Disappearance of radiator fluid

My 2005 Nissan Sentra loses about a teacup of fluid from the radiator overflow bottle every 3,000 to 5,000 miles. I first noticed this at 3,000 miles - have had it in to the dealer over 12 times and he looks at it, cannot visually find a leak, has sent it behind the wall twice only to mark a line on the bottle and add fluid. The car now has 68,000 miles on it, runs like a charm, starts right away, gets great mileage and for the first time in its history, the “Check engine light” came on for 3 miles. It went out. I took it to the Nissan dealer who took it behind the wall, then told me I had a P0303 error - the 3rd cylinder was misfiring - which meant I needed a new head gasket at a cost of over $900. Notice the car is now ‘out of warranty’. I have driven it another 1,000 miles and it starts and runs beautifully. What is causing this? Do I fix it or drive it?

How did they justify the leaking head gasket diagnosis? A misfire can be caused by many things, and the small amount of coolant you are losing is not much to worry about. There are tests to positively confirm a leaking head gasket. Did the dealer perform any of these tests?

I suggest you get another opinion, from someone other than the Nissan dealer. Maybe all you need are new spark plugs.

It’s not possible to go directly from a misfiring cylinder code to a new headgasket diagnosis.

If he didn’t do any other analysis such as a pressure leakdown test and/or checking the coolant for the presence of hydrocarbons, and/or watching the coolant bubble while the engine runs (that’d be the combustion gasses blowing through the headgasket breech into the water jacket and working their way up to the radiator fill), then I’d be extremely suspicious and go elsewhere.

If he did other analysis and determined that you indeed have a breech in the headgasket in the #3 cylinder, then that would explain the coolant losses…coolant is being drawn into your cyliders in small amounts in the intake stroke and burned. If you continue to drive it the breech will become bigger through erosion, your coolant losses will increase, and ultimately the heat from the combustion process blowing into your water jacket will overtake your cooling systems ability to dissipate it and you’ll overheat. Meanwhile, you may even develop a breech into one of your oil passages, your oil will become contaminated with coolant, and your main bearings will begin to disintegrate. In short, if you have a headgasket failure it needs to be fixed.

Like any major, potentially costly repair, you want a good diagnosis and a good second opinion before proceeding anyhow.

I received no paper work for the tests they did. He orally indicated that he pressure tested it - opened number 3 cylinder and found it dry. He got to this point by going into the computer chip memory bank. I’m the one that suggested the head gasket leak - as I have for 12 times at the dealer. I am on my 5th service manager and only once - at 22,000 miles would they put anything in writing. I think you have a good point on the spark plug misfire! I’ve also considered ‘bad gas’ as a possibility for a quick ‘light on’ warning.

I have felt, since 3,000 miles, the head gasket was at fault - my opinion. The 5 service managers that I have dealt with didn’t seem concerned. The latest manager did run the ‘chip check’ and informed me that the car would be hard to start, run rough and eventually destroy the engine if not fixed. In my mind, I have a rough time with this as the car has run without any problems for 68,000 miles with this limited loss of fluid. The light only came on once for 3 miles and has not reoccured and it starts and runs as well as when new. I definitely will be getting a second opinion as has been suggested!

if you had a head gasket fault 65,000 miles ago (when the car was new) you would have ruined you engine by now.

so i doubt seriously that this is a head gasket leak. (this is unless you have proof by some test [not just your hunch])

As earlier mentioned there is NO connection between a misfire and a head gasket. The (also mentioned) tests would either confirm, or eliminate a leak of exhaust gas into the coolant, a reduced pressure on one cylinder, or just looking into the radiator for bubbles.

Also, you dont specify, but what exactly do you mean when you say a “teacup from the overflow bottle?” Does the antifreeze leak out of the reservoir? or is the reservoir low? Is there any stain under the car? Just curious, but what surface do you park on regularly? Any chance to put a clean piece of cardboard under the car to check for drips?

How does this overflow? How are you determining that this is a teacup full? What is the level at when you start the car up cold? (Min, Max, or in between) When you add fluid what level do you fill the overflow bottle up to?

You do realize that the level in the overflow tank DOES change up and down as the car is cold, hot, and either cooling down or heating up? For instance if you actually filled up the overflow bottle to the TOP, as you drive the bottle would overflow, and when you let the car cool down it would be lower (by the amount of coolant sucked back into the radiator.)

When making my first oil change, I noticed that the anti-freeze in the overflow coolant bottle was slightly below ‘minimum’ with the engine cold. I brought it up to a 1/3 of the expansion area, leaving room for expansion and overflow. When the dealer looked at it, he saw no visual leakage, no smudge marks, hand tests - feeling for moisture in areas not visible - did not detect any moisture. He filled it to the max each time and the engine was hot. He also suggested I put cardboard under the car to check for leakage. The car sits in a concrete floor garage and no indication of leakage has been shown on the concrete floor nor on cardboard put there. There is no steam coming off the engine or white vapor out the exhaust. Oil changes show no sign of water. I too believe the engine should have fried itself if it was a serious head gasket leak. I only add fluid when the engine is cold and the resevoir shows below minimum. The fluid has never disappeared completely from the resevoir but tends to consume anything over the minimum line.
It was the dealers ‘supposed test’ - which I did not watch - on the memory chip that resulted in the code error. The “check engine” light also did not reappear after the car sat overnight. I did drive 30 miles to the dealer - without the light - and he said the code would still be stored in the chip - which I cannot argue with. All other fluids in the car are fine and the gas cap seals tight. There was no apparent reason for the light to come on at this point and then go out and stay out after driving less than 4 miles in the city.

there is another option, if the car tests out fine, and the radiator holds pressure, the expansion tank itself may have a crack in it. i have seen a tank with a crack about half way up, and it could be a similiar problem with yours. if the tank was cracked, when the fluid expanded, and rose up it would seep out, and upon parking (and cooling) it would contract and NOT leak, but there would be a loss of coolant. since it leaks and doesn’t leave any coolant while parked (cooling down) it seems it only leaks upon heating up. kind of far fetched, but what else is there?

have you tried leaving the tank as is, at the lower level to see if it works lower than the marks?

There’s a scientific method for determining a head gasket problem and while a 303 code could mean a head gasket fault this diagnosis should not be tossed around lightly.

A compression test, cooling system pressure test, hydrocarbon test, and the use of a vacuum gauge should all be used in the diagnosis of a potential head gasket fault.

Normally, one suspects a 303 misfire code as being the spark plug, wire, etc.
If a head gasket was bad enough to cause a 303 code then the engine should be running slightly rough at idle. I’m extremely dubious about your having a bad head gasket and I also believe that any shop should always write down the results, on paper, of any testing they do in this area.

After the vehicle has been sitting all night and is stone cold, loosen the radiator cap. If you hear a faint hiss then chances are you do not have a cooling system leak anywhere, even in the head gasket.
Tighten the cap back up, start the engine and allow it to idle for about 45 seconds or so. Shut the engine off and quickly loosen the radiator cap. You should NOT hear a faint hiss at all. If you do then it’s at least possible you could have a head gasket problem and this falls back on the testing methods mentioned; all of which should be used IMHO.

Are those MIN and MAX readings on the bottle for a hot, running engine or a cold one at rest?

(Also, if any coolant is entering the combustion chamber this is usually noticeable by reading the spark plugs for any abnormality.)

Thanks! I’ll check it out in the morning. The 303 code only came up once and at that point the coolant bottle was over half full and the car had been running over 30 miles at highway speed without a glitch. I only added fluid when the engine was cold and the fluid was at the minimum line. The dealer was the one who wanted to top it off at the maximum line and it was always hot when he did it. I definitely will have a non-Nissan mechanic check it out the first part of the week - when they can get it in.

We thought we had inspected the bottle, hoses and clips on several occasions. I will check again. I am at my wits end as I have never encountered something like this before. I have even given thought that there could be a leak in the defroster area when the heater is turned on and the fluid evaporates prior to being able to leak. It’s almost too far fetched for me to believe and I have not checked this out.

It’s morning. I removed the radiator cap, which was under pressure. My wife thinks she heard something. I then started the engine, let it run for about a minute - which may have been too long because after I shut it off and opened the radiator cap, anti-freeze ran over the top. It started on the first spin. I recapped the radiator - started it again and went to church - just came back from church and the engine starts perfectly, runs smoothly and has plenty of pep. I’ll try again tomorrow before heading out to a private shop mechanic.