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1997 Honda Civic overheating issue

I just received this car as a freebie but it has come with an issue or two. The most pressing is a cooling issue. They gave it to me with the words, “The radiator leaks”. Upon some testing this doesn’t seem to be the whole picture.

  1. If I fill the radiator up, leave the car parked over night, the next morning the radiator is still full.
    so I assume it is leaking from steam venting or from something else.
  2. The car overheats very fast when the AC is on and the vehicle is stopped. Within about 10 minutes it went through every drop in the radiator.
  3. When driving with the AC fan on medium speed, it can go a solid 30-45 minutes with no issue.
  4. If I turn the AC fan on to high it takes a matter of minutes for it to begin to over heat.

A friend mentioned something about a weeper valve? I know very little about cars. So if there was any insight as to what it may be that would be excellent.

Thanks for the time.

When the AC is on and the car idling in the driveway, you loose all the coolant in the radiator in 10 minutes? You’d think there’d either be lots of steam in the engine compartment or coolant leaking on the ground under the car when that happens. Do you see either?

Remember that the overflow tank could be empty but the radiator is still full. Are you checking the overflow tank (a plastic bottle usually off to the side of the radiator) or the radiator itself?

When the engine overheats, how are you making this determination? By a dash coolant temp gauge? Or some other way?

When it overheats, are the radiator fans (in the engine compartment) spinning like banshees? They should be.

There is a ton of steam. Both fans go. I know it is empty because after it is done it takes almost a full 2 gallons to refill. So it is going somewhere. I haven’t noticed any puddles underneath at all. The dash gauge goes way up when it starts to overheat. Which is also how I know the radiator is out of water. I mean that every time that happens it is at least a gallon of water lower than before.

So when it has liquid, it cools fine, but running it seems to make it lose liquid very fast. Higher AC fan speed means it looses coolant much faster.

“you lose all the coolant in the radiator in 10 minutes” ?? that will result in serious engine damage if you do this only once. Such as a blown head gasket.

Or, as George suggested, do you mean the coolant in the overflow tank?

Have you pulled the oil dipstick out and looked at the oil?


Ok, I see, yeah, there must be a lot of steam to lose that much coolant that fast. Can you tell where the steam is coming from? Is it all coming from the radiator leak ? The cooling system has to be pressurized to work correctly. Otherwise it will almost always overheat. If the radiator is leaking, you pretty much have to correct that first in order to have any chance at a correct diagnosis. Replace the thermostat and radiator cap at the same time. Then if it still overheats, next step is probably a cooling system pressure test.

As others have mentioned, if the coolant runs out and the dash temp gauge goes to max, even just idling in the driveway, you may have already done some damage to the engine.

You should have a second cooling fan that energizes whenever the AC is on. I’ll bet it isn’t energizing.

But that’s too fast a coolant depletion rate to be attributable to just that without also seeking other contributing causes. You may want to perform a pressure test on the cooling system. You may have a leak.

Flow test the system. That will test the radiator for flow and the water pump. You can buy a kit or have it done. Your radiator may be gumped up inside or the pump’s impellars may be eroded.

In addition, I believe this '97 uses the traditional pressure cap on the radiator that releases at 15 or 16 PSI to allow too-hot coolant to blow into and overflow the reservoir bottle, blowing excess onto the ground. Normally it allows expanding coolant to flow into the bottle and draws it back into the engine as the volume contracts when the engine cools, but if it’s overheating it’ll blow too much out and there won’t be enough in the bottle to refill the engine. A new pressure cap is a cheap try.

A thermostat is always a cheap thing to try.

If there’s cloudiness in the coolant, or gump under the cap, you may have a blown headgasket. I’d suggest a chemical test of the coolant for hydrocarbons, but in this case it’s flushing so fast that the test might be misleading. You may want to go straight to a pressure leakdown test of the cylinders. The kit is cheap and easy to use. You simply remove the sparkplugs and put a hose/plug/gage assemblage into each cylinder after turning the crankshaft by hand (via the crank bolt) until both valves are closed (you can see this with the valvecover removed) and pump about 15 psi of air into the cylinder, then monitor the gage and see how much it leaks down. The directions come with the kit. If it’s a distributor-based system, you can also tell when both valves are closed by turning the crank until the distributor rotor is at the cylinder’s pickup point for the spark voltage… it’s easier than removing the valvecover.

The “AC fan speed” is misleading. The only fan speed that controls is the fan pushing the air through the cabin ductwork. That has some minimal influence on the engine system’s ability to dissipate heat, but it isn’t major, and your symptoms are backwards for this to be causative. A “hi” fan speed would extend the time to overheat, your symptoms do it backwards. The fan that complements the engine cooling fan, that fan behind the radiator, only has one speed.

In summary,

  1. make sure the secondary cooling fan goes on when the AC is engaged.
  2. have a flow test done on the cooling system. This will test the radiator and the water pump.
  3. try changing the thermostat and radiator cap and purge the system of any air, but don’t get optimistic.
  4. test the system for leakage under pressure.
  5. test for a headgasket breech.

Post the results. We do care.

Have you, or anyone checked the AC condenser for a build up of bugs or bent fins that is blocking airflow through it and the radiator? I’d start there, but there is also at least one other problem. It could be just the radiator cap if your lucky, but I suspect it could be much worse.

BTW, if you are using just water, that is also part of the problem. Parts of the cooling system will be above the boiling point of water.

It happens with coolant/water mix.
When I see the gauge creep up I turn it off, but I just got the car a week ago so I can’t attest for what was done before hand.
The radiator doesn’t lose water unless running.

I don’t know what to say about the higher AC fan thing, it is exactly what happens. With the AC on and teh fan set to 2, it goes about 30 minutes in the hot 115 degree weather we have. If I turn the blower fan to 4 It lasts about 10 minutes.

The temp creeps up (I have seen it go to high once but now I just shut it down)
I open up the cap and it is about a gallon lower than when I started it.

When there is water in it, everything cools great, it just starts to burn through water/coolant very fast.

I would assume it is bad to use only coolant rather than a 50/50 mix to see if that helps?

I can get a new cap no problem though.

One thing that could cause the temp to rise faster with the fan on high is that the AC condenser is blocked. That would block airflow to the radiator and with the blower fan on high, the AC is dumping more heat to the condenser and that would transfer to the radiator.

But that does not account for the coolant loss. I suspect that the problem is the water pump which is driven by the timing belt. Your timing belt should be changed every 7 years or 105k miles, whichever comes first. The water pump should be changed with the belt and if it is leaking, it can cause the belt to break and that will ruin your engine. This is an interference engine and that means valves and pistons collide when the belt breaks.

If you see coolant coming from the bottom front of your engine, do not drive any further. Coolant is very bad for the belt. I would call your Honda dealer and get a quote for a timing belt service, thats the belt, water pump, coolant, oil seals etc. Honda dealers often have a special on this that is less expensive than an independent mechanic.

There are a lot of other places it could be leaking that would not be as expensive, but you need to locate the leak. Worse case is the head gasket is leaking and if so, you would see the coolant coming out the tailpipe, possibly as steam or white vapor/smoke.

Check your oil too. If it looks like a chocolate milkshake, then coolant is getting into the oil and that too is very bad for the engine. It won’t run long like that.

Oil looks fine, though it does lose a little, but it is an older car with 200k+ miles.

It is only overheating due to loss of coolant. I was hoping to have it narrowed down to something specific as my mechanic allows me to buy my own parts. But I think the best course of action is probably just to have him look it over and do what needs to be done. On a very fixed income (hence free car with issues is the only thing I got).

Thanks for the insights guys, looks like it could be too many things to buy a part without having my guy look at it first.

I think you may have the cause and effect reversed. It may be losing fluid because it’s overheating, rather than overheating because it’s losing fluid.

The difference?

If it’s losing fluid because it’s overheating, you need to find the cause of the overheating. That can be a clogged radiator, a worn out water pump, or even a blown head gasket.

If it’s overheating because it’s losing fluid, you need to look for where/how the loss is happening. Possibilities include a leak, which could be in the radiator, the water pump, or even the heater core, or a bad radiator cap allowing the fluid to blow out rather than holding pressure.

Start by going back to my earlier post. That’ll get you started on determining which of the two possibilities is the cause and which is the effect.

Over the internet not possible of course to make a diagnosis. But I’d guess if you are losing coolant and seeing steam – but only when the engine is running – you have a radiator leak, near the top of the radiator. I had that happen on my early 90’s Corolla 3-4 years ago, so a radiator leak on your 97 wouldn’t be very surprising. My Corolla’s radiator sprunk a leak at the junction of the metal part and the plastic tank above that, near the top of the radiator. The replacement aftermarket part cost around $90 is all, and it took maybe 45 minutes to replace.