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Loss of coolant

'95 Civic 220k 1.5 auto runs great, 40 mpg. I call her “LUKA”. Recently noticed a slight loss of coolant, about 1/2 cup per 200 miles. No drips or puddles, no coolant in oil, just changed 500 miles ago and still golden and clean. I may have noticed a little more exhaust, maybe my imagination, certainly not a cloud of steam. Ideas? I intend to slip a piece of cardboard under her this weekend and let her sit and alternatively run the engine to check for small leaks, can’t do it right now as it rains every other day . . . hope for a dry weekend. Comments? Rocketman

Sounds like the start of a blown head gasket. Loss of coolant with no puddle under the car, “more exhaust” is the steam from the coolant leaking into the cylinder and becoming steam. Classic head gasket failure. Get some stop-leak in into the radiator ASAP and start saving your money for a new head gasket. If you are very lucky the stop-leak might solve it for a long time, if not, keep your cell phone handy for the tow truck.

Thanks Mustangman . . . kinda what I was thinking . . . but the steam isn’t all that pronounced, I just figured it was due to the cooler Fall temps . . . no steam in the warm afternoons, mostly in the mornings. The coolant loss isn’t really bad, I’m going to look for a leak this weekend and start pricing the parts for the head gasket, maybe timing belt and water pump while I have the head off. My problem is time to do it as I’m really busy this time of year, I have two jobs and I’m a high school soccer coach and we’re right in the middle of the season. Thanks again! Rocketman

A ½ cup per 200 miles works out to about .06 teaspoons per mile, or just a few drops. With this amount you could have a small leak that evaporates before reaching the ground. Assuming it’s the head gasket seems a bit premature. Try borrowing a UV light from your science dept. Or buy a UV flashlight. In the South West they sell them for spotting scorpions at night. Your coolant may fluoresce just as it is, if it does look around for possible leaks. Don’t forget to consider the heater core.

It might just be a small external coolant leak. A hose or something. Or sometimes you’ll get a little leak from the water pump, which means time for a new one. Take a flashlight and look in all the nooks and crannies, especially the waterpump. Usually there is a small visible hole in water pumps; it’s there for a place the leak to go. If there’s a water pump leak, water comes from that hole.

If your radiator is orginal, I wouldn’t at all be surprised if it is spring a leak too. No problem, radiator replacements are usually cheap – especially for cars that have a big sales volume, like the Civic. There’s people making replacement radiators like crazy for Civics some place in the world as you are reading this post.

Your idea of putting some paper or cardboard underneath and looking for drips is probably the place to start. At 200k+ could be a head gasket, but I wouldn’t assume so at this point of the investigation. If you do develop evidence to support a leaking head gasket, no harm done to retorque the head bolts first to see if it stops the problem.

Have you checked your transmission fluid? There is a heat exchanger for the AT fluid in the bottom tank of your radiator.

Check the lip around the top and bottom radiator tanks, they can start to leak and it can be hard to notice at first. Also check all the hoses, our 97 Accord started losing coolant at about the same rate as your Civic, but it turned out to be the heater hose just under the distributor, the distributor had been leaking oil and caused the heater hose to swell up. There is enough heat in that area to evaporate the coolant before it builds up.

I recently had a cooling system leak that was hard to replicate and then get underneath when the engine was hot. The only way to create the problem was block part of the radiator to get it a bit hotter than the middle of the gauge, then run up hill. But getting home to my ramps was long enough to let the pressure drop just enough that the leak would stop, and residual water would have evaporated, even when I let it idle in my driveway afterward. So I borrowed a cooling system pressure tester from Autozone, pumped it up to 14 psi, and found a leak in a grand total of 87 seconds without running the engine. MUCH easier. So if your problem is a small leak in a hose or the radiator as suggested above, that’s the best way to search for it. I hope that turns out to be the explanation for your coolant loss. Think good thoughts.

Finally had a dry day to look at my minor coolant leak. No drips whatsoever after running the engine and sitting the car. So I ran the engine, went for a ride, then pulled into my driveway and let the engine run. Within a few minutes I found coolant coming from under the radiator cap as the coolant was trying to get into the overflow. Inspection of the cap revealed a crushed gasket, which I ordered for tomorrow at AutoZone. I replaced the radiator 2-3 years ago but didn;t replace the cap ( a new one did not come with it) so the cap is 17 years old. Gonna try a new cap tomorrow. The overflow has me puzzled. Is it normal to have coolant going into the overflow when the temp isn’t spiking? The temp never went up a hair. I’ll let you guys know. Thanks for the responses. Rocketman

I guess it is possible the overflow tube is plugged. That overflow tube is supposed to allow any fluid pushed up past the cap by the coolant pressure. The cap is designed to let fluid past it once the pressure reaches a certain psi, so that the fluid isn’t lost and the pressure stays within limits. A block on that tube (between the cap and the overflow tank) might put more pressure on the radiator than it is supposed to endure. Worth a look anyways.

Update! Problem solved! I simply changed the radiator cap (the old one was 17 years old and had two cracked gaskets inside) , filled it up with coolant and then drove 125 miles round trip to one of my jobs. Let it cool off and viola . . . didn’t lose a drop! Go figure. A cap. Guess it’s a good idea to start simple . Thanks again! Rocketman

Yes on “start simple”. It doesn’t get much better than this…no tools or skills necessary, probably don’t even get your hands dirty, …and cheap. Wish more problems were that simple!

You need a pressure test of the whole cooling system. A small external leak will show up that way. I have had numerous of these small leaks over the years, ususually a rad hose, heater hose and twice the heater core. If the interior smells of stale currie, and the windshield fogs up ever so slightly, you have a leaking heater core.

If the pressure test shows no external leak, you have the beginning of a failing head gasket.

If that is the case, I would repair it now, rather thatn let it get worse and leave you stranded somewhere.

Thanks Doc . . . I’ll give it a system pressure test as soon as I can. No smells in the passenger compartment . . . no windshield fogging beyond what normally happens due to weather, but nonetheless I don’t want to worry about this forever. A pressure test is easy and cheap, my favorite type of test! Rocketman

Hey Doc! I pressure tested the system this past weekend (first chance I had) and found a leak on the heater hose going from the head to the heater core! It was right at the core on the firewall down really low and the coolant apparently dripped onto the exhaust and was vaporized! Changed the hose and refilled with coolant, glad I checked and I’m really glad you made the suggestion. You may have saved me from one of those “dark and rainy nights” episodes. Thanks Doc! Rocketman