03 LS Coolant loss after shut down

[airboss]

Gentlemen,
Re: 2003 LS 125K
I have read as many threads as seemed relevent to this problem but nothing yet has addressed it completely. I will try to make this initial thread as complete as possible so nobody wastes their valuable time.

Symptoms:
1. Within 2 minutes after shut down, collant begins flowing from center / rear of engine guessing over bell housing. But unable to see source.
2. Car has not over heated because I keep filling up the degass.
3. Car runs normal temp even at hwy speeds and 90 degree ambient temp.
4. If car is run short distances the problem does not appear.
****Degass bottle is never filled above cold mark****

Problems addressed prior to the current problem:
1. DCCV replaced 3months ago.
2. Degass and Thermostate replaced 1 yr ago.
*** The proper bleeding procedures were followed both times ***
*** Only Ford Gold coolant used ****

Initial steps already taken:
1. Degass removed inspected and re installed...OK.
2. Re-bled system per proceedures.
3. Heater intake box removed to get a better visual on aluminum coolant crossover tubes...No appearent leak upon shutdown after 20 minute engine run on lift. Temp Normal.
4. Electrical circuit to Aux collant pump tested at fuse and relay...OK
5. Electrical circuit at Aux pump no 12V during run with heater set on 90 degree or upon shut down ?????

Finally the questions: Thanks for your patience!
1. Since the aux coolant pump (ACP) provides cool down circulation upon shut down, could engine block coolant cook-off be significantly increasing the system pressure to the point of forcing a crimp fitting leak if the ACP fails to activate?
2. What triggers the ACP?
3. Does the CHT trigger the ACP?
4. Does the ACP always run when the cabin heater is selected 90 degree?
5. Does the ACP always run upon shut down?
6. When should I expect to find 12V at the pump connector?

Thanks to anyone who has experienced or has knowledge of this problem and can direct me.

 

[joegr]

AFAIK, the aux pump only really runs when the engine is on and some heating is called for. I can't verify that it's ever really used for post shutdown cooling or not.

Your problem, if correctly described, is probably either failure of the intake manifold or the gasket between the manifold and the block. I have heard of this happening at least once.

Any serious overheat condition would force coolant out through the pressure relief in the degas bottle cap, but not anywhere else.

 

[airboss]

Thanks Joegr for the quick response. I have verified that the ACP does indeed run after shutdown but is temperature activated through the EATC module where ever that is? I cannot find any spec as to the trigger temp.

I follow you... if there is an intake leak I suppose it could pressurize the cooling system but wouldn't that give me some other symptoms. Again, I have not had any overheating problems and the car drives strong, with 22.1 MPG and no codes or misfires. As long as the car is running it stays cool and doesn't discharge coolant. I conclude from your comment that the Degass cap also acts as a pressure relief valve. I didn't know that. If the coolant exits on the port side I will suspect the over pressurization. Thanks. Would you agree that my next step is to apply 12V to the pump and see if it responds at all. If it does I can take it off the list of prime suspects. Cheers

 

[Elemino]

Maybe the bleed hose is leaking?

 

[joegr]

The aux pump is controlled by the DATC module. That's the thing with the AC display and buttons.

The cooling system pressure should hit about 16 psi and stay there when the engine reaches temperature. This pressure should not increase when it is overheating, because the degas cap will release any excess and regulate it to 15/16 PSI.

If you can get very hot air out of the AC (set it to 90) with the engine at idle, the aux pump is working.

 

[airboss]

Thanks to both Elemino and Joegr for the Critical thinking! I had drafted a flowchart for my troubleshooting but did not include torqueing the hot bleed tube with a screwdriver instead of fingers. I have now found that I get an additional complete turn with the tool. Air could have been entering slowly since the change of the DCCV 3 months ago. Additonally if the degass cap releases at 15/16 psi, excessive pressure chould not be a cause, midigating the failure of the aluminum crossover. I get good heat at idle, so now expect the ACP to be performing adequately. Will double check tomorrow by momentarily applying 12V directly to the DC motor.
Great to have others to discuss the challenge with. Cheers