I have searched every where Air leak

[diverman555]

The new M923 has a secondary system air leak. When I shut the truck down, both primary and secondary gauges will be on 120 lbs. After about 5 minutes the secondary system will start venting air, and it sounds like it is coming from the front of the engine. I have on several times opened the hood and waited and when it started I have not been able to find where it could be coming from. It drains to 10 lbs and stops. Even when I'm sure I'm within inches of finding no luck. I have searched the TM's and no luck. Could someone shed some light please.

 

[nf6x]

I would spray soapy water on every air fitting I could find, looking for bubbles. Also, don't overlook the glad hands at the front of the truck (especially the emergency one), in case the shutoff valves are leaking. Good luck!

 

[doghead]

Maybe the fan clutch is leaking.

 

[juanprado]

I would suggest checking the governor on the firewall close to the coolant overflow tank as it could be sticking and venting. They are inexpensive and any hd parts store carries it.

happy Hunting.

 

[diverman555]

Doghead, that would be right where the air sound is coming from. How would I check that.

 

[jw4x4]

After shutdown, I have air coming out of the valve located next to the upper radiator hose up by the fan shroud. I believe this is the valve DH is eluding to. I may end up replacing that valve.

 

[diverman555]

That is exactly where the sound is coming from. Now to look up what that valve is called.
Thank you.

 

[319]

Gee whiz Mark, aren't these guys great??

 

[diverman555]

After spending 11/2 hours in the TM's, I believe the part is the pressure protection valve, but I can't find in the TM's where exactly it is, or how to service or replace it. I have found in a couple places where it says what it does, but that is it.
DOGHEAD help!
JW4x4 did you find anything in the TM's?
YES they sure are great, cause I still can't find it.
We need a smiley face with me pulling my hair out.

 

[diverman555]

This link goes to the part but I'm not sure where it goes. Pressure Protection Valve, KN-31000 (12450226)
Is this the part your talking about?

 

[nf6x]

Are you talking about the part that is mounted on the thermostat housing (top of the engine, where the upper radiator hose attaches), and which has an air line leading from it to the fan clutch? Well, I'm having a hard time finding that one in the TMs, but I don't think it's that pressure protection valve. I found similar stuff for the A2 trucks, but not for the A0/A1 trucks. It would be a thermostatic valve which cuts off air pressure to the fan clutch when the engine temperature rises too high, and then that causes the fan clutch to engage.

Maybe this smiley is close enough:

 

[diverman555]

Active duty friend

I think we are in luck, I have a friend who is active duty 18 years, works in truck maint daily. saw him yesterday and told him of the issue. He said he would look on their online TM program which is much better than our and trace down the secondary air system. He just needs a couple days.
And yes I do have a friend and I don't have to pay him.LOL