98 civic ex coolant loss (no other symptoms)

i’ve got a 98 civic ex with 151k that has a really strange problem that multiple mechanics (and i) can’t make heads or tails of:

basically, all that’s happening is that my coolant levels are dropping very quickly, but there’s no sign of anything else bad going on at all. pressure tests everywhere are ok, the oil is clear, exhaust is fine, coolant color is fine, there’s no sign of a leak anywhere, etc. but if i drive for more than 5-10 minutes, i’ll often have to reload the coolant as it’s dropped pretty far below the max in the overflow tank.

the engine runs smooth (it’s a little louder than when i bought the thing at 110k, but only marginally so, and this definitely isn’t something i’m worried about), mileage and engine temp are fine, never had anything close to an overheat, etc. literally the only thing going wrong is that the coolant is going down too quickly.

my most trusted local mechanic can’t make heads or tails of this, either. he said that the only thing he can think of is that there’s an internal leak somewhere, but he also said that makes no sense considering that there’s no even slight hint of a head gasket problem.

the only thing worth mentioning is that i had my radiator replaced in march of this year by a mechanic that i’ve since discovered is a pretty complete idiot (he didn’t tighten hoses adequately afterward, and jammed the wrong type of oil pan plug into my pan, costing me a couple hundred bucks). it turns out that this repair was unnecessary, and that what we thought was a bad radiator was the overflow tank/hose seal breaking due to extremely cold temperatures (~-50 degrees–this car goes back and forth from VA to northern saskatchewan in canada with me, where i split my time).

any thoughts? any tests that i should have done that we haven’t already? i need this car to not die on me when/if i take it back north in a month or so, as it’s pretty dangerous to break down in the middle of nowhere when it’s that cold.

This CANNOT be that hard of an issue to solve…

Is your rug wet in the car…the passenger footwell area?

Do you have STEAM coming from your tailpipe?

Leaks? Puddles?

Start it up and leave it in one spot… Fill the rad and see what happens…IF you have a constant steam cloud coming form the tailpipe…(just like when the engine is cold and warming up)…If you have steam when the engine and exhaust is hot…then that steam is your coolant…

Honestly this wont be hard to target if you just pay attention…put a dry piece of cardboard under the car and start it up and let it get hot… Could also be that it leaks when Hot and driving…and the system is under pressure?


The only advice I can give you is that a 14 year old economy car with 151,999 miles on it and an undiagnosed coolant leak is not what I would chose to commute to northern Saskatchewan.

rug wet? nope.

steam? no. the exhaust is completely clear at cold start, after idling a while, and after driving at highway speeds for 15+ minutes.

leaks/puddles? no sign of anything. i’ve done the cardboard test, and there’s no sign of anything.

the leaking when hot and driving thing is the only thing that i can think of, too, but shouldn’t that continue if i heat up the engine at high speed and then sit it in the driveway afterward?

the only sign of anything leaky is that there seems to be more gunk than usual under the distributor on the left side of the engine, but i and other mechanics have assumed that that’s residual stuff from when we discovered the leaky hoses due to the horrible rad replacement earlier this year (no sign of anything new forming and the gunk here is old-looking).

the next step we’re going to try is to clean the heck out of the engine and see if anything new forms.

ha, yeah re: the car i’m talking about/northern sk. the thing is that i commute up there to do volunteer work on a native reserve and it’s kind of important that i don’t drive somthing nice up there as a white guy or it makes me seem a little too foreign to the locals, which can lead to bad things in a multitude of areas as the work i do there depends a lot on trust, etc. between those concerns and the wild temp changes between sk winters and va summers, there’s no way i’m bringing something remotely valuable up there, which would both make my work harder and just be a hemmoraging of money.

if i can’t figure out what’s wrong here, i’m going to pick up a used awd to take back up there this time, but i’d rather not spend that money unless necessary.

I had the same issue on our 97 Accord. In my case, the root cause was the distributor shaft o-ring. It was leaking oil onto one of the heater hoses just below it. The oil caused the heater hose to swell up and it developed a small leak. The leak was hard to detect because it did not accumulate under the hose and as it ran down the side of the engine, it would evaporate before it could drip onto the ground.

The Accord and the Civic do not share the same engine, but if you have a heater hose just under the distributor and the accumulated “gunk” under it, then this would be worth a close inspection. Put a paper towel under the hose and see if it gets wet, thats how I found mine.

Hmmmm…That gunk is your distributor O-ring leaking at the distributor…SUPER COMMON on that and all HOndas really…

Wow…seems you have invested some time and energy here… Have you by chance smelled your exhaust? Smell normal? Also…have you looked at the drain to your A/C system for residue of coolant? Might be time to get out the Dye kit…

As Keith mentioned…This is the Dreaded Upper heater supply hose…ALSO MASSIVELY COMMON Issue…thankfully it is easily remedied…not hard at all to replace and costs about 11 bucks

I beg to differ on the “not hard to replace” part of your statement. On the Accord, it required removal of the upper intake manifold to get at the clamps to the heater core. I replaced all my heater hoses and teh heater control valve at that time.

well, i just picked up the poor thing, and it seems to have magically fixed itself. the mechanic checked the distributor/heater hose, and all was fine. the only thing that i can think might have happened is that the loose hoses due to the crap radiator job allowed enough air to get into the system that when we bled it the other day, it didn’t quite get rid of all the air in the lines?

in any case, they ran it for an hour and it was fine, then i drove home for 20 minutes and it was fine. i’ve got a month before i head back, so i’m just going to keep a steady eye on things for a while and see what happens.

thanks for the help, everyone.

Naw Keith…I just sold my 96 and did it on that one…I also just did 3 of those hoses last week (pre 94’ which are MUCH easier also)… 8 total last month…super duper common… I usually check the hose and warn the customer about it PRE-failure…so I change a lot of those puppies. Having the car on the lift is a Godsend also…but that’s almost cheating… Yeah I hear you about the heater core hoses and being hard to get to…not from the bottom tho…I stopped trying to do it from above LONG ago… LOL You removed the intake? Jeez Louise bro! From the bottom Grasshopper…from the bottom. I CAN see why you did that tho as I pondered it at one time…briefly…but pondered it nonetheless… LOL… Man that would turn it into a JOB bro…

What I do is remove the distributor (On 92 - 00 models)…and its cake from there…BUT from the bottom! lol Much easier than with distrubutor in situ as that clamp on the head is HARD to get to for sure! I’ve probably done more than 80 of those hoses thus far…practice makes perfect I guess… They’re easy to ME now…but I think you may be right…maybe I shouldn’t have said that…Not easy for all I guess. Maybe a bitch if you leave that distributor in place tho for sure…But I ALWAYS remove it…because the oil it leaks onto the hose is what softens the rubber and kills the hose…so I tackle two issues at one time… Fix the oil leak and do the hose in one shot

IF you didn’t get all the air out of the system you would have known it right off the batt as the AIC valve would have been throwing a fit…and your idle quality would be non existent…It would have been “hunting” all over the place till bled… It was probably the lower rad hose leaking when you were moving…or a loose rad drain… Sounds like the guy who did the Rad job was really absentminded eh?


I removed the distributor to replace the o-ring. The tangs on the hose clamp at the heater core pointed up. I got those off with a long, offset needle nose pliers. I could not pull the hoses off, even from the bottom, just needed more room to get leverage. I ended up cutting one off. They had been there for 14 years.

Removing the upper half of the intake is easy.

I have been using a bit of a trick to get hoses off…You use a pick…usually angled (I have a nice non sharpened Snap-On pick sold just for this purpose) You loosen the clamp and then use the pick to lift up a portion of the hose as if you were going to pry it off…but dont pry…once the pick is inserted between the hose and whatever its on…you spray WD-40 or Blaster on it…then move the pick around further to spread the lube…

The hoses then pop of as if they were Buttered ! I guess they sort of ARE buttered at that point…but Yeah…using a pick to get off stuck hoses works like a charm…and its safer…no smashed or cut knuckles any more…no more deformed or damaged heater cores or broken (usually plastic) heater valves etc… Been doing this for almost 20 years now. The hoses at the core and valve are REALLY stuck on there arent they?

Ever hear of doing that? It was a surprise to me when I heard/saw it done years ago.


I don’t have a Snap On pick, but every other pick i bought bent like it was made from butter.

OP. you may find that the problem returns. A few other suggestions:

  1. Check the radiator cap. You could be vaporizing the coolant out of the radiator.

  2. Check the oil. Mayonnaise appearance would signal a head gasket problem even if the engine seems to run fine.