I took my truck in for what I thought was going to be expensive headgasket work due to a gradual unexplained loss of coolant.

Left it overnight and called the next day to check the status and he told me that they could find absolutely no evidence that the headgasket it leaking:

- No oil in coolant
- No coolant in oil
- No exhaust gases in coolant (they checked 4 times)
- No steam or billowy smoke other than a bit of steam early in the mornings when cold (goes away after a minute or so)
- Kept system under pressure (16 lbs) overnight, with no leaks surfacing

What gives? What else could explain me having to refill the coolant tank every 500 miles or so?

 

Coolant leak?
No really- I've got two micro holes on my rad- it won't leak enough to see the pond underneath the car, bul when the system is under pressure it will leak a drop of coolant that dries out.Drop by drop -Ihave to add 0.5l every 5000km.

 

Well that's what I was initially thinking, until he told me they had cardboard under the truck for more than 12 hours, while under 16lbs. of pressure, with no leakage whatsoever.

 

But when the engine is running metal expands,and antifreeze vaporizes. Look for the green white spots on the rad, and around ALL hoses especially connections.I'm sure you'll find the cause.
And yes-did you bleed the system completly?

 

How much coolant to you observe dissapearing when you have to add? Could your tank cap have a leak or other that might let coolant evaporate?

Really guessing here, but maybe one of the smaller water lines under the plenum, above the intake, has a small leak and fluid could gather on the intake instead of on the floor. That area of the engine is really hard to see and I know there is at least one hose that is almost buried at the back of the intake and two that go through the throttle body.

 

I had a heater hose start leaking on the back of the block (water bypass block) and because it was back there it would drip down the back of the hot block and evaporate before it hit ground. but it only leaked AFTER the system got up to pressure (meaning the motor was hot)

i fought that for a good 4 months till the leek got bad enough were it started leaking on to the ground and i could finnally track it down.

same problem can be for the rad. small leeks evaporate before they make a puddle. (but only leak after it heats up and things expand)

 

I had a top seam rad tank leak that had to get worse before I was able to find it.
You could try parking over cardboard yourself after a drive.
There's a dye that can be put into the cooling system to check for leaks with a uv light, if you don't want to wait it out.

 

Don't forget the heater core hoses under the dash.

 

I had this problem in my 92 also. It was the coolent resivoir tank. The seam where it was molded had a small crack in it so everytime the hot radiator dumped some coolent into it it would leak out a little bit (too small to notice on the ground) and I was slowly loosing coolent.

That would also explain why a preassure test does not cause a leak.

A $10 junkyard resivoir and 5 minutes of work fixed it all.


Lamm

 

If the engine was running while it was under pressure, then you could be certainabout everything, but when it gets hot, the hoses could even get squishy and seep water out, you don't have an oily greasy windsheild interior do you?

 

Thanks for all the replies. For some reason, YT stopped sending me e-mails so I didn't know there were this many replies!

I sure hope it's a pinhole leak somewhere in an obscure hose. A few questions:

- Where are the heater hoses located under the dash? I haven't noticed any internal leaks, but haven't been looking for any either.

- Is it possible that I have a headgasket failure so small that there would be no signs of exhaust gases in the coolant, or is it the type of thing where if there's no exhaust gases, there's no headgasket failure?

I sure hope that it's something small like a coolant reservoir leak.

 

Not to rain on your parade, but when my HG went I had a slow coolant loss that held pressure warm or cold, gurgling heater sounds and a good amount of steam on cold mornings that didn't last more than 30 secs. The mechanic didn't think it was a HG at all but I asked him to check torque on the head bolts. He retorqued them about five over spec. It all stopped for six months, then I started breaking spark plugs on the number six cylinder and found that I was beginning to get chocolate milk where my oil was supposed to be. So I guess you can have a slow small leak that is difficult to diagnose and is fairly harmless if caught in time and monitored. The engine ran fine and pulled well all over the hills on the Olympic penninsula.

 

Do you mean to say they found no evidence of coolant in your exhaust gases?
You keep saying it the other way around.
Analyzing the exhaust gas for coolant will tell you for sure that you leaking into a cylinder.

 

My coolant was disappearing without any visible sign. When the shop hooked it up to test for contamination from the combustion chamber, it showed up immediately. In response to your question, I'm not sure, but I think the test would show exhaust gases.

Maybe your leak is at or beyond the radiator cap. This would explain the pressure holding steady during the test, but not while running. I would replace the cap, inspect the hose to the overflow and look at everything on or around the overflow.