Hi,

I have a 91 honda civic, 1.5 L and 149K miles on it. Last week I just noticied a high engine temperature and so I stopped and check the coolant and it was empty and so do the radiator.

I immediately bought a 50/50 coolant and filled the radiator and filled the coolant tank between max and min. For this it consumed the full 1 gallon coolant.

Today I noticed the coolant tank was empty again and the coolant in the radiator was also little less, I think I would have driven the vehicle for about 30 miles between this.

As mentioned in the other similar messages, I don't see any smoke in the exhaust and there is no visible leaks on the radiator pipes too. The oil dip stick shows the oil condition as normal, nothing milky white and the oil level has not decreased a bit since I changed the oil which was before 1500 miles.

What could be the problem?

Thanks

Start your car and pull the radiator cap off and see if it blows coolant out.
Of course don't do it why it really hot.
Do it first thing in the morning why it is cool.

Take it to a shop and have them pressure test to see where the leak is

Other solution... check owners manual and see what the capacity of your radiator is

The radiator could be the issue. If you bought green coolant, look for green residue on the radiator at the top. If you bought blue, look for blue. I had a cracked radiator that was cracked at the top, and when the coolant would get hot, steam would get out at that place. The crack was not visible at all, but you would see steam going out and when I turned it off and it cooled down, I could see green residue on the top at the place where it was steaming.

Also, my friend with a '91 Civic DX has had a cracked hose that was only letting coolant out when it got hot. While it was cold, no coolant would go out.

I just want to say that the fact that there are no visible cracks doesn't have to mean there are no cracks at all.

Because you say your oil is fine, I'd say that your head is still not warped and head gasket is not blown... if any of those happened, you would burn oil as well as coolant. But since you're not burning anything (no white smoke), I'd say there's a hidden crack somewhere.

Try not to drive the car around much, because your engine head is made of aluminum, and it can get warped if the car overheats. Make sure you always add coolant before EACH drive you take with your car.

And I also agree with above post about taking it to a shop to do the pressure test of the coolant system. It will point out the problem much easier.

I agree, have the radiator and cap pressure tested for leaks. If there's a leak in the radiator or cap you will see it right away and you’ll know for sure. My 1990 Civic was losing antifreeze and I got a friend that had a radiator tester and in a few minuets we could see were it was leaking and when we tested the cap it wouldn’t hold any pressure. Hope this helps.
Regards
Rjohns

I started the car and opened the radiator cap and it was not throwing any coolant, but some coolant came out as if it was overflowing momentarily.

I had the same problem on my Civic 91 DX. It was leaking one quart about every three weeks, and then stop leaking. Every time I replace the 1 quart of coolant, it would disappear again. I put coolant leak sealant liquid in the radiator, and it stopped the problem. However, it reappeared again about 6 month later. I put more of the sealant into the system, even though the instructions said "Not to add more sealant to coolant that already has sealant applied to it." Now my car gets coolant steam coming from the hood, but the rate of the leaking coolant is still about the same, one quart every three weeks. So the sealant seems to do the job, if you do not want expensive repair on the car, but it should be used as instructed.

Top up the coolant and drive your car for about 30KM during day time. Stop your car and look for any leaking rubber hose. Usually the rubber hoses from and to the radiator is a issue. Check also the cabin heater coolant supply and return lines for any leak. I had experienced leak in the radiator supply and return hoses in my 2002 honda civic. Try it.