My 2002 Ecotec Sunfire with 200k is losing a small amount of coolant based on my having to top off an inch or two in the reservoir every other week, but I can't find any sign of a leak. I left it idling for an hour with a sheet of cardboard underneath and nothing. I left the sheet there overnight, and nothing. Hose attachments are all tight and the engine is bone dry. No overheating issues and no suspicious exhaust. It runs perfectly fine.
Any thoughts on where to investigate next?
Thanks.

Cant say for sure but my older cav used to blow coolant out of the overflow while driving. Turned out to be a clogged rad.


ReD RaiN

As an update, I rented a cooling system pressure tester and my system won't hold pressure at all. Once I pressurize to 15 psi, the needle slowly begins falling and in a couple of minutes all pressure is gone. I couldn't see or hear any escaping fluid during the test. The bottom of my engine is bone dry, as is the radiator, all the hoses, and the connections on the pipe that goes from the thermostat to the back of the water pump. I don't smell or see coolant in the passenger compartment, and I pulled a cold oil sample from the drain plug and the oil looks perfectly normal.
I'm totally stymied.

Head gasket leaking into one or more cylinders?
A small leak might not affect engine performance, and the coolant would go out with the exhaust.

Time to check those spark plugs and find out if they are nice and clean from a steam bath. Seriously, the head gasket may be going and it is just a slight leak at this time. If the spark plugs look normal, then either the heater core is leaking or the radiator. Heater cores are no fun to replace but I would imagine there would be a smell in the cabin if that were the case.

I pulled the plugs and they all look approximately the same, clean. This car gets almost entirely highway miles. I don't see a drop from the radiator, and I don't smell or feel anything in the cabin. I'm changing out the surge tank on the chance that something is leaking there, and I'll see how that pans out.

I had a similar problem with mine. Was a clogged radiator, when it got hot, even a little it would boil out the overflow. A new radiator is fairly cheap.

Othan than the fact that mine had a mismatched head I had to mill to fit, which the donkey manure before me did, and gooped the holes with jb weld, I had a compression leak despite no visual bad spots in the old head gasket.

These cars by this time get "loose". I had no power or driveability issues if I kept it out of higher rpms (5-6000 rpm). If I consistently pushed it hard I could overheat it though.

Considering you dont have an appalling mismatched head, I suggest running a decent (no large particulate crap) gasket fix in a can now (blue devil, bars stop leak) and keep the revs down the whole time you do the pricess. This kindof stuff does work for the small stuff as long as the compression leak isnt blowing at idle, because once the engine isnt running but still hot, the coolant pressure can get it in there, and some "around" it too. I suggest bypassing the heater core for this job.

I just replaced the head gasket bolts and the gasket which I had modify extensively with the head, but it ran a lonnnng time with the compression leak with no overheat issues. I hated doing this job on the 2.4, just about as much as I hate the plastic "thermostat" housing spigot pos thing on the side of the head. Im making one custom tomorrow, and I would check that extensively if I were you, they suck bad. On these engines a drop or two can disappear really easily when hot or just collect without dripping on many places on top of the transmission, if there was a leak not to the head, its definitely your culprit.
..I used a whole tube of red gasket seaker on that pos like 2 weeks ago and it has failed again already. Time for a metal one, I may take a picture for those diy people here.

Cheers.

John Myers wrote:I had a similar problem with mine. Was a clogged radiator, when it got hot, even a little it would boil out the overflow. A new radiator is fairly cheap.

Happened to my buddy's truck, no signs of leak at all. We just recently installed the new cai, fabfours bumper and winch on his truck. Pressure test fails intermittently and the new radiator solved the problem.

Update: Well I put a new coolant reservoir and cap on and nothing changed, so I lived with it over the winter. In troubleshooting this year, I've done the following:
New water pump
New radiator
Compression test: all cylinders fine/about the same
Leak down test: All cylinders in the green about 15-20% and no bubbles showing up in the coolant tank
I currently have my heater core bypassed to eliminate that as the source of the leak.
No overheating issues
No white smoke/exhaust
Oil looks perfect
Not a drop of coolant under the car
I pressurized the system to 15 psi and it loses about 1 psi/10 minutes

I seem to be losing about 1-2 mL of coolant/mile in this hot weather. Which seems excessive and an amount that should show up somewhere, either as contaminated oil or something symptomatic of a head gasket issue.

I'm completely flummoxed. I really down't want to put any "system sealer" inside my engine beyond the old school Bar's leak tabs made of ginger powder and walnut shell.

Any insights?

Thanks

Dan