Cooling System Leak on Expedition - Need Help To Find It

[Fitz98]

98 Expedition 5.4 4x4.
I have a cooling system leak.
Cooling fluid is sitting under intake on the top of block. I siphoned the fluid since it was hard to reach. I filled the reservoir bottle and heard it trickling (Not a drip, it is a steady thin stream that I can see directly behind the alternator) Truck was not running at the time.
In order to see it better, I will need to remove alternator and start taking things apart. Maybe someone can help diagnose what cooling system part(s) could fail behind the alternator.
There looks to be a plastic looking plenum assembly on the bottom of the intake which is where it looked like the stream was coming from.

 

[bdcardinal]

So on these illustrations, see the 8555 highlighted? That presses into the back of the water pump and feeds the 18663 on the other illustration. The 18663 runs under the intake and feeds the heater hoses, there are different ones based on if you have a port off of it on the back of the intake or not. There are o-rings on the 8555 which create the seal for the 18663. You can get the 2 o-rings by themselves but if you get the 8555 it comes with them and is cheaper.

 

[Fitz98]

That would make sense. I was the guy who had the transmission fluid mixing with my engine coolant. I can see how the tranny fluid would swell that seal. How invasive is it to change those seals?

 

[bdcardinal]

Originally Posted by Fitz98
That would make sense. I was the guy who had the transmission fluid mixing with my engine coolant. I can see how the tranny fluid would swell that seal. How invasive is it to change those seals?


Once you have the intake off it is a 5 minute job.

 

[Fitz98]

You were spot on with your troubleshooting. Thanks. Once I had the intake off, I could see the leak around the tube. I did have a hard time getting the tube freed up for removal and wrecked the tube end prying it off. It seemed to have some corrosion on the tube and the seals were all gunked up, I couldn't even see the seals when I removed the tube, until I started cleaning the 8555 part.
A couple more questions:
1) Does the new part 8555 install from the water pump side or does it press in from the intake side? It didn't even budge while I was removing the tube 18663. Is there a shoulder on it that might be preventing me from pulling it out from the intake side, or is the shoulder on the intake side and I just need to get a pair of vice grips on it to work it loose? Just trying to determine if I need to remove water pump and what I am getting in to trying to work it loose.
2) Is it worth removing the water pump to replace the whole 8555 assembly if it goes in from the water pump side, or just replace the O-rings on the intake side. I don't want to have to remove the intake again and would rather not take off the water pump if not needed.
2) What is the sensor in the picture? It has been submerged in the coolant. Should it be replaced while I have the intake off, or just let it be
3) Any other parts you recommend changing while the intake is off?

 

[Fitz98]

 

[bdcardinal]

I seem to remember it pushing in behind the water pump. The water pump isn't that hard to get off.

 

[Fitz98]

Do you know what that sensor is going into the top of the block?

 

[mattd]

That's the knock sensor. It connects to the main engine harness

 

[Fitz98]

Do the knock sensors on the Expeditions hold up pretty well, or should I replace it while intake is off?

 

[bdcardinal]

They do hold up well, but considering it was completely submerged in coolant for an unknown period of time I would replace it if it were my ride.