Bizzare (cold) coolant leak

[Cheaper Jeeper]

Came out of work yesterday and saw a big puddle of coolant under the front end of my truck. After spending a couple of minutes looking around under the hood and front end I could see that it was dripping from the underside of the harmonic balancer. A little more looking and it seems like it might be coming from the underside of the water pump - maybe somewhere towards the driver's side.

Here's the bizzare part. When I filled it back up with water (6 quarts) and started it up, the leak seemed to stop almost instantly. I drove it 40 miles and stopped several times on the way home. No signs of leaks. After I got it home and parked, it still wasn't leaking. BUT, when I came out and checked it after it had been sitting for about 5-6 hours and cooled down, it was leaking again! A steady drip...drip...drip from the bottom of the harmonic balancer just like before.

So what is up with that? I have never seen an engine leak when sitting cold but NOT leak when running and warm before. Usually when they warm up and the coolant pressure rises, they leak worse. In my experience they always leak worse when running than when they aren't running - due to the pressure created by the water pump.

Anybody ever seen anything like this? My first thought is that maybe it is leaking on the suction side of the water pump where it bolts to the block. Where are the suction ports on the whater pump? Top? Bottom? Passenger side? Driver's side? Any other ideas/theories?

 

[ddec4me]

Cold water leaks are a common occurance especially on diesel engines. I see them on a regular basis at our dealership. This is really common with waterpumps as when cold everything shrinks so tolerances are greater allowing a leak to form around shafts and seals. Once the engine heats up everything expands and seals the leak. The cummins M11 and ISM engine water pumps are notorious for this. My water pump did the exact same about 6 months ago it started as a small drip and within a week it was a pretty good leak.

 

[Dsl_Dog_Treat]

Might want to grab a coolant system pressure tester to see what's going on with the system. Autozone rents the test kits.

Sounds typical of a head gasket leak as well.

You can either get the UV dye and add it to the collant and hit it with a black light after making sure the marker has had ample circulatory time.
Or dust the motor down with talcum powder and that will also point to the leak during a pressure test.

 

[Agnem]

Based on where your seeing it, it's almost a certainty that it's time for a new water pump. The Moosestang is doing the same thing, plus I have some noise that I know is the water pump.

 

[Cheaper Jeeper]

...Sounds typical of a head gasket leak as well...

I thought about that as a possibliity, BUT ruled it out because every drop of the coolant is dripping from the bottom (perimeter) of the harmonic balancer and the outer ring of the balancer is wet. In order for a head gasket leak to drip from there, the water would have to run down the surface of the block and either run accross the snout of the crankshaft onto the balancer (and even then it would be on the INSIDE surface - not the outside surface of the balancer) OR run along one of the arms of the water pump and then drip onto the balancer.

Maybe I'm whistling as I pass the graveyard here, but both of those seem pretty unlikely. Ockam's razor tells me to look for horses (not zebras) whenever I hear hoofbeats!

 

[93turbo_animal]

water pump I had the same thing happan on my 93 and my mustang once warmed up no leak till they got worse then they started leaking all the time

 

[Dsl_Dog_Treat]

Yeah,now that I re-read what ya posted.
Water pump.

 

[Cheaper Jeeper]

So, how hard is it to change the water pump on a 6.9? What all do you have to take off to get to it (besides the belts of course)?

 

[Agnem]

Everything.

Seriously. The biggest PITA part is unbolting all the accessories and scraping the front cover for a new gasket. Actually swapping the pump is the easy part. It's a little heavy, so a couple of guide studs temporarily inserted in the top bolt holes works to your advantage.

 

[Cheaper Jeeper]

Everything.

Seriously. The biggest PITA part is unbolting all the accessories and scraping the front cover for a new gasket. Actually swapping the pump is the easy part. It's a little heavy, so a couple of guide studs temporarily inserted in the top bolt holes works to your advantage.

So basically loosening everything up to get the belts slack and scraping the old gasket off the block are the hard parts? Piece 'o cake!

 

[tuckerd1]

Like Mel said it's time consuming, but it is pretty simple. Definitely sounds like a water pump leak to me.

 

[Cheaper Jeeper]

Autozone had reman pumps for $26 bucks. Anybody had good/bad experience with their reman stuff?

 

[OLDBULL8]

My re-man pump from Azone is just fine. The only re-man part is to put in a new seal,shaft bearing and impeller. Don't forget the top 2 bolt's are shorter,mine came with new top 2 bolt's and gasket. Take the 2 old top bolt's and cut the heads off and use for guide bolt's. He wanted to know the inlet and outlet, looky there.

You must be registered for see images

 

[1991idi]

So what is up with that? I have never seen an engine leak when sitting cold but NOT leak when running and warm before. Usually when they warm up and the coolant pressure rises, they leak worse. In my experience they always leak worse when running than when they aren't running - due to the pressure created by the water pump.
Anybody ever seen anything like this? My first thought is that maybe it is leaking on the suction side of the water pump where it bolts to the block. Where are the suction ports on the whater pump? Top? Bottom? Passenger side? Driver's side? Any other ideas/theories?

Quick FYI- the pump doesnt create pressure (only flow) Pressure is from the expansion of the coolant as it heats up.
Just something i noticed reading your post.
Everyone seems on the right track for the source of the leak, but double check as it sint possible to have an accurate diagnosis over a computer- just a pointer in the (hopefully) right direction

 

[RLDSL]

Most likely coming out of the weep hole in the water pump. It is sealed internally and when the seal begins to fail coolant will start to drip out when the engine cools down and clearances loosen up