RE: [DML] Re: Water pump woes?

["IN2TIME" <Gary@xxxx>]

I often hear about how someone's car got low on coolant and "got a bit
hot". They put some water in the overflow tank and the next time they
drive the car, it overheats again, and again, and again. Often they
explain that "at least the gage never got above XXX degrees". If they
eventually get all of the air out "it works fine". If not, they take it
to a repair shop for a new water pump, or radiator, or engine. If the
shop knows what they are doing, they get all of the air out too, and "it
works fine".

I've always wanted to explain what "really" happens when a DeLorean gets
air-locked, but I never put the required time into it - until now. 

I've decided to call this: 

"Memoirs of a DeLorean Cooling System"

For some "unknown" reason, your DeLorean gets really low on coolant.
- With that shiny new Overflow Tank you need x-ray vision - Right?
You add a mix of water and antifreeze to the Coolant Overflow Tank.
- You didn't really fill the system - just the Tank and a hose.
At this point, you think the system is full and you drive the car.
- The system didn't really fill up, because the air couldn't get out.
The pump outlet has a circuit to send "coolant" through the engine.
- It's not a good air pump - but air won't cool the engine anyway.
Some engine-heated coolant/air gets pumped to the Heater Core.
- This is a downhill path - Air tends to rise in coolant - Hmmm.
There is a "T" in this circuit to purge air to the Overflow Tank.
- But the "T" is down in front of the heads - not a high point.
If it's really hot out, you've set the A/C Mode Switch to Max A/C.
- In the Max A/C mode, you don't get this flow - or the purging.
The pump also has to push the coolant/air through the thermostat.
- But the thermostat is initially closed - for quick "warm-ups" :)
The main flow starts when the thermostat opens (at about 160 degrees).
- Cross your fingers - Air won't conduct much heat to the thermostat.
Now the engine coolant/air mixes with coolant/air from the radiator.
- I hope you're beginning to see the pattern developing here.
The pump tries to push the coolant/air DOWN past the thermostat switch.
- If the switch doesn't get hot (and close), the fan doesn't run.
The coolant/air is pumped to the front - to the top of the radiator. 
- Now, the radiator is also air-bound - and works rather poorly.
The coolant exits the bottom of the radiator through a big hose.
- From here the coolant goes to a "Y" under the spare tire.
The air tries to exit the top of the radiator through a small hose.
- At least the designer didn't expect the air to go out the bottom.
Perhaps I spoke too soon. The small hose leads downward to the "Y"
- What law of physics is going to force the air down the hose?
Just then you head down a steep hill - and hear a gurgling sound.
- A big bubble of air is now racing back to the pump and engine. 
Eventually the coolant/air reaches the "Y" to the Overflow Tank.
- If any air gets past the "Y", the pump sucks it up and tries again.
Air getting to the Overflow Tank is replaced by coolant - maybe.
- When the quart or two of coolant is used up, you pump air again.
Note: The Temperature Gage Sending Unit is on top of the engine. 
- It may only tell you is how hot the air is - not the coolant.
But by this time, the 280°F engine coolant has turned into steam.
- The actual temperature depends on coolant mixture and cap pressure.
Stem pressure blows any remaining coolant out of the overflow tank.
- As the system, and your temper, cool off - air gets sucked back in.

Since you've read this far, you probably want to know the moral of the
story. Right? Well, there are several:

- The bleeder won't bleed until the engine temp is 160°F.
- Even then, it can only bleed what is at the top of the engine.
- Air in the rest of the system eventually gets back to the engine.
- Jacking up the back of the car can help get the air to the engine.
- Install a continuous air-bleed bypass - they really do work!
- The bypass purges the air to the tank when the water reaches 160°F.
(If you tap it in just below the thermostat, it always purges :)
- Without one, the Overflow Tank doesn't indicate the "system" level.
- Even with a bypass, you still have to check the Overflow Tank level.
- If the system needs frequent addition of coolant, fix the leaks.

But those are just my opinions, and I could be wrong :)

Gary
www.IN2TIME.com