I have a coolant leak that I am trying to figure out from where it comes since several weeks. Every week I had a a quart of coolant in the radiator.

No trace of leaks on the floor, no coolant in the crankase, all hoses are tight, radiator cap changed a month ago, engine dry everywhere.

Today. I saw a spot of coolant on the floor and from the way the car was parked, it is on the left side and could come from the transmission.

I have not looked under the car yet but is it possible that the coolant line that goes from the bottom of the radiator to the transmission could be part metal and part braided rubber hose which would explain the leak at the transmission.

The Nissan and Hayes shop manuals are not clear on the subject and the parts book confusing with two different parts numbers.

The transmission is a 3N71B

The car is fully original and the coolant line that goes to the transmission has never been touched.

If it's leaking from the line you described, it would leak trans fluid not coolant. As far as coolant goes, the thermostat housing/water outlet on the left side of the block that could leak from either mounting surface.

I have a coolant leak that I am trying to figure out from where it comes since several weeks. Every week I had a a quart of coolant in the radiator.

No trace of leaks on the floor, no coolant in the crankase, all hoses are tight, radiator cap changed a month ago, engine dry everywhere.

Today. I saw a spot of coolant on the floor and from the way the car was parked, it is on the left side and could come from the transmission.

The transmission is a 3N71B

The car is fully original and the coolant line that goes to the transmission has never been touched.

From the limited information given . you had a quart of coolant in the radiator ??? Check the oil in your automatic trans. Sounds like you have a problem with the radiator . The trans cooler in the lower tank may be leaking . if you find cooant in the trans oil , have it surviced right away

I'm pretty sure he meant 'add' a quart. The trans cooler is simply a coil of tubing in the bottom of the radiator. Nothing but transmission fluid flows through those lines and that cooler. In order for coolant to get in there, there would have to be a hole in the tubing. Were that the case you'd also be experiencing tranmission problems since you say you've had the problem for 'several weeks'.

There is no coolant mixed with the transmission oil nor in the crankcase and the bottom of the radiator is dry. A real mystery.

How much coolant are you finding on the floor over night. You say you are finding it under the trans . Could it be coming from the rear of the head and running down the bell housing back on to the trans and down. If you had a problem with the trans cooler in the radiator most definitely you would have oil in the coolant . There is no coolant any where back of the engine other than the heater . You would find plenty of coolant on the floor on the passenger side. Is this a 240 with SUs ? If so there is a small metal line that runs from the intake manifold around the rear of the head and it connects to hose near the #6 spark plug. Check around there for a leak when you are checking the head to block seal . Gary