Hello.

I have taken my car into the shop numerous times. They have replaced the water pump and the hose to the radiator/engine. They have pressure tested the whole coolant system and cannot find any leaks.

However, every time I open my radiator cap, it need lots of water. If I drive for long distances or go a week without putting water in, it usually overheats.

I, and the mechanic, are stumped. There also appears to be no apparent loss from leaking on the ground. In January of 2004 I had the head gasket replaced as well. The secondary symptom I have noticed is a decrease in fuel efficiency. I have no idea if the two are related. The car has had all regular maintenance and only has 104,000 miles.

Does anyone have any ideas of where to look? It appears that some people have had similar problems, but not as persistent as mine. Any advice is appreciated.

Thanks!

Hate to say but cracked block comes to mind. Could be a hairline crack on the inside wall. Not saying it is but it comes to mind, another thing that comes to mind is the thermostat, when that little baby stays open some time it'll run the coolent straight through overheating the engine on little longer then usual trips and well burn some coolent, or another thing comes to mind as well, the head to block mating surface may be warped slightly letting some go into the combutsion chamber and get burned up. One way to check if it's a crack or that is well the smell of the exhaust, if its kind of sweet smelling then well its one of the two, or if its not, it may be the thermostat. Don't know on your type of car but its worth a try. If it has a heater coil as well if they get stopped up they will bulge the hose and sometimes leak and just keep the engine from cooling and burn some coolent hope it's the thermostat or something minor.

Have you tested or replaced the radiator cap? When they pressure test the system, don't they remove the cap and put the test fixture in its place? With a head gasket, cracked block, bad heater core, etc. it should show up on the pressure test. If the coolant is leaking into the engine, it should show up somewhere, large white, sweet smelling clouds of exhaust, or excess, milky brown oil. The heater core should have a drain near the bottom of the firewall. It will be about a half inch rubber tube that comes out and down. Wad up a little paper and stick it in it, not enough to stop it up. Drive the car, when it isn't raining and see if the paper gets wet. Roll up a paper towel, and wrap it around under the radiator cap and see if it gets wet when you drive the car.

Yeah never thought about the radiator cap, but you would know if it was leaking, it would smoke or leave a residue under there. But yeah try what he said, I do it all the time,

Ok, I ran a few of the tests since I first posted.

One, I filled the radiator with water and let it sit overnight. I checked it this morning and it was at the same level.

I also wrapped a paper towel around the cap to test it out. I drove around a while today and it didn't have any moisture on it when I got done driving. There was also no residual from coolant.

I looked at the exhaust, can't seem to see the white/sweet smoke, so no luck there.

I checked the look and level of the oil. Both are normal.

I did stumble across one thing. One of the other threads with a similar problem suggested to check the tube from the radiator to the coolant tank. I pulled off the tube going to the coolant and some came out. I tried to pull it off the radiator but it wasn't budging and I didn't want to force it. I'm not sure if this means anything.

I'm not sure of what/where the firewall looks like to find the heating coil, so I didn't perform that test.

Any other ideas?

Your guys' help is much appreciated.

Hmmmmm you know it could be the overflow tank. Has the tank got coolant in it, might be that's cracked if it doesn't or most likely the tube's crcked open going to the tank. Should be a couple clips an each end one to the top around the radiator cap on most and one to the top of the tank. Could be its leaking. Could be its leaking around where its at at the radiator. Some can get very tiny pinholes in them and leak when very hot and have pressure behind them and not when cool. :)

I looked the tube connecting my radiator to my coolant tank again. There is coolant in the tank. There is, however, coolant on top of the opening of the tank... and looks like there is residue around it as well. I think this may be the problem (or part of it). It may have also escaped the pressure test. Is it as simple as buying a new tube?

It would be nice if this was the problem.

May be the tube has split at the top or the cap on the top of the tank has lost its seal or doesn't seal right. Only thing I can come up with now of the top of my head :) but that would cause coolent loss, may be the hole to the tank from the hose is plugged, did you see if that was clear, I had one time where one got some of that stop leak crap and went through and plugged the hell out of it and another time where just some crap got stuck in there.

I had thought about asking about the over flow tank. It too is under pressure, and its cap can leak just like the radiator cap, or the hose between can leak. When everything is working correctly, the radiator stays clear full all the time. When the engine is cold, the overflow tank will be part empty. As the coolant heats up, it expands and the excess flows into the over flow tank. When the engine cools off, coolant is drawn back in the radiator to keep it full. If the coolant leaks out of the overflow tank, it is not there to keep the radiator full.

Yeah it isn't but it is there and well the coolent goes back in and might just might have a pinhole of sorts, me I had the full monty of sorts, radiator then hoses then thermostat and heater coil, which is just like a mini radiator for your heat, and the cap on the overflow. 25 year old car of course, but rubber gives and you might have yourself a pinhole, me myself had a pinhole, leaked like a mother when going and well sealed perfect and leaked non when cold, hard to find when cold but it was a pinhole. Very very tiny. But the overflow on some models are the only way to fill the radiator with out a mechanic. Because when hot the extra goes in the tank and when cold it goes back in the radiator.

It seems like the overflow tank has coolant in there even when it off. Hmmm.

Oh, yes, the fire wall is what separates the engine compartment from the passenger compartment.

Yeah the fire wall is basically what it is a fire wall, keeps the engine when in a wreck from hitting you but push it down and outwards. Um the tank probably isn't cracked but a hose may be punchered and its letting some out when hot, did a pressure test on one and well never gave the problem but when running and hot well it showed it.

I ran my car around tonight, got it plenty warm, and I popped the hood. I couldn't see the leak, but there was a fizzing sound. Sounded like it was coming from the cap, but I know it wasn't.

You guys think it's the tube? Do you happen to know the name of that part?

Well on such a car no, but if you have a napa or advance auto or either autozone, they will know and you can just ask them and they can get it for you, sounds to me you said you heard a fizzing, may be a leak somewhere where you cannot see