240z undetectable coolant leak

[richard1]

Recently, I found than only the inner left front fender well was stained with coolant from the frame rail up to the vent duct connecting to the radiator support. At first, I thought that it was one of the hose from the transmission cooler that was the problem but it is not the case.

For sure, this streak of coolant is shot from the fan but it is impossible to find from where it is coming. Here is what has been checked:

-The upper and lower radiator hose......they are new from last year and tight.

-The water pump..........replaced last year.

-The radiator........doesn't leak and has been replaced by a brand new one two years ago. Top and bottom tank are dry (copper radiator not aluminum).

-Radiator cap........new from the same time.

-Thermostat housing........no leak.

-Small hose connecting to the thermostat housing from the intake manifold......dry and no leak.

-Head gasket..........dry.

-Coolant..........clean

There is never any coolant spot on the floor, the radiator is always full, the water pump is not noisy and doesn't show any sign of leak around the front of the engine after complete cleaning of the erea.

It is very mysterious and I wondering where to search for any clue.

Thanks in advance for any suggestions.

[Reverend]

Coolant overflow pipe? In my Z it drips sometime.

[richard1]

Coolant overflow pipe? In my Z it drips sometime.

No, it would have been too easy.

[grantf]

I am guessing the water pump has a small leak.

[Captain Obvious]

Not to be a smartass, but if the radiator is always full..... Are you sure you're looking for a coolant leak?

I once had a car that would lose coolant slowly over time, and I spent years looking for that leak. Never a spot on the ground. No signs of coolant anywhere in the engine compartment. Compression test turned up no clues.

Turns out that I had a tiny tiny pin hole in the radiator, and it would only leak when the engine temperature and coolant pressure peaked after you shut it off. A hair thin stream of coolant would spray out of the front of the car, cleverly missing even the grill slats, leaving behind no trace of wetness anywhere. It hit the ground about five feet or so away from the car, half of it probably evaporating before it ever even hit the ground.

I finally discovered it one day when I was standing a couple of feet in front of the car and noticed a slow growing warm wet spot in my pants. It turned out to be my car whizzing on me. That's my story and I'm sticking to it. On that occasion anyway!

[black gold man]

Are you sure its coolant? When fan clutch leaks it makes a mess.

[adamr]

I have a leaking freeze plug under my header. I think more than one is leaking. For the longest time I was baffled. Maybe that's it.

[madkaw]

Thats a funny story!

Not to be a smartass, but if the radiator is always full..... Are you sure you're looking for a coolant leak?

I once had a car that would lose coolant slowly over time, and I spent years looking for that leak. Never a spot on the ground. No signs of coolant anywhere in the engine compartment. Compression test turned up no clues

Turns out that I had a tiny tiny pin hole in the radiator, and it would only leak when the engine temperature and coolant pressure peaked after you shut it off. A hair thin stream of coolant would spray out of the front of the car, cleverly missing even the grill slats, leaving behind no trace of wetness anywhere. It hit the ground about five feet or so away from the car, half of it probably evaporating before it ever even hit the ground.

I finally discovered it one day when I was standing a couple of feet in front of the car and noticed a slow growing warm wet spot in my pants. It turned out to be my car whizzing on me. That's my story and I'm sticking to it. On that occasion anyway!

[5thhorsemann]

Pressure test the system, they do make tools for testing the cooling system. It's a whole lot faster and easier than waiting for the ghost in the machine to show its self.

[Diseazd]

I am guessing the water pump has a small leak.

I agree. There's a small weep hole dead center under the front of the water pump. Put your finger under the pump and see if it's damp after driving. The drip would "hit the fan" and sling the coolant to the side.

[cygnusx1]

small coolant leaks tend to occur only while driving, and dry up by the time you even open the hood. Radiator pin-hole or a weeping waterpump is likely. Go borrow a pressure tester from the local auto parts store.

[richard1]

I agree. There's a small weep hole dead center under the front of the water pump. Put your finger under the pump and see if it's damp after driving. The drip would "hit the fan" and sling the coolant to the side.

Today it became a bit worse and after close examination, i made the decision to remove the water pump after I bought a new one. This sucker has just not even some play in the bearing but just enough to drip a bit (dry streak) at the bottom of the casting close to the "hole".

I inspected the radiator and it is fine.

Thanks to everybody for their comments.