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Old 02-05-2018, 07:38 PM
97 SL320 97 SL320 is offline
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Originally Posted by rreeuuvveenn View Post
Filled the coolant tank, till the top, NO bubbles, no change in coolant level,

While engine is idling,

The pressure in the cylinders is almost 2000 psi,

So why should push 100 psi, down the injectors, to see bubbles,
The 2,000 PSI is only for a very short period of time, the 100 PSI for a long period of time and will uncover any real leaks.

If there is a fixed size hole, 2 x pressure does not equal 2 x the flow. Think of a storm / screen door pneumatic closer. The door closes at a certain rate by it's self, push with 2x the force of the spring and it won't move 2X the speed, it will move at a somewhat slower rate than 2x speed.

There is a term for this that I can't recall right now, it is a fluid dynamics issue. Basically, a fluid or air can only move at a certain maximum speed before becoming so turbulent the fluid it's self causes a restriction.

On the engine that was using a quart every 4,000 miles, the head gasket looked perfect. There was only a very slight discolored area where coolant was making it's way into the combustion chamber. If I hadn't done a leak down test looking at the radiator level, finding where the coolant was being lost would have been impossible.

Doing a leak down narrowed things to a specific cylinder. Actually 2 cylinders, one on each side of a GM 4.3 V6. Rather than have the car down for a longer period of time, I sourced replacement heads, built them up then swapped. The head faces on both heads had a slightly low spot in the same place causing loss of coolant.
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