Riddle me this...

Every now and then the coolant resivour in my truck will go down half an inch. I'll fill it up, and it will go down again. Usually takes it a couple months. No leaks anywhere. Runs fine. Idles the same as it has since day one. No oil in the radiator (that I can see). Now it gets interesting... Tuesday I put washer fluid in the truck, truck hasnt moved in a day, resivour for coolant is at full line. Wednesday, move the truck from the street to the driveway. Thats it. Pop the hood, coolant is down 1/2" from the day before... WTF.. so I crack the cap on the radiator (truck had sat for a couple hours after moving it 30yards) and it pours out a bunch of coolant like there is pressure still in there....

So yea.. I have a couple theories, but I would like to hear yours. Thanks!

 

Gremlins. Those darned little creatures are always givin me trouble!

 

It's either boiling off or you have leak in the seam of the radiator (like I did)

For your sake, I hope it's boiling off. Darn radiators aren't cheap.

 

There's no leak, I leave my truck parked most of the week and there's never anything under it.

It boiling off is fine, thats what I figured.. but whats got me wondering is where did 1 cut/8 ounces of water go to sitting for one day then driving to the driveway a whole 30feet? That is whats got me wondering...

 

somebody is stealing it when youre not looking...

or you could revert to the gremlin theory...

another one ive noticed a lot of is, trucks eat things...

 

Check the water pump weep hole. Its on the bottom, look up at the pump from the passenger side, if coolant is leaking from it you need a new water pump, had to have mine replaced at 30,000. Wait, gotta add that to my sig...

And i know there are no leaks...mine didn't leave a puddle for the longest time, and my coolant resevoir did the same thing. Check it, it might leak some and burn it off the motor.

 

If you started it cold dropped it onto gear and moved it only 30 yards and then shut it off and then waited several hours before opening the rad cap there should not have been any pressure on the system or at least not enough to burp out any coolent.

Are you checking the reservoir with the engine cold and is the outside temp about the same each time? Have you looked on the engine oil dipstick for signs of water drops mixed in the oil on the stick? I would run the engine for a few min, not enough to get hot, but just warm then check the dipstick....at full operating temp it will more than likely burn off the water/coolent if its getting in there and you wont necessarily see it on the dipstick, especially if it’s only a small internal leak.

Do you notice any smell of coolent inside the cab....does the windshield fog when you first turn on the heater or is there an oily film on the inside of the windshield?

I would start by replacing the rad cap....Then check the reservoir very carefully for any signs of leakage. Make sure the hose is good and open between the reservoir and Rad. Then look at all the other hose connections for signs of weepage and finaly go over the rad. with a fine tooth comb looking for any signs of leakage.

If that does not turn up anything then I would have it pressure tested both cold and hot and go from there.

 

are you sure its even dissapearing? on my 97 i used to have the same problem. i'd fill the coolant overflow reservoir to the fill line, and the next day, a week later, etc etc (random) it would be low, but then sometimes if i'd wait and look at it again, a day,week,etc later, it would be normal. the explanation i received is that the level can fluctuate depending on engine and ambient temperatures and such... so it might just be that?

 

After 40K miles I noticed that the bottom of the reservoir was barely damp, so I had the cooling system flushed and the coolant in there looked normal. I'll be keeping an eye on it but I'm not worried right now. It hasn't been running hot or obviously leaking.

 

1. Water will evaporate from the resevoir, slowly over time.
2. Radiator is a pressurized system. Anytime I shut off my truck I can hear it slowly draining back into the resevoir tank. That explains temporary level changes.
3. Invisible Coolant ****'s!

 

I should have mentioned that I noticed it dry w/ the truck cold.

 

I had this problem with my 02 4cyl. Took me months to find my problem.. It was the overflow bottle. It had tiny cracks in it. I couldn't see or smell it but it was going somewhere. Try some radiator dye. After using the dye, under the hood looked like a rave party. The spray pattern helped me track down where it was coming from. Hope this helps.

 

Why don't you pressure test the cooling system?

 

because 13 years later he no longer owns the truck or the leak has gotten worse and part replaced by now.