Good luck!

 

Well guys, finally threw in the towel. Last week the heater core started leaking, what with everything else that's wrong with it we decided to park it for now, went out and bought a 2010 Hyundai Elantra (with all sorts of warranties guaranteeing I won't be working on a car for a while). We're going to keep the old Civic for a while, until someone comes along that wants to get it running as it should. Can't afford to dump any more money into it. Thanks for all your help, advice, and encouragement!!!

 

Head Gasket or cracked head..

 

jeeez

If you lived closer I'd buy that baby