Hello all,
So I noticed that I was a bit low on coolant this morning (about a cm worth on the reservoir tank) and I did some investigating. I checked the normal things ........ ie hose connections, radiator, color of the oil, etc and couldn't find where it is leaking from. Then I went to squeeze the upper radiator tube to see if I could perhaps force some coolant out and to my surprise I heard an "air leak" sound coming from the coolant reservoir. I got closer to the to the tank and squeezed the hose again a few times and it sure enough the sound was coming from the cap. So, what I wanted to know is if this is supposed to happen. Does the cap release pressure of some sort? I should mention that there wasnt any coolant on top of the reservoir and also the truck runs well (it does not overheat at all). Any help will be greatly appreciated. Thanks

 

it should only release pressure after I think 15 pounds... it should not be leaking if you are just squeezing the hoses

 

There wouldn't be any coolant on top of the tank unlessthe tank itself was broken. The coolant would pass through the overflow tube which you can see coming from the neck of the tank and terminates about 6" down. The cap reading on those is 1.4 bar or about 18lbs roughly, (don't have my conversion table in front of me.) The bar rating is on the bottom of the cap. The cap is similar to the BMW and others. It uses three o rings and different ports to pressurize and release as needed. Unless you have a grip like a wrestler, you couldn't make a good cap open to the atmosphere. In fact, in practicle terms, given the size of the cooling system and the flexibility of hoses etc, you'd offset the pressure from your hand within the system. Check the cap and look for a missing o ring, but like thermostats and other low price, parts that have a finite life span, just replace it. Be sure it IS the cap and not the tank though. Check the neck carefully. Next thing to ponder is whether there is excessive pressure getting into the system that makes the failed part just a symptom of something more. For instance, a head gasket leak at a combustion chamber to a coolant port. A motor is in simple terms a big pump, moving lots of compressed air and at 9.35 to 1 compression ratio, that's a lot of potential pressure. Case in point, a customer with a 3.0 liter Toyota motor (the black eye to an otherwise brilliant auto maker) came in with a similar issue. While that tank is a non pressure style witha radiator cap for pressure, his was doing what I am speaking of. In other words, excessive pressures in the combustion chamber coupled with a poor design, allowed for a small amount, but consistant amount of compressed air/spent fuel into the cooling system. My first clue, he was losing coolant slowly AND at start up in the am, the engine ran a little rough. It cleared up after driving but the issue kept going on for awhile unchecked. When I filled the tank, after adding tracer dye, the overflow tube was blowing bubbles into the tank. That means at idle, not up to tempurature (so it shouldn't have been popping the cap open, it was pressurizing the system. Consequent inspection with plugs pulled and the pressure tester on it showed that by morning one cylinder had about two teaspoons of coolant visible with a fiber optic probe looking into the chamber.

A long winded way to give some insight to the idea that there can be many things that give you the problem you have. good luck

 

I'd put money it was a 7m

 

Hey thanks for the input. Bandit, I do have strong hands, but it it only takes minimal squeezing pressure to make the air sound (I could probably do it with two fingers). Also, the problem will occur whether or not the truck is warmed up or not. When the truck is warm the pressure in the hose will be a bit more but I can still squeeze it (warning...... those things get hot) and get the noise. Moreover I figured I'd mention that I warmed the truck up this morning in order to see if I could see coolant spewing out of the overflow pipe and I noticed that when the truck got warm the coolant level in the expansion tank raised until it looked like it was completely full (up past the cold level to the top of the tank). So, I'm going to go get a new cap on Monday but I wanted to know if I should keep the truck parked until then. I kinda need to use it but I will make due without it in order to keep her alive. Thanks

 

PM me with your tele number, I would like to call and talk to you about this.