Hi everyone, i have a 1991 Accord (CB9) with the F22A6 engine. Starting a few months ago i noticed quite a significant coolant loss. After a 1200mile drive i need to refill about 1-2 liter/quarts water, but driving in town, it takes about 1-2 l every week over only 100-200miles. I changed the radiator cap and later tested it with a pressure tester, and it is fine. I checked all the hose connections, even all the small one's under the intake manifold, using a pressure tester at the radiator and later also with the engine running and hot. Even the waterpump does not leak much (if at all) - i haven't removed the timing belt cover but i pulled out its gasket down below, and even there is nothing dripping out. There is nothing dripping anywhere under the car.

There is another symptom, that i initially thought to be unrelated: In the first few seconds after starting the engine from cold, it does not run well, as if it misfires or so, but after 2-5 seconds it runs fine. I have been adding fuel system cleaner to the fuel since a few weeks, but it does not improve.

Now, how likely is it that the coolant escapes into one of the cylinders through a crack or headgasket leak, and how to properly diagnose this? I haven't checked the compression after this coolant loss appeared, but with the radiator cap off, the coolant level does not go up after starting the engine. The oil is not milky, so no coolant gets mixed into the oil. The engine never overheated in the last 12 years and 170kmiles, since i had it. It does not overheat now also, the temperature gauge shows all fine.

Or could the coolant escape somewhere else?

 

Compression test it

 

The head gasket is blown. The rough start in the morning is coolant entering one or more of the cylinders and is interfering with the spark event. Remove the spark plugs and look for rust on the threads or tips. Also use a flashlight and look into the cylinders and you will find one or more of the cylinders are cleaner than the others.

 

Thank you. Earlier today I tested the compression with the engine cold: All cylinders show about 140psi (139-142), which is within specs (135-170psi). The sparkplugs don't show anything unusual either, no rust. I will measure the comression with the engine warm sometime soon. Then i will also look into the cylinders with a flashlight.

If indeed the headgasket is blown, the leak is probably still rather small. What are the chances of successfully fixing this with one of those coolant additives, like sawdust? And which one would be good? Any experiences? (I don't think i have enough time for a proper headgasket repair.)

 

Your compression numbers indicate your head is fine. Rent a cooling system tester and pressurize the system and find the leak.

 

Compression numbers wont indicate a fault in this case. Dont bother with further testing in that vein. You can however rent a cooling system pressure tester and pressurize the system 5 to 10 psi higher than spec. Leave the tester on for 4 to 5 hours(If no immediate leaks surface of course.) After 4 or 5 hours, look into the cylinders for the offending hole(s)
Blue Devil seems to be the best one I have come across.

 

Great info here, but there are other things you need to check before you go too far in your diagnosis.

These Honda motors are designed to release some coolant into the reservoir if the pressure exceeds the radiator cap's PSI rating. When the engine cools down, it actually sucks "some" coolant back from the reservoir. With this said, you must be sure that the hose from your radiator neck to your reservoir is AIR TIGHT (no leaks). Also, if you take off the reservoir cap, there should be a short hose connected to it and running to the bottom of the reservoir. This hose MUST be there, and THIS MUST ALSO BE AIR TIGHT. If there is any leak in any of these hoses or connections, your cooling system will suck back AIR instead of coolant from the reservoir. If your cooling system sucks in air, your coolant may reach boiling temperatures as it is ejected into the reservoir, and it will evaporate into the atmosphere. This will mislead you to think that you are burning it in the engine's combustion chamber, assuming that there are no signs of leakage. A simple Zip tie will usually work to keep these lines air tight.

This is something that a lot of us overlook. And be sure that you keep the proper level of coolant in the reservoir too. In a good functioning coolant system, the coolant in the reservoir will actually rise and fall along with the engine's temperature. The reservoir DOES NOT ONLY CATCH OVERFLOWING COOLANT. It provides coolant to your engine if a negative pressure situation occurs.

A simple way to test your rubber lines is to remove the line from the radiator neck and blow it (like a balloon) while you pinch/plug the other end at the reservoir cap. If there is a hole, replace the hose with a new one. If it does not fit tightly when it is installed, put a zip tie on it to keep it air tight. Repeat the same thing with the shorter hose inside the reservoir.

Another important fact:
Your radiator AND cap should have two (2) good seals:
1) The small rubber on the cap should seat properly in the radiator and is under pressure from the cap's spring.
2) The bigger rubber on the cap should seat well on the top part of the radiator neck. This must be air tight as well.

If either of the rubbers on the cap are worn, damaged, or missing, you need to replace the cap with a new one.

If everything I mentioned checks out fine, then proceed with further diagnosis as the other members have suggested.

Good Luck, and I hope I helped!

 

Thanks for all your advise. I did use a pressure tester, but even after keeping the system under pressure for ~1 hour there is no external leak, no dripping, nothing. Over an hour the pressure goes slightly down, from about 18psi to around 17.7, but maybe even the pressure tester itself might loose that much? I haven't followed DCFIVER's advise yet, on keeping it pressurized for really long and looking into the cylinders, but i planning to do that later.

I did check the overflow container and related parts, as Spiff671 advised. They seem to be fine. Strangely though, the level in the overflow container is always the same, it never changes, never even gets any higher, what i would expect if the sucking back does not work. Just inside the radiator or the actual pressurized system the coolant gets lost.

Since it's going to get cold (below freezing) next week, i have added antifreeze and one of those head gasket sealants that are compatible with antifreeze, and i'll see what will happen.

 

My last guess would be the heater core is leaking. It's possible the block has a hairline crack that is allowing coolant to spill into the oil but not into the combustion chamber. You should drain your oil and check the color and consistency.

 

It's probably one of the hoses on the back of the block. Don't put that sealant **** in your cooling system.

The answer to find a hard to find coolant leak is always this: buy coolant dye. Borrow or pick up a $10 black light and start looking one night after a day of running. It'll be bright as day where your leak is.

Your head gasket is fine. You can ignore whoever posted that.

I advise you to replace all the hoses back there once one has sprung. It's a bitch doing it once every few months. I speak from experience.