Brill

The Jeep is a 2004 WJ with the 4.7L engine and about 125k miles. I bought it about 3000 miles/2 months ago. Shortly after I first purchased it I discovered a major coolant leak from the radiator. Had the radiator, all the hoses, and the cap replaced. Shop did a pressure test. I thought everything was fine.

I didn't notice any coolant loss over the next few weeks, but then I started to notice a slow, but noticeable drop (1/2-1 inch) of the coolant level in the reservoir. I filled it up and kept an eye on it the next couple of weeks. Still a slow drop.

Heater blows hot. Carpet is dry. No milkshake in the oil. No white smoke or odd smell from the exhaust. No visible leaks that I can see and no puddles on the ground. The engine starts and runs very smooth. Temp is almost always about 195-200 and never goes above 210.

Thinking it might be something like the head gasket I rented a block tester, but I'm having trouble using it. With the radiator cap off and the engine running the coolant in the radiator keeps slowly and steadily rising until it overflows. No bubbles at all and it's not gushing out - just a slow and steady rise. What does this indicate?

JPXJMOAB

The only other thing it could be is a water pump weeping.

dave1123

Okay, here's one thing I found out about Mopar water pumps. Most water pumps have a weep hole in the shaft bearing. We all know that, right? Well, my 4.0 seemed to have this slow disappearance of coolant as well and I could smell coolant but saw no leaks. One day, we fired it up on the lift to bleed the brakes and there was a gush of coolant from the front of the motor, then it stopped. In looking on-line for a new pump, the AC Delco listing mentioned a "weep chamber." A What? It seems there is a small, about 1 tablespoon, chamber under the pump shaft that catches and holds a small amount of weepage and allows it to evaporate. When the weepage gets too much, it drips into the pulley and is thrown off on startup. I'm assuming here that your 4.7 has the same thing on it.

The slow steady rise in the radiator is simply the coolant expanding that normally goes into the reservoir. Left open long enough and you'll get steam bubbles from the head(s) because it's not pressurized.

Bugout4x4

Experience like this is exactly why I joined this forum! Mine is doing this right now and I have been racking my brain to find it. Apparently mine is barely leaking into this little reservoir but never building up enough to throw any out yet. But I keep smelling it, noticing a slight slow level drop over a weeks period yet cannot find the source. This may be it!


Great find Dave! Thanks!

Brill

So the coolant rising like that is normal then? How do you do the block test if the coolant keeps rising out?

dave1123

I don't understand what you refer to as a "block test". A simple pressure test will show where the leak is. Most pressure tests bring the pressure up to about 5 lbs above normal and will show even the slightest leak. If you're talking about a head gasket leak test, there is a devise that goes on the rad cap and the liguid in it will turn blue if exhaust gasses are present.

Bugout4x4

Pressure test is done cold and not running. The leak is more often apt to reveal it's self cold while everything is contracted. If checking for exhaust gasses do it cold before starting, Take an old towel and soak up enough coolant to give it a couple inches of air in the neck. install the exhaust gas detector then start and let run for a just a bit. Normally it should tell you if you have gasses in the system before the coolant gets warm enough to expand very much.

Brill

Trying to test for the exhaust gases, not a pressure test. The fluid in the radiator rises up and overflows even when the engine is just started being dead cold.

Bugout4x4

Let it push some out then, You need to have some air space in the neck or it will just push coolant into the detector. Just be sure and burp it when refilling. I found the easiest way to burp these things I put it in low range and drive front wheel on the filler neck side up onto a ramp or tall curb to lean it to get the fill cap higher than the engine. I also have to push the throttle body linkage a bit to raise the RPMS while topping off and putting the cap back on after no more air comes out.

blueseasons

So let me get this straight. MOPAR builds leaky water pumps, intentionally? What could the rational possibly be for building a water pump that leaks a little, not enough to drip, so coolant constantly needs to be added?

Bugout4x4

I have seen even fairly new pumps seep a little in extreme cold conditions due to the shaft contracting. Maybe they don't want to get anyone excited until it really gushes out? lol.


I would rather see it leak when it does leak even a little bit.

dave1123

The major problem with letting it leak is the serpentine belt doesn't like coolant and many times will fly off if it gets wet, especially since the water pump drives off the BACK of the belt, not the ribbed side.

Brill

I actually tried siphoning out about a pint as it was rising, but it just kept coming.

blueseasons

I don't feel left out. I don't experience any of this with mine. The only time I ever smelled coolant , of lost any was when my heater core was leaking. I have never in my life heard of a vehicle/water pump that was built/designed to lose coolant. Boggles my mind.

Brill

Finally found the leak fortunately. It was actually leaking from two places that apparently only leak when it's cold outside.

It was about 47 degrees this morning - started the engine, and immediately saw the two leaks. The lower radiator hose wasn't tightened enough, and the coolant temp sensor needed replacing.